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Angie Schmitt writes in Streetsblog USA that city streets with the widest lanes — 12 feet or wider — are associated with greater crash rates and higher impact speeds and that there is hard evidence that wider lanes increase risk on city streets. Dewan Masud Karim conducted a wide-ranging review of existing research as well as an examination of crash databases in two cities, taking into consideration 190 randomly selected intersections in Tokyo and 70 in Toronto. Looking at the crash databases, Karim found that collision rates escalate as lane widths exceed about 10.5 feet. According to Karim "human behavior is impacted by the street environment, and narrower lanes in urban areas result in less aggressive driving and more ability to slow or stop a vehicle over a short distance to avoid collision. Designers of streets can utilize the “unused space” to provide an enhanced public realm, including cycling facilities and wider sidewalks, or to save money on the asphalt not used by motorists." Karim concluded that there is a sweet spot for lane widths on city streets, between about 10 and 10.5 feet.
According to Jeff Speck the fundamental error that underlies the practice of traffic engineering is an outright refusal to acknowledge that human behavior is impacted by its environment and it applies to safety planning, as traffic engineers, designing for the drunk who's texting at midnight, widen our city streets so that the things that drivers might hit are further away. "When lanes are built too wide, many bad things happen. In a sentence: pedestrians are forced to walk further across streets on which cars are moving too fast and bikes don't fit," writes Speck adding that a pedestrian hit by a car traveling 30 mph at the time of impact is between seven and nine times as likely to be killed as one hit by a car traveling 20 mph This tremendously sharp upward fatality curve means that, at urban motoring speeds, every single mile per hour counts. "Every urban 12-foot lane that is not narrowed to 10 feet represents a form of criminal negligence; every injury and death, perhaps avoidable, not avoided—by choice."
Original Submission
(Score: 1, Insightful) by Anonymous Coward on Thursday June 04 2015, @05:08AM
Here is another study indicating that either:
1. Lanes are wider in dangerous areas (They might have gotten cause and effect reversed)
2. Danger is correlated with lane width due to come confounding factor (curves? Large Vehicles? higher speed limits? Bad road conditions?)
3. Wider lanes causes danger indirectly, perhaps it increases use of the road, resulting in more throughput, or higher speeds (there might be the goals of having the road in the first place) which then increase the crash rates and crash speeds.
4. Width is dangerous by itself, and don't have benefits.
Really, did they notice that freeways have wider lanes than little city streets and more crashes at higher speeds? There was a similar paper recently about how one way roads were designed to increase traffic flow, but have the nasty effect of increasing accidents. The goal of road design is often more throughput and/or faster traffic. More faster traffic == more accidents. Um, duh. If you make a road 5 feet wide its really safe, but also not useful as a road...
I want to see the same plot broken down by speed limit at least, or a 3d plot of throughput vs lane width vs crash rate. If you want to do real science though try a controlled experiment.
(Score: 1) by dj245 on Thursday June 04 2015, @02:02PM
Here is another study indicating that either:
1. Lanes are wider in dangerous areas (They might have gotten cause and effect reversed)
That's kind of a circular cause and effect though. I would fully expect that wider lanes are employed in newer areas. 50 years ago they weren't building ultrawide lanes in urban areas. So, if the old areas are fine but the new ones aren't as safe, that means something is different between them in regards to the road design. Maybe it's the lane width, maybe it is something else. But the lane width seems the most likely culprit. I've ridden around in Tokyo. People don't get up to very high speeds in any urban area because all the roads are narrow.