Why 12-Foot Traffic Lanes Are Disastrous for Safety and Must Be Replaced Now

[thelakelander]

A friend of mine heads an office in the White House. I never see him anymore, except at the occasional black tie design dinner, where he is always good for a couple of gin and tonics as the crowd disperses. At the last such event, he asked me a question. Or maybe he didn't. But I answered it.

"What's the number one most important thing that we have to fight for?" I said. "You mean, besides corporations being people and money being speech?"

"Besides that."

"Well that's easy: 10-foot lanes instead of 12-foot lanes."

"Explain."

And so I did, brilliantly. So brilliantly that the White House issued an Executive Order the very next day. Or so I imagined; such is the power of gin.

Sobered by my now palpable failure, I have steeled myself for the task of explaining here, in a manner that can never be disputed or ignored, why the single best thing we can do for the health, wealth, and integrity of this great nation is to forbid the construction, ever again, of any traffic lane wider than 10 feet.

(Before beginning, let me thank the traffic engineers Paul Moore and Theodore Petritsch, who taught me most of this stuff. Yes, there are some good ones out there. This article borrows heavily from an article by Petritsch, "The Influence of Lane Widths on Safety and Capacity: A Summary of the Latest Findings.")

Full article: http://www.citylab.com/design/2014/10/why-12-foot-traffic-lanes-are-disastrous-for-safety-and-must-be-replaced-now/381117/

[ChriswUfGator]

Agree with pretty much everything he says. Traffic engineering focuses too much on removing bottlenecks. Not all bottlenecks are bad for various reasons, they force traffic patterns to be pedestrian friendly, they force people to live closer to work, etc.

[Jumpinjack]

One really dangerous feature of our roads in Florida is the slip lane or dedicated right turn lane. They make it too easy to keep up speed while whipping around a corner.

[I-10east]

Frustrating drivers with stalled traffic flow situations (bottle necks, no turning lanes, narrow lanes etc etc) isn't beneficial to pedestrian and driver safety either IMO. I don't think that is being addressed here. I think that there's a 'sweet spot' in the middle for pedestrians/bicyclists and cars. From a citylab POV, it's like 98 percent peds/bike with 2 percent vehicular traffic in mind, very lop-sized IMO.

[tufsu1]

^ if that was the case, they wouldn't be supporting narrowing lanes to from 12' to 10'.  They would be supporting no vehicle lanes.

[NIMBY]

Interesting and compelling.  However, upon checking the study he cites to silence the "short-sleeved white shirt and a pocket protector" crowd, he leaves out key details of the study that weaken his argument.

He says that  "Effective Utilization of Street Width on Urban Arterials," was completed by the TRB itself. It found the following: '... all projects evaluated during the course of the study that consisted of lane widths exclusively of 10 feet or more [rather than 12 feet] resulted in accident rates that were either reduced or unchanged.' "

That quote is correct, but incomplete.  The actual TRB document summary says: "It was found that projects where narrower lanes are used to provide space for installation of a center two-way left-turn lane [TWLTL] generally reduce accidents by 24-53 percent. Projects where narrower lanes were installed to provide additional through lanes on an arterial street generally did not affect midblock accident rates, but did increase accident rates at intersections.  None of the projects involving narrower lanes had any effect on the accident severity distribution."

The TRB document also says: "This evaluation included 35 sites located in five states. It was found that lane widths narrower than 11 ft can be used effectively in urban arterial street improvement projects where the additional space provided can be used to relieve traffic congestion or address specific accident patterns.  Narrower lanes may result in increases in some specific accident types, such as same-direction sideswipe collisions, but other design features of a project may reduce other accident types by as much or more.  Improvement strategies involving narrower lanes nearly always reduce accident rates when the purpose of the project is to make an improvement known to reduce accidents, such as installation of a center TWLTL or removal of curb parking."

The lane width reductions were not the only changes made.  The study actually attributes the differences in crashes to the provision of the TWLTL (a.k.a. suicide lane) where none previously existed.  This manipulation weakens the whole article and argument.

[fieldafm]

From a citylab POV, it's like 98 percent peds/bike with 2 percent vehicular traffic in mind, very lop-sized IMO.

The author is Jeff Speck, one of the foremost scholars in the country on walkability, not some hack blogger.

Btw, he just released his walkability study/recommendations for downtown West Palm Beach. You can read them here: https://www.scribd.com/doc/241343071/West-Palm-Beach-Downtown-Walkability-Study.

For all the PR FDOT is putting out recently about how they are 'adapting' (hogwash), they are still battling Speck on the intersection issue I highlighted here:  http://www.metrojacksonville.com/forum/index.php?topic=21578.0

[NIMBY]

FDOT updated their standards today to include an option for reduced vehicle lane widths and increased bicycle lane widths within urban areas.

http://www.dot.state.fl.us/rddesign/Bulletin/RDB14-17.pdf

Summary:
"This bulletin modifies the criteria for Urban Arterial Travel Lane Width, Bicycle Lane Facilities and related Bicycle Lane Markings. Specifically, this bulletin establishes eleven foot travel lanes for roadways with a divided typical section in or within one mile of an urban area and with a Design Speed of 45 mph or Jess. This bulletin also establishes seven foot Buffered Bicycle Lanes as the standard for marked bike lanes."

[IrvAdams]

Good move. Sounds very positive. I wonder if retrofitting existing roadways is in the plans?

[thelakelander]

FDOT District 5 is allowing for 10.5' wide lanes in constrained urban environments.

[Steve]

On Riverside Ave, if you'd go to 10 foot lanes, that frees up six feet per direction. What's the minimum for parallel parking? If you want to slow traffic, that will certainly do it.

[thelakelander]

Is Riverside Avenue still a FDOT street?  If so, I doubt anything less than 7' or 8' in width.  If it isn't an FDOT street, I recommend a taking out two lanes, reducing the with of the remaining adding parallel parking along with protected or buffered bike lanes.

[Steve]

Yea, it's not US 17 anymore, but it's still FL 211

[thelakelander]

I just found out, the part in Brooklyn isn't a state road anymore either. So the city can do anything it wants with the street.

[Steve]

Where does FL211 start?