Abstract
Traffic impact analyses (TIA) are widely used by local governments to assess the traffic impacts of proposed land use developments. TIAs are often measured in terms of expected changes to traffic flows through nearby intersections using a metric called “level of service” (LOS). This process tends to be biased against higher-density developments in urban areas where traffic is already congested and travel alternatives are plentiful. Researchers have found that the projected traffic impacts of developments in already built-up areas tend to be overestimated, which leads to higher traffic impact fees and related costs associated with the TIA process. Often, local residents use such analyses as evidence to oppose new developments on traffic grounds. The result is that TIAs can help discourage new housing production in built-up areas where demand is greatest, which likely exacerbates the housing affordability crises in places like California.In essence, the logic of TIAs is that the human activities and the built environment in cities should vary to keep nearby traffic flowing smoothly. The fundamental problem with LOS-based TIAs is that they measure vehicle mobility and not the more fundamental goals of economic and social accessibility. While California has been a national leader in changing the metric by which traffic impacts are evaluated under the California Environmental Quality Act, from LOS to vehicle miles of travel effects, LOS-based analyses of development proposals are still typically conducted by local governments — even in the Golden State.This study reviewed and synthesized research on TIAs and their effects on land use planning, and found that mobility-focused transportation planning likely contributes to the housing affordability crisis plaguing many places. Further, research shows that gradually shifting away from mobility-centered metrics, like LOS, and toward more accessibility-centered evaluation tools, will enable more comprehensive assessments of development impacts, which could help ease California’s housing affordability crisis.
