Highway engineers have historically surrendered to the specs in the AASHTO Green Book which has been an inviolable bible, which proclaims 12-foot wide roads as being etched in granite.
It's a case of bigger not necessarily being better.
City planner and author, Jeff Speck, argues in an article appearing in the online CityLab, a magazine for “people who are creating the cities of the future—and those who want to live there,” that if busy traffic lanes in cities were narrowed to 10-feet wide instead of 12 feet, lives will be saved.
The problem is that when state DOTs bring streets through cities, they apply highway standards to the street width. With 12-foot versus 10-foot width roads, the argument that the wider roads have greater carrying capacity was dispelled in an article Speck cites written by Theodore Petritsch, P.E. PTOE. Highway engineers have historically surrendered to the specs in the AASHTO Green Book which has been an inviolable bible, which proclaims 12-foot wide roads as being etched in granite.
Petritsch states that the wider 12-foot lane gobbles up space that could be used for sidewalks and bicycle lanes which make the city or suburb more livable. Plus, wider lanes force pedestrians to walk further across streets where cars are moving too fast and bikes don't fit.
Speck stated: “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?”
The research and logic supports the notion that in high capacity urban/suburban streets that are a narrower 10-feet are actually less dangerous for motorists, walkers, and bicyclists. Driving speed is slower and motorists are forced to be more aware, thus making it safer.