Local transit agencies are providing more trips than in the past but the costs to provide them are rising far faster, according to a new report, putting the burden on riders and taxpayers who pay the way.

The cost of running Metro has grown by at least 28 percent over a four-year period, according to the draft report from the National Capital Region Transportation Planning Board, more than five times faster than ridership has grown in that same time.

Metro is the largest transit agency locally, providing four out of every five transit trips in the region in the 2009 fiscal year. But the Washington region now boasts 17 different public transit services, the report shows, ranging from commuter trains such as MARC to express bus lines and local bus services.

Like Metro, nearly all the local transit systems also saw their ridership grow between the 2006 and 2009 fiscal years, the report shows, as the region added people and record gas prices in 2008 pushed more people out of their cars. (Only the City of Fairfax's CUE bus had a 6 percent ridership drop, the report showed, while ridership on Fairfax County's Connector stayed steady.)

Likewise their costs all grew during the four-year period, ranging from 3 percent growth during that time to 83 percent.

But some of the local systems grew faster than their costs, meaning more bang for their buck over the four years.

Although the D.C. Circulator's operating costs grew by 83 percent in the four-year period, its ridership grew by 93 percent in that same time, nearly doubling from 2.07 million trips to 4 million per year. The local bus system began in 2005 and has steadily increased the number of routes to five.

Arlington's ART ridership also outpaced its cost increases, with a 54 percent ridership increase compared with a 44 percent operating cost spike.

Those changes make sense to Christopher Zimmerman, who serves on the boards of Metro and Arlington County. "The Fairfax Connector has been around awhile so you don't see a lot of changes. Circulator is brand new, ART's in between," Zimmerman said. "So it's not surprising you'd see a lot of changes on the Circulator."

Metro, the region's behemoth, has been around the longest and thus doesn't change as drastically.

"Metro's operating costs are rising faster than ridership because expenses are rising," said Metro spokeswoman Angela Gates. She cited increased employee health care costs, increased contributions to employee pensions because of the poor performance of the stock market and the rising cost of liability insurance. She also said costs rose as Metro provided more rail service in that time, running more electricity-hogging eight-car trains and extending the Yellow and Red lines.

Zimmerman notes that some of the newer transit companies have newer equipment that runs faster and cheaper. They also may be able to run their buses in less congested areas. "It could be Metrobus is getting stuck on their routes more in traffic," he said.

Just as with other transportation modes, nearly all transit systems are subsidized in some way. When ridership costs and trips grow at the same rate, those subsidy rates can stay steady. But they can tip like a seesaw when the ridership and costs grow at different rates.

Smaller and newer agencies are more likely to see larger swings than more established, larger ones as adding a single bus route can make a bigger difference for them in terms of costs and riders.

Yet Zimmerman said it's important to look at the collective network and how it can be more efficient for riders and taxpayers to increase the flow and reduce traffic for all vehicles. "They're all run by taxpayers," he said. "We want them to be a relatively seamless system."