Often as part of our advocacy work we request city planners re-think the standard width for lanes. These requests are often met with concern regarding safety, congestion, street capacity and comfort within the status quo. Our reason for asking, however, is also based on the fact that narrower lanes are proven to increase safety without negatively impacting congestion.
- How Did We Get Here?
- Why We Like Narrow Lanes
- Frequenty Heard Arguments
- Read Further (Seinfeld Bonus)
For many years city planners and engineers have been translating AASHTO guidelines recommending lane widths from 10 to 12 feet as a 12 foot standard. The thought is that the wider the lane, the safer it is.
In the United States, six states require a minimum of 12-foot lanes and another 24 states require 11-foot lanes. Here in the East Bay, 12′ is often the norm as well. The city of Dublin’s General Plan, for example, recommends 12′ wide lanes as the standard lane width.
Sidenote: we are specifically discussing high-volume streets. A typical residential street can be as narrow as 12-feet (or even narrower in some older cities) and handle traffic in two directions.
Many of these guidelines were established without significant data to prove their effectiveness.
However, in the past year a number of studies have been published demonstrating that these early assumptions are shaky, if not completely false. Instead of making our streets safer, wide lanes encourage speeding, increase crossing times for pedestrians, and are a cause for more collisions.
The good news is, these excessively wide streets are great candidates for a retrofit and redesign, and have all the room we need to build beautiful multi-modal complete streets.
At the 2015 National Bike Summit in Washington DC, Ellen Dunham-Jones, author of Retrofitting Suburbia, spoke on the subject of our sprawling streets and what to do with them:
“There are many smart ways to do more and make up for past faults in redeveloping these spaces,” she said. “Chase the ghosts away with thoughtful, environmentally friendly, social places. Now is the time to see these spaces as an opportunity – a challenge to take, not to avoid.”
Why we like narrow lanes
The NACTO guide states that “Lane widths of 10 feet are appropriate in urban areas and have a positive impact on a street’s safety without impacting traffic operations.” Here’s why:
Studies show that the wider the lane, the faster cars will drive. Not only are the numbers of collisions reduced by reducing lane widths, but they are also less fatal.
Given the empirical evidence that favours ‘narrower is safer’, the ‘wider is safer’ approach based on intuition should be discarded once and for all. Narrower lane width, combined with other livable streets elements in urban areas, result in less aggressive driving and the ability to slow or stop a vehicle over shorter distances to avoid a collision.
A car can come to a complete stop or brake suddenly more effectively when going slower, avoiding collisions altogether. In addition, the lower the speed of the vehicle, the less likely it is to be fatal. A pedestrian hit by a car traveling 30MPH is between seven and nine times as likely to be killed as one hit by a car traveling 20MPH.
Some streets in the Bay Area are already narrow, and operate without any issues. For example (note this is not an exhaustive list by any means!):
Safety aside, why do we want narrower lanes? One obvious answer is more room for bike lanes and for buffered bike lanes.
When a road diet is not a possibility on a busy street, reducing lane widths can reallocate space to bicyclists and make the addition of a bike lane possible. By making better use of the space available, the overall capacity of the street is increased and different types of users are better accommodated.
The addition of bike lanes would make the sidewalks safer to walk on and would help create the feeling of a reduced crossing time.
There are many additional ways to use the extra space freed by narrower lanes:
- Widened sidewalks and street furniture
- Crosswalk bulb-outs
- Green space
- Parklets, public space, and on-street bike corrals
- and so much more!
Frequently Heard Arguments
A common rebuttal to reducing lanes from 12 to 10 feet is that doing so will be conducive to more congestion. But smart design can accommodate slim lanes and traffic alike—something New York City recently discovered when it narrowed car lanes to make way for bike lanes. In a study entitled “Narrower Lanes, Safer Streets“, Dewan Masud Karim found that traffic capacity in Toronto was actually highest for lanes right around 10-feet wide.
“Traffic delays on urban roads are principally determined by junctions, not by mid-block free flow speeds,” he writes. “Reducing lane width to 3.0 m [~10 feet] in urban environments should therefore, not lead to congestion. (…) So long as all other geometric and traffic signalization conditions remain constant, there is no measurable decrease in urban street capacity when through lane widths are narrowed from 12 feet to 10 feet”
The accommodation of large vehicles, particularly trucks, buses and emergency vehicles are sensitive issues when asking for narrower traffic lanes. General consensus from studies is that on streets with a low volume of large vehicles (less than 5%), narrower lanes do not pose any significant risks.
From Dewan Masud Karim, “Narrower Lanes, Safer Streets“:
“To test the assumption that large vehicles cannot use relatively narrower lanes, a percentage of large vehicles were compared against a different lane width category. Contrary to conventional belief, no differences were found between narrower (3.0 to 3.3m – 9.8 to 10.8 feet) and wider travel lanes (over 3.3m). Curb lanes are generally wider than other travel lanes and thus carry slightly higher large vehicles, but the difference is insignificant.”
“The degree of truck proportion in total traffic, and their separation distance from bicycles influences the lane width selection. Oregon DOT (2013) concludes that the low volume trucks (less than 5%) experience no operational problems for narrower lane widths and suggests considering extra width on streets with more than 10 percent trucks, and streets with horizontal curves and tractor-trailer combination trucks.”
Regarding emergency vehicles, on large streets the presence of multiple lanes often leaves sufficient space for drivers to pull out of the way of emergency vehicles. In addition, in many cases when we are speaking with planners narrowing the actual width of the entire space is not on the table unless funding is available to widen sidewalks, and the changes discussed are often restricted to striping and paint.
“Furthermore, although wide and open streets are often seen as providing faster travel time for emergency vehicles, researchers have found that roadway connectivity is a more significant factor leading to reduced (or increased) distances to reach destinations.”
Roadway connectivity refers to the built environment, the size of blocks, and being able to get to one destination via multiple routes. In extreme examples, a downtown grid offers numerous paths to a particular intersection while a cul-de-sac heavy suburb may require a 5-mile drive to travel between two points 1/2 mile away, no matter how wide the lanes are.
Regarding bus routes, the minimum width required varies between 10.5 and 11 feet. One possible solution is to stripe the outside lane, most occupied by buses, at 11 feet and the inner lane (or lanes) be narrowed to 10 feet.
The following three studies show that that is not the case:
- Effective Utilization of Street Width on Urban Arterials by the TRB, which found that “… 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.”
- The Influence of Lane Widths on Safety and Capacity: A Summary of the Latest Findings cites these findings by the Florida DOT: “The measured saturation flow rates are similar for lane widths between 10 feet and 12 feet … Thus, so long as all other geometric and traffic remain constant, there is no measurable decrease in urban street capacity when through lane widths are narrowed from 12 feet to 10 feet.”
- Relationship of Lane Width to Safety for Urban and Suburban Arterials by the conservative Midwest Research Center. Comparing 10- to 11-foot lanes to 12-foot lanes, it found: “A safety evaluation of lane widths for arterial roadway segments found no indication, except in limited cases, that the use of narrower lanes increases crash frequencies. The lane widths in the analyses conducted were generally either not statistically significant or indicated that narrower lanes were associated with lower rather than higher crash frequencies.”
Bonus Research Point: Seinfeld shows just how dangerous wide (and luxurious) lanes really are.
NACTO’s Urban Street Design Guide, section on Lane Width.
Many of the arguments and numbers above are pulled from the following two City Lab articles which we highly encourage as further reading:
- City Lab “10-Foot Traffic Lanes Are Safer—and Still Move Plenty of Cars” by Eric Jaffe. July 28, 2015
- City Lab “Why 12-Foot Traffic Lanes Are Disastrous for Safety and Must Be Replaced Now” by Jeff Speck. Oct 6, 2014