BRIDGEPORT — Saying that the Metro-North Waterbury branch is proof that "if you build it, riders will come," U.S. Sen. Chris Murphy said Monday that he'll push for more mass transit money in the next Senate transportation funding bill.

States in the traffic-choked Northeast need to improve and expand mass transit to develop their economies, but federal aid isn't enough to maintain what already exists, Murphy said at a press conference on the platform of Bridgeport's train station.

"There's a thirst for mass transit," Murphy said after riding the 9:12 a.m. from Waterbury to talk with riders.

To show their support, municipal leaders from the Naugatuck Valley took part in Murphy's prearranged journey. Waterbury Mayor Neil O'Leary and state Sen. Joan Hartley, D-Waterbury, climbed onto the 9:12 with Murphy at the Waterbury station, and a series of mayors and first selectmen joined at various stops as the train headed south to Bridgeport.

Communities such as Derby, Shelton, Ansonia, Seymour, Beacon Falls, Naugatuck and Waterbury seek to promote their housing stock as affordable options for Fairfield County teachers, firefighters, police, retail managers and other workers.

Metro-North's Waterbury branch serves that market because it connects to the main New Haven line while bypassing the rush-hour traffic that has gradually made the southern end of Route 8 nearly as congested as I-95. At numerous forums over the past several years, residents have predicted ridership would rise quickly if the railroad offered more frequent, reliable service.

"This is an economic development lifeline. The cities need consistent, clean service so we can be attractive places to live," O'Leary said. "We have very affordable housing. You can get a house here for $150,000 that would cost $400,000 in Middlebury. If you can get to your job in Fairfield County in a reasonable time, why not live in Waterbury or Naugatuck?"

Naugatuck Mayor Bob Mezzo agreed, saying "I've never been more excited about the prospects for this line. It's always been an underutilized asset."

Connecticut is using its own money to upgrade the decrepit Waterbury branch. It has committed $70 million for work that would allow much greater frequency of trains. Currently, service is sharply limited because only one train can be on the 27-mile track at once. Even on weekdays, riders could wait up to 2 1/2 hours if they miss a train. Hartley said that's holding back economic development as well as job growth.

"There's no secret our economy rises and falls with our transportation system," Hartley said.

Annual ridership on the branch languished for years before climbing steadily from 64,000 in 2003, peaking at 143,000 in 2010. It was just 125,000 last year; rail advocates blame the infrequent schedule along with extended track repairs that sidelined trains and forced commuters onto buses.

Jim Gildea, vice chairman of the Connecticut Commuter Rail Council, said Waterbury branch riders have been passionate about improving the quality of service. With a reliable schedule of reasonably frequent trains timed to commuters' needs, the line's ridership would rise, Gildea said.

Gov. Dannel P. Malloy has committed to installing a modern signal system and new rail sidings for the Waterbury branch, which would allow better frequency.

"More regular service on the Waterbury branch line will unlock thousands of jobs and millions of dollars in economic development potential all along the Route 8 corridor, and we need to start demanding that the federal government be a true partner with these new state investments," Murphy said.

Connecticut needs more federal funding to maintain and expand mass transit systems while adding new ones, the mayors and first selectmen agreed. The state gets about $200 million a year in federal aid for all of its rail and bus systems, a figure that Murphy called "a pittance."

But the conservative majority in Congress is insistent on budget rollbacks and has been generally lukewarm or hostile to mass transit. Murphy acknowledged the push to boost funding for commuter rail, bus and subway systems in the region is "definitely an uphill battle."