final exam questions and answers, Exams of Civil Engineering

Download final exam questions and answers and more Exams Civil Engineering in PDF only on Docsity! Transport modeling Chapter Three Introduction to Transport Modeling What do mean modeling in transportation Engineering? What do mean travel forecasting? What is the function? What types of data used? What are the factors of transport modeling? What are the FSM and purpose? Introduction to Transport Modeling  Model is simplified representations of reality which can be used to explore the consequences of particular policies or strategies.  They are deliberately simplified in order to keep them manageable and to avoid extraneous detail while hopefully encapsulating the important features of the system of interest.  It is that estimates can be made of likely outcomes more quickly and at lower cost and risk than would be possible through implementation and monitoring. Cont’d The choice of method of modelling depends on:  The purpose of the exercise  The level of detail and accuracy required and  The resources available. Uses in Today Transport Model  Providing traffic data for the future  Traffic Congestion, delay and accident  Environmental condition (air pollution and noise)  Parking difficulties  Future transport costs for people and for business/industry  Accessibility and mobility, etc  Analyzing the effect of alternative traffic plans/projects  Providing traffic data for “Cost-Benefit-Analysis”  Providing traffic data for calculating the development of traffic accidents and environmental conditions. Data requirements for transport modeling  Socio-economic data  Travel surveys  Land use inventory  Network data  It is graphical representations of the transport system.  It usually represented as a set of zones and links.  It encompasses large enough area to study all significant impacts and influences. Demand forecasting approaches There are two TD forecasting situations in transport planning: i) Travel demand studies for urban area  This approach requires extensive databases be prepared using home interview and/or roadside interview surveys.  The information gathered provides useful insight concerning the characteristics of the trip maker, such as age, sex, income, auto ownership, and so forth, the land use at each end of the trip, and the mode of travel. Cont’d  Travel demand forecasting in urban areas are three major factors affecting the demand for urban travels. a) Land use characteristics  b) Socioeconomic characteristics c) The availability of transport facilities and services ii) Intercity travel demand forecasting  Data that are used in this situation are generally aggregated to a greater extent than for urban travel forecasting such as city population, average city income, and travel time or cost between city pairs. Basic steps in Travel Demand Forecast a) Defining the study area Defining the study area and subdividing it into traffic zones is the primary task to be accomplished prior to collecting and summarizing the data. The selection of zones is based on  Homogenous socio economic characteristics  Minimum intra zone trips  Physical, political and historical boundaries  Zones should not be defined within other zones  The zone should generate and attract approximately equal trips, households, population or area. Transport System Modeling There are four stage in transport modeling 1. Trip Generation (production and attraction): models calculate the number of trips generated by (Oi-origin) and attracted to (Dj-destination) each zone in the study area 2. Trip Distribution: models calculate the trip pattern connecting trip productions and attractions 3. Mode Choice: models distribute trips from one origin (zone) to a destination to the different modes of transport 4. Traffic Assignment: car trips are distributed to the road network and public transport trips distributed to the public transport network. Cont’d Tri p generation How frequently to travel Trip distribution Where to travel to Mode split Which mode to use Assignment Which route to take Trip Generation  is the process of determining the number of trips that will begin or end in each traffic analysis zone within a study area.  Since the trips are determined without regard to destination, they are referred to as trip ends.  Each trip has two ends, and these are described in terms of trip purpose, or whether the trips are either produced by a traffic zone or attracted to a traffic zone.  Example a home-to-work trip would be considered to have a trip end produced in the home zone and attracted to the work zone. Cont’d Factors affecting trip production  At the HH level, the following are used in several studies  Income – the higher the income the higher is the trip generation rate  Car ownership – car owning household will generate more trips than a non-car owning household and also the more cars there are in the household, the more the number of trips generated.  Household structure (number of employed persons) Cont’d  Family size – the bigger the family, the more trips there are likely to be generated.  At an individual level, the following can be added to the above  age  gender  employments condition Cont’d Factors affecting trip attraction  Roofed space available for industrial, commercial and other services  Zonal employment, categorized in different groups (especially public attractive and non-public attractive employment)  Shopping center  Schools, universities  Entertainment (theaters, cinemas, sport arenas etc) Trip Distribution  It is provide a better idea on the pattern of trip making, from where to where do trips take place.  It is a process by which the trips generated in one zone are allocated to other zones in the study area. There are two methods in use trip distribution a) Gravity model b) Growth factor model a) Gravity model Cont’d If the zone adjustment factor given kij = 1 for all zones and friction factor ( travel time factor) fij = and c = exponent factor =2. The gravity model equation becomes Cont’d Where Tij = number of trips that are produced in zone i and attracted to zone j Pi = the total number of trips produced in zone i Aj = number of trips attracted to zone j Fij = a value which has an inverse function of travel time Kij = socioeconomic adjustment factor for interchange ij  The values of Pi and Aj have been determined in the trip generation process.  The sum of the trip production for all zones must be equal to the sum of trip attraction for all zones. Cont’d Where Ajk = adjusted attraction factor for attraction zone (column) j, iteration k Ajk = Aj when k=1 Cjk = actual attraction (column) total for zone j, iteration k Aj = desired attraction total for attraction zone (column) j j = attraction zone number, j=1, 2, 3…..n n = number of zones k = iteration number, k=1, 2, 3….n Cont’d  To produce a mathematically correct result, repeat the trip distribution computation using the modified attraction values,  So that the number of attracted will be increased or reduced as required.  Therefore, the new attraction factors are adjusted downward by multiplying the original attraction value by the ratio of the original to estimated attraction values. Mode Choice (Mode Split)  Mode choice is that aspect of the demand analysis process that determines the number (or percentage) of trips between zones that are made by private mode (automobile) and by public transport mode (transit).  The selection of one mode or another is a complex process that depends on factors such as  The traveler’s income The availability of transit service or auto ownership, and The relative advantages of each mode in terms of travel time, cost, comfort, convenience, and safety. Cont’d  Firstly quantitative factor such as  Relative travel time: in vehicle waiting and walking time by each mode  Relative monetary costs (fares, fuel and direct cost)  Availability and cost of parking  Second qualitative factors which are less easy to measure  Comfort and convinces  Reliability regulation  Protection security Cont’d Different model formulation exists to predict mode choice but most common formulation is called the Logit model. Where 𝑃𝑖𝑚= is the probability that traveler i will select alternative m; 𝑈𝑖𝑚=is the utility function representing traveler i selecting alternative m 𝑈𝑖𝑠= is the utility function representing traveler i selecting alternative s (s is a notation for all available alternatives) Cont’d Concept of Utility In general, discrete choice model postulate that: “The probability of individuals choosing a given option is a function of their socioeconomic characteristics and the relative attractiveness of the option.” where: Ui = f (X i. k) Ui = a0 + a1 (Travel time) + a2 (Wait time)+ a3 (Cost) Cont’d The major aims of traffic assignment procedures are:  To estimate the volume of traffic on the links of the network and obtain aggregate network measures.  To analyze the travel pattern of each origin to destination (O- D) pair.  To identify congested links and to collect traffic data useful for the design of future junctions Cont’d Primary Requirements to model trip assignment to:  Develop good aggregate network measures  Estimate zone to zone travel cost for a given level of demand  Obtain reasonable link flows to identify heavily congested links  Identify routes used between O-D pairs  Analyze which O-D pairs use a particular route Cont’d Trip assignment are the following data are required: (1) Number of trips that will be made from one zone to another (this information was determined in the trip distribution phase) (2) Available highway or transit routes between zones (3) How long it will take to travel on each route (4) A decision rule (or algorithm) that explains how motorists or transit users select a route and (5) External trips that were not considered in the previous trip generation and distribution steps.