Today, 750,000 riders will use the Washington Metro. In Atlanta, more than 200,000 will pass through the turnstiles of MARTA. On the West Coast, Bay Area residents will take BART 400,000 times.

It’s easy to take these subway systems for granted. Yet, without a little-known federal agency that celebrated its fiftieth birthday last week, it’s likely none of them would have ever been built.

That agency would be the Federal Transit Administration (FTA), which began life as the Urban Mass Transportation Administration when Lyndon Johnson signed it into existence on July 9, 1964.

Under-appreciated by all but the wonkiest of transportation wonks, the FTA has played a fundamental role in the construction of virtually every major U.S. mass-transit system since the 1960s.

Even today, despite chronic underfunding, it is underwriting some of the country’s most important transit projects, from New York’s East Side Access to the Silver Line in the suburbs of Washington, D.C.

Still, there is room for improvement. While the FTA’s impact over the past fifty years has been tremendous, its influence has been limited—by tradition and by law—to financing new projects.

It’s an unfortunate reality, as there are dozens of cash-strapped transit agencies across the country that could vastly improve their existing bus and rail service with a little bit of federal money.

The FTA has played a fundamental role in the construction of virtually every major U.S. mass-transit system …

Moreover, the restriction of FTA financing to “new only” sometimes encourages cities to plan projects they don’t really need.

That’s what happened in Cincinnati, where the city is building a streetcar line with the help of $25 million in FTA aid. The merits of streetcars aside (and, as this blog has written, there aren’t many), that same amount of money would likely go much further improving the existing Cincinnati bus service, whose entire operating budget is only about $90 million.

The problem is that, as with so much of the federal government, the FTA is largely a reactive agency, responding to local requests rather than actively involving itself in transit planning. As a result, transit agencies with the experience and know-how of applying for federal funding tend to bring home the bulk of the available cash.

Operating at its best, the FTA would do just the opposite: jump-starting smart projects in the rapidly sprawling parts of the country that would benefit most from good transit planning.

None of the ten fastest-growing states in the country received more than $20 per capita in FTA funding last year. New Jersey, meanwhile, with its strong public-transportation tradition, was awarded almost $150 per capita.

This isn’t to say projects in dense northeastern states don’t deserve federal help—they do. But, there’s a real opportunity for the FTA to play a more influential role in shaping public transit in the United States.

By actively encouraging new public transit in places that need it, while also helping improve service where it already exists, the FTA can play as important a role in the next fifty years as it did in the past fifty.

And that’s something worth celebrating.