Guide to Calculating Mobility Management Benefits Victoria Transport Policy Institute
TDM Program Benefits Analysis
A study by Winters, et al. (2007) evaluates commute trip reduction (CTR) program
impacts on transportation system performance in the Puget Sound region.
The Washington State Department of Transportation (WSDOT) maintains comprehensive databases of CTR plans and employee travel characteristics. The CTR programs include various bicycle, carpool, vanpool and transit incentives. These databases were used to calculate the impacts of these programs on vehicle traffic in the Seattle downtown area. WSDOT compared two scenarios: Scenario A “With TDM” represented existing traffic conditions on the network with current CTR programs, and Scenario B “Without TDM” represented traffic conditions after trips reduced because of CTR programs added onto the network, i.e., as though CTR did not exist in the study area. The comparison used a microscopic simulation model, CORSIM, to evaluate the impacts of CTR programs on roadway traffic. WSDOT conducted the analysis for the duration of the peak periods defined for this study from 5:30 AM to 10:15 AM for AM peak and from 3:00 PM to 7:45 for PM peak.
WSDOT estimated the cumulative delay reduction to be 152,489 and 169,486 vehicle- minutes for the AM and PM periods respectively due to programs in the analyzed corridor . The CTR programs caused a total reduction of 102 lane-miles of spatial congestion in the AM peak period and 143 lane-miles in the PM peak period. the study reported a significant total reduction in travel time of 60 and 45 minutes for the AM and PM peak periods respectively. The average speed increased up to 19 mph for the AM and up to 11 mph for the PM peak period. The cumulative VMT reductions ranged from 17,297 vehicle-miles in the AM to 14,511 vehicle-miles in the PM peak period. Fuel savings for all travelers, not just those using non-single occupant vehicles, were estimated (passive) to be 3,489 gallons during the AM peak period and 4,314 gallons during the PM periods. The total estimated peak hour emission reductions due to improved traffic flow were 16.4 and 21.7 kilograms of hydrocarbon (HC) emissions and 1,109 and 1,545 kilograms of carbon monoxide (CO) emissions for the AM and PM peak periods, respectively. These results indicate that the CTR programs provide significant benefits, including reduced traffic delay, reduced spatial and temporal extent of congestion, reduced emissions and fuel savings.
These results do not encompass all the impacts. The analysis was limited to an 8.6-mile corridor and the study only takes into account the impact of 189 CTR employers in the region. However, there might be more worksites with CTR programs. Therefore, CTR programs might provide even greater regional benefits. In many areas of the study corridor and/or times of day, mobility management made a significant impact on congestion, but TDM, like every other transportation solution, will not eliminate delay for every congested segment or time period. Sensitivity analysis indicates that even a small reduction (4%) in vehicle trips could provide significant benefits.