Declining gas prices and fewer public transportation options are forcing travelers back behind the wheel, according to a new study by DePaul University’s Chaddick Institute for Metropolitan Development.

“Low fuel prices have a serious downside,” said Joseph Schwieterman, professor in the School of Public Service and director of the institute. “When more people choose to drive, there can be a snowball effect that limits the public transportation options available to others, who then feel compelled to drive as well.” The study is co-authored by C. Scott Smith, assistant director of the institute; and graduate student Riley O’Neil.

Researchers found:

• Lower fuel prices and heightened competition from airlines have weakened demand for Amtrak and express coach bus lines. Despite a recent uptick, new service offerings have lagged and not kept pace with the country’s rising population.

• Gaps in ground transportation have emerged, making efforts to avoid driving on some popular routes more difficult than just a few years ago. These gaps are due to both slowed investment in new routes, as well as cutbacks by express coach lines outside of the busy Northeast region.

• Numerous metropolitan areas remain largely inaccessible to travelers who seek to avoid flying or driving but are unwilling to use conventional bus lines such as Greyhound. These “Pockets of Pain” include Phoenix; Columbus, Ohio; Dayton, Ohio; Tulsa, Oklahoma; Ft. Myers, Fla.; and Sarasota, Fla.

• Some short- and mid-distance routes with more than one million trips a year have no service by Amtrak or express coach lines, including Los Angeles to Phoenix; Cleveland to Detroit; Chicago to Columbus; Las Vegas to Phoenix; and Ft. Myers to Tampa.

Researchers at DePaul have been following the ebb and flow of bus and rail travel in the U.S. for more than a decade. Starting in 2005, optimism ran high that expansions to the intercity bus and rail system would provide travelers with increasingly viable alternatives to driving, particularly on short- and middle-distance routes, explained Schwieterman.

However by 2015, the hoped-for transformation of this intercity travel market has lost steam. Bus and train traffic had ebbed, buffeted by low fuel prices, heightened competition from airlines, and barriers to planned service improvements. The rollout of new trains slowed. Express coach lines began trimming frequency on some routes and ended service to other cities altogether.

“Everyone should take notice when momentum to improve bus and rail service diminishes, as these modes are critical to the mobility of those who cannot or prefer not to drive while also enhancing safety and fuel efficiency,” said Smith.

Drawing upon these findings, the researchers outline steps that public entities can take to give travelers more opportunities for ground-based intercity services. For example, researchers call for more effective arrangements to support states working together to improve rail corridors. They call for planners to follow the example of Boston, Denver, and Washington, D.C., by creating dedicated, centrally-located bus terminals that can help relieve overburdened curbside pickup spots. In addition, researchers cite Amtrak’s “Thruway Bus Network” program, which connects riders on buses and trains, as a model for other cities to follow. Schwieterman says California, Michigan, and Oregon have seen boosts in ridership through the program.

“There are proven ways for planners to better coordinate bus and rail services, and these success stories from around the country show that there are practical opportunities to help people lessen their dependence on driving,” said Schwieterman.

The full report is available for download, here.