PTE 2024 Module 4: Introduction to Travel Demand Forecasting (Part 1) PDF

Republic of the Philippines DON HONORIO VENTURA STATE UNIVERSITY Cabambangan, Villa de Bacolor, Pampanga COLLEGE OF ENGINEERING AND ARCHITECTURE Department of Civil Engineering A. Course C...

Republic of the Philippines DON HONORIO VENTURA STATE UNIVERSITY Cabambangan, Villa de Bacolor, Pampanga COLLEGE OF ENGINEERING AND ARCHITECTURE Department of Civil Engineering A. Course Code / Title : PTE 413 – Principles of Transportation Engineering B. Module Number : Module 4 – Introduction to Travel Demand Forecasting (Part 1) C. Time Frame : D. Description : This module emphasizes transportation planning. This will help students understand how transportation design affects the cost, convenience, speed, security, and safety of people, animals, and things. This course will focus on the Four-Step Forecasting Model, which uses trip generation, distribution, modal split, and route assignment to forecast future travel demand between origin and destination zones. Ineffective analysis of these initial steps will have a significant impact on the effectiveness of the existing and proposed transport systems. This module also discusses data collection; what to collect, how to collect, and how to process data. E. Objectives : At the end of this module, the learner should be able to: 1. Illustrate how the changes in the transport and land-use system affect each other. 2. Identify effective and existing measures on how to manage increasing number of travel demand. 3. Explain the overview, importance of travel demand forecasting and how the based-line data/trips can be obtained. 4. Familiarize the difference and discuss briefly the four (4) step forecasting model. 5. Learn the role and importance of Data Collection in Transportation Planning 6. Determine the three (3) important aspects of Data Collection. 7. Know the basic information required from a data collection, defining the study area, dividing the area into zones, and transport network characteristics. 8. Understand the behavior and factors affecting the travel through household data. 9. Identify three aspects of data preparation which are the data correction, data expansion, and data validation. Contents: SYSTEM COMPONENTS SIMULATING CHANGES IN TRANSPORT SECTOR Transport Sub – System  Travel time estimation  Traffic volume forecast  Network performance (travel speed, congestion, length of travel) SIMULATING CHANGES IN LAND USE SECTOR Land Use Sub – System  Trip generation  Residential and employment location, firm location  Changes in travel behavior TRAVEL DEMAND MANAGEMENT  Building roads has produced a car-oriented society in which the other modal alternatives have little opportunity to co-exist  Car ownership beyond the ability of the transport planner to control directly. But the car use and ownership are affected by land use and density, both elements that planners can affect.  A great deal of attention in planning is being paid to densification and integration. This includes concentrating development along well-served transport corridors (transport – oriented development) and increasing densities in areas undergoing rehabilitation  Managing the demand for travel is made up of many small interventions that cumulatively can have impact of car use but improve the livability of cities.   A sample of well – practiced and successful interventions include:  Park and Ride  Traffic Calming  Priority lane for buses, and high – occupancy vehicles  Alternate work schedules  Promoting bicycle use  Car sharing  Enhancing pedestrian areas  Improving public transit  Parking management DYNAMICS OF URBAN TRANSPORTATION TRANSPORTATION PLANNING Functional area within transportation engineering that deals with the relationship of land use to travel patterns and travel demands.  TRANSPORT DEMAND MODELS Refer to a series of mathematical equations that are used to represent how choices are made when people travel. Travel demand occurs because of thousands of individual travelers making individual decisions on how, where, and when to travel. These decisions are affected by many factors such as family situations, characteristics of the person making the trip, and the choices (destination, route, and mode) available for the trip. TRAVEL DEMAND FORECASTING Number of persons/vehicles expected to travel between a particular origin and destination via a particular route and mode of travel over a given period. Required for:  New construction  Expansion/improvement of existing facilities Trip is a one-way movement from a point of origin to a point of destination. Classification of trips:  By purpose (work, school, shop, other)  By Time of Day (a.m., p.m., peak, off-peak)  By Person Type (income, car ownership, family size, accessibility, etc.) TYPES OF SURVEY 1. Infrastructure and existing services inventories (public and private transport networks, signals) 2. Land use inventory 3. O-D Travel Surveys and associated traffic counts (Household Interview Surveys (HIS), Cordon line and Screen line Surveys; Flow, Speed and Travel Time Surveys 4. Socio – Economic Information (e.g. income, car ownership, family size) Objectives of Person – trip (PT) Survey  To capture the socio-economic profile of households in the study area  To establish detailed trip information of household members in the study area   By the end of the travel demand forecasting process, the traffic volumes (the number of vehicles per unit time) on the roads will be produced, which provide useful information about the congestion on the streets.  Thereafter, transportation planners can select the best transportation projects by reviewing the resulting levels of congestion from a series of transportation alternatives. Travel demand modeling aims to establish the spatial distribution of travel explicitly by means of an appropriate system of zones. Modeling of demand thus implies a procedure for predicting what travel decisions people would like to make given the generalized travel cost of each alternative. Four decisions are the basis of the traditional travel demand model: 1. Choice and reason to travel 2. Destination to travel to 3. Mode by which to travel 4. Route on which to travel The general form of the four-stage model is given in the right figure. The classic model is presented as a sequence of four sub models: trip generation, trip distribution, modal split, trip assignment. The model starts with defining the study area and dividing them into several zones and considering all the transport network in the system. The database also includes the current (base year) levels of population, economic activity like employment, shopping space, educational, and leisure facilities of each zone. Then the trip generation model is evolved which uses the above data to estimate the total number of trips generated and attracted by each zone. The next step is the allocation of these trips from each zone to various other destination zones in the study area using trip distribution models. The output of the above model is a trip matrix which denote the trips from each zone to every other zones. In the succeeding step the trips are allocated to different modes based on the modal attributes using the modal split models. This is essentially slicing the trip matrix for various modes generated to a mode specific trip matrix. Finally, each trip matrix is assigned to the route network of that mode using the trip assignment models. The step will give the loading on each link of the network. 4 – STEP SEQUENTIAL MODEL 1. Trip Generation Calculate the number of trips starting in each zone for a particular trip purpose 2. Trip Distribution Produce a table of the number of trips starting in each zone and ending up in each other zone.  3. Modal Choice / Modal Split Complete the allocation of the various trips among the available transportation systems (bus, train, pedestrian, and private vehicles) 4. Trip/Route Assignment Identify the specific routes on each transportation system that will be selected by the travelers. DATA COLLECTION Data collection is one of the most important steps in modeling. Only if accurate data is available, modeling becomes successful. The four-step forecasting model, an important tool for forecasting future demand and performance of a transportation system, was developed for evaluating largescale infrastructure projects. Since these models are applied to large systems, they require information about travelers of the area influenced by the system. Here the data requirement is very high, and may take years for the data collection, data analysis, and model development. In addition, meticulous planning and systematic approach are needed for accurate data collection and processing. This lesson covers three important aspects of data collection, namely, survey design, household data collection, and data analysis SURVEY DESIGN Designing the data collection survey for the transportation projects is not easy. It requires considerable experience, skill, and a sound understanding of the study area. It is also important to know the purpose of the study and details of the modeling approaches since data requirement is influenced by these. Further, many practical considerations like availability of time and money also have a strong bearing on the survey design. In this section, we will discuss the basic information required from a data collection, defining the study area, dividing the area into zones, and transport network characteristics.  a. INFORMATION NEEDED Typical information required from the data collection can be grouped into four categories: 1. Socio-economic data – this includes income, vehicle ownership, family size, etc. This is essential in building trip generation and modal split models. 2. Travel surveys - Origin-destination travel survey at households and traffic data from cordon lines and screen lines. Former data include the number of trips made by each member of the household, the direction of travel, destination, the cost of the travel, etc. The latter include the traffic flow, speed and travel time measurements. These data will be used primarily for the calibration of the models, especially the trip distribution models. 3. Land Use Inventory – This includes data on the housing density at a residential zone, establishments at commercial and industrial zones. This data is especially useful for trip generation models. 4. Network data – This includes data on the transport network and existing inventories which consist of road network, traffic signals, junctions etc. The service inventories include data on public and private transport networks. These particulars are useful for the model calibration, especially for the assignment models. b. STUDY AREA Once the nature of the study is identified, the study area can be defined to encompass the area of expected policy impact. The study area need not be confirmed by political boundaries but bounded by the area influenced by the transportation systems. The boundary of the study area is defined by what is called as external cordon or simply the cordon line. A sample of the zoning of a study area is shown in figure provided. Interactions with the area outside the cordon are defined via external stations which effectively serve as doorways to trips, into, out of, and through the study area. In short, study area should be defined such that majority of trips have their origin and destination in the study area and should be bigger than the area-of-interest covering the transportation project. c. ZONING Once the study area is defined, it is then divided into several small units called traffic analysis zones (TAZ) or simply zones. The zone within the study area is called internal zones. Zones are modeled as if all their attributes and properties were concentrated in a single point called the zone centroid. The centroids are connected to the nearest road junction or rail station by centroid connectors. Both centroid and centroid connectors are notional, and it is assumed that all people have same travel cost from the centroid to the nearest transport facility which is the average for a zone. The intersection from outside world is normally represented through external zones. The external zones are defined by the catchment area of the major transport links feeding to the study area. Although the list is not complete, few guidelines are given below for selecting zones. 1. Zones should match other administrative divisions, particularly census zones.  2. Zones should have homogeneous characteristics, especially in land use, population etc. 3. Zone boundaries should match cordon and screen lines but should not match major roads. 4. Zones should be as smaller in size as possible so that the error in aggregation caused by the assumption that all activities are concentrated at the zone centroids is minimum. d. NETWORK Transport network consists of roads, junctions, bus stops, rails, railway station etc. Normally road network and rail network are represented separately. Road network is considered as directed graph of nodes and links. Each node and links have their own properties. Road link is normally represented with attributes like starting node, ending node, road length, free flow speed, capacity, number of lanes or road width, type of road like divided or undivided etc. Road junctions or nodes are represented with attributes like node number, starting nodes of all links joining the current node, type of intersection (uncontrolled, roundabout, signalized, etc.). Similarly public transport network like bus transit network and rail network are represented, but with attributes relevant to them. These may include frequency of service, fare of travel, line capacity, station capacity etc. This completes the inventory of base-year transportation facility. HOUSEHOLD DATA To understand the behavior and factors affecting the travel, one has got the origin of travel when the decision for travel is made. It is where people live as family which is the household. Therefore, household data is the most basic and authentic information about the travel pattern of a city. Ideally one should take the details of all the people in the study to get complete travel details. However, this is not feasible due to large requirement of time and resources needed. In addition, this will cause difficulties in handling these large data in modeling stage. Therefore, same sample households are randomly selected, and survey is conducted to get the household data. Higher sample size is required for large population size, and vice-versa. Normally minimum ten percent samples are required for population less than 50,000. But for a population more than one million require only one percent for the same accuracy. a. QUESTIONNAIRE DESIGN The next step in the survey is the questionnaire design. A good design will ensure better response from the respondent and will significantly improve the quality of data. Design of questionnaire is more of an art than a science. However, few guiding principles can be laid out. The questionnaire should be simple, direct, should take minimum time, and should cause minimum burden to the respondent. Traditional household survey has three major sections: household characteristics, personal characteristics, and trip details. i. Household characteristics - This section includes a set of questions designed to obtain socioeconomic information about the household. Relevant questions are number of members in the house, no. of employed people, number of unemployed people, age and sex of the members in the house etc., number of two-wheelers in the house, number of cycles, number of cars in the house etc., house ownership and family income.  ii. Personal characteristics - This part includes questions designed to classify the household members (older than 5) according to the following aspects: relation to the head of the household (e.g. wife, son), sex, age, possession of a driving license, educational level, and activity. iii. Trip data - This part of the survey aims at detecting and characterizing all trips made by the household members identified in the first part. A trip is normally defined as any movement greater than 300 meters from an origin to a destination with a given purpose. Trips are characterized on the basis of variables such as: origin and destination, trip purpose, trip start and ending times, mode used, walking distance, public-transport line and transfer station or bus stop (if applicable). b. SURVEY ADMINISTRATION Once the questionnaire is ready, the next step is to conduct the actual survey with the help of enumerators. Enumerators must be trained first by briefing them about the details of the survey and how to conduct the survey. They will be given random household addresses and the questionnaire set. They must first get permission to be surveyed from the household. They may select a typical working day for the survey and ask the members of the household about the details required in the questionnaire. They may take care that each member of the household should answer about their own travel details, except for children below 12 years. Trip details of children below 5 years are normally ignored. Since the actual survey may take place any time during the day, the respondents are required to answer the question about the travel details of the previous day. There are many methods of the administration of the survey and some of them are discussed below: i. Telephonic - This enumerator may use telephone to fix an appointment and then conduct detailed telephonic interview. This is very popular in western countries where phone penetration is very high. ii. Mail back – The enumerator drops the questionnaire to the respondent and asks them to fill the details and mail them back with required information. Care should be taken to design the questionnaire so that it is self-explanatory. iii. Face-to-face – the enumerator visits the home of the respondent and asks the questions and fills up the questionnaire by himself. This is not a very socially acceptable method in the developed countries, as these are treated as intrusion to privacy. However, in many developed countries, especially with less educated people, this is the most effective method. DATA PREPARATION The raw data collected in the survey need to be processed before direct application in the model. This is necessary, because of various errors, except in the survey both in the selection of sample houses as well as error in filling details. In this section, we will discuss three aspects of data preparation: data correction, data expansion, and data validation.  a. DATA CORRECTION Various studies have identified few important errors that need to be corrected, and are listed below: i. Household size correction - it may be possible that while choosing the random samples, one may choose either larger or smaller than the average size of the population as observed in the census data and correction should be made accordingly, ii. Socio-demographic corrections – it is possible that there may be differences between the distribution of the variables sex, age, etc. between the survey, and the population as observed from the census data. This correction is done after the household size correction. iii. Non-response correction – it is possible that there may not be a response from many respondents, possible because they are on travel every day. Corrections should be made to accommodate this, after the previous two corrections. iv. Non-reported trip correction – in many surveys people underestimate the nonmandatory trips and the actual trips will be much higher than the reported ones. Appropriate correction needs to be applied for this. b. SAMPLE EXPANSION The second step in the data preparation is to amplify the survey data to represent the total population of the zone. This is done with the help of expansion factor which is defined as the ratio of the total number of households addressed in the population to that of the surveyed. A simple expansion factor Fi for the zone i could be of the following form. 𝑎 𝐹𝑖 = 𝑏−𝑑 Where a is the total number of households in the original population list, b is the total number of addresses selected as the original sample, and d is the number of samples where no response was obtained. c. VALIDATION OF RESULTS To have confidence on the data collected from a sample population, three validation tests are adopted usually. The first simply considers the consistency of the data by a field visit normally done after data entry stage. The second validation is done by choosing a computational check of the variables. For example, if age of a person is shown some high unrealistic values like 150 years. The last is a logical check done for the internal consistency of the data. For example, if the age of a person is less than 18 years, then he cannot have a driving license. Once these corrections are done, the data is ready to be used in modeling. OTHER SURVEYS In addition to the household surveys, these other surveys are needed for complete modeling involving four stage models. Their primary use is for the calibration and validation of the models or act as complementary to the household survey. These include O-D surveys, roadside interviews, and cordon and screen line counts. a. O-D SURVEY Sometime for small studies, or to get a feel of the O-D pattern without doing elaborate survey, workspace interviews are conducted to find the origin-destination of employers in a location. Although they are biased in terms of the destination, they are random in terms of the mode of travel. b. ROADSIDE INTERVIEWS These provide trips not registered in a household survey, especially external-internal trips. This involves asking questions to a sample of drivers and passengers of vehicles crossing a particular location. Unlike household survey, the respondent will be asked with few questions like origin, destination, and trip purpose. Other information like age, sex, and income can also be added, but it should be noted that at roadside, drivers will not be willing to spend much time for survey. c. CORDON AND SCREEN-LINE SURVEY These provide useful information about trips from and to external zones. For large study area, internal cordon line can be defined, and surveying can be conducted. The objective of the survey is primarily to collect the origin and destination zones and for this many suitable methods can be adopted. It could be either recording the license plate number at all the external cordon points or by post-card method. Screen lines divide the study area into large natural zones, like either side of a river, with few crossing points between them. The procedure for both cordon-line and screen-line survey are like road-side interview. However, these counts are primarily used for calibration and validation of the model