Wednesday, September 01, 2010
Public transit is often seen as part of the transportation sector’s sustainability solution, usually for environmental reasons. Transit service can reduce emissions of criteria pollutants and greenhouse gases by reducing vehicles miles traveled (VMT) and the number of cold starts. However, public transit systems can also contribute to social and economic sustainability by relieving congestion, stimulating economic development, and improving accessibility and mobility for all, regardless of car ownership. Given the limited funding available for new public transit infrastructure, it makes sense to prioritize projects that meet multiple sustainability goals simultaneously.
Not all transit service equally meets multiple sustainability goals. Transit service designed to serve work trips and primarily accessed by personal vehicle has limited social and environmental sustainability benefits. It provides limited increases in accessibility and mobility, especially for transit dependent communities who need all trip types served. Environmental benefits are also limited since personal vehicles are still used to access the transit and for all other trip types.
It is understandable why many transit systems have focused on serving the work trip. Work trips tend to be predictable and concentrated; traditionally work trips have two weekday peaks and the destinations are clustered in high density downtown or suburban employment districts. Focusing on the peak period trips also contributes to congestion reduction efforts. However, as work trips are under 30% of VMT and 20% of person trips in the United States, transit usage for non-work trips is critical for transit to make significant reductions in emissions.
Transit dependent on park & ride access does little to influence land use patterns. In fact a high speed connection to job centers with plenty of free parking could facilitate urban sprawl. People can live further and further away from their job without sacrificing commute time. For transit to have the synergetic benefits with land use, it needs to be focused on non-motorized access. Non-motorized access to transit also has public health benefits.
The factors impacting the levels of non-motorized access and non-work trip usage include transit service design and operations, land use, demographics of riders, and regional policies and priorities. In Atlanta, the impact of service type is clearly shown by the difference between MARTA local bus and heavy rail service and the express bus service run by GRTA.
Atlanta, overall, is higher than the national average on both variables. However, these factors should be taken into consideration as Atlanta prioritizes new transit service.
In order for transit to serve both social and environmental sustainability goals, it must serve both dependent and choice riders. Environmental goals will only be met if people with cars take transit instead of driving. Social goals will only be met if transit increases mobility for everyone, especially those without cars. Transit systems with the resources to attract choice riders, but designed to serve dependent riders are best situated to meet both environmental and social sustainability goals.