Can Transit-Oriented Development Reduce Peak-Hour Congestion?

This paper presents a study of whether transit-oriented development (TOD) helps reduce peak-hour congestion, a topic of ongoing public debate. Applying conventional four-step travel demand modeling techniques, the study simulates traffic outcomes in three TOD scenarios in the Austin, Texas, area, where a commuter rail line is under construction and TOD proposals are being developed. With TOD, the portion of congested roadway in the Austin region is estimated to decrease by nearly 770 lane miles. Daily vehicle miles traveled (VMT) are reduced by 10 to 12 million in the region, or by 3.5 to 4.5 person miles traveled (PMT) per person. This magnitude of congestion relief for peak-hour commuting indicates a potentially significant amount of savings in highway investments through TOD practice. No major modal shifts from driving to transit or non-motorized modes occur in the TOD scenario. Still, PMT for transit is estimated to grow significantly. TOD's role as a congestion relief strategy largely lies in the concentrated development that shortens average trip length and hence generates less VMT and PMT than low-density sprawl. The study results also reveal challenges facing TOD practice: the non-TOD area benefits more than the TOD area, although TOD improves congestion regionwide. Traffic conditions in the TOD area may actually worsen due to the TOD-based concentration of people and jobs. Promoting walking or biking to minimize local driving is thus critical for TOD to succeed.