Exploring the relationship between transit supply and parking demand

By Saumya Jain

In a recent study, researchers from Australia look closely at the relationship between parking demand and proximity and quality of service supply of public transit. When other socioeconomic factors were considered, the quality of transit service became much more important than proximity alone in determining parking demand. This will be helpful in the ongoing discussion about where and how to reduce or eliminate required parking as part of development.

The planning profession has debated the appropriate way to approach parking minimums, and some cities have completely eliminated them. Last year, the Institute of Traffic Engineers also made significant changes in their Parking Generation Manual by lowering parking-supply requirements and incorporating variables like density, land use, active transportation, and public transit, in the decision making process. Though it is widely accepted that these variables have a substantial impact on parking demand, there is still room for more in-depth analysis.

Using a case study of Melbourne, Australia, the researchers explore the relationship between parking demand for new residential apartment buildings and their proximity to high-frequency public transport. The researchers used census variables such as car ownership per household and zero-vehicle households as a proxy to understanding parking demand. They also incorporated socioeconomic variables like population density, average household size, median household income, and households with dependent children to understand how these influence travel behavior, car ownership, and parking demand.

Having done two different analyses—a bivariate analysis that only looked at the relationship between parking demand and proximity to transit stations, and a second that incorporated all the dependent variables as well—the two analyses showed quite distinct results. The relationship between parking demand and proximity to a transit stop was quite significant in the bivariate analysis. But in the multivariate analysis, with incorporating other socioeconomic variables that affect car ownership, this relationship weakened. Instead, the quality and frequency of public transit service was most important, showing a strong association such that, “a 10 percent increase in public transport service supply in the AM peak (within 800 m) is associated with a 0.9–1.2 percent reduction in car ownership and a 0.8–1.4 percent increase in zero car households, depending on apartment size.” Through their study, the researchers also found that their current parking minimums are oversupplying buildings, especially for occupants of larger apartments.

This study yet again emphasizes the need to revisit our parking minimums and to better understand the relationship of car ownership with accessibility to alternate means of transportation. The empirical analysis provided through this study can also help policy makers choose and justify transit over parking minimums.

Saumya Jain is a Senior Associate at SSTI.