Public transit investment and sustainable transportation: A review of studies of transit's impact on traffic congestion and air quality

The Effects of Urban Public Transit Investment on Traffic Congestion and Air Quality

“…It is clear that the market failures endemic to the urban transportation sector are not being adequately addressed by existing regulatory policies [4]. The market failures in the auto and transit sectors have long been of interest [4].…”

“…The first potential role for government is to provide transportation infrastructure in the form of roads and public transit systems and also to operate public transit services. Once the infrastructure is in place, the second potential role for government is to employ policy instruments (such as taxes and other forms of regulation relating to safety, environmental standards, travel demand management policies, and so forth) in order to address the market failures that are inherent to unregulated transportation activity and also to determine the operational aspects of public transit service [4,5].…”

“…A contentious issue currently confronting transportation analysts and policy-makers is what the effects of public transit investment on congestion and on air quality are and therefore what the appropriate level of public transit investment should be [4]. While public transit receives plenty of political support for its "green" reputation and its contribution to sustainability, there have been relatively few studies examining the ex post effects of public transit investment on traffic congestion or air quality [4].…”

“…For example, previous empirical studies examining the relationship between transit supply and traffic congestion are limited, and the findings of these studies vary [4]. There is also an ongoing debate in policy circles regarding the efficacy of public transit investment as a means of addressing traffic congestion, for example [6][7][8], all display skepticism regarding the congestion-reduction possibilities of public transit, while [9] advocates for transit investment [4].…”

“…There is also an ongoing debate in policy circles regarding the efficacy of public transit investment as a means of addressing traffic congestion, for example [6][7][8], all display skepticism regarding the congestion-reduction possibilities of public transit, while [9] advocates for transit investment [4]. Although investment in public transit may lead to short-term reductions in congestion due to a "substitution effect," in the long run, it may be less effective due to the "induced demand effect" [4,10,11].…”