A new study from the Brookings Institution calls for states to play a greater role in supporting Amtrak, the subsidized rail service that is experiencing record levels of ridership and growing at an impressive clip.

Since 1997, Amtrak ridership has grown 55 percent to more than 31 million riders in 2012, an all-time high. In that same period, its been the fastest-growing mode of transportation, according to Brookings. Those figures come at the same time many of its critics paint Amtrak as a bloated agency that relies heavily on federal support to function.

The report comes during a year Congressional leaders are poised to address reauthorization of the rail program. Rep. Bill Shuster, who chairs the House Transportation and Infrastructure Committee, said this week he doesn't believe Amtrak should be entirely cut off from federal support but thinks its subsidies could be reduced.

Brookings, however, advocates for a slightly different approach: growing the state contributions to Amtrak.

The last rail bill required states to play a larger role in providing financial support to Amtrak. In October, states will be required to provide operational funds to help fund Amtrak in high-speed corridors and in corridors less than 750 miles. Long-distance route are exempt from those rules.

But Brooking calls for a new agreement between Amtrak and states that would require states to take on a larger role in sharing operational costs for Amtrak's longest routes -- those exceeding 750 miles -- which right now states aren't required to support.

Robert Puentes, one of the authors, says such a policy would force policymakers to seriously evaluate those longer routes and decide whether they truly serve an important need. "If there's no state support for these routes, they should not be operating," Puentes tells Governing. "It shouldn't be something Washington is dictating."

Brookings notes that Amtrak's shortest-distance corridors, those under 400 miles, have a positive operating balance, while those exceeding that threshold had a negative balance. It attributes that disparity due to the short routes' high ridership as well as the state support they're received. "The remarkable shift toward federal-state collaboration on Amtrak should not be underestimated," Puentes and his colleagues write.

Keeping Amtrak effective will require building on its relationship with states and enacting a similar partnership for longer routes too, the authors argue. They say such requirements would amount to more than just a responsibility shift from the feds to the states and would instead would mean states would share with Amtrak in risks and rewards.

Another option Brookings touts is replacing those long-distance routes with shorter services linking metro areas, which they believe may be a more efficient model.