copyright 1996, Tracy-Williams Consulting
At a minimum, arterial streets should get wide curb lanes. Such lanes allow motorists and bicyclists to share the roadway more comfortably. Installing these involves widening the right-most through lane.

What makes a wide curb lane?

The consensus in the profession seems to be a lane between 14 and 16 feet in width. Many designers use 14 feet while some use 15 feet. Few go much wider, however, due to concerns about motorists sharing the lane side-by-side. Note that the lane width does not include a gutter pan, since the gutter is generally unrideable and the joint between the pavement and the concrete can be dangerous.

When a wide curb lane approaches an intersection with a right-turn-only lane, the extra space should be added to the through lane adjacent to the turn lane. In addition, it may be worthwhile to evaluate the need for the right-turn-only lane. If turning volumes aren't too high, a wide curb lane could serve through motorists and bicyclists as well as turning traffic.

The diagram below shows a typical road with wide curb lanes.

How do you create a wide curb lane?

There are several ways to do this. Restriping the travel lanes to marginally narrow the inner lanes can provide extra space for the outside lane. According to the Highway Capacity Manual, narrowing travel lanes from 12 feet to 11 feet under urban conditions only reduces the capacity of the lane by a few percentage points. This approach has been used in Missoula, Montana, where a multi-lane bridge was restriped from four 13-foot lanes to two 11-foot inside lanes and two 15-foot outside lanes. In other cases, eliminating a travel lane or parking can free up space for a wide curb lane.

Of course on a new roadway, creating wide curb lanes can be much easier. To accomplish this, make sure that locally-used design standards include wide curb lanes.

What are the benefits?

The primary benefits of wide curb lanes are (1) to give extra clearance between bicyclists and passing motorists and (2) to reduce conflicts between through motor traffic and cars entering or leaving commercial driveways.

The wide curb lane approach will accommodate experienced riders well but will not attract other bicyclists. In our experience, the less experienced riders don't really view wide curb lanes as a bicycling improvement.

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