The following article is an excerpt written by our urban planner, Jeff Speck, and it clearly highlights the facts supporting narrower lanes as stated by U.S. safety and transportation agencies.
Bottom line: Just because we may be conditioned to travel faster on wider lanes -- doesn't make it right, safe, and suitable to where people live.
Excerpt by Jeff Speck
A little background: First, we are talking only about high-volume streets here.
Neighborhood streets can have much narrower lanes. The classic American residential street has a 12-foot lane that handles traffic in two directions. And many busy streets in my hometown of Washington, D.C., have eight-foot lanes that function wonderfully. These are as safe and efficient as they are illegal in most of the United States, and we New Urbanists have written about them plenty before, and built more than a few. But what concerns us here are downtown streets, suburban arterials and collectors, and those other streets that are expected to handle a good amount of traffic, and are thus subject to the mandate of free flow.
Second, you should know that these streets used to be made up of 10-foot lanes.
Many of them still exist, especially in older cities, where there is no room for anything larger. The success of these streets has had little impact on the traffic-engineering establishment, which, over the decades, has pushed the standard upward, almost nationwide, first to 11 feet, and then to 12. Now, in almost every place I work, I find that certain streets are held to a 12-foot standard, if not by the city, then by a state or a county department of transportation.
States and counties believe that wider lanes are safer. And in this belief, they are "dead" wrong.
In some cases, a state or county controls only a small number of downtown streets. In other cases, they control them all. In a typical city, like Cedar Rapids or Fort Lauderdale, the most important street or streets downtown are owned by the state. In Boise, every single downtown street is owned by the Ada County Highway District, an organization that, if it won't relinquish its streets to the city, should at least feel obliged to change its name. And states and counties almost always apply a 12-foot standard.
Why do they do this? Because they believe that wider lanes are safer. And in this belief, they are dead wrong. Or, to be more accurate, they are wrong, and thousands of Americans are dead.
They are wrong because of a fundamental error that underlies the practice of traffic engineering—and many other disciplines—an outright refusal to acknowledge that human behavior is impacted by its environment. This error applies to traffic planning, as state DOTs widen highways to reduce congestion, in complete ignorance of all the data proving that new lanes will be clogged by the new drivers that they invite. 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.
The logic is simple enough, and makes reasonable sense when applied to the design of high-speed roads. Think about your behavior when you enter a highway. If you are like me, you take note of the posted speed limit, set your cruise control for 5 m.p.h. above that limit, and you're good to go. We do this because we know that we will encounter a consistent environment free of impediments to high-speed travel. Traffic engineers know that we will behave this way, and that is why they design highways for speeds well above their posted speed limits.
Unfortunately, trained to expect this sort of behavior, highway engineers apply the same logic to the design of city streets, where people behave in an entirely different way.
On city streets, most drivers ignore posted speed limits, and instead drive the speed at which they feel safe.
That speed is set by the cues provided by the environment. Are there other cars near me? Is an intersection approaching? Can I see around that corner? Are there trees and buildings near the road? Are there people walking or biking nearby? And: How wide is my lane?
When lanes are built too wide, pedestrians are forced to walk further across streets on which cars are moving too fast and bikes don't fit.
All of these factors matter, and others, too. The simplest one to discuss, and probably the most impactful, is lane width. 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.
The following paragraphs lay out the evidence against 12-foot lanes, evidence compiled by traffic engineers, for traffic engineers.
First, we will investigate what the American Association of State Highway and Transportation Officials Green Book, the traffic engineers' bible, has to say on the subject. Then we will review the very few studies that compare crash statistics and driver speeds on lanes of different widths. These will allow us to draw some clear conclusions about safety.
Consulting the Green Book
For traffic engineers, AASHTO is the keeper of the flame. Its "Green Book," the Policy on Geometric Design of Highways and Streets, is the primary source for determining whether a road design is an accepted practice. As such, it is useful in protecting engineers against lawsuits; if something is in the Green Book, it's "safe."
Given the protection it affords, nobody questions the Green Book. Never mind that very little of it is evidence-based, and that there are no footnotes justifying its pronouncements. I mean, does the Bible have footnotes?
Whether or not it reflects reality, the Green Book's position on lane widths is more than relevant, since the engineers need its blessing to modify a standard. Theodore Petritsch relates this position as follows: