Study finds dynamic ridesharing can boost TDM effectiveness

By Chris McCahill

The market for dynamic, taxi-like services is rapidly changing. On-demand ridesharing platforms like Uber and Lyft are growing in popularity, and automakers are clamoring to launch autonomous cars that could someday serve as self-driving taxis. That leaves many transportation planners and policymakers wondering how these services might ultimately affect trip making, travel behavior, and traffic. For example, convenient ridesharing services could lure away transit users and lead people to make more trips, thereby causing vehicle-miles of travel (VMT) to rise, or they could make compact living more attractive and reduce automobile ownership rates, thereby reducing VMT.

In a newly released report from the Mineta Transportation Institute, researchers found that ridesharing might actually reduce VMT in the San Francisco Bay area by as much as 23 percent over the long run—more than land use, transit, and VMT pricing policies alone.

The study relies on MTC’s activity-based microsimulation travel demand model, which is more advanced than most regional models, to estimate the effects of transit-oriented development, increased per-mile vehicle costs, and dynamic ridesharing on VMT and emissions. In three of the scenarios tested, housing densities near transit stations increase by 10, 20, or 50 percent. In three other scenarios, vehicle operating costs increase by the same percentages. According to the results, TOD alone reduces VMT by 0.2 to 0.6 percent, while pricing reduces VMT by 3 to 13 percent.

The researchers also analyzed each of those scenarios to determine the number of “ride-sharable” trips, given current knowledge about ridesharing use. Assuming a moderate participation rate (50 percent of eligible trips), VMT is reduced by 9 percent exclusively through ridesharing. Although the researchers didn’t find any major synergies, they note that moderate ridesharing combined with vehicle pricing reduces VMT by 11 to 19 percent, depending on the per mile costs of driving. Assuming full participation in ridesharing (100 percent of eligible trips), VMT is reduced by anywhere from 23 to 29 percent.

This suggests that many agencies should be taking a serious look at the potential of ridesharing and other dynamic taxi services to help meet people’s travel needs while easing travel demand.

The researchers also tested how TOD and pricing might affect demand for battery electric vehicles (BEV). According to their models, TOD increases the market by less than 1 percent, while pricing increases it by 7 percent, presumably because household travel is reduced to within BEV range. Their models also suggest that the influence of land use and pricing policies on BEV use drops considerably as the vehicles’ ranges increase from 50 to 100 miles.

Chris McCahill is a Senior Associate at SSTI.