Research Team: PI: Brian D. Taylor Team:

About this project:

This translational research will build on a series of recent research projects and papers by the author and his current and former students on shifting from a mobility to an access focus in evaluating the causes and (especially) consequences of traffic congestion on the functioning of cities and their economic agglomerations (Mondschein and Taylor 2017; Osman, et al. 2018; Thomas, et al. 2018). This work has turned traffic impact analysis on its head by considering how the spatial arrangement of destinations makes it easier or harder to access them — regardless of the traffic speeds on adjacent roadways. Mondschein and Taylor (2017) show that trip-making in metropolitan tends to be higher than would otherwise be expected in built-up, congested central city areas, and lower than expected in outlying congested suburban areas. This presents a paradox: congestion appears to depress activity in outlying areas (as conventional wisdom would suggest), but increase activity in built-up congested areas, contrary expectations. Similarly, Osman, et al. (2018) show that new business establishments in tradeable (or “basic”) industries in the San Francisco Bay Area tend to locate in the most congested areas, contrary to conventional wisdom that congestion is a cost firms seek to avoid.

Of course people are not making more trips and firms are not locating in congested areas because they are attracted to the congestion; they are doing these things because they are attracted to the agglomerations of opportunities built-up, congested areas so often host. So in some areas, particularly in central cities, adding more density (and destinations) can (but doesn’t always) increase accessibility, even if nearby traffic speeds decline. The VMT analyses emerging from SB 743 begin to get at such effects on accessibility, but only partially. Indeed, Thomas et al. (2018) develop an accessibility measure for employment in the Bay Area and show that increasing the number of nearby destinations does far more to increase access for travelers than congestion mitigation — more even than congestion elimination.

This translational project will build on this recent research by the author and his colleagues, as well as the burgeoning literature on operationalizing access into transportation planning and engineering to develop and test some new analytical tools to evaluate the access impacts of developments. Our goal will be to develop something practical for professional practice, as Duranton and Guerra (2016) have shown convincingly that, while conceptually elegant, operationalizing access into planning practice presents some significant challenges. For this reason, we will aim for parsimony and will endeavor to test it by comparing and contrasting it (or perhaps multiple iterations of this tool) with traditional LOS analyses as well as California’s new VMT measure.

What problem does this research aim to address?

For decades evaluation of the benefits and costs of new- or re- development in urban areas has centered on the effects of development on nearby traffic flows. Historically, and in most states outside of California, if traffic impact analyses determine that a proposed housing or commercial development unacceptably degrades traffic level-of-service (LOS) on nearby streets, the proposed development will not be approved by local governments unless and until the traffic effects of the new development are mitigated, typically either by reducing the scale of the proposal, or by making improvements (often in the form of capacity expansions) to nearby roads or intersections. The logic of such an evaluation model is that smooth traffic flows are a primary, even central, goal of urban areas, which has the effect of discouraging the sorts of densely developed places that are more easily accessed by foot, bike, shared mobility, and public transit, and pushing developments to greenfields on the suburban fringe where marginal impacts of added traffic are small.

To overcome the traffic flow focus of traffic impact analyses, the California legislature passed and then-Governor Brown signed SB 743 in 2013, which mandated a change in the way that transportation impacts are analyzed under CEQA. In the six years since, the Governor’s Office of Planning and Research promulgated new CEQA Guidelines to replace LOS with a new focus on how proposed developments affect vehicle miles of travel (VMT), where less VMT per capita (and more travel by means other than driving) is better, and more driving is worse. These new guidelines were finalized only last year, so their effects in practice are not yet well known.

While most observers agree that a new focus on VMT offers a more holistic picture of transportation impact than LOS-focused analyses, the new analytical model still centers on adjacent road networks (traffic flow with the former, and less driving with the latter) largely distinct from the how the proposed development might be expected to benefit cities generally, and agglomerations of activities specifically. In other words, the “impacts” of development are still evaluated in terms of reducing many of the negative environmental externalities of (auto) mobility, and not in terms of how development affects accessibility.

Yet a large and growing body of research argues against focusing on mobility (whether to improve the driving experience traditionally or to discourage driving more recently) rather than access to destinations in evaluating the role of transportation systems in urban systems (see for example, Levine, Grengs, and Merlin 2019; Levinson 2016; Levinson, Marshall, and Axhausen 2017; Levinson and King 2019). These works by eminent transportation scholars suggest that the move in California from LOS to VMT is a step in the right direction, but not the last step. A more conceptually complete and practical accessibility impact analysis tool is needed to better understand the effects of development on urban systems.

What are the expected impacts and benefits of the research?

This research translation will be presented in three products intended to inform progress in transportation impact analyses: (1) A final report approximately 10,000 words in length detailing the logic of shifting to an access-based analytical tool and describing the derivation and testing of that tool, (2) an ITS Policy Brief approximately 500 words in length synthesizing the results of this study, and (3) a web-based tool for researchers and practitioners to test and evaluate using their own data and projects.

By |October 3, 2019|Categories: Traffic, Transportation & Communities