Transportation Flashcards
Trip generation
Deals with the number of trips that a particular site is likely to generate. Thus, it is a byproduct of land use and intensity of use, factors which “induce” people to travel. The propensity to make trips is also dependent on the characteristics of the journey, trip purpose, and socioeconomic characteristics of the person making the trip (income, age, auto ownership).
Origin-Destination Survey
This survey requires that roadblocks be set up along major routes. The imaginary line that denotes the boundary of the study area is known as the cordon line. Motorists within the cordon area can then be sampled and asked questions on where they are coming from (address or point of origin) and where they are going (destination). That questionnaire is generally mailed back by the respondent.
Cross tabulation models
They allow for estimates of trip generation rates based on land use type, purpose, or socioeconomic characteristics. Trip generation models, tables, and surveys all have their own sources of error and should only be seen as estimates.
Typical Trip Generation Rates
11 daily trip ends for every 1,000 square feet of general office space 9.6 daily trip ends per single family residential dwelling 6.6 daily trip ends per apartment unit 43 daily trip ends per 1,000 square feet of shopping center space 7 daily trip ends per 1,000 square feet of light industrial development
Trip Distribution
Examines where people are going. Provides info on # of people going between zones. Also looks at distances, time, cost, nature of trip, socio-econ characteristics, and transpo systems.
Gravity Model
Estimates # of trips based on attractiveness of a spot compared to trip length to get there
Seasonal Hour Volume
the peak hour volume during different seasons;
Design Hour Volume (DHV)
the capacity of the roadway to handle traffic.
Traffic assignment
AKA trip assignment. allows us to use network models to predict the distribution of traffic for each roadway (the routes that will be used), by the hour. Peak volumes can then be compared with DHV to see which, if any, roadways are going to experience traffic over their design capacity; i.e., where the congestion is going to be.
Vehicle Miles Traveled (VMT)
a measure of vehicular mobility obtained from travel inventories. Vehicle miles of travel is a function of many factors, including topography, population density, travel distances between home and other daily destinations (such as work, shopping, and recreation), and the availability of mass transit.
High VMT
indicates that more vehicles are on the road to meet growing employment, errand, and other travel demands. It can also mean that the trip origins and destinations are getting further apart and travel times are becoming longer.
Functional Classification
Criticized because it doesn’t account for context of the area. Local - serves local land uses Collectors- collect traffic from locals and funnel to arterials Arterials- major through roads can be major or minor and urban or rural
Roadways standards from FHWA
are traced to post WWII studies where standards are based on subdivision design.
Street Patterns
- Grid, a street pattern common in ancient cities and often advocated by New Urbanist planners for facilitating pedestrian access; variants of the classic grid include the block grid, curved block grid, and curved grid;
- Loop streets with minimum and maximum depth standards;
- Cul-de-sacs with maximum length and minimum radius standards of 400-450 feet long and 40-foot turn-around radius;
- Plaza and hammerhead street style, usually insufficient for vehicular turn-around.
Highway Capacity Manual
published by the Transportation Research Board, provides concepts, guidelines, and procedures for computing highway capacity and quality of service based on road type.
