Traffic Generated by Mixed-Use Developments—Six-Region Study Using Consistent Built Environmental Measures

Abstract

Current methods of traffic impact analysis, which rely on rates and adjustments from the Institute of Transportation Engineers, are believed to understate the traffic benefits of mixed-use developments (MXDs), leading to higher impact fees, exactions, and negotiated payments than should be the case and discouraging development of otherwise desirable projects. The purpose of this study was to develop new methodology for more accurately predicting the traffic impacts of MXDs. Standard protocols were used to identify and generate datasets for MXDs in six large and diverse metropolitan regions. Data from household travel surveys and GIS databases were pooled for these MXDs, and travel and built environmental variables were consistently defined across regions. Hierarchical modeling was used to estimate models for internal capture of trips within MXDs, walking and transit use on external trips, and trip length for external automobile trips. MXDs with diverse activities on-site are shown to capture a large share of trips internally, reducing their traffic impacts relative to conventional suburban developments. Smaller MXDs in walkable areas with good transit access generate significant shares of walk and transit trips, thus also mitigating traffic impacts. Centrally located MXDs, small and large, generate shorter vehicle trips, which reduces their impacts relative to outlying developments.

Using trip chaining and joint travel as mediating variables to explore the relationships among travel behavior, socio-demographics and urban form

“…Densities of residential population, retail employment, non-retail employment, intersections, and bus stops are calculated at the TAZ level (per square mile). In addition, a job-population balance index adopted from Ewing et al (2011) and Akar et al (2016) is included in this study. The equation of job-population index is presented as follows.…”

La proximidad en Barcelona. Un análisis desde los tiempos de desplazamiento cotidianos

“…Por lo general, se ha tratado de delimitar lo densa que la ciudad tiene que ser para generar desplazamientos más cortos. O cuán mixtos deben ser los usos del suelo a fin de obtener la diversidad necesaria para generar proximidad (Cera, 2003;Geurs y Van Wee, 2004;Ewing et al, 2011). En la mayoría de los casos se analizan asentamientos urbanos ya existentes y se trata de calcular los efectos que un cambio particular en estos territorios puede tener en la movilidad de sus habitantes.…”

Phantom trips: Overestimating the traffic impacts of new development

“…The limited applicability of ITE-published rates to mixed-use, high-density centers has long been recognized, and ITE's publications themselves have extensive caveats to this effect. However, practices have evolved to allow developers to adjust down their trip generation rates in certain contexts (Ewing et al 2011;Millard-Ball and Siegman 2006;Cervero and Arrington 2008;Lee et al 2011;Clifton et al 2012;Bochner et al 2011;Handy et al 2013). 5 Thus, data and practice now at least partially address the special circumstances of mixed-use and transit-oriented development.…”

“…If trip generation estimates are inflated, then catering for "phantom trips" may lead to roads with more and wider lanes and intersections with longer signal phases-and, in turn, to urban places that are hostile to pedestrians and devote too much land to vehicle infrastructure (Millard-Ball and Siegman 2006). Ewing et al (2011) describe some of the long-run effects of inflated estimates of traffic, notably heightened community concerns about a project's impact, which can result in the project being scaled back. The market demand may then resurface at another location, often at a lower density and with more traffic.…”