The primary safety issues with reductions in lane width are crash types related to lane departure, including run-off-the road crashes. Wide lanes are beneficial to substantive safety for two primary reasons:
On urban arterials with posted speeds 45 mph or less there is no substantive safety benefit between 10-, 11-, and 12-foot lanes. Lane width affects safety differently for varying roadway types. It is a factor in safety performance for rural two-lane, two-way roadways and rural multilane highways, but not for urban and suburban arterials. Crash modification factors (CMFs) for lane width are established on average annual daily traffic volume and generally predicted the number of crashes increases with decreased lane width and with increased average annual daily traffic volume.
Lane widths of 10 feet are appropriate in urban areas and have a positive impact on a street’s safety without impacting traffic operations. Lanes greater than 11 feet should not be used as they may cause unintended speeding and assume valuable right of way at the expense of other modes. This includes the use of wide outside lanes for bicyclist accommodation. Wide outside lanes are not an effective means of accommodating bicyclists in urban areas.
