Wednesday, June 27, 2012

Put Your Road on a Diet


Do you ever complain about the high speed of traffic near your house? When running local errands, do you sometimes glance down at your speedometer and start praying the local police are taking a donut break? If the answer to either of these is yes, there’s a good chance the roads in question are engineered for speeds that are too high. They may be wide and straight like an expressway, but with the hidden danger of cross-traffic and driveways.

In a lot of communities, residents along these overbuilt roads agitate to lower speed limits, but these are inevitably ignored by impatient motorists. In others, local planners opt for speed tables that slow traffic down with the implicit threat of jarring drivers’ teeth out. A better option that can’t be ignored and won’t damage your bone structure is a road diet.

A road diet is a narrowing of the amount of space available to vehicular traffic. For example, if a road is four lanes wide, a road diet might take it down to two through lanes, plus a center turn lane along with two bike lanes. This is exactly what the Virginia Department of Transportation (VDOT) did to Lawyers Road in Reston, a community near Washington, DC. 
Lawyers Road in Reston, Virginia. Now you can turn left and ride your bike with less fear of imminent death. Courtesy of VDOT

By giving bicyclists their own reserved space, VDOT sought to reduce the risk of a car/bike collision. Traffic attempting to turn left could get out of the through lanes and into the center turn lane, thus reducing the risk of rear-end collisions. The center turn lane also served as a buffer between the through lanes, so head-on collisions would be less likely. 

So far, the diet appears to be working. An unscientific VDOT survey found that 69% of the respondents felt safer on the reconfigured road, while 47% biked on it more often. That perception of safety was real: crashes were down from 15 in the year before the diet to 3 in the first year afterwards. What is really interesting is that 71% wanted to see similar diets elsewhere in northern Virginia. 

Sounds great, right? Sure, but keep in mind that most people have no idea what a road diet is. When you tell them, “We’re going to narrow this road to make it work better,” they look at you as though you have begun speaking to them in an obscure Dutch dialect. I know this because I’ve tried it (the road diet suggestion, not the Dutch dialect). At least one person I floated the concept by vowed to fight to his last breath to stop it, because he thought it would hinder his daily commute. 

Cameron Street, a one-way route in Alexandria, Virginia near King Street/Old Town Metro Station. This is about as busy as it gets, yet some find the idea of replacing a vehicular lane with a bike lane to be tantamount to setting their car on fire. Photo by the author.

As a chocoholic would find when confronted with Mississippi Mud Pie, diets don’t always stick. A DDOT (District Department of Transportation) planner recently told me that Benning Road in Washington, DC underwent a road diet that created substantial backups at some traffic lights. Complaints from users and residents in the area forced the city to remove it. Why did it fail? Simple: the traffic count was too high.
Road diets only work if the road isn’t already a parking lot. One study from the University of Kentucky showed that success was likely if the traffic count was 17,000 vehicles or less per day. In some cases, that number could be as high as 23,000. That maximum depended on the side street volume and the number of traffic signals. Lawyers Road in Reston handled a mere 10,000 vehicles per day, perhaps explaining its success.

Road diets need not be confined to multi-lane thoroughfares. Two-lane roads can benefit from these. In a park near Williamsport, PA, planners narrowed the road by adding bike lane and closed a gap between two bike trails. Drivers slow down because they perceive their space as being tighter, like you might feel on a narrow mountain road. Drivers have been trained for generations to stay between the lines; bike lanes such as these play off of that indoctrination. 

Note how much narrower this road near Williamsport, Pennsylvania, looks with the bike lanes added. Although this location is semi-rural with long sight-lines, vehicles moved a lot slower than I expected. Photo by the author.

Going back to the Lawyers Road example, the success of this project has spawned an extension that will imitate the Williamsport example. VDOT is thinking of replacing each of the two 18-foot lanes with a 12-foot lane plus a 6-foot bike lane. Crash rates, based on previous experience, are expected to decline by 30%. Plus, cyclists who refuse to ride in traffic will be encouraged to use this route (see my previous post on the advantages of separating bikes and cars).

So, if transportation planners propose a road diet along your route, take a deep breath and don’t panic. Unless the traffic count is well over 20,000 vehicles today, which would be a major road as opposed to a simple street, traffic will actually flow better. Fewer crashes mean fewer bottlenecks. Plus, some of those people who blocked your path before might get out of their cars and use their bikes in lanes that are out of your path.

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