Engineers resist narrow lanes, but change is coming

A little over a month ago, Johns Hopkins University released the largest-ever research on travel lane width and safety, providing conclusive evidence that 9- and 10-foot lanes do not contribute to greater automobile crashes and, in some cases, reduce collisions. Traffic engineers have long shunned narrower lanes—which benefit walkable cities by providing more room for pedestrians, bicyclists, and landscaping—citing safety concerns.

New urbanists have been making the case for narrow streets as a necessary component of walkable neighborhoods for 30 years, and the message has largely gone unheeded by the civil engineering profession. (There have been signs of progress, such as when the Institute of Transportation Engineers worked with CNU on the 2010 Designing Walkable Urban Thoroughfares, a recommended practice). And yet as a rule, engineers have continued to design overly wide streets in places that could be more walkable. But engineers could not ignore research from such a prestigious and health-focused institution—especially since the study was widely reported.

Soon after the study hit social media and the airwaves in November, the American Society of Civil Engineers (ASCE) surveyed their members on narrow travel lanes and the results are revealing. Poll results were shared on the Pro-Urb listserv by civil engineer Paul Crabtree. See below for the answers and the comments.

Proponents of walkable places may think the results depressing. Less than a third of civil engineers accept that “yes, narrow lanes are safer” and, therefore, “many lower-speed traffic lanes should be made narrower (9-foot or 10-foot wide), either by retrofit or from the planning stage.” Most engineers either deny the safety benefits of narrow lanes or they find other reasons to support wide lanes.  

And yet, there are more optimistic interpretations. There is no older survey to compare to, but I would estimate the support for narrower lanes was very low in the past—probably single digits—judging by the pervasive preference for wide lanes over the last 50 years. That would be good news if we can get narrow lanes on nearly a third of new streets or retrofits.

Granted, we need a wide application of skinny streets to change the nationwide problem of automobile-dominated communities. A new mindset among street designers would improve most Americans' lives and help cities adapt to and mitigate climate change by allowing for more nonautomotive mobility. In that respect, too many engineers think “narrow lanes aren’t the answer to safety issues.”

More than a third of engineers picked answer number three, which at least acknowledges the safety potential of narrow travel lanes. They may be safer, the engineers say, but they “cause too many other problems.” I would flip that around and look at the problems caused by wide travel lanes on streets in cities and towns. Wide lanes restrict space for any other activity besides automotive travel within the right of way. Generous sidewalks? Protected bike lanes? Better landscaping? Forget about it, in most cases, with overwide travel lanes. Moreover, wide lanes encourage higher speeds, which make the social functions of streets difficult. Few will walk, let alone linger and socialize, on a street where cars are moving at a deadly speed. The sense of danger is palpable; the noise unpleasant. No one will sit at cafe tables a few feet away from traffic moving faster than 40 miles per hour. Wide lanes discourage active living, which is why Johns Hopkins did the study. Wide lanes and fast traffic reduce steps, creating health impacts. Routinely designing wide lanes reduces the function of streets, which have historically served as the heart of communities, to moving automobiles. The third answer could have been reworded given the Johns Hopkins research results: “We know that wide travel lanes do not improve safety, and they cause too many other problems.”

In Confessions of a Recovering Engineer, Charles Marohn wrote that the civil engineering profession values higher speeds on thoroughfares. Recognizing the problems of narrower lanes, but not of wider lanes, is consistent with that value. In other words, the issue is not a rational analysis of safety, but of a desire to design streets so cars can go fast—even through neighborhoods and downtowns.

To be sure, narrow lanes raise issues—such as the risk to truck and bus mirrors. City buses are only 8.5 feet wide, but with side mirrors they are 10.5 feet wide. Despite that, the damage reported to truck and bus mirrors is less than one would imagine, according to a study conducted by the Florida DOT of 9- and 10-foot lanes statewide over five years. It turns out that bus and truck drivers proceed carefully with narrow lanes. That care saves lives, not just mirrors. Yearly mirror damage in the Miami-Dade County system on narrow lane thoroughfares was reported at $35,000.

There are other valid reasons to support wider lanes in particular circumstances—on more heavily traveled streets that serve as bus routes, for example. Higher speed roads through rural or natural areas often benefit from wider lanes. 

Although the Johns Hopkins study affirmed narrow travel lanes' safety, the researchers generally promote context-sensitive design. They conducted extensive interviews with state departments of transportation, and were most impressed with the Context Classification System being implemented in Florida, created by new urbanist traffic engineers.

This Florida system allows thoroughfares to be designed according to the rural-to-urban Transect, which justifies different designs for downtowns and walkable neighborhoods as opposed to rural highways. “Perhaps the most important takeaway from our interview with FDOT was their innovative context classification system that helps traffic engineers to differentiate between an arterial (or other road classes) in a low-speed (such as downtown) versus high-speed context,” the Johns Hopkins researchers explained.

In places planned to be walkable, narrow (10-foot) travel lanes are now the default standard in Florida. Wider lanes must be justified for a specific reason. That's a big departure from conventional practice, which typically uses 12-foot lanes for streets in cities, towns, and suburbs. Twelve-foot lanes are also used on Interstates and facilitate higher speeds. State engineers in Florida are reportedly comfortable with the new system, because it provides a rational way to differentiate context and justify narrow lanes under specific circumstances. 

The ASCE survey shows the challenges to reforming street design to accommodate walking, cycling, and mixed-use neighborhoods. Nevertheless, there are silver linings. Sixty-two percent of engineers recognize the potential safety benefits of narrow lanes, including 28 percent that clearly want more of them. That’s progress, but we need more. Providing engineers with a better way to design streets according to context may be the key to allowing more of them to feel comfortable with narrow lanes.