Regional Travel Modeling Unit 6: Aggregate Modeling

Puget Sound Regional Council’s travel model Forecast future travel patterns and conditions within the four counties (King, Kitsap, Pierce, and Snohomish) of the Puget Sound region Represents the state of the art for regional travel modeling Analyze the likely impacts of travel forecasts on the region’s transportation infrastructure and environment Interacts directly with the land use model (UrbanSim), and it is the primary source of input data for the air quality (EPA Moves) and benefit-cost analysis (BCA) tools * Puget Sound Regional Council (PSRC) is the Seattle region’s MPO

Modeling Framework

Seven basic components Household vehicle availability Person trip generation Trip distribution Mode choice (passenger travel) Time of day Trucks Vehicle trip assignment

Commercial and Passenger Handled Separately Truck trips are generated, distributed, and then assigned to specific routes. There is no truck mode choice model as all travel is assumed to occur via the truck mode. Uses TAZ-level employment data provided by UrbanSim to estimate truck trip generation. The truck model converts trucks to passenger car equivalents (PCE) prior to route assignment. – accounts for the fact that large trucks occupy more space on roadways than do passenger cars – important for representing the contribution of truck travel to congestion and overall travel speeds. – light trucks represent 1.0 PCE; medium trucks represent 1.5 PCEs and; heavy trucks represent 2.0 PCEs.

Basic unit: TAZ Transportation Analysis Zone 938 in 4 county region Estimate truck trips at the TAZ level based on employment in that zone

5 time periods 1) AM Peak Period (6:00 am to 9:00 am); 2) Mid-Day (9:00 am to 3:00 pm); 3) PM Peak Period (3:00 pm to 6:00 pm); 4) Evening (6:00 pm to 10:00 pm); 5) Night (10:00 pm to 6:00 am).

Three truck types Light Trucks – Four or more tires, two axles and weighing less than 16,000 pounds – commercial vehicles such as taxis, rental cars, school buses, ambulances, etc Medium Trucks – Six or more tires, two to four axles, and weighing between 16,000 and 52,000 pounds Heavy Trucks – Double- or triple-unit, having 5 or more axles, and weighing more than 52,000 pounds

Trips estimated from employment Confidentiality issues result in generally underestimated total employment Certain kinds of manufacturing that are not included in the PSRC land use model (primarily construction and resources employment) – Ag/forestry/fishing – Mining – Construction – Manufacturing – products – Manufacturing – equipment – Communication, transportation, utility – Wholesale – Retail – Financial, real estate, service (fires) – Government – Education

Trip rates Attraction and production both estimated from employment using different factors Only change due to changes in employment – Not transportation system performance – No elasticity of demand with respect to travel cost Special generators – Ports and warehousing districts – Survey based

External trips Generated and/or destined for outside the region 1997 TRANSEARCH data SFTA data

Validation The FASTruck model was validated system wide based on a limited set of truck counts for medium and heavy trucks. Light-truck travel was validated on a system wide basis to ensure that the assignments of these trucks did not significantly affect the assignments of passenger cars. The existing FASTruck model does include all non-personal-use vehicles.

Trip destination Gravity model approach – Closer TAZes attract more trips – Different for each truck class Estimated from consultant report SFTA survey Distributed over the day – From PSRC screenline counts from trucks

Network Traffic assignment with equilibrium assumption Congestion effects captured with link performance functions Only the highway network is used – Recall zone to zone travel Trucks assigned along with all other traffic – All vehicles on same link travel same speed – Reduce truck speeds by 25%