This morning, as my Megabus pulled into Union Station, I saw, for the first time, a streetcar hanging out on H Street NE. It wasn’t doing much, although the construction workers on the Hopscotch Bridge just beyond it certainly were. But once safety certification is complete, city officials say it’ll be running within 30 days. That may not meet Mayor Vince Gray‘s very ambitious promise of passenger service “probably starting in January, not later than early February,” but it does mean we’ll be seeing streetcars in operation very soon. So what should we expect?

Not speed. As I lay out in a story published today in Next City ($1.99 payment or subscription required), faster transit isn’t really what streetcars are for. The H Street line will be following largely the same path as the X2 Metrobus, and while it won’t have to kneel down to pick up passengers, it also won’t be able to weave around double-parked cars or right-lane traffic jams, so there’s not much reason to think it’ll be any quicker than the bus. The city’s study of various options for extending the H Street line westward to Georgetown anticipates that a likely streetcar route would be 6 to 14 percent faster than a bus alternative—-but that route would have a dedicated lane for about a third of the line, something the H Street portion won’t have.

A new report out from the Institution for Transportation and Development Policy, published after I wrote my piece, shows just how slow streetcars can be, compared with other transit modes like bus rapid transit and light rail transit. Take a look at this chart:

Now, this isn’t to say that streetcars are inherently slower; as the ITDP study argues, it’s all about execution. A streetcar running in a shared traffic lane will be slower than a bus in a dedicated lane, and vice versa.

The same phenomenon applies to development potential, which is what many advocates argue streetcars are best at. Some of the people behind Portland’s streetcar—-a model for its counterparts in D.C. and elsewhere—-refer to it as “development-oriented transit,” turning the oft-invoked “transit-oriented development” on its head. There’s plenty of evidence that the streetcar has had a major impact on Portland’s development: Following the start of the effort to build the city’s first streetcar line, the percentage of central-business-district development occurring within a block of that line jumped from 19 percent to 55 percent.

Critics charge that a streetcar’s boost to development has less to do with the streetcar itself than with changes to zoning and subsidies to encourage development in the area, and the ITDP study mostly backs up that argument. While streetcar proponents counter that a streetcar line’s fixed route, symbolized by tracks in the ground, sends a signal to developers that the city’s committed and the route won’t change, no one really argues that development will shoot up without the zoning to support it.

So as the city continues to plan and build its billion-dollar, 22-mile priority streetcar network, the question residents should be asking isn’t so much “how fast will it go?” as “what will the city do to support it?” The answer will make the difference between a bus with a different reputation and a true tool for changing the city—-for better or worse.

Photo via D.C. Department of Transportation on Flickr