Livable streets advocates often recommend the use of 9′ to 10′ wide travel lanes instead of wider 11′ to 12′ lanes for several reasons, including: lower construction costs, [...] lower maintenance costs, lower travel speeds and less injurious crashes, and smaller footprint which can allow limited right of way to be reallocated to other uses such as on-street parking, bike lanes, or landscaping.
When the folks at Walkable West Palm Beach learned that they had a state highway with nine foot lanes in their own city, they set out to investigate. Traffic engineers so often argue that streets need to be wide for safety purposes i.e. to avoid sideswipes, to avoid swerving, etc. So Walkable West Palm Beach wanted to figure out whether those claims that wide = safe and narrow = dangerous were actually true on nearby nine-foot-lane Forest Hill Boulevard. Haussmann continues:
An analysis of crash data obtained by Walkable WPB from FDOT for Forest Hill Boulevard also supports the theory that narrow lanes are as safe as wider lanes. For the 0.787 mile portion of Forest Hill Boulevard just east of the I-95 interchange to S. Dixie Highway there were 60 crashes from January 1, 2011 to December 31, 2013. [...] This crash rate is less than the average crash rate provided by FDOT.
In addition to being safe, this narrow-laned highway is also much more pleasant to walk along and more visually appealing than a typical 12-lane stroad. Haussmann adds:
The Forest Hill Boulevard section is more nuanced and contextually sensitive to the area where it is located. Designing a street section for an urban environment involves tradeoffs. We must avoid the tyranny of specialists who demand that we design roads to optimize only one outcome for one mode of transportation at the expense of other modes. The “standard” five lane road shown with 62′ of asphalt optimizes auto comfort at the expense of higher maintenance costs, greater stormwater runoff, less comfort for pedestrians, and lower property values. A question that engineers and the public should be asking is if the benefits that wider lanes provide for automobiles outweigh the costs. Does the design make sense for the context in which it is located?