Transit systems in the U.S. are reducing the greenhouse gases that are the leading cause of climate change. Without them, American cities would be even bigger producers of air pollution and sprawl.
That's the conclusion of a new, landmark study from the Transportation Research Board (TRB) which confirms the very bedrock ideas held about transit—starting with its measurable effect on the compactness of U.S. cities.
In “Quantifying Transit’s Impact on GHG Emissions and Energy Use—The Land Use Component” a team of researchers found that without transit U.S. cities would consume 37% more land.
The report also confirms that transit ridership reduces vehicle miles traveled (VMT), fuel use and related greenhouse gas (GHG) emissions by 2% nationwide.
“This is a substantial change given that only 4% of passenger trips are currently made by transit in U.S. metropolitan areas,” TRB writes.
But, where the report breaks new ground is in confirming how the presence of transit complements the use of other modes of transportation.
The TRB, which is a national research lab performing major, scientifically rigorous studies, quantified what it calls the “land-use effect” of transit while looking at the effect transit systems have in 300 regions and inside 12 U.S. cities.
What they found is that when transit is located in compact, walkable areas it has a land-use “multiplier effect” of reducing VMT and lowering GHG emissions from 1% to 21%.
While many reports have looked for how land-use contributes to better transit, for the first time a report quantifies how much transit contributes to reducing vehicle miles traveled and improves air quality through the reduction of greenhouse gases.
The report provides some important forecasting tools for transit agencies and regions thinking about the link between transit and development (aka transit-oriented development). Broadly speaking, the report is able to confirm transit’s inherent benefits of reducing VMT and improving air quality.
For instance, TRB used a statistical model to forecast that a 1% increase in transit route density and/or a 1% increase in frequency of transit would improve a city’s “compactness” and lower GHG emissions by 0.2% (or 0.4% for doing both).
How that translates in a region like Los Angeles—which plans to expand by 430 new route miles of high-quality transit by 2040: The corresponding land use benefit would be a reduction of regional VMT by 0.3%, saving 12 million gallons of gasoline per year and reducing GHG emissions by 116,000 tons per year, TRB notes.
They also drilled down to the neighborhood level in cities like Portland and Salt Lake City and found that substantive transit investments produced 19% and 15% VMT reductions, respectively. Those numbers refer only to the “land-use benefit” of having transit in compact places. In other words, transit and supportive land use does, in measurable quantities, promote walking and biking as well. Portland’s transit system directly produces an additional 4% VMT reduction.
Another key finding bolsters the case for a recent boom in light rail and streetcar service in cities.
“Looking on average at adding a rail station to a neighborhood that did not previously have rail access is associated with a 9% increase in activity density (combined population and employment density) within a 1-mile radius of the rail station,” TRB says.
The land-use effect of transit has been particularly noticeable in cities that have a strategic plan to grow their transit system like Portland, which also benefits from a regional growth plan that provides incentives to develop in the urbanized area.
“If the Portland, Oregon urbanized area (3,325 people per square mile) had never had public transportation, Portland would resemble a city like Ithaca, New York (1,351 people per square mile) or Fort Collins, Colorado (1,422 people per square mile) in development style. Housing the Portland population at those densities would consume an extra 788 square miles of land,” TRB writes.
“The average resident of the Portland area currently drives 18.9 miles a day; without transit, residents would drive 24.5 miles a day,” TRB adds.
The transit land-use effect is also quite pronounced in college towns like Ames, Iowa (21% VMT reduction) and Champaign, Illinois (16%). Cities like Kansas City, Missouri with a traditional compact core, a lot of mid-century flight and a small, recent influx of city residents experienced a smaller (5%) VMT reduction.