Below for illustration is 4 different lane treatments commonly used on urban arterial roads — these all just so happen to be the same road, Chandler Blvd, in the City of Phoenix:
- multiple, narrow lanes; directly next to curb and gutter
- wide outside lane, the rightmost through lane. The lane to the right of the solid white line is a right-turn-only (wide lanes are unusual here in Phoenix);
- multiple, narrow lanes; with edge line and small shoulder next to curb and gutter
- multiple, narrow lanes; next to a designated bike lane
For our purposes here, “narrow” refers to “too narrow for a bicycle and a vehicle to travel safely side by side within the lane”, and “wide” means it is wide enough to safely share side by side. In the areas in the picture, the narrow lanes are all approximately 11′; the wide lane is perhaps 15′.