Over-Wide Streets? You May Regret It
A thoroughfare with 10-foot lanes and safe, multimodal transportation.
A clear body of evidence has accumulated that narrower lanes are safer on major urban thoroughfares that also include pedestrians.
Another study recently published supports 10-foot travel lanes over the 12-foot common practice on medium- and high-volume urban thoroughfares. Planner andWalkable City author Jeff Speck wrote an article last fall stating that state DOTs and county road commissions “have blood on their hands” for building over-wide lanes in urban areas. He called for a 10-foot-wide standard, citing a history of studies demonstrating that the Big Asphalt approach is dangerous.
Big Asphalt at Tysons Corner, Virginia, near a new Metro station.
Speck’s words are strong, but imagine the engineer who specifies 12-foot lanes on a major urban thoroughfare with anticipated pedestrian activity and someone is killed. Given the current evidence, does the question emerge as to whether that person’s life was put in unnecessary danger? Indeed.
Speck challenged engineers to present evidence that he is wrong–instead, research is confirming Speck’s position.
This new study, presented to the Canadian Institute of Traffic Engineers in June, compares Toronto and Tokyo and shows that 10-foot lanes have the fewest crash frequencies and can handle just as much traffic for both cars and large vehicles (trucks, buses). The maximum traffic volume is shown in streets with lanes 3 meters wide (slightly less than 10 feet). “Wider lanes introduce unstable maneuvering and higher interactions, particularly curb lanes,” the authors write. Plus, narrower lanes handle greater pedestrian and bicycle traffic.
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.
If anything, the paper understates the safety advantages of narrow lanes by treating the crashes at lower speeds as the same as crashes at higher speeds. One would much rather have 10 or 20 minor fender benders than one severe accident with a disabling injury or death.
Narrower lanes reduce vehicle speed, which has a big impact on fatalities in urban places. The average speed at collision in Toronto, with wider lanes, is 34 percent higher. That is likely to result in accidents of much greater severity. Although accidents appear to go up with lane widths narrower than 10 feet, these accidents are also likely to be less severe. Tokyo has a lot of streets that are narrower than those deemed “safest,” yet that city has by far the safest roads while maintaining the highest capacity. That question deserves further study.
New urbanists often propose 11-foot lanes rather than 10-feet on major thoroughfares—that avoids a fight with the state DOT or city engineer. This may be fine if other elements of the design—such as street trees, building facades, on-street parking—contribute to slow traffic. But if these elements are compromised or missing, the 11-foot lanes will still encourage speeding.
Another reason to like 10-foot lanes is that they are cheap. Other elements of a walkable streetscape, while vital, tend to be more expensive—especially in retrofits.
The latest research clearly shows that 10-foot lanes are worth fighting for on major urban thoroughfares. (On low-volume residential streets, even narrower streets are called for.)
Narrower lanes slow traffic and help descend the “curve of death.”
Chris McCahill of the State Smart Transportation Initiative summarizes the new study in this way:
Side impact- and turn-related crash rates are lowest at intersections where average lane widths are between 10 and 10.5 feet, according to a study presented at the Canadian Institute of Transportation’s annual meeting last month. This challenges the long-held, but often disputed, assumption that wider lanes are safer.
The study looked at vehicle-to-vehicle crashes at 70 signalized intersections in Toronto and 190 in Tokyo over periods of four to five years. Crash rates were highest where average lane widths at the approaches were narrower than 10 feet or wider than 10.5 feet. Intersection approaches with 10-foot lanes also carried the highest traffic volumes. Bicycle and pedestrian volumes generally increased as lanes became narrower. There was no significant difference in truck volumes.
Narrower lane widths (10 to 11 feet) are sanctioned in national policies outlined by AASHTO, particularly for urban areas, but the official standards in many states prohibit them. According to a 2010 study published in the ITE Journal, six states require a minimum of 12-foot lanes and another 24 states require 11-foot lanes.
When it comes to saving lives and allowing public life to thrive, a foot or two makes all the difference.
Robert Steuteville is editor and executive director of Better Cities & Towns.
View original article here.