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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: 4, Insightful) by shortscreen on Thursday June 04 2015, @05:54AM
First of all, Mr. Speck needs to get over himself. Criminal negligence? Please. Now, if his idea for improved safety is to have vehicles travel at 20mph instead of 30mph, why doesn't he just say that instead of this baloney about making lanes narrower?
I've heard ideas like this before, but I have a hard time imagining what is going through a person's head. Apparently the root of the problem is that people are having way too much fun driving in shitty urban traffic! Whereas we know that people behave most safely when their task is as frustrating, tedious, and stressful as possible. So we can fix this! Just add more obstacles, more bottlenecks, more confusing signage, more lanes that begin and end and merge and diverge, some spikes that randomly pop out of the road, bottomless pits, death rays that cycle on and off, and... oh! let's make the lanes smaller too!
(Score: 2) by bradley13 on Thursday June 04 2015, @06:55AM
"Whereas we know that people behave most safely when their task is as frustrating, tedious, and stressful as possible. So we can fix this!"
Exactly. Not too far from where I live there is this really terrible intersection: 5 or 6 roads coming in, several crossing tram tracks, a couple of bus lanes, bicycles pedestrian crossings - it's a huge mess, there's nothing to be done because it's a nexus in the middle of a city that has grown up around it. This intersection has a really low accident rate. This, because everyone knows it's bloody dangerous; and everyone is very careful whenever they go through it.
This does not mean that we should make all of our intersections equally dangerous: that's drawing the wrong conclusion.
Where you have need to keep traffic speeds down, fine, make narrower lanes. But make sure that those are not regular commuting routes. Meanwhile, provide commuting routes with wide lanes, away from pedestrians, bicycle lanes, etc..
Everyone is somebody else's weirdo.
(Score: 2) by Phoenix666 on Thursday June 04 2015, @12:57PM
Regular commuting routes should be done on the subway, by express bus, or light rail. If you live in an urban area with sufficient density, commuting by bike trumps even those. Commuting by car is madness.
Engineering roads to be narrower and safer is better for everyone, drivers included. When the road is so wide and design too permissive, risk-taking drivers produce chaotic traffic and accidents that are constantly stressful and dangerous for risk-averse drivers. The result is traffic moves worse through such areas. NYC has started re-engineering its roads along these lines, and as a pedestrian, cyclist, and driver the payoff has been instant for all three modes of travel. The lights have been re-timed so that if you go a constant 23mph you hit all greens in your car, which is beyond wonderful--no more jack-rabbit starts, slaloming between lanes to beat lights, etc. The bikes have their own protected lane, which makes a huge difference if you're a new cyclist. Pedestrians get to not be run down by speeding SUVs.
The only ones who lose are gearheads in their muscle cars, you know, the guys who pull up next to you at stoplights and rev their engines? Personally, it puts a smile on my face if traffic calming frustrates the hell out of those guys.
Washington DC delenda est.
(Score: 2) by c0lo on Thursday June 04 2015, @09:51AM
magic roundabouts [wikipedia.org]
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 3, Insightful) by Katastic on Thursday June 04 2015, @10:35AM
The magic words here: Correlation doesn't equal causation.
Just because narrower roads have less accidentals/slower drivers DOES NOT mean it causes safer roads. You have to control for ALL other factors, but first you must KNOW those factors before you can control for them.
Smaller roads typically also have higher amounts of pedestrians, jay walkers, higher amounts of broken patches of road, and other hazards you have to watch for, as well as higher amounts of sharp turns to avoid large lines of badly parked cars. And those are just off the top of my head.
(Score: 0) by Anonymous Coward on Thursday June 04 2015, @03:08PM
Yes, that actually is what you have to do!
Here's a traffic engineering secret: speed limits are irrelevant. Drivers ignore them and instead go as fast as they feel safe going. No more, no less.
So if you (as an engineer) want to slow down the traffic, you can't do it simply by lowering the speed limit; you have to change the geometry of the road to force the drivers to feel less safe!
(Score: 0) by Anonymous Coward on Thursday June 04 2015, @04:55PM
Replace the airbags with a large spike.
(Score: 2) by darkfeline on Thursday June 04 2015, @07:31PM
Because drivers already obey posted speed limits as it is, right? I love it when I'm driving 5 above the speed limit and everyone else is breezing right past me.
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