STEAM

Surface Transportation Efficiency Analysis Model (STEAM) was developed for the Federal Highway Administration as a framework for state and regional agencies to assess investments in multi-modal urban transportation infrastructure, as well as policy alternatives such as pricing and demand management measures. STEAM can be used to analyze investments at the regional and corridor levels.

Project Types Evaluated: Multi-modal transportation systems incorporating up to seven modes (default data given for auto, carpool, truck, local bus, express bus, light rail, and heavy rail). Consequences are accounted for at the corridor or regional levels.

Scope of Application: Analysis is done for total average weekday traffic or for peak and off-peak periods separately. Multiple trip purposes may be considered. The study area is partitioned into traffic analysis zones and aggregated to districts where separate benefit and cost factors may be specified and results reported. The model is closely linked to outputs from the 4-step urban transportation planning process.

Benefit Categories Considered:

• • Travel times and vehicle operating costs

  • Accidents

  • Emissions (CO, NO_x, PM₁₀, VOC, with cold-start component)

  • Energy consumption

  • Noise

Cost Categories Considered:

• • Infrastructure investments and operating costs

Economic Performance Measures Provided:

• • Net present worth for each alternative in question

  • Benefit-cost ratio for each alternative in question

Other Quantitative Impacts Considered:

• • Congestion

  • Global warming (CO₂ greenhouse gas emissions)

  • Access to jobs

  • Revenues and transfers (revenues) from fares, tolls, and fuel taxes

  • Levels of risk in the estimated results (probability distributions for key outputs)

STEAM is maintained and distributed by the FHWA. The software and user's manual (Cambridge Systematics, 2000) may be downloaded at no cost from the agency's website.

Example

DeCorla-Souza and Hunt (1999) describe a STEAM application to a very congested 12-mile long central freeway corridor in a rapidly growing western city. The corridor population is expected to increase by 100% and corridor employment by 140% during the next 20 years. Three alternatives were considered:

"No-Build" — Completes all capacity enhancement projects in the regional long-range plan except for central freeway improvements. A planned light rail line is to be built in the central freeway corridor.

"Build" — As above, except that the central freeway would be expanded from 3 to 5 lanes in each direction. The light rail line would still be built.

"TDM/Tolls" — Similar to "No-Build" except that a $1 toll would be charged to every central freeway user, regardless of trip length. Tolling would be electronic with no added delays. The light rail and bus services in the corridor would be expanded by 25% to further encourage mode shift.

Inputs obtained for each alternative from the regional 4-step models include person-trip matrices by mode and purpose and vehicle-trip matrices for personal vehicles and internal truck travel; trip time and cost matrices skimmed from the highway and transit networks; and loaded highway network link volumes. The personal travel modes include auto, carpool, bus, walk-accessed light rail and drive-accessed light rail for trip purposes homebased (HB) work, HB college, HB other, and non-homebased, as well as for external-internal and external-external (through) auto trips. To simplify the STEAM analysis, all trips were combined into one aggregate person-trip matrix for each of the five modes, and one truck trip matrix. Vehicle occupancies and estimates of the proportions of zone-to-zone trips paying tolls were obtained from manipulation of the available trip matrices.

Selected results of the analysis for a 20-year evaluation period are the following: