TRANSPORTATION MODELING

• Introduction to UTPS [Urban (or UMTA) Transportation Planning System]

Planning... (RTP) must ...

1) assess needs
2) assess fiscal capacity
3) outline improvements
4) quantify benefits
The regional transportation model
also known as ...
-UTPS - Urban (or UMTA) Transportation Planning System
-UTMS - Urban Transportation Modeling System
-UTM - Urban Transportation Models
-UTPM - Urban Transportation Planning Models
-UTM - Transportation Planning Models
-TDM - Travel Demand Models (however, more commonly, Travel Demand Management)
This process is a sequential, 4-step process (more recent work is being done on simultaneous and dynamic models)

We will mainly discuss the sequential-type model in this class

Transportation models are computerized procedures for estimating changes in travel patterns in response to changes in ...

- development - develop open space into a shopping center
- transportation system - add bypass
- demographics - as populations change, the demand in the network is changing, therefore, changes in the network are necessary
... given certain assumptions about existing and future travel behavior, for freeways, expressways and major streets.

Federal Highway Administration (FHWA), Urban Mass Transportation Administration (UMTA) - [now Federal Transit Administration (FTA)] developed the process known as the UTMS, ...

... the well known process is ...

1) trip generation - analysis resulting in productions and attractions
2) trip distribution - analysis predicting zone to zone flows
3) modal split - analysis determines type of transport and vehicle occupancy
4) traffic assignment - which path will vehicles take through a network (congested or otherwise)
Models must be calibrated (parameters estimated)

we can think of two basic components, supply and demand.

supply = network = roads, highway, (transit) systems
demand = trips = f(land use), so must know land use/demographics/activity
History of modeling process

Process originally developed in the 1950s in the Chicago Area Transportation Study (CATS) and Detroit studies.

With the advent of computers, the process became automated.

-FHWA developed Planpac in the 1960s
-UMTA developed UTPS
-the two were merged in the 1970s to the UTPS as the sequential process essentially remains today
-P.C. implementations occurred during the 1980s (Tranplan, MINUTP, EMME2, QRSII, TModel, ...)
 
• Building Networks (computer depiction)

link-node networks (graphical, non-graphical)

Nodes ...
- minimum requirements are x, y, and node number
- could also have attributes e.g. QRSII associates prohibited turns, signalization, delay by movement with nodes

Links ...
- attributes: number of lanes, capacity, travel time (free flow or loaded), speed (free flow or loaded), jurisdiction, assignment group, one or two-way designation, distance, facility type, intersection control, ...

do not include local roads (use centroid connectors to represent local roads)
 

• Representing Travel Demand

TAZs ...
- smallest unit of travel demand (not DUs, at least not in the sequesntial model)
- represent all demand as originating from a point (centroid)

Rules of thumb for TAZ design
- equal size
- one per thousand population
- homogeneous land use
- not split up by network, jurisdiction, or physical barriers
- share boundaries with enumeration districts
- allow for growth

Connect demand to supply via the centroid connector

Travel Forecasting Guidelines: Caltrans Model

note: this section is based on a project report prepared for the State of California Department of Transportation (Caltrans). Click here to see the full report

These travel forecasting guidelines are the results of Caltrans effort to meet both Federal (1990) and California (1988) Clean Air Acts and California's Congestion Management Program (1990).

The project report represents Caltrans effort to bring some uniformity to regional travel demand forecast models which have been variously inconsistent
1. in their levels of sophistication and
2. their relative accuracy.

The primary purpose for regional modeling of travel was to determine the need for major highway invetments. When used for this purpose, rough approximations of forecast volumes was sufficient to determine when major new widenings or new facilities were needed.

In the current regulatory and legislative environment, significantly greater accuracy and sensitivity is necessary. Greater accuracy is desired as a means for more efficiently planning for transportation facilities or facility management programs. With the pressure of inadequate funds for meeting all transportation needs, Caltrans had the need for modeling guidelines which would make it possible to prioritize the allocation of state project funds for projects within regions or regions on a more equitable basis.

The guidelines are expected to be used extensively by two important audiences. These include executive management level officials determining whether existing modeling practice is acceptable or technical staff evaluating their own modeling capabilities. The guidelines can be use to
1. insure that modeling is performed correctly;
2. achieve a minimum acceptable level of accuracy;
3. provide some standardization and through it, better understanding of the modeling being performed;
4. adopt universally accepted definitions and terms;
5. meet requirements of specific legislation in the state; and
6. conform with what might be established as a legal basis for acceptable practice.

Introduction to Tranplan

see: Tranplan Manual, General Description, Networks and Highway NIS sections

1. Tranplan is a "modular program" concept
   • Has relationship to 4 step Urban Transportation Planning Model (UTPM) process
   • See Des Moines flowchart (handout)
   • Uses control files, data, executables and creates output
     
2. Control file
   • ASCII file that "controls" the way Tranplan runs, can be created in any text editor
   • Contains name of executable module within Tranplan which user wishes to excecute
   • Tranplan has different filenames for files (internal and DOS)
   • Headers allow user to provide identifying information to the file
   • Options allow user to specify variables when running module
   • Parametersare similiar to options
   • Data can be included from external sources
3. Data files (standalone)
   • $include option allows user to incorporate external data into Tranplan
   • Filename specification option
4. Executable programs
   • Running under windows (TPCTRL)
   • Example: build highway network, matrix update, report highway load, load highway network
   • Combining control files is possible (rather than seperate control file to run each module)
5. Output files
   • Standard output (ASCII) contains information on errors and other output
   • Output files usually binary, may be ASCII (binary files read by HNIS)
   • Optional output files (some modules only)
6. Viewing binary output in NIS
   • Interface which allows a more graphic viewing of data
   • Runs from windows (HNIS)
7. Converting binary output to ASCII
   • Using tranplan utilities (TPMISC)