From Atlanta to Washington, D.C., cities across the country are progressing on controversial new streetcar lines that are pitting transit planners against developers and elected officials.

At the center of the debate? Streetcars' rather lousy ability to actually transport anyone anywhere.

That fact has riled professional transit planners, many of whom have called the new lines a waste of money and political capital. They are this era's equivalent of "bridges to nowhere," examples of wasteful spending that don't serve real transportation needs.

Well damn the torpedoes, full speed ahead! writes D.C.-based blogger David Alpert in CityLab. (Incidentally, for most mixed-traffic streetcars, "full speed" isn't much.) In his rather incendiary article, Alpert asks, Are pro-transit, anti-streetcar people just making the perfect the enemy of the good?

The right answer is, Of course not! (What serious transit advocate ever called these new streetcar lines "good"?)

But the problem with the streetcar fad isn't boosters like Alpert. Nor, even, is it the small-time politicians who show up at the ribbon cuttings.

The real root of the problem behind the streetcar craze? The system of federal transit funding that virtually guarantees silly streetcar projects get built.

Where the streetcar meets the gravy train

Traditionally, the federal government's role in transit has been very limited. Funding for new construction is an exception, thanks in part to a small group of "discretionary" grant programs that award money to state and local projects through a competitive application process.

The problem is that while many of the DOT grantees are very deserving transit projects, such as light-rail extensions in Charlotte and Dallas, a substantial number are wasteful follies.

In the case of TIGER grants, a temporary program created in 2009 by the Recovery Act, more than a quarter of the $1.2 billion granted to urban transit projects has gone to streetcars.

Among these is Salt Lake City's S-Line, which opened last December and carries just 1,000 daily riders on its two-mile route.

As transit expert Yonah Freemark has noted, a large part of the problem is that the S-Line runs only every 20 minutes even at rush hour, meaning it simply isn't dependable enough for commuters to be worthy of comparison with car ownership. Even on new systems where the trains run twice as often — such as the new Tucson streetcar — ridership levels remain under 5,000 per day.

This is the fundamental problem with streetcars: Regardless of their frequency or geography, there are very few situations when investment in other forms of transit would not have been a much better use of taxpayers' money.

In Tucson, for example, the $196 million spent on just building the streetcar could have gone to funding nearly four years of bus service for the city — or to increasing frequency on the many Tucson bus lines that run only once every 30 minutes.

We know what works

Most aggravating of all is the fact that we know what works when it comes to planning good transit.

Just ask residents of Phoenix or Houston, two cities with new traffic-segregated light-rail systems where ridership is booming. Or in Cleveland, where a six-year-old rapid-transit bus line has been massively successful.

These transit projects have brought all of the economic development benefits that streetcar supporters love to cite, while also actually improving mobility and accessibility for thousands of local residents.

A wheel in the ditch, a wheel on the track

Washington's problematic policy on transit is hardly news. The perverse federal incentives that encourage cities to build new transit lines rather than improve existing ones is a well-known issue.

But the streetcar craze shows that DOT's problems are even more basic than that. Even among new projects, the department has shown little interest in either incentivizing "good" transit or discouraging the "bad" in terms of the grants it awards.

The impact cannot be underestimated. By and large, these new streetcar projects aren't supported substantially enough to stay afloat without federal money. If DOT made clear that it considered streetcars a waste of money and time, many cities would axe their streetcar proposals overnight.

Until that changes, we can only expect more useless streetcar proposals to keep coming down the pipeline.

Very, very slowly down the pipeline.