1 Flashcards
1
What is travel demand?
The number of persons or vehicles per unit time expected to travel on a given segment of a transportation system under specific conditions
What are the methods for forecasting travel demand?
Methods range from simple extrapolation of observed trends to sophisticated computerized processes involving extensive data gathering and mathematical modeling
What are the two basic demand forecasting situations in transportation planning?
- Urban Travel Demand Forecast
- Intercity Travel Demand
What information was required for urban travel demand forecasts developed in the 1950s and 1960s?
Extensive databases using home interview and/or roadside interview surveys
What are the three factors influencing urban travel demand?
- Location and intensity of land use
- Socioeconomic characteristics of people
- Extent, cost, and quality of available transportation services
How do land-use characteristics affect travel demand?
The amount of traffic generated depends on how the land is used, e.g., shopping centers vs. residential complexes
How do socioeconomic characteristics influence travel demand?
Lifestyles and values affect transportation resource decisions, with high-income areas generating more auto trips
What is the role of transportation facilities in travel demand?
Availability of transportation facilities and services (supply) affects demand; travelers consider service levels when choosing modes
What is the purpose of travel demand forecasting in urban transportation planning?
To predict travel behavior and resulting demand for a specific future time frame based on land use, trip makers, and transportation system nature
Why is understanding existing travel patterns important in transportation planning?
It helps identify traffic-related problems and develop forecasting models
What are the five characteristics of travel?
- Functional classification
- System extent
- System usage
- System performance/capacity
- System condition
How is travel demand measured?
In different ways for different analyses, including:
* Trip
* Trip end
* Traffic volume
* Person trip and vehicle trip
* Passenger vehicle and freight vehicle
* Person-mile traveled and vehicle-mile traveled
What is the significance of the time frame for travel surveys?
Travel demand varies seasonally and weekly, necessitating careful selection of survey time frames
What are Origin-Destination (O-D) surveys used for?
To classify trips into internal, external-internal, and through trips for forecasting and policy development
What is traffic forecasting?
Estimating the number of vehicles or people that will use a specific transportation facility in the future
What are the four steps of travel demand forecasting?
- Trip Generation
- Trip Distribution
- Modal Split
- Traffic Assignment
What is trip generation?
The first step in the four-step modeling procedure that establishes the total number of trips generated in a study area
What is trip distribution?
Allocating trip ends from the generation model to specific origins and destinations using transportation network characteristics
What is modal split?
The percentage of travelers using a specific mode of transport compared to all trips made
What does travel assignment estimate?
The volumes on the transportation system, including present-day and forecasted volumes
What is the Origin-Destination (OD) Matrix?
A table that summarizes the number of trips generated and attracted between defined zones
What methods can be used for estimating trip generation?
- Growth rate method
- Category analysis
- Regression model
What is the Gravity Model in trip distribution?
A method where trips are proportional to the number of trips produced and attracted by each zone and inversely proportional to the distance between zones
What is the generalized cost in modal split?
A method that quantifies both quantifiable and unquantifiable costs incurred during a trip using a specified mode
What is the disaggregate choice model?
A method assuming a person will use the mode offering maximum utility
What is the utility function for travel in a medium-sized city by car, bus, and light rail?
U = A -0.02X1 – 0.05X2
Where X1 is the cost of travel in pesos and X2 is the travel time (min).
What happens to the share of car users when a parking fee of P30 per trip is imposed?
The share of car is reduced from 36 percent to 24 percent, resulting in a shift to bus and rail with increased shares of 32 percent and 44 percent, respectively.
List the factors that affect modal split.
- Characteristics of the trip maker
- Characteristics of the journey
- Characteristics of the transport facility
What is the primary assumption in traffic assignment regarding route choice?
Car drivers will use the route or routes that allow them to reach their destination in the least time or distance.
What are the basic components used to represent a road network?
- Nodes (representing zone centroids)
- Links (representing roads connecting the zones)
What is the prerequisite for route assignment in traffic assignment?
Determination of the shortest path from one node to another.
What algorithm is commonly used to find the shortest path in a road network?
Dijkstra’s algorithm.
Describe the first step of Dijkstra’s algorithm.
Label the starting node with a value equal to 0, which is permanent.
In Dijkstra’s algorithm, how are temporary labels assigned?
Adjacent unlabelled nodes are given a label equal to the weight of the link plus the value of the previously labelled node.
What is the outcome once the final node has a permanent label in Dijkstra’s algorithm?
The shortest path has a length given by its permanent value.
What is the all-or-nothing assignment method?
All trips are assigned to the shortest path from the point of origin to the point of destination.
What is the basic process for conducting an all-or-nothing assignment?
- Find the minimum path between zones
- Assign all trips with the minimum path
- Repeat for all OD pairs
What does the constant assignment ratio method assume?
The number of trips assigned to a route is inversely proportional to the travel time or cost of that route.
List the basic steps for the constant assignment ratio method.
- Find possible routes between zones
- Calculate the level of service on each route
- Distribute trips inversely proportional to LOS
What principle does the incremental assignment method rely on?
Wardrop’s Principle, which states that routes used have equal level of service.
What are the steps involved in the incremental assignment method?
- Assign 1/n of the trips to a route
- Calculate the new level of service
- Assign the next 1/n trips
- Repeat until all trips are assigned
List the factors that affect traffic assignment.
- Speed limit
- Number of lanes
- Length of road
- Density of intersection
- Time of travel
