Transportation Planning and Traffic Studies PDF

Module 3: TRANSPORTATION PLANNING AND TRAFFIC STUDIES Module Overview The process of transportation planning involves the elements of situation and problem definition, search for solutions and performance analysis, as well as evaluation and choice of project. The process is usefu...

Module 3: TRANSPORTATION PLANNING AND TRAFFIC STUDIES Module Overview The process of transportation planning involves the elements of situation and problem definition, search for solutions and performance analysis, as well as evaluation and choice of project. The process is useful for describing the effects of a proposed transportation alternative and for explaining the benefits to the traveler of a new transportation system and its impacts on the community. The highway and traffic engineer are responsible for developing forecasts of travel demand, conducting evaluations based on economic and noneconomic factors, and identifying alternatives for short-, medium-, and long-range purposes. Transportation planning decisions are not randomly assigned but are done based on engineering data gathered through traffic studies. This will be a guide to simple, reliable traffic survey techniques, suitable for urban road traffic in developing countries such as the Philippines. It covers surveys for urban traffic engineering but does not cover road safety or transport planning. Lesson 3.1: IMPORTANCE OF SURVEYS THE NEED FOR SURVEYS Surveys are required for both national and strategic traffic issues, and for local traffic planning, engineering and management purposes. Traffic data are important to a wide range of decision-making processes in the planning, construction, operating and maintenance of the transport system. Information is needed to support not only the case for transport investment (infrastructure planning, design and construction), but also to indicate how to make best use of existing road facilities (traffic management and maintenance policy). The traffic data required from surveys is of transport supply (inventories and characteristics of the vehicles and infrastructure which comprise the system), transport demand (the amount the system is used and the patterns of movement) or performance (how well the system accommodates the demand placed upon it, measured in terms of traffic speeds, journey times and delay). Table 1.1 lists the main types of survey that are further described in subsequent chapters. The collection of traffic data is organized either as part of general background monitoring of traffic developments or as part of a detailed traffic investigation. Traffic monitoring is the consistent and regular (periodic or continuous) surveying of traffic data, either nationally or locally, for a range of planning purposes: to calculate historical trends, in supply, demand and performance; to calculate hourly, daily, and seasonal variation factors; to provide a summary of the existing system, in terms of supply, demand, and performance, and identify existing problems; to determine the timing and sample rate of further surveys; as a base for predicting future demand and performance, in order to plan improvements. Detailed data collection is required for the investigation of specific problems, the design of improvements, and for 'before and after' evaluation of the impact of changes. 'Before and after' surveys are a special type of monitoring to gauge the effects of a specific action. `After' surveys should be carried out long enough after implementation of the scheme to allow new traffic patterns to become fully established (typically 2-4 weeks), but not so long as to allow underlying traffic trends to affect the outcome. It is also desirable to carry out simultaneous 'control' surveys in a different part of the city, to reveal any underlying changes to traffic conditions. Source: Transport Research Laboratory: Overseas Road note 11 - - - Lesson 3.2: SURVEY PLANNING GENERAL CONSIDERATIONS Road classification system Roads have two basic but possibly conflicting, functions: to move traffic smoothly and without interruption, and to provide access. The provision of access will often necessitate interruption to traffic flow, hence the conflict. The function of any specific road, therefore, is a balance between these two extremes, and is defined by a road hierarchy. The concept of road hierarchy is fundamental to safe and efficient traffic operations and planning. The classification of a road's function within the hierarchy should also have a significant effect on its design standards (geometry, structure, etc.). Therefore, it is important in any study of the traffic network to describe the road links in terms of their classification within the hierarchy. Figure shows a possible classification system which should be amended to suit local conditions (Institution of Highways and Transportation and the Department of Transport, 1987). Example of a road hierarchy Vehicle classification system A fully comprehensive classified count may identify up to 20 different vehicle types It is rare that such detail will be required, however, and in order to minimize survey difficulties, five groups will often be sufficient based upon the sub-groups. The group or category number is based on the number of tires on the vehicle.  - Sub-divisions should be chosen to include groups of common interest. For example, in a transport planning study, divisions may be according to vehicle occupancy; for a road damage study, they may be by vehicle weight; and for traffic signals studies they may be according to their passenger car unit values. Each class must be distinguished from the others by a unique characteristic which can be seen easily in a moving traffic stream on a busy street. For example, methods which involve the counting of the number of tires are more reliable than those which require estimation of length or weight. For clarification, a sketch or photograph of vehicle types should always be given to survey staff. - - - 38 Sample of Road Categories and Function - - - -  - Sample Simplified Vehicle Classification - - - - -  40 Traffic variation and sampling Traffic variations are usually cyclical, and may be hourly, daily, or seasonal. The most appropriate days and times of survey depend on survey objectives (for example, whether average values or peak values are required). Surveys should not be conducted when traffic flow is affected by abnormal conditions, such as accidents, roadworks, public holidays, public processions, and severe weather conditions (particularly heavy rain). Separate measurements may be required for seasonal rainy and dry periods. A particular problem in developing cities is that interruptions to traffic flows can be so common as to be considered part of the normal traffic scene. In this case the influence of the disruption should be noted, along with the traffic performance values being evaluated. The aim of any survey should be to collect only as much data as is required to give an estimate at the desired level of accuracy. Appendix A gives detailed guidance on the use of simple statistical procedures to help choose the sample size. Vision: Mission: - - - - Lesson 3.3: FIELDWORK PREPARATION Human resources A traffic engineer develops the general requirements into a work plan and program. He must choose the appropriate survey method for the task and conditions and decide on locations and times. He must also ensure the correct preparation and training of both Supervisor and Surveyors. Survey Supervisors undertake the surveys with teams of Surveyors. There should be no more than 10 Surveyors per Supervisor; larger teams are difficult to manage. The Supervisor must ensure the accuracy of observations and recording, timekeeping and completion of survey form headings. He must also support the survey team in general, by maintaining the supplies of forms, materials, and equipment. He also records changes in traffic conditions (for example, accidents, weather, traffic controls) using a log (see Appendix B). Shift lengths depend upon the intensity and rate of work, as well as any legal constraints or government recommendations on working hours. In surveys with a high work-rate (for example recording vehicle registration numbers) attention spans are relatively short, and shifts should be broken up into sessions of half an hour to one hour, with short breaks in between. In general, shifts should be too short rather than too long; no Surveyor should be asked to do more than is comfortably possible. One Surveyor, however competent, should never be required to record more than twelve items (for example, three classes of vehicle and four turning movements). Two-way traffic is regarded as two items, even if not recorded separately. As a rule of thumb, one experienced surveyor using a pencil and appropriate form can simultaneously record:  - twelve items, up to a flow of 300 veh/hr.  - four items, up to 600 veh/hr.  - two items, up to 1200 veh/hr.  - one item up to 1800 veh/hr. Rates for inexperienced Surveyors should be about two-thirds of these values. For high volume flows in excess of 1800 veh/hr. the use of tally counters will help. Other less satisfactory techniques include counting in groups of ten, and creating sub-divisions of items for separate Surveyors to monitor (e.g. counting by lane or sub- dividing the vehicle categories). Survey duration should be sub-divided so that anomalies can be identified by comparing different short periods and discussed with the Surveyors involved. For example, even if the required data from a survey is the 1-hour total volume, it should be divided into 15-minute periods.  42 Equipment Lists of equipment and materials are included with the individual survey instructions. The Supervisor must specify the equipment needed by each Surveyor. Again, space is provided for this purpose on the Supervisor's field log sheet (see Appendix B). Watches are used extensively in traffic surveys. It is recommended that digital chronometer watches which can display hour, minute, and second simultaneously be used for all timing tasks. (Stopwatches are not recommended as they are prone to operator error.) All watches should be individually numbered, and each should be checked against a reliably accurate standard from time to time. Survey forms and instructions Survey form design should be simple, with enough space to record the data easily even under busy field conditions. Margins at left, right, and bottom of the form should be large enough to allow it to be clipped to a board, and filing holes to be punched, without obscuring information. Heading information should include the project title, survey type, and blank spaces for the Surveyor to enter the exact location (e.g. road name), a sketch plan showing the site and location of the surveyor (with measurements to an accuracy of 50m), date and time, Surveyor's name, weather conditions during the survey, and any other information concerning unusual traffic conditions. Each Surveyor and Supervisor must have clear, detailed written instructions and training for each survey form and each survey task. This will include a detailed description of each individual task and how the survey form(s) should be filled in, with examples. It should be impressed upon them that every single item of header information must be completed on every sheet. To avoid ambiguity, it should also be emphasized that no box or column is ever left blank; value zero is shown by the figure zero (not a dash), and suitable abbreviations are used for `not available' (n/av), or `not applicable' (n/a). Appendix C contains instructions and blank forms for each of the surveys described in the following discussions. Pilot survey Pilot surveys are full field tests of a survey method, preferably at the location of the main survey itself. Though they are sometimes omitted for reasons of economy, experience has shown that pilot surreys are a vital part of ensuring acceptable data quality. They can also help plan sample size and survey duration, thus ensuring the most effective use of available time and money. If the pilot is well prepared, and proves to be successful, the pilot survey data may become part of the main data set. Liaison with other agencies The approval of the police may be required for any activity on the highway, and their permanent presence may be necessary for some types of survey. However, as far as possible, the police must be made aware that there should be no unusual police presence or activity in the survey area which could affect Vision: Mission: - - - - - For in - the traffic characteristics being measured in the survey (for example, additional enforcement of speed limits or drivers becoming conscious by the presence of police). Surveyor safety Any work close to moving traffic has potential dangers. All survey staff should have suitable insurance cover, and each individual should be given a verbal briefing on traffic safety precautions as well as a copy of the safety card or similar. There may be legal obligations on the part of the survey organizers in respect of safety; these must be established and adhered to. Vision: Mission: - - - - - Lesson 3.4: DATA HANDLING Data processing converts raw field data into a standard format, from which summary statistics, tables, and graphs can be prepared. Analysis is the process of drawing conclusions from this data. Both processing and analysis should begin as soon as possible, because potential errors are more easily identified and corrected if the surveyor concerned can be questioned. Also, additional surveys are more easily organized, if required. The main types of mistake are incorrect application of random or systematic sampling, measurement errors (misreading or misrecording, usually arising from Surveyors being required to record more information than can comfortably be achieved, use of ambiguous definitions or lack of adequate Surveyor training) and blunders (the result of direct human error). Measurement errors are often difficult to detect later. Serious blunders are usually detectable if proper data checking procedures are followed. However, every attempt should be made to avoid measurement errors and blunders from the start, as many errors cannot be identified once the data are collected. For in - Safety card example Processing and error checking Data processing usually involves the transfer of raw data from the field sheets onto summary sheets or directly into computer files. This transcription process itself can be a major source of error and must be carried out with care. The transcriber should also remain alert to the possibility that the data contain errors and report any observations which appear to be in error. With computer records Vision: Mission: - - - - -  46 it is easy to make specific error checks at the first stage of data processing. The most obvious check is for data to be entered twice, independently, and compared for differences. The traffic engineer should look for unusual values or patterns in lists, tables, diagrams, and graphs. Discussion of unusual results with the Supervisors is often very productive. For example, a traffic volume histogram may show a large fluctuation from one 15-minute period to the next. There are no fixed rules, but an investigation could be carried out as follows:  consider what reasons could have caused the fluctuation, for example, an effect such as that shown in the log.  consider whether the Surveyor forgot to change time periods every 15 minutes, resulting in periods being longer or shorter than 15 minutes. The Surveyor should be questioned about this and the original survey forms examined. If this was the cause, the effect could be reduced by combining 15-minute periods into, say, one hour periods instead.  compare existing data from other surreys, to see if the effect was present at adjacent locations at the same time; at the same location, at the same time; at the same location and time on different days.  if no other data exist, carry out an additional (short)check survey at the same location and time of day.  if no clear conclusion emerges, a judgement must be made on whether the data should be included in the analysis. When an error is suspected in an individual measurement, it should be corrected or discarded. It should be corrected only if the correct value is known with reasonable certainty. It is important not to throw away data lust because it might be in error: stronger evidence is needed. In most studies a few extreme values will not materially affect the results. However, in studies interested mainly in extreme values (for example, observance of speed limits) the treatment of extreme values needs to be rather more thorough, and include a visual assessment of a histogram of all the data. Data processing resource needs (excluding analysis) vary considerably between different types of surveys. As a rule of thumb, processing time can take about twice the time of field data collection. Computers do not necessarily speed up procedures as much as might be expected, though direct entry of observations into a hand-held computer clearly has the promise of much reduced processing time. Analysis Analysis seeks to draw conclusions relevant to the study objectives from the data characteristics and trends established in the surreys. Statistical techniques can be used to indicate, for example, whether there is a relationship between variables under examination or whether a significant difference has resulted from a particular road treatment. However, the analysis cannot, of itself, say anything about causes; why does one variable respond to a change in another or why a particular treatment has had some success? It is the job of the traffic engineer to design surveys which will yield data that can be used to test and quantify a hypothesis. To demonstrate, for example, that higher Vision: Mission: - - - - For in - speeds result from a road widening the survey must be designed to screen out all possible alternative factors (different traffic flows, weather conditions, etc.). The use of control surrey data may be a powerful tool in this analytical process. Page 47 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. Lesson 3.5: TRANSPORTATION SURVEYS ROAD INVENTORY SURVEYS The road infrastructure consists of links, junctions, parking spaces and terminals. The physical characteristics which will influence its use include its current geometrics and pavement structure, its traffic controls (signs, signals, road markings, and parking restrictions), sidewalks, shoulders, adjacent land use, service provision (for example, gas, water, electricity, telephones) and the intensity of non-traffic activities which encroach upon road space (for example, hawkers, builder's materials, market stalls etc.). The purpose of the inventory survey is to record this information. The detail of an inventory survey can be varied to suit needs. An approximate, but simple survey method involves Surveyors walking or driving along a link and locating objects or points by the distance (chainage) along the link and the offset from the center line. Chainage can be taken from a vehicle odometer or measured by pacing or measuring wheel. As much as possible, inventory Surveyors should be restricted to observation and measurement, as opposed to making any judgements. Junctions generally require a more detailed approach than links with, for example, measurements of corner radii and turning restrictions. Traffic signal information should normally be collected in a form consistent with the equipment manufacturer's specifications. The rate of progress of an inventory survey obviously depends upon the data items to be noted and the accuracy of measurements. However, a simple link survey for traffic planning purposes should progress at approximately 0.5 - 1.0 km/h. Link surveys can be carried out by pairs of Surveyors, one surveying to the left of the centerline, and the other to the right. The field sheets themselves are the main output from the survey. They should be filed and referenced to a master map showing the area covered by each field sheet. Individual road links and junctions can be related to a network, by a system of link and node numbering. Existing link/node numbers should be used if these exist (for example for accident reporting or signal maintenance) as this will permit ease of cross-referencing with other survey material. PARKING SURVEYS Parking surveys provide the data upon which the parking policy for an area can be decided. The provision of parking is obviously a major factor, primarily for private cars, in the accessibility of an area. Parking management is also a most effective low-cost traffic policy instrument Car parking spaces can be classified into on-street or off- street; public (i.e. available to the public) or private; formal (i.e. marked and controlled spaces) or informal. Parking and stopping spaces must also be provided for commercial vehicles (primarily delivering and collecting freight) and public transport vehicles (for picking up and setting down passengers). Other characteristics of For instructional purposes only 1st Semester SY 2020-2021 49 parking are dimensions and layout (including access roads); time controls; charges and costs; banned and restricted locations. Parking demand characteristics include: Accumulation  the number of parked vehicles in an area, at any given moment. A graph showing the variation of accumulation in a city center during the day, can be compared with the parking supply to show when there is over- or under-provision of parking space. Parking duration  the time one vehicle remains parked in one place. Parking load  the total demand on an area over a period of time, measured in vehicle- hours. It is the sum total of all vehicle durations, (equal to the area under the accumulation graph). Parking volume  total number of vehicles using the parking facilities over a period of time (usually one day). Turnover  rate of use of parking spaces, calculated by dividing the parking volume by the number of spaces. Arrival and departure rates  which affect the design of entry and exit facilities, particularly for off- streetcar parks. Two surveys are described here: parking inventory surveys, which determine the existing supply, by recording the number and location of spaces; parking patrol surreys which monitor demand and are usually for on-street (curbside) parking but can be used for off-street facilities. The two are usually undertaken together. Page 49 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No.  50 CEng 132n: Principles of Highway and Railroad Engineering An example of a completed link inventory form Page 50 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. For instructional purposes only 1st Semester SY 2020-2021 51 Coding a Network (from Leonard and Gower 1982) PARKING INVENTORY SURVEY This survey requires a base map, upon which the surveyor marks the location and number of parking spaces. The map should be approximately 1:500 scale, depending upon the amount of detailed information to be recorded. A sketch map is perfectly adequate, but officially published maps may be preferred. The parking inventory may also be incorporated into the road link and junction inventory maps. Where more than one form is required for a study area, a master reference map of the study area will be necessary, showing the area covered by each sketch sheet. The location and number of formal parking spaces is usually determined easily because the spaces are marked. The number of informal parking spaces requires some judgement. Curbside car parking spaces can be assumed to be Page 51 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No.  52 CEng 132n: Principles of Highway and Railroad Engineering 6 meters long and 2.5 meters wide. For informal areas, it is necessary to count the actual number of parked vehicles at a time of peak demand. PARKING PATROL SURVEY Surveyors patrol a predetermined route, with a predetermined number of parking spaces. The patrol is divided into a number of sections. Surveyors record the location of all parked vehicles, their registration number, and vehicle type using Form D which can be modified to allow the type of parking to be recorded on the form, by providing an additional column alongside the vehicle registration number. The area to be surveyed is decided from study objectives and the parking spaces within that area are identified from a parking inventory surrey. In addition to public spaces, the survey can include private, informal (e.g. waste ground), and illegal spaces (footpaths, no-parking areas), as required. The patrol interval depends on whether parking at that location short or long stay is but is typically 15 minutes. With low turnover, the patrol interval can be as long as 45 - 60 minutes; with high turnover 15 - 20 minutes is more appropriate. Preliminary data can be obtained from a pilot survey. The patrol interval should include an allowance of 5 minutes for rest and contingencies. The length of route is determined by the patrol interval (less 5 minutes), together with the Surveyor's walk speed. Typical walk speed is 20 meters/minute, although it depends on the amount of data the surveyor has to record; high turnover means more data and a slower speed. If parking accumulation is required without associated duration, only the total number of each type of vehicle parked in each section needs to be recorded on each patrol. Therefore, less data is collected, walk speeds are increased, and considerably longer routes are possible. Alternatively, data can be collected from a car, although a driver will be required. Routes should be defined to end at the start point, so that the surveyor wastes no time in returning to the starting point. A simple circuit may be defined by a Surveyor walking up one side of a street and back on the other. Routes are sub-divided into sections, typically of 20 spaces, to allow the identification of sections with different characteristics (for example duration, turnover). Section boundaries should occur where characteristics are expected to change, for example with change of adjacent land use from offices to shops. Data is then summarized by section. Output Vehicle arrivals, departures and accumulation can be calculated and entered into the boxes on the survey form itself. Parking duration is estimated by noting the patrol time at which each registration number was first seen, and the time at which it was last seen. The same result is obtained by counting the number of observations of a particular vehicle registration and multiplying by the patrol interval. Note, however, that if the vehicle is present on the first or last patrol only a minimum duration can be calculated. Different vehicle types (or parking types) can be dealt with separately. Page 52 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. For instructional purposes only 1st Semester SY 2020-2021 53 Bar charts can be drawn to summarize the parking duration pattern, if necessary, by vehicle type. If examination of these indicates this is warranted, bar charts for adjacent sections can be combined. An example of a Parking Inventory Survey (From Wells, Traffic Engineering - An Introduction) Page 53 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No.  54 CEng 132n: Principles of Highway and Railroad Engineering Parking patrol example Page 54 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. For instructional purposes only 1st Semester SY 2020-2021 55 Parking Patrol Survey form example ORIGIN - DESTINATION SURVEYS: REGISTRATION NUMBER METHOD Origin-destination (O-D) data is used to analyze the effect of proposals for change (for example, a new traffic management scheme, or a new road) on travel through a study area. The O-D data is kept constant, but routes and journey times can be changed; the impact of the proposal on individual trips and cumulative volumes, travel times, and costs can be assessed. O-D data is usually presented as a matrix of trip volumes between each origin and Page 55 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No.  56 CEng 132n: Principles of Highway and Railroad Engineering destination. The origin and destination points are the start and end zones of a trip but can also be the entry and exit points on the study area cordon. O-D information can be derived from home or roadside interviews, postcard and sticker surveys and by registration number plate surveys. For long term transport planning studies, and large urban areas, where it is important to establish the social and economic characteristics of transport users, interview surveys are best. Registration number plate surveys obtain less information but are easier to implement and are suitable for determining existing patterns of movement in small study areas. Surveys dealing only with local area traffic schemes are considered. The Registration Number Method is an observation survey which matches the number plates of vehicles which enter and exit the defined study area, in order to accumulate an O-D matrix. If observers are scattered throughout the study area, as well as at the cordon, the method can also be used to obtain large samples of travel time data between observation points and to determine routing of individual vehicles through the study area. The main problems with registration number surveys are that many reliable surveyors are needed, survey planning and coordination is complex and data processing and analysis are complicated and time-consuming (computerization of the registration-matching process is almost essential). Method Surveyors record the registration numbers of vehicles in- bound and out-bound to the study area, together with the time of observation and class of vehicle, if required. Two Surveyors are required at each observation point, one for each direction of traffic flow. Additional Surveyors can be located at intermediate points inside the study area, providing further information on routing and travel time. Each sighting of a vehicle provides more information on its travel time and routing, and possible stops inside the study area. The study area should be as small as possible consistent with study objectives, in order to minimize the number of Surveyors needed and to minimize the amount of data processing. The study area is defined by a cordon which should be drawn in such a way that vehicles entering or leaving the area cross the cordon only once. Usually it is not possible to record the registration numbers of all vehicles, so in practice a subset of the total flow is chosen. It is important that the subset is chosen such that Surveyors at all points can record 100 per cent of the subset; it is much better to record 100 per cent of a small subset than, say, 85 per cent of a larger one. The proportion which the subset forms of the total flow must be known. The most common method of choosing a sub-set is to use the last digit of the vehicle registration number. If any number between 0 and 9 is equally likely to occur, then the choice of any number automatically results in a 10 per cent subset. If two numbers are chosen, then a 20 per cent subset is selected. The last digit is chosen because it is most likely to be a random number. The Page 56 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. For instructional purposes only 1st Semester SY 2020-2021 57 method is simple but requires every number plate to be scanned before deciding whether it has to be recorded. Alternatively, vehicle color can be used to distinguish the subset provided that the color is not ambiguous; red is a poor choice, ranging from maroon to orange. Grey and white are often sufficiently unambiguous. (The pilot study should be used to check Surveyors' recognition of the color.) Selection by color can bias the results; for example, black is unambiguous, but there are few black cars in most cities and many of these may be official vehicles. Two (or more) colors may be used to provide a sufficient sample. If vehicle color is used, the simultaneous volume count must also be classified by color (as well as vehicle type) for expansion purposes. To avoid any cause for doubt, it is recommended that the whole registration number (letters and numbers) should be recorded in full. Form F is used to record the information. It is also possible to record data on either a tape recorder or hand- held microcomputer. For tape recorders the information is recorded verbally, doubling the rate of data acquisition because the surveyor does not take his eyes off the traffic. However, transcription can take longer than the survey itself, and other problems arise from equipment failure etc. Handheld microcomputers record time automatically, which if required makes recording twice as fast as using pencil and paper. If time is not to be recorded, then they do not have this advantage and are also subject to equipment failure problems. An experienced Surveyor can record up to 300 registration numbers (of four numbers and three letters) per hour, using pencil and paper. The rate varies according to local conditions, the type of registration number, the size of the plate and numerals, etc. The rate will be lower with inexperienced personnel and if other information is recorded; for example, time of observation reduces the rate by more than 50 per cent and vehicle type, reduces the rate by about 20 per cent. A pilot survey will help establish work rates. Output The survey begins at the same time at all locations, so that just after the start of the survey vehicles will be leaving the area which were not recorded entering it. Furthermore, just before the finish, vehicles enter the area which will not be recorded leaving it These vehicles should be ignored to obtain a clear picture of the proportion of through traffic The easiest way to remove most of them from the data set is to estimate the average time (`n' minutes) it would take to cross the survey area without stopping and to discard all registration numbers of vehicles which left or entered the area within `n' minutes of the start or finish of the survey. This is done before matching takes place. Computer processing is recommended for matching all registration numbers between each entry and exit point pair, which have a positive travel time. The output file should list the entry point, exit point, registration number, (if used) vehicle type, entry time, and journey time. Assuming no errors, vehicles entering the study area will have been matched to an exit point, except for vehicles which either entered during the survey and stayed in the area until after the survey was finished or which were in the area when the survey started Page 57 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No.  58 CEng 132n: Principles of Highway and Railroad Engineering but left during the survey. These vehicles form part of the "stopping" traffic discussed below. To identify stopping vehicles a histogram, is drawn of the travel times between each entry and exit point. The vehicles with the shorter travel times represent the non-stopping traffic, and the "tail" of longer travel times are for those vehicles which stopped in the area for some reason. It is necessary to decide the boundary between the two types. A simple rule is best employed, and applied to all cases: for example, using the first gap in the histogram longer than one minute. For the whole area, non-stopping traffic can be expressed as a proportion of total traffic in the survey period, total traffic being all (non- stopping and stopping) matched vehicles plus the unmatched vehicles discussed. Knowing the sample proportion, it is simple to factor the sample data to give an estimate of the total flows of non-stopping traffic. Page 58 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. For instructional purposes only 1st Semester SY 2020-2021 59 TRAFFIC VOLUME AND CLASSIFICATION SURVEYS The purpose of these surveys is to collect data on the number and types of vehicles passing a specified point on a link (link counts) or making specified movements at a junction (turning counts). The occupancy of vehicles may also be recorded to provide data on the volumes of people using the road space. Volume of traffic is expressed as a rate of flow, usually either as vehicles per hour (veh/h), in particular the peak hour demand on the road, or vehicles per day (veh/day), often converted into the value "AADT" (Annual Average Daily Traffic). By definition AADT can be known definitively only from a continuous count over a full year. However, factors for modifying short period counts to estimate AADT can be developed using long period counts for a limited number of sites which are chosen to represent the main types of road in the network. The annual counts at the sample sites will indicate seasonal, daily and hourly variation and hence the factors which relate traffic volumes (measured at any specific time) to the AADT, for that class of road. In urban areas peaks in traffic demand arise primarily because of home-to-work trips, occurring typically at the beginning and end of the normal working day. The `peak hour factor' expresses peak hour volume on a route as a proportion of the AADT. The peak hour factor for a particular route is often a consideration in classifying routes by type. As a rule of thumb, on urban roads the peak hour traffic is usually around 10 per cent of AADT (Note that the US Highway Capacity Manual defines peak hour factor in a different way - TRB, 1985). Examples of presenting traffic volume data are shown. These include volume maps, with a geographical background overlaid by bandwidths representing traffic volumes (see Fig 6.1 a); desire line diagrams, more often used for Transport Planning Studies, but which can also be useful in the planning stages of local area traffic surveys; junction turning movements. Traffic volume surveys are carried out by either manual or automatic traffic counts. Manual counts are particularly useful for vehicle classification, checking automatic counter accuracy, and surveying vehicle occupancy. Automatic traffic counts, using traffic counter equipment, are normally used only on links, and are particularly suitable for long-term data collection, and analysis of seasonal, daily, and hourly variations. In most studies, a combination of automatic and manual counts is needed. MANUAL TRAFFIC COUNTS In a manual count a surveyor stands by the roadside, counting and classifying the vehicles as they pass, dividing the survey into fixed time periods. It is normal for the surveyor to record only one direction of flow. Link counts should be located on straight sections of road for good visibility. Duration can be from a few minutes to several days, depending on purpose. Most counts are carried out for one day, starting before the morning peak hour, and extending for 12, 14 or 16 hours. Count periods are usually 15 minutes, with results summarized hourly. Shorter periods may be used for special purposes. Even when hourly counts are the most detailed data required, 15- Page 59 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No.  60 CEng 132n: Principles of Highway and Railroad Engineering minute periods should be used as errors are more easily identified (particularly start-up and close- down errors). Turning movement counts are carried out in the same manner as link counts, except that the turning movement of each vehicle is recorded, and the vehicle classification system is simplified (to compensate for the extra demands on Surveyors). These surveys are primarily concerned with the performance of the junction during peak periods, and survey duration is often confined to the morning and afternoon peak periods, typically between 2 and 4 hours each. Count periods are usually 15 minutes. However, at signalized junctions’ short- term volumes are determined by signal operations, and cycle times in excess of 2 minutes, or count periods less than 15 minutes, may cause apparent fluctuations in flow. In such cases it is best to record flow for each cycle, using the cycle time as the counting period. Example of a Registration Plate Matching Survey Data Reduction Page 60 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. For instructional purposes only 1st Semester SY 2020-2021 61 Presentation of Network Traffic Data Page 61 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No.  62 CEng 132n: Principles of Highway and Railroad Engineering Presentation Survey forms Survey forms must be designed for the specific needs of the study. Typical examples of completed field forms are shown which also illustrates the three- common pencil-and-paper methods of recording and classifying each vehicle. The 'five-bar gate' method is the most versatile and is applicable to both link and turning counts. It records data quickly (without the need for extreme neatness), is the most economical in use of space on the survey form and can be summarized quickly. The 'initial letter' method is appropriate for surveys with short periods of high flow, when field manpower is limited. It has the fastest rate of data recording where one surveyor must record several items and is very fast for counts in only one direction, as the Surveyor's need to look down at the survey form is limited. It does require longer processing time than other methods, neatness to distinguish the symbols and more processing manpower. The 'crossing out numbers' method is best with low or medium continuous flow. Page 62 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. For instructional purposes only 1st Semester SY 2020-2021 63 It is the least flexible of the methods and has the slowest recording rate. However, there are no problems of Surveyors 'losing count', and totaling is immediate. Alternatively, hand tallies can be used to record specific vehicle classes. They are faster and more accurate than pencil and paper methods, because only the total is recorded, at the end of each count period, and the surveyor is looking at the traffic flow almost continuously. However, vehicles can be missed while recording the cumulative total at the end of each count period. Note that tally counters should not be reset at the end of each time period as this waste too much time, rather the cumulative total should be recorded at the end of each period. Tallies are also subject to mechanical failure and should be checked regularly; a common fault is not registering every vehicle. Errors with manual counts usually arise from one of three sources: failure to define vehicle classification unambiguously, which can lead to undetected errors; failure to observe time periods accurately; surveyors having to count vehicles at a faster rate than they are capable. Particular attention should be given to these problems during the pilot survey. AUTOMATIC TRAFFIC COUNTS Equipment Automatic traffic counter equipment consists of a detector, to detect the vehicle, and a counter to record the information. The most common types of detector used in traffic counting are a hollow rubber pneumatic tube, held to the road surface by special clips, or an inductance loop (several turns of wire laid on or in the road surface in a rectangular or diamond shape). Pneumatic tubes detect the movement of a vehicle as the tube is depressed by a tire; this creates a pulse of air which closes a diaphragm in the recorder adding one axle (usually half a vehicle) to the counter total. Tubes should be installed in accordance with the following guidelines: -the count site must not be located where braking or acceleration occurs, or where overtaking is common, such as near junctions, bus stops, or other parking locations.  the count site must not be located near areas where children play or walk to school, as children are tempted to tamper with the counter or tube.  at the count site the road should be straight, level, and free from flooding.  the tube must be fixed at right angles to the direction of traffic flow.  the tube must be straight when fixed, and it should be stretched some 10 per cent to ensure it remains straight.  the tube must be clamped firmly to the road, with at least one clamp per lane of traffic, plus one near each curb.  the counter should be securely locked to a pole or tree, but the tube must not cross a footpath.  the tube and counter must be checked frequently for damage or malfunction. Page 63 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No.  64 CEng 132n: Principles of Highway and Railroad Engineering Pneumatic tube detectors record axles, and the counter assumes that two axles equals one vehicle. This overestimates the number of vehicles, and a correction factor should be applied, calculated from classified count data (short sample count if necessary, but including both peak and off-peak data), as follows: Correction Factor = Number of vehicles 1⁄2 x Number of axles on those vehicles A correction factor is calculated for a specific site, but various sites can be averaged to produce factors for an area, or different classifications of roads. Page 64 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. For instructional purposes only 1st Semester SY 2020-2021 65 Alternative Methods of Traffic Counts Page 65 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No.  66 CEng 132n: Principles of Highway and Railroad Engineering Automatic traffic counters A loop detector detects the presence, rather than the movement of a vehicle. The counter passes an alternating electric current through the loop, creating a magnetic field above the loop. The presence of a metal vehicle in the magnetic field causes a change in the electrical inductance, which is recorded by a sensor in the counter. Non-metallic vehicles cannot be detected, and pedal cycles are very difficult to detect because of their shape. Loops are usually permanent installations, laid in a shallow slot cut into the road surface, and sealed in by epoxy resin and bitumen. However, temporary loops can be fixed with sticky tape to the road surface. For loop wire specifications and installation, refer to the counter manual. Page 66 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. For instructional purposes only 1st Semester SY 2020-2021 67 Counters are either non-storage or storage. The former accumulates a running total, which must be read manually on site but do not record data by time period. They have limited applications for measuring total volumes over a week, month, or longer. Storage counters store count data for specified time periods, for future retrieval. They are complex and expensive, but highly desirable in urban areas where hourly variations in traffic are of concern. Modern counters record data by electronic means, either on magnetic cassette tapes, or in solid-state memory. Data can be transcribed manually but is more efficiently transcribed and summarized by computer. A counter should be checked with at least 50 vehicles, including all major vehicle classes, over a range of speeds. This is necessary to ensure that all vehicle types which should be counted are being counted, and those not required (for example pedal cycles) are not being counted. Combatting equipment errors Automatic traffic counters require a continuing program of checking and maintenance, by trained technicians with access to a supply of spare parts. More sophisticated machines need more specialized maintenance without which they may prove to be of limited use. Poorly adjusted equipment gives rise to consistent over-or under-counting, while the sensitivity of the counter may deteriorate over time due, for example, to a partly blocked detector tube. Page 67 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No.  68 CEng 132n: Principles of Highway and Railroad Engineering SPOT SPEED SURVEYS The speed of vehicles can be measured instantaneously (spot speed), or averaged over distance or time. The spot speed of a vehicle varies continuously, as the vehicle accelerates or brakes. Spot speed data is used to:  determine observance of, and suitability of, existing speed limits.  establish suitable new speed limits.  determine a suitable design speed for geometric design of the highway.  provide information for use in road safety and enforcement program.  assist the location of certain traffic signs.  determine speed-flow relationships and traffic densities (May, 1990). Spot speed surveys can also be used to establish trends (monitoring), for example in before and after studies. Spot speeds are usually measured on links (not at junctions) and are surveyed separately for each direction, with the surveyor normally positioned on the side of the road of the direction being surveyed. Spot-speed data is collected by either a radar speed gun (which gives automatic direct measurement) or short-base methods: timing a vehicle over a known short distance, either manually with a stopwatch or automatically using modern loop or twin-tube devices. Radar speed guns are suited to relatively narrow roads at low or medium flows, when vehicles travel past the observer individually. They are not suited to heavy traffic volumes, congestion or multi-lane roads. Furthermore, they are complex to use, require significant training of survey staff, and are expensive. Methods where vehicles are timed over a short base line are suitable for almost all traffic conditions and types of road. They require only simple and inexpensive equipment and are less obtrusive; the main problem is overcoming parallax error. This is reduced if a high vantage point is available. The presence of surveyors, equipment, or unusual markings on the road surface can affect driver behavior. The need to make the surveyors inconspicuous can affect choice of survey method and location. RADAR SPEED GUNS The location of the survey, sampling of vehicles and recording of results, are exactly the same as for the manual short base method described below. The main requirements of the radar speed gun are that the operator is fully trained on the accurate use of the equipment and that the speed gun, and its operator, are concealed from drivers. Measurements can be made from inside a parked car, but the car should not be parked in any location which affects the speed of the vehicles surveyed. Page 68 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. For instructional purposes only 1st Semester SY 2020-2021 69 Speed Survey using ‘Short-Base’ method MANUAL SHORT-BASE METHOD The survey location is usually at the middle of a road link. A specific point is chosen on the link, determined if appropriate by the study objectives (for example at a pedestrian crossing, to investigate an accident problem). A short- base length is created, over which vehicles can be timed. The length will depend on speeds on the road, with longer bases needed for higher speeds. Table below relates approximate lengths to average speeds. Short Base Lengths Average Speed of Traffic (km/h) Short-base Length Below 40 20 40-65 50 Above 65 75 Another approximate guide to length is that no vehicle in the traffic stream should take less than 2 seconds to traverse the short-base, in the traffic conditions prevailing during the survey. The ends of the short-base length are marked on the road surface with paint, chalk, or tape lines; the lines should be as inconspicuous as possible to drivers. Alternatively, the downstream line can be defined by the surveyor standing directly opposite a roadside object (for example, a power pole or tree) on the Page 69 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No.  70 CEng 132n: Principles of Highway and Railroad Engineering opposite kerb. The Surveyor must always be at the downstream end. The short- base length must be measured accurately, preferably with a metal tape- measure rather than a measuring wheel. In addition, a "sampling line" is marked upstream of the start line. The sampling line is needed so the surveyor can select the sample vehicle before he starts to record its travel time. The Surveyor must be able to see the sampling line and both timing lines, for all lanes of traffic; the pilot survey should determine whether a high vantage point is required. Sample vehicles are selected at the "sampling line". The survey supervisor should define which vehicles are to be surveyed. This might be every nth vehicle or according to some other method to ensure an unbiased sample (For example, as the surveyor looks up he notes the first vehicle in any lane to cross the sampling line and selects the next vehicle in any lane to cross the sampling line. This is the "sample vehicle". The Surveyor starts the stopwatch as the sample vehicle crosses the upstream start line and stops it as the same vehicle crosses the downstream line. The time is recorded on the survey form, together with vehicle type and whether or not it was a following vehicle in a platoon. The procedure is repeated for the next vehicle, and so on through the survey period. Unlike other types of survey, spot speed surveys are usually concerned with the non-peak periods of traffic flow, when speeds are higher. For example, where free-flow speeds are needed for setting speed limits, periods of low volume and good weather are specifically chosen. Definition of the target population is particularly important for spot-speed surveys, and may be:  all vehicles in the traffic-stream.  all vehicles with some choice of speed: for example, vehicles at the head of a platoon or single vehicles, on a fairly busy road.  all vehicles with a free choice of speed: this would be at low flows, when a complete choice is available. Survey forms should allow space for a description of the chosen sampling method. It is not always necessary to include all vehicle classes; for example, cars alone are often the target population. If more than one class of vehicle is included, the class of each vehicle should be marked on the survey form. Output Vehicle speeds are calculated from the times and known short-base distance. Results may be presented numerically or graphically. The most common graphical outputs are histograms and cumulative distributions of speeds which allow the extremes of the speed range to be seen. Numerical results can be mean speeds; the range of speeds; the proportion of vehicles above or below a certain speed (for road safety and enforcement). The 85th percentile is commonly used to describe speeds. This excludes extremely fast drivers (and gross measuring errors) and gives an estimate of what the majority of drivers consider a top limit. Page 70 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. For instructional purposes only 1st Semester SY 2020-2021 71 Example of a frequency distribution (for spot-speed data) Page 71 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No.  72 CEng 132n: Principles of Highway and Railroad Engineering NETWORK SPEEDS AND DELAY SURVEYS: THE FLOATING CAR METHOD Average network travel times and journey speeds are a major measure of road traffic performance. Not only are they an indication of existing road link and network performance, but they help identify specific congestion spots and are important as an input to traffic models and road investment appraisals. The basic method for measuring network speed and delay (and its causes) is the Floating Car Method. Other techniques which could be adapted to achieve the same purpose are the license plate survey and the elevated observer method. The advantages of the floating car technique are its direct and accurate measurement of travel times and delays, and personal experience of the causes of delays. The main disadvantages are the large resources required for a comprehensive survey of a network, and problems of the survey vehicle exceeding the speed limit. The floating car method only surveys cars. Other vehicle types can be surveyed by following a selected vehicle. However, it is difficult to choose random vehicles to follow and the route of the vehicle is not known in advance. Safety may also be a problem, especially at high speed or in heavy traffic. For a comprehensive study of a traffic network, surveyed links should include all the main road network, and various minor roads. As a monitoring technique for `before and after' surveys, specific turning movements should be identified for inclusion in the survey which represent `typical' movements through the site. Method The survey car is driven along a pre-determined route, at the typical speed of other cars. Surveyors in the car record the time at pre-determined timing points and the duration and cause of all stops and delays. In addition, the distance between the timing points must be measured. If a good quality map exists (scale down to 1:2500) it can be used. Alternatively, the distance must be measured on the street using a measuring wheel. Pilot surveys should coverall survey links, at the same times of day as the full survey. This is to familiarize survey staff with the method and routes and test the number of survey cars needed. Practice should also establish the driving style required to "float" or maintain one's position in the traffic stream, i.e. for the survey car to overtake the same number of vehicles as overtake it along the length of the route. The driver should not allow his driving style to change in response to the pressures of the survey. Number of runs, routes and timing points To account for different traffic conditions throughout the day, each survey run should be related to a particular time period. Typically, these periods are morning and afternoon peaks, daytime off-peak, evening post-peak. A minimum of three runs is recommended for each time period. Maximum route length capable of being covered in one run can be estimated from the duration of each time period being studied, the number of runs required and typical assumed speeds. For example, in a 2-hour period Page 72 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. For instructional purposes only 1st Semester SY 2020-2021 73 requiring 4 runs, the maximum route travel time would be 30 minutes; allowing (say) 10 minutes for turnaround and unexpected problems leaving 20 minutes travel time; route length at an assumed 15 km/h would be 5 km. Route selection then depends upon covering the chosen network in the most efficient way. Survey links should be identified on a road network map of the study area, together with one-way streets and banned turns. The following points must be considered: - most links are 2-way and must be surveyed in both directions. - circular routes are easier to operate; furthermore, U-turning vehicles can create problems of safety and delay, and it may be easier to have two vehicles circulating in opposite directions. - in general, if more than one survey car is needed, it is better to use short routes with one car per route (per direction) than longer routes with more than one car per route. - for before and after studies, the routes chosen for the before study must be repeated exactly, after the planned changes have been implemented. Timing points should be located at every main road junction. Additional timing points should be added where there is a long distance between adjacent junctions, or where significant changes in characteristics occur (for example, road widening; a major traffic generator such as a market). There is little extra survey effort involved in adding extra timing points, and the extra information need not be processed if not required. Each timing point must be a specific, easily identified, fixed point; a written description is required, with sketch map. At junctions, timing points will usually be the point of exit from the junction so that all delay associated with the approach to, and operation of, the junction is included with the approach link. Intermediate timing points are best located by roadside poles (for example, streetlight, telephone, road sign). To measure junction delay, it is best to have timing points just before a point which represents the longest queue length. Page 73 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No.  74 CEng 132n: Principles of Highway and Railroad Engineering Typical routes for moving observer/journey time surveys An example of a completed Journey Time/Moving Observer Delay Survey Output Data are usually presented by link (separately by direction), either as travel time or speed, and can then be aggregated for journeys or routes. Data from Page 74 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. For instructional purposes only 1st Semester SY 2020-2021 75 individual runs should be presented individually as they represent conditions at different times of day; simple averages can be calculated, but give biased results, as more runs are made when speeds are high and delays few. If the average of runs within a period is needed for some special purpose, this can only be done by ensuring the despatcher has sent every car off (in that period) at equal intervals. To do this the dispatching interval should be rather greater than the longest circuit time in the pilot survey at the most congested time. Travel times for each link or route can be compared by time of day and may be compared with the corresponding traffic flow by time of day. Page 75 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No.  76 CEng 132n: Principles of Highway and Railroad Engineering JUNCTION DELAY SURVEYS Delay is extra journey time incurred when a vehicle is impeded, in excess of the journey time if not impeded. Most delays in an urban area arise at junctions or accesses. Junction delay is a measure of junction performance, usually presented in the form of average delay per vehicle. The data can be used to compare junctions and indicate those most in need of improvement (either in design or control) or to compare junction delay before and after an improvement. There are two alternative survey techniques which are the Stopped Vehicle Count Method (counting the number of stationary queueing vehicles at fixed time intervals) and the Elevated Observer Method (timing sampled individual vehicles from a high vantage point). When comparing delay survey results (for example, in a before and after study), it is essential that the same survey method has been used. The stopped vehicle count method:  - provides only total and average delay and cannot distinguish between delays for different turning movements.  - does not take account of delays other than on junction approaches; therefore the method is not generally suitable for junctions where a significant proportion of delay is within the junction area (for example roundabouts).  - relies on a clear determination of the number of stopped vehicles. Where the queue is "rolling" - as at roundabouts - the method is not reliable. How- ever the method works well at traffic signals. The elevated observer method is suitable for all kinds of junctions, where high vantage points are available, from which all approaches to the junction are visible. In addition to mean and total delay:  - distribution of delay can be calculated.  - delay can be estimated separately by turning movement.  - delays can be divided between the junction approach and the shared junction area.  - the cause of delay to each sample vehicle can be recorded (for example, junction controls, pedestrians, other stopped vehicle). STOPPED VEHICLE COUNT SURVEY METHOD The number of stopped vehicles queueing on an approach to the function is counted at fixed intervals, usually 15 or 30 seconds, over a period of five or ten minutes. The total volume of traffic is counted at the same time. At sites where the whole queue cannot be counted by one Surveyor, or where vehicle classification is required, the approach must be sub-divided. The distance between the stop line and a point at least 10 meters beyond the back of the longest queue is divided into a number of `boxes' such that each box is small enough for a Surveyor to be able to maintain a continuous count of the number of stopped vehicles in it. The front wheels determine the box the vehicle Page 76 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. For instructional purposes only 1st Semester SY 2020-2021 77 is in, except that the first and last boxes should include all vehicles in front of or behind the box, respectively. A sketch plan should be prepared, showing for every approach: - the number of approach lanes, and any special fixed features (for example, bus stops, major accesses). - junction controls and signs. For signalized junctions, measure cycle time based on the average values over 5 cycles and note whether left turn on red is allowed. - whether delay is related to traffic movements on any other approach (for example, at roundabouts, and for opposed right turn vehicles at signals). - the longest queue normally observed during the peak period. If queues extend back to the next major junction upstream then the `floating car method' or registration plate matching survey should be used instead. Delay Survey using ‘Short-Base’ method Page 77 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No.  78 CEng 132n: Principles of Highway and Railroad Engineering Delay Measurement by Stopped Vehicle method Not more than three vehicle classes per Surveyor should be used, and the same classes should be used for delay and for flow. Non-motorized vehicles are not usually included. An observation interval of between 10 and 30 seconds should be chosen (preferably an exact factor of 60 seconds) but must not be an exact factor of any regular signal cycle time occurring during the survey. The observation interval remains fixed throughout the survey and is the same for all approaches. Duration is usually 5 or 10 minutes at a time, which allows the different approaches to a junction to be surveyed in rotation. (All approaches must be surveyed simultaneously if delays on them are related.) Output Total delay should be presented for each approach and for each time period studied. A grand total for all approaches may also be given provided the data were all collected at the same time. The total delay (in vehicle hours) on the approach during the duration of the survey is calculated by multiplying the total number of queueing vehicles counted in the survey period, by the fixed time interval (converted into hours). The average delay is calculated by dividing the total delay by the traffic volume in the same period. Page 78 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. For instructional purposes only 1st Semester SY 2020-2021 79 ELEVATED OBSERVER SURVEY Method An elevated location is found from where a Surveyor can see all the approaches to the junction. Individual vehicles are timed between fixed timing points on each approach. Vehicles are identified as either "delayed" or "not- delayed" and average travel times between the timing points determined for each category. The total and average delay is derived from the difference in travel times between the two sets. For each approach three points must be identified which are visible to the Surveyor. The finish timing point can be either the exit from the junction, as defined in the travel time surrey, or the stop line. The start timing point must be at least 10 metres beyond the longest anticipated queue and related to a fixed, easily identifiable object. The sampling point should be at least 20 metres in advance of the start point. A pilot survey should be used to test the procedure (which is similar in nature to the short base method for speeds-chapter 7) during the most congested time of the proposed survey period. Output The calculations of delay can be made separately by vehicle class, turning movement, or time period. The average undelayed travel time is calculated from the travel times of those vehicles identified as undelayed. For the vehicles identified as delayed, their individual delay time is calculated by subtracting the average undelayed time for that class, from the sample vehicle travel time. Mean delay is estimated by calculating the mean of all the sample vehicle delays. Total delay is estimated by multiplying mean delay by the traffic volume on that approach. The values for each approach can be added to give total junction delay in the survey period. Page 79 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No.  80 CEng 132n: Principles of Highway and Railroad Engineering SATURATION FLOW The maximum sustainable flow of traffic past a point is known as the saturation flow (or sat flow). It is a fundamental characteristic of a road and an important element of traffic engineering design studies, particularly related to traffic signal control and junction design. In order to compare flows of different vehicle mix, saturation flows are usually expressed in passenger car units (PCUs) in which vehicles are given a value equivalent to the number of cars that they displace from the traffic stream. The measurement of saturation flow, PCU values and other signal-related issues, such as lost time, is difficult. For the purpose of this manual, two alternative simplified methods for estimating sat flows at a signalized junction are outlined. These are the Flow Profile Method and the Saturated Period Count. The flow profile method consists of dividing the signal green time into regular, short, intervals (typically 6 seconds) and counting the vehicles which cross the stop line during these intervals. More details of this method, including its application to lost time measurement, are given in RRL (1963). The Saturated Period Count requires the classified counting of vehicles passing in only one interval, the duration of this interval being chosen to ensure saturation. Examples of completed survey forms for both of these methods are given. For both methods an inventory of the junction is completed during the pilot study and the movements to be counted are established. If the composition of the traffic stream is stable, and especially if more than 85 per cent are cars, the saturation flow may be measured using one `all-vehicle' category and then converted to PCUs by multiplying by the factor F, where Where N is the number of each type of vehicle in the traffic stream, and PCU their passenger car unit value (see below). An example of a completed Delay by Stopped Vehicle form Page 80 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. For instructional purposes only 1st Semester SY 2020-2021 81 An example of completed Survey Sheets for Saturation Flow Surveys If, as is often the case in developing cities, traffic composition is very variable from cycle to cycle, and no vehicle type is dominant, then this conversion Page 81 of Vision: A globally competitive university for science, technology, and environmental conservation. 130 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No.  82 CEng 132n: Principles of Highway and Railroad Engineering cannot be used. Groups of vehicles having a common average PCU value should be recorded in this case. Before the surveys, the number of signal cycles to be measured must be determined. As a general guide, 25 cycles should be enough at most sites, with up to 75 being required at key junctions in the network. For very quiet or unimportant sites, it may be sufficient to estimate saturation flow using previous studies. Measurements should ideally be made at sites which are free of all o