Street Classifications Drive Overdesigned Streets

Since World War II, U.S. street design standards have gotten away from traditional street grid pattern that disperses traffic more evenly. Instead, the use of a street hierarchy has been emphasized. Streets are classified into a system of increasing volume and speed: residential, collector, minor arterial, and major arterial.

This classification philosophy, enshrined in professional manuals such as A Policy on Geometric Design of Highways and Streets (the "Green Book") , purposely de-emphasizes accommodations for users other than private vehicles on the highest volume streets.

Although the Green Book has been revised over time to encourage all modes, the street hierarchy approach tends to lock into place the private-vehicle bias, leading to over-design of streets to accommodate ever higher volumes and speeds during the few congested hours of the day.

Major arterials typically space pedestrian crossing opportunities up to a mile apart, ignore the needs of bicyclists, and may not even provide sidewalks or anything more than a sign on a pole for a bus stop. Speed "limits" are set by measuring prevailing speeds and establishing the 85th percentile speed as the posted limit. As vehicle technology improves and vehicles travel ever faster, the speed limit is correspondingly ratcheted upward.

Little wonder then that pedestrian and bicycle deaths and injuries occur in such high numbers on urban arterials. Another result is that the sterile, hostile environments of urban arterials carve up neighborhoods, separate shoppers from available parking and school children from their schools.

This type of environment creates a natural incentive to combine as many products and services as possible into a single destination. Hence the big box mega-stores such as WalMart, that offer everything from groceries to snowmobiles.