Compact design or higher density especially within a quarter or half mile of a transit facility, can impact travel behavior by reducing travel distances for daily activities, improving mobility options, and creating environments for people to rely on non-automobile modes.
Potential strategies to support compact design include the following:
- Support higher commercial and residential development intensities
- Allow for greater building height and bulk
- Require minimum building intensities
- Encourage parcel assembly
Compact design strategies may be complimented by a variety of strategies for adjacent uses that mitigate the impact of higher development intensities. These may include the following:
- Mitigating noise, pollution, shading, and traffic impacts on adjacent residential areas
- Respect landmarks, historic buildings, or other places of aesthetic value
Research shows an association between compact design, vehicle travel, and transit use. As residential density increases, vehicle travel decreases and the use of non-automobile modes, including transit, increases (Ewing and Cervero, 2010; Boarnet et. al., 2008; Boarnet and Handy, 2010). Newman and Kenworth (2011) found a strong relationship between density and vehicle travel with the largest reductions in VMT occurring as density increases from low (less than 25 people per acre) to moderate (60 to 120 people per acre). Though some research has also shown that greater employment densities are associated with reduced vehicle commuting and lower VMT (Barnes, 2003), larger research samples have found that employment density had little effect on VMT (National Research Council, 2009; Boarnet and Handy, 2014).
Two meta-analyses concluded that the elasticity of VMT with respect to density is:
- -0.05 to -0.12 (Niemeier, Bai, and Handy, 2011), meaning that increasing density by 1% reduces vehicle travel by 0.5% to 1.2%.
- -0.04 (Ewing and Cervero, 2010).
Academic debate continues as to why VMT declines in compact areas and by how much it changes. Compact areas often have a combination of characteristics, such as land use mix, walkability, regional accessibility, reduced parking, and residential self-selection. These characteristics are all associated with lower VMT.
Research from Ewing and Cervero also suggests that compact design has a more significant impact on transit mode choice or transit trips than VMT. The meta-analysis found that the weighted average elasticity of transit use related to density was 0.07, with the high end of the research sample around 0.4 for residential density.