Highway and Railway Engineering PDF

Highway and Railway Eng… CIV 0311 - 1 | 1st Semester LESSON 1 Function: ▪ The Department of Public Works and Highways functions as the...

Highway and Railway Eng… CIV 0311 - 1 | 1st Semester LESSON 1 Function: ▪ The Department of Public Works and Highways functions as the engineering and TRANSPORTATION ENGINEERING construction arm of the Government tasked → is the application of technology and and to continuously develop its technology for the management of transportation infrastructure, purpose of ensuring the safety of all mobility service, traffic, and travelers for various infrastructure facilities and securing for all travel modes, in order to provide for the safe, public works and highways the highest efficient, rapid, comfortable, convenient, efficiency and quality in construction. economical, and environmentally sustainable ▪ DPWH is currently responsible for the movement of people and goods. planning, design, construction and maintenance of infrastructure, especially the MAIN BRANCHES OF TRANSPORTATION ENG: national highways, flood control and water ▪ Traffic engineering resources development system, and other ▪ Highway engineering public works in accordance with national ▪ Port and Harbor engineering development objectives. ▪ Airport engineering ▪ Railway engineering. HISTORY OF DPWH ▪ considered as old as the Philippine HIGHWAY ENGINEERING government, its existence dates back to → a branch of civil engineering dealing with the about four (4) centuries at the time of the planning, location, design, construction, and Spanish colonial era. maintenance of highways and with the regulations ▪ It emerged from its embryonic form in 1565 and control devices employed in highway traffic when the first settlement roads were operations. constructed by forced labor. RAILWAY ENGINEERING o Fortresses then were connected by → a branch of civil engineering dealing with the improved trails as supply lines and location, construction, and maintenance of railroads means of communications. o As Spain was in its expansion HIGHWAY program in the islands, it resorted to → a main road, especially one connecting major a policy of attraction by way of public towns or cities. works construction. HISTORY OF HIGHWAYS IN THE PHILIPPINES o In order to pursue their objective, the King of Spain designated the Spanish DPWH: Department of Public Works and Highways Governor General in the country as Mandate: Chief of Public Works assisted by a. The DPWH is mandated to undertake (a) the “Junta Consultiva” through a Royal planning of infrastructure, such as national Degree in 1867. roads and bridges, flood control, water resources projects and other public works, and; b. the design, construction, and maintenance of national roads and bridges, and major flood control systems. LMTC|1  THE DPWH TIMELINE primary roads or other 1898 Dept. of War & Public Works national secondary roads 1902 Dept. of Commerce & Police Applicable Bypass/Diversion Roads – Roads 1916 Dept. of Commerce & only for that divert through traffic away from Communications Primary and the city/municipality business centers 1931 Dept. of Public Works and Secondary (with affirmative feasibility study) Communications Roads Roads that would connect or fill the 1951 Dept. of Public Works, Transpo. gap between adjoining national roads and Communications (protruding) to form a continuous 1954 Bureau of Public Highways national road network. 1974 Dept. of Public Highways National Other existing roads under DPWH 1976 Ministry of Public Works, Transpo. Tertiary Road which perform a local function and Communications LOCAL ROADS 1979 Two (2) Separate Ministries: Provincial ▪ Connect cities and ▪ Ministry of Transpo. and Roads municipalities without Communications traversing National Roads. ▪ Ministry of Public Works ▪ Connect National Roads to 1981 Ministry of Public Works and barangays through rural Highways areas. 1987 Dept. of Public Works and ▪ Connect to major provincial Highways government infrastructure. Municipal ▪ Roads within a Poblacion and City ▪ Roads that connect to ROAD FUNCTIONAL CLASSIFICATION Roads Provincial and National Road Road Functional Classification Roads Classification Criteria ▪ Roads that provide inter- NATIONAL ROADS barangay connections to National A contiguous length of significant major Municipal and City Primary road sections extending linearly Infrastructure without Roads without any breaks or forks that traversing Provincial Roads connect major cities (at least around Barangay Other Public Roads (officially turned 100,000 population) comprising the Roads over to LGUs) within the barangay main trunk line or the backbone of the and not covered in the above national road system. definitions National ▪ Directly connect cities to Expressways Highways with limited access, Secondary national primary roads, normally with interchanges; may Roads except in metropolitan areas include facilities for levying tolls for ▪ Directly connect maior ports passage in an open or closed and major ferry terminals to system. national primary ▪ Directly connect major FUNCTIONAL CLASSIFICATION OF ROADS airports to national primary roads → is the process by which streets and highways are ▪ Directly connect tourist grouped into classes, or systems, according to the service centers to national character of service they are intended to provide. primary roads a. ARTERIALS – provide the highest level of ▪ Directly connect cities (not included in the category of mobility and the highest speeds over the major cities) longest uninterrupted distance. ▪ Directly connect provincial b. COLLECTORS – major and minor roads that capitals within the same connect local roads and streets with arterials. region Collectors provide less mobility than arterials ▪ Directly connect major at lower speeds and for shorter distances. national government infrastructure to national LMTC|2  c. LOCAL ROADS – provide limited mobility ▪ Is a 3, 379.73 km-long route extending from and are the primary access to residential Laoag City (north) to Zamboanga City areas, businesses, farms, and other local (south). areas METRO MANILA MAJOR ROAD NETWORK CIRCUMFERENTIAL ROADS SURFACE TYPE ▪ Concrete ▪ Asphalt ▪ Gravel ▪ Earth METRO MANILA MAJOR ROAD NETWORK PAN – PHILIPPINE HIGHWAY RADIA ROADS ▪ also known as Daang Maharlika ▪ is a 3,379.83-kilometer network of roads, expressways, bridges, and ferry services that connect the islands of Luzon, Samar, Leyte, and Mindanao in the Philippines, serving as the country's principal transport backbone. ▪ It is the longest highway in the Philippines that forms the country's north– south backbone component of the National Route 1 (N1) of the Philippine highway network. The entire highway is designated as Asian Highway 26 (AH26) of the Asian Highway Network. o The northern terminus of the highway is in Laoag and the southern terminusis in Zamboanga City. ASIAN HIGHWAY 26 (AH26) ▪ is a portion of the Asian Highway Network (AH) that was designated to the Philippines. ▪ also known as the Pan – Philippine Highway. LMTC|3  TRANSPORTATION IN THE PHILIPPINES Philippine Highway Act of 1953 DEPARTMENT OF TRANSPORTATION RA No. 917: AN ACT TO PROVIDE FOR AN (DOTr) EFFECTIVE HIGHWAY ADMINISTRATION, → is the primary policy, planning, programming, MODIFY APPORTIONMENT OF HIGHWAY coordinating, implementing and administrative entity FUNDS AND GIVE AID TO THE PROVINCES, of the executive branch of the government on the CHARTERED CITIES AND MUNICIPALITIES IN promotion, development and regulation of a THE CONSTRUCTION OF ROADS AND dependable and coordinated network of STREETS, AND FOR OTHER PURPOSES. transportation systems, as well as in the fast, safe, Date Signed: June 20, 1953 efficient and reliable transportation services. BUILD BUILD BUILD PROGRAM DOTr SECTORS → is the centerpiece program of the Duterte ❖ Road Sector administration that aims to usher the “Golden age of o LTFRB infrastructure” in the Philippines. Lack of o LTO infrastructure has long been cited as the “Achilles’ o OTC heel” of Philippine economic development. o TRB o BBB Program seeks to accelerate public ❖ Railways Sector infrastructure expenditure from an average o LRTA of 2.9 percent of gross domestic product o PNR (GDP) during the Aquino regime to about 7.3 o MRT percent at the end of the Duterte ❖ Maritime Sector administration. o PPA o This will cost around P8 trillion to P9 trillion o PCG from 2016 to 2022 to address the huge o MARINA infrastructure backlog in the country. o PMMA ❖ Aviation Sector o CAAP o CABN o MRT o Airport Authorities PHILIPPINE RAILWAYS INSTITUTE (PRI) → a research and training center under the administrative supervision of the Department of Transportation, shall be the planning, implementing, regulating, and administrative entity for the development of human resources in the railway sector to ensure efficient, reliable, and safe railway transportation services. LMTC|4  LESSON 2 rationality must be avoided because they might believe that as professionals, they are uniquely PLANNING STAGE FOR HIGHWAY super qualified to judge what is best PROJECTS for the society in their field of expert and competence. PROJECT DEVELOPMENT CYCLE o They must accept that their personal values and goals are different from other participants. PLANNER’S FUNCTIONS: ▪ To prepare preliminary design, scoop of study and initial work program. Know the basic needs, plan and objectives of affected persons. o Ex. → is the application of technology and Feasibility Study Environmental Impact Assessment Parcellary Survey Resettlement Action Plan,etc.) ▪ Exploration of alternatives. Data gathering by contacting the representatives of other agencies involved. PLANNER ▪ Detailed analysis. Prepare detailed plan for → also referred as Planning Engineer. appropriate community interaction. → they prepare projects that undergo various, ▪ Secure formal ratification from the local rigorous and careful studies. officials and have the results documented. If o They work out in exchanging information as nothing goes wrong, this step is considered to the needs, goals and alternative solutions final. of those who are affected, and to incorporate o Good ethics demand that planners them into the planning and decision making. should understand that their role is to o Planners should act as coordinators, provide knowledge and unbiased catalysts, work as community advocates and information. To be partisan and should not be either partisan or advocate to emotionally involved, will only a particular solution. jeopardize their credibility. This might give them the feeling of personal PLANNER’S ROLES: defeat and disillusionment with their ▪ To provide technical and organizational profession, if the solutions that they support. offered are only thrown into the trash ▪ To receive input or information on the needs can. and goals of affected persons group or agencies. ▪ Incorporate the above for planning and making decision. o The planner’s role must be of a clarifier, expediters, conciliators and impartial negotiators. The myth of LMTC|5  PLANNING DIFFICULTIES ▪ Economic – is the cost of benefits more than ▪ Financial – funding source due to economic the cost of investment? condition. INVESTMENT COST AND BENEFIT COST OF ▪ Political – pressure from the politicians. HIGHWAY PROJECTS ▪ Technical – objective process based on A. Quantifiable Market Value: technical knowledge is overpowered by 1. Cost of highway as to: political decision. a. Planning Cost b. Right of way appropriations c. Construction costs d. Maintenance costs e. Operating costs 2. Cost benefits to highway users: a. Vehicles operating costs (including congestion cost) net PRE – FEASIBILITY STUDY income or decrease in costs of → is a preliminary study undertaken to determine, vehicle operation per year. analyze, and select the best business scenarios. b. Travel savings time FEASIBILITY STUDY (commercial). Net increase or → is an engineering study based on test work and decrease in travel time engineering analysis, which presents enough multiplied by the peso value of information to determine whether or not the project commercial time. should be advanced to be final engineering and c. Motorist’s safety (economic construction stage. cost accident). Net change in → This is a “go/no-go” decision point, thereby expected number of accidents implying that sometimes the answer is NO. times the average cost per accident per year. OUTLINE FOR A FEASIBILITY STUDY (FS) FOR B. Non-Quantifiable Non-Market Value: A ROAD PROJECT 1. Cost benefits to highway user: ▪ Traffic – The volume and composition of the a. Motorists safety – Accident traffic in the area are among the controlling cost of pain suffering and factors in determining the type of deprivation. improvement and the benefits to be realized b. Comfort and conversion – from the FS. Discomfort, inconvenience and ▪ Engineering Aspect – Present road strain of driving. condition, alternative technical solution, c. Aesthetic from driving viewpoint preliminary surveys, availability of resources, – Benefit of pleasing views and construction problems, project execution and scenery from road. scheduling. C. Quantifiable Non-Market Value: ▪ Management – Construction organization, 1. Cost benefits to highway users – maintenance and operational organization. Traveling saving time (non- ▪ Environmental – How to mitigate negative commercial) Minutes save per impacts of the project with the environment vehicle trip. ▪ Social – effect of the project to the society The intent of financial expenditures for highways ▪ Financial – Construction capital cost, and public transportations are enumerated as maintenance and operation cost, revenues follows: (for incoming generating roads ex. Toll fees) 1. To augment the country’s level of economy. and financial profitability (benefits cost) 2. To provide easy access to working place. LMTC|6 3. To facilitate public services; police, fire for substitute, or an alternative but shall protection etc. passed rigorous test 4. To facilitate medical care, schooling and delivery of related basic services. HIGHWAY PROGRAMMING APPROACHES: 5. To give landowner benefits to transportation 1. Financial resources are either short or long and increase property assessment. ranged implementation by the agency's 6. Benefit to motor vehicle users through lower functions like construction, operations, and cost of operations and maintenance. maintenance. 7. Benefit in time saving. 2. Recognition of the legislative and 8. Less road accident. administrative desire and constraint. 9. To give maximum comfort and ease of travel. 3. Tentative priorities based on economic analysis, critical situations, present and HIGHWAY PROGRAMMING future expected level of traffic and claims ➔ involves a process of selecting and based on political subdivisions. scheduling projects on the basis of the 4. Providing continuity of route system and relative urgency of the work. coordination with other transportation mode. ➔ A key element of process is the matching of 5. Selection of projects based on availability of needed projects with available funds to labor and materials, including climatic accomplish the objectives during a given conditions. period. 6. Scheduling the project implementation in o This determines what are the feasible coordination with other agencies, acquiring projects that should be included on right of way and making final plan and the annual infrastructure program. specifications. 7. Budgetary reserve to cover emergencies like floods and other natural disasters THREE (3) INSEPARABLE SETS OF INPUT 1. Economic – Deals with the questions of resources. 2. Financial – of who pays and who spends, how much, and where? 3. Political and Administration – This involves decision making. o In highway programming, projects are prioritized. Those that are most economically viable were selected, if they fit into the financial capability and of course political criteria. Projects that failed on either financial or political criteria are abandoned, modified LMTC|7  LESSON 3 ❖ TRAFFIC CHARACTERISTICS ✓ Primarily involves traffic volumes and traffic characteristics. HIGHWAY DESIGN o Consider the ffg: ➔ is a process in Highway Engineering where ▪ Average Daily Traffic (ADT) the most appropriate location, alignment ▪ Peak hour traffic and shape of a highway are selected. ▪ Directional Distribution HIGHWAY CHARACTERISTICS: ▪ Composition of traffic ▪ Projection of future traffic ▪ Self-explaining roads demands ▪ Roads that encourage safe speeds ❖ PHYSICAL ELEMENTS/CHARACTERISTICS ▪ Forgiving roadsides ✓ Includes: ▪ Functionality ▪ Highway capacity ▪ Predictability ▪ Access control and management ▪ Homogeneity ▪ Pedestrians (bus stops, loading areas, stairs) FIVE (5) MAJOR FACTORS: ▪ Bicycle facilities and environment 1. Human Factors and Driver Performance (Highways should complement 2. Vehicles their environment) 3. Traffic Characteristics ❖ ECONOMIC FACTORS 4. Physical Elements ✓ Concerned with the cost of a proposed 5. Economic Factors improvement and the benefits resulting from it. ❖ HUMAN FACTORS AND DRIVER PERFORMANCE DESIGN DATA ✓ Determines how effectively will the drivers MOST COMMON DATA NEEDED FOR HIGHWAY be able to use the road. DESIGN o Driver tasks that include vehicle ▪ Field Survey Information (Topo) control (factors such as sight ▪ Alignment distances, reaction times, passing ▪ Spatial Data (Barangays, Protected Sites, maneuvers are important) Ancestral Domains, etc) o Use of the facility by older drivers ▪ AADT (Annual Average Daily Traffic) and older pedestrians ▪ Subsurface Investigations o Errors due to driver deficiencies and ▪ Catchment Areas (For Cross Drain Design) situational demands ▪ Existing Streams/Rivers o Speed ▪ Existing Structures and Utility Services ❖ VEHICLES ✓ Determines what types of vehicles will use ❖ FIELD SURVEY INFORMATION (TOPO) the road. o Designers should consider the Topographic Surveys (Topo) largest design vehicle that is likely to → is a 3D representation of the project site. use the facility taking also into Most common ways of generating a consideration the frequency of the topographic survey is through the said vehicle. use of: o This is also important in choosing ▪ Contours the design of critical features like ▪ COGO Points curve radii. ▪ DEM LMTC|8 ❖ ALIGNMENT ❖ CATCHMENT AREAS → Also called the Horizontal control. → is an area of land that collects water after → is the route of the road, defined as a rainfall. series of horizontal tangents and curves. o Water flows down into these areas Factors that affect an alignment: and collects into rivers and streams. ▪ Design Speed o Catchment areas are necessary for ▪ Profile the design of cross drains ▪ Road Right-of-Way o Catchment areas can be determined ▪ Environmental Impact using any GIS software ▪ Economic cost ❖ EXISTING STREAMS/RIVERS ▪ Political Intervention → are necessary for the effective planning ❖ SPATIAL DATA and design of box culverts, bridges and → helps in better decision making when possible outfalls. designing highways. → Can also be determined using GIS o GIS software is commonly used software or via field surveys. for identifying spatial data. o QGIS is an example of a GIS ❖ EXISTING STRUCTURES AND UTILITY software. SERVICES ▪ Barangays, Municipalities → are necessary especially when the project ▪ Critical and Proclaimed Watersheds involves road widening. ▪ Historical and Heritage Sites → This is acquired through field surveys. ▪ Mangrove Forests ▪ Ancestral Domains DESIGN PROCEDURES ❖ ANNUAL AVERAGE DAILY TRAFFIC For road openings: (AADT) 1. Obtain topographic survey through any of → is the total volume of vehicle traffic on the different methods a highway or road for a year divided by 2. Plot the data in any road analysis software 365 days. (Civil 3D, MX Road, OpenRoads) to model → It is a measurement of how busy a road the surface is. 3. Plot the alignment → It directly affects highway 4. Adjust the alignment making sure all factors characteristics such as: are put into consideration ▪ Pavement thickness 5. Generate the existing profile ▪ Level of Service (LOS) 6. Create a design profile making sure that it ❖ SUBSURFACE INVESTIGATIONS passes all design criteria and standards Investigations below the subgrade level. 7. Create the cross section depending on the ▪ For areas with light cut and fill, necessary features of the highway investigations should be fulfilled with 8. Generate the corridor at least a depth of 1.5 m below the 9. Layout the drainage system proposed subgrade 10. If using a pipe network for storm drains, do ▪ For areas with deep cut, or with large Rainfall Analysis and Runoff Analysis in embankments across marshland, or Storm and Sanitary Analysis (SSA) if the subsurface information 11. If using retaining walls and structures, use indicates the presence of weak slope stability software like GEO5 for layers, the depth shall depend on the analysis existing topography and nature of the 12. Add traffic signs and markings as needed soil 13. Iterate until optimum design is achieved LMTC|9  DESIGN CRITERIA & STANDARDS decide on what to do and initiate a maneuver to avoid the said threat. ALIGNMENT DESIGN ▪ Passing Sight Distance – is the o The most efficient alignment is a straight line. minimum distance required to safely o But, due to several factors, alignment design make a normal passing maneuver on 2- is not THAT straightforward. lane highways. HORIZONTAL ALIGNMENT SUPERELEVATION ▪ Horizontal alignment design should be safe o Centrifugal force is counteracted by the ▪ It should also be cost efficient frictional force ▪ Must take the impact to the environment into o In portions with superelevation, the weight of consideration the car helps in counteracting the centrifugal ▪ Must take right-of-way issues into force consideration ▪ Drivers should feel comfortable Dos and Don’ts in horizontal alignment design: ▪ Alignment should follow the natural curve of the ground RADIUS OF CURVES ▪ Avoid alignments that will result in a very o Flatter curves are recommended steep profile o Curves should fit the natural swing or ▪ Avoid sudden curves after a long straight directional bend of the ground segment o Reasonable cost should also be considered rather than to follow blindly the minimum DESIGN SPEED curvature allowable ➔ is the target speed at which drivers are o Avoid curves with a small radius after a long intended to travel on a street, and not, as straight segment often misused, the maximum operating o Avoid kinks speed. Type of Terrain: ▪ Level ▪ Rolling ▪ Mountainous o Expressways should be designed for speeds WIDENING OF CURVES not less than 80 kph. o is implemented for roads with 2 lanes o Design speed along a highway can vary o This is to give allowance for long vehicles to depending on the topology or facility complete a turning maneuver in a curve requirements without falling outside the pavement SIGHT DISTANCES ➔ is the distance at which a driver of a vehicle can see an object of specified height on the road ahead ▪ Stopping Sight Distance – is the minimum distance required for a vehicle, VERTICAL ALIGNMENT travelling at the design speed, to stop ➔ Also called the Profile before reaching an object in its path. ➔ they serve as the vertical control ▪ Decision Sight Distance – is the o The profile should be consistent with distance needed for a driver to detect an topography unexpected threat, recognize the threat, L M T C | 10  o User flat curves and avoid curves of oThe most commonly used method is maximum degree the Rational Formula: 𝒄𝒍𝑨 𝑸𝒑 = 𝟑. 𝟔 Where: Qp = design discharge, m3/s c = runoff coefficient I = rainfall intensity within the time GRADIENT of concentration, mm/hr o Maximum grades of 5% are considered A = catchment area, km2 appropriate for a design speed of 110 kph ❖ DESIGN FLOOD FREQUENCY o For a design speed of 50 kph maximum o The design of drainage structures grades are generally in the range of 7 to 12% considers estimates of the magnitude depending on topography of floods based on frequency of o In the Philippines the maximum grade widely occurrence used is 6% o It differs depending on the type of o On through cut sections grade should be at drainage structure or condition being least 0.50% to provide longitudinal drainage considered o Allow sufficient ❖ CROSS SLOPE grade on → or crossfall is the slope of the surface of a through cut pavement measured at right angles to the sections to avoid horizontal alignment ponding. o The smoother the surface the more efficient it is in shedding water, but DRAINAGE DESIGN hazardous conditions likely to result o Water is one of the most common enemy of from a thin film of water on the any highway infrastructure and can infiltrate surface should not be overlooked parts of the highway both from above and o Surface Type: High, Intermediate, below Low o Water from above can cause erosion of ❖ STORM DRAINS slopes (Storm water) o Road drainage should be designed o Water from below can push the pavement up for a 15 year flood Design Capacity, or it can cause the underlying soil to collapse with a check capacity of a 25 year and cause serious damage to the highway flood (Water table) o Minimum flow velocity should be at o The alignment of the highway and its 0.8 m/s at pipe full; Maximum velocity relationship with the drainage systems is the to be adopted or piped drainage foremost concern of the hydraulic engineer systems is 5 m/s o One of the most common software used for o Minimum pipe size adopted should drainage design is Storm and Sanitary be 910 mm in order to allow the Analysis (SSA) passage of debris and minimize the risk of blockage ❖ RAINFALL ANALYSIS o Rainfall Intensity Duration PAVEMENT DESIGN Frequency (RIDF) can be acquired Pavement – is defined as that portion of the road or from PAG-ASA highway, placed above the subgrade specifically for ❖ RUNOFF ANALYSIS the support of and to provide a running surface for o Estimate the peak flow and flow vehicular traffic hydrograph L M T C | 11 PAVEMENT DESIGN – is the process of determining the thickness and strength of a pavement laid on a soil foundation (subgrade) for the purpose of providing an even non-skid, stable and desirable surface, permitting efficient, rapid and safe flow of traffic in accordance with specified loads Three (3) Types of Pavements found in the Philippines: ▪ Flexible or Asphalt pavement ▪ Rigid or Concrete pavement ▪ Unbound, gravel surfaced, unsealed or ‘unpaved’ roads (usually restricted to local rural access or temporary roads). o These are a subset of flexible pavement EARTHWORKS Factors that influence the performance of a pavement are: ▪ Traffic (volume and loading) ▪ Subgrade support strength, or stiffness ▪ Water (which affects most pavement materials) ▪ Pavement material performance ▪ Quality of construction EARTHWORKS o One of the most frequent disturbances in road operation is slope failure. Some causes of slope failure include: - Decrease in soil strength due to water seepage - Changes in the balance of gravity due to artificial cut and fills - Increase in pore pressure due to heavy rainfall - Increase in gravity acceleration during earthquakes Factors affecting design: - Height – for high embankments, it is sometimes necessary to provide lateral support such as retaining structures or other structural measures - Slopes - Foundation - Loading - Selection of Embankment Materials - Groundwater L M T C | 12  LESSON 4 that the design features of the highway govern DIVISION OF HIGHWAY DESIGN Design Speed Implications: ▪ Geometric Design o At higher running speeds a rider or ▪ Intersection Design driver has less time to react to a ▪ Highway Drainage Design situation and therefore there is the ▪ Pavement Design likelihood that an error will result in a ▪ Earthworks crash; ▪ Road Facilities o Momentum and kinetic energy of a ▪ Roadway lighting vehicle increases rapidly with speed ▪ The sudden dissipation of this energy in a crash means that GEOMETRIC DESIGN OF HIGHWAYS the injury to occupants is ➔ one of the divisions of highway design more sever concerned with the positioning of the physical elements of the roadway according ❖ SIGHT DISTANCE to standards and constraints o The distance at which a driver of a vehicle can see an object ahead of Three Main Parts of Geometric Design time. 1. Alignment (Horizontal –Plan) – is the route o Adequate sight distances should be of the road, defined as a series of horizontal available along the full length of a tangents and curves. road for vehicles to be able to stop (or 2. Grade line (Vertical -Profile) – is the vertical overtake) safely. aspect of the road, including crest and sag curves, and the straight grade lines Types of Sight Distance: connecting them. 1. Stopping (Non-Passing) Sight 3. Cross Section - shows the position and Distance number of vehicle and bicycle lanes and 2. Decision Sight Distance sidewalks, along with their cross slope or 3. Passing Sight Distance banking. Cross sections also show drainage features, pavement structure and other items Stopping (Non-Passing) Sight Distance outside the category of geometric design. o Available distance on a roadway to enable a vehicle traveling at the Geometric Design Elements design speed to stop before reaching ▪ Design parameters (speed, vehicle, volume) a stationary object ▪ Sight distance (Visibility) o applied where only one obstacle must ▪ Horizontal Alignment (curves, radius of be seen in the roadway and dealt curvature, super-elevation) with. ▪ Vertical Alignment (vertical curve, gradient) SSD Calculation: ▪ Combination of Horizontal and Vertical o Minimum sight distance for the driver to stop Alignment without colliding at any point of the highway. ▪ Cross Section SSD = Lag Distance (Reaction Time) + Braking ▪ Drainage Distance (After application of brakes) ❖ DESIGN SPEED 𝑣2 → defined as the maximum safe speed that SSD = 𝑣𝑡 + ± 𝑛 2𝑔(𝑓 100 ) can be maintained over a specified section of highway when conditions are so favorable L M T C | 13