Streetsblog.net

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» The District of Columbia is installing streetcar tracks along Benning Road, Northeast, a nice advance for the city’s transit options. But it’s doing so in a way that will limit the speed and accessibility of trains.

Secretary of Transportation Ray LaHood’s announcement that he would award $130 million to streetcar projects across the country early next year excited transit advocates, who hope that the mode will soon become a frequent sight in American cities. Indeed, there are plenty of towns seriously considering building streetcar lines — at least 45 in North America as of the most recent count. Since streetcars, like local buses, run in lanes shared with automobiles, implementing them efficiently requires studying traffic patterns and attempting to find ways to avoid problems that could impair the efficiency of transit service. When the first projects get off the ground in 2010, one hopes that they’ll be built right.

Among those cities thus far that have committed to spending some of their own money — rather than just hoping the federal government will pick up 100% of the tab — is Washington, D.C. Though it has yet to secure all of the necessary funds for the massive system it plans to build, the city has already begun installing track on H Street and Benning Road Northeast, a prime corridor for improved transit investments. Once it assembles the necessary financing, it will add overhead catenary and begin running the service, potentially in two years.

The District has posted some relevant photographs on its Facebook page, and the images are indicative of the problems this corridor will encounter once it begins carrying trams. Of course, Washington isn’t alone, because streetcars face some fundamental difficulties as a result of the fact that they share their rights-of-way with automobiles. But its decisions about how streetcar tracks will be installed will plague the service provided by the vehicles and ultimately limit their utility.

Below, I have documented some of the quotidian situations that will result in delayed traffic as a result of the design of the District’s streetcar system. None of the problems are unique to streetcars — in fact, they’re shared with any vehicle that must share its running way with automobiles, including buses. But streetcars are put in a particular predicament in each of the cases noted below because, unlike buses, they can’t change lanes. If systems are designed with major flaws, such as those illustrated below, this means that these trains will operate at significantly lower speeds than equivalent buses; the result: a big investment investment in public transportation could actually mean less mobility.

But take note, other cities: these structural issues can be resolved through better designed streets.

Entering streetcar lane: The most obvious problem with streetcars, of course, is that they run in the street. That makes their construction relatively cheap, since tracks can simply be laid in a preexisting roadway. But because the streets are shared, cars can weave in and out of lanes, including those used by trains. This will force streetcar drivers to operate their vehicles overly cautiously and at limited speeds. By the same measure, while a bus has the ability to change lanes to pass stopped or slow cars, a streetcar is forced to maintain its course, even if that means getting stuck. There is no way to solve this problem unless some of the streetcar’s path is made limited-access.

Blocked turn lane: Because D.C.’s system is designed with left-turn lanes to the left of the median-operated streetcar, cars have to pass through the streetcar lane in order to take a left at intersections. When there are too many cars and streetcars in that lane heading straight rather than left, cars from lanes further to the left will have trouble making the turn to the left-most lane. This could be a problem especially if there is reticence among some drivers to operate in the streetcar lane; they will remain in the middle lane until the last possible moment, where they may get stuck. Cities with streetcars hoping to combat this problem could install signage encouraging drivers to stay out of the streetcar lane most of the time, while also encouraging people hoping to turn left to move over as quickly as possible.

Too many turners: If D.C. gives its left-turn drivers their own signals, it could mean streetcars are held up by the number of cars waiting for a green light because of the limited length of the left-turn lane, which would push some left-turners into the streetcar lane. Even if the traffic light for vehicles heading straight is green, streetcars would be blocked in the above situation; this could force streetcars to wait for the next light cycle. At intersections with high expected rates of left turns, D.C. would benefit from longer left-turn lanes than what is currently being built. Alternatively, it could eliminate some left-hand turns and encourage drivers to take alternate routes to reach their final destinations.

Blocked turns: On the other hand, if Washington’s system does not have separate left-turn lights, through streetcar traffic could be significantly affected by left-turn drivers, especially if their cars are in turn blocked by pedestrians crossing in the allowed travel direction. This problem will be most prevalent at intersections with significant pedestrian and left-turn traffic; there, a separate left-turn signal might be necessary — as long as left-turn lanes are adequately long and streetcars are given signal priority before left-turning cars.

Stuck at the light: Because of the shortness of the left turn lanes, two streetcars in a row (possible on several of the corridors D.C. is studying for its system, since they’ll service multiple lines) could block the possibility of left turns by automobiles entirely when stopped at a red light. If left-turn lanes were lengthened to ensure they are longer than at least two streetcars plus a car, this would solve the problem.

Stuck at the station: Whether stations are positioned before the signal or after, when they stop to pick up passengers, streetcars will slow down following traffic (including other streetcars), especially if surrounding traffic is heavy. This occurs with buses as well, but since their stations are in the lower-speed outside lanes, their effect 0n surrounding traffic is more limited than median-running streetcars. On the other hand, if streetcar stops are timed with red lights ahead, changing to green once passenger pick-up and drop-off has terminated, this problem could be eliminated.

Conclusions: The fundamental problems with all of these approaches is that they encourage car traffic to move more quickly, effectively limiting any attempt to provide streetcars with a time advantage. To get a streetcar to move more quickly, the traffic system must be designed to move all vehicles more quickly, because they share the same lanes.

This raises questions about the value of streetcars in general — wouldn’t it make more sense to operate these trains more like light rail?  Cities could do just that simply by installing cheap ground-level barriers between streetcar and car lanes, and eliminating the left-turn lanes to the left of the streetcars (or moving the trams to the outside lanes), all while instituting aggressive signal priority. These approaches would dramatically improve the efficiency and speed of streetcars and provide them a relative advantage over automobile traffic, which would be limited by fewer travel lanes than before, ultimately leading to more public transportation usage. That’s a valuable goal.