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lane width and car width
Walkable City Rules has multiple (short) chapters on proper lane width. US lanes tend to be 10 to 12 feet wide, with newer ones being 11 or 12 feet. 10 feet is said to facilitate 45 MPH traffic, 12 feet 70 MPH, so 12 feet on city streets sounds pretty nuts! But traffic engineers/departments of transportation engineer for traffic flow and being 'safe' for cars, so engineer for higher than the posted speed... but then, people drive at the speed which feels comfortable to them, which isn't safe for anyone else. An older slow-flow lane is 8 feet wide; with two of them oncoming cars can pass each other but will probably slow down out of anxiety. Yield flow is like 12 feet wide, where passing happens by a car pulling into a parking gap to let the other one by. (This of course assumes that you *have* curb parking, which isn't full.)
An obvious question is how this all relates to the width of vehicles. After looking at lots of Wikipedia pages, I can say that most cars are 1.8-1.9 meters, or 5.9 to 6.23 feet. The US requires clearance lights on vehicles wider than 80 inches, aka 6'8" or 2.03 meters. The old VW Beetle was 1.54 m wide, while an old Big Car like the Chevy Caprice was 2.02 m wide (as well as up to 5.7 meters long.) So a 7 foot lane is all you need if you're careful, and 10 seems rather luxurious -- thus the 45 MPH speeds.
Buses are another matter; Speck gives 8'6" as the typical width for buses, or 2.6 meters; my own lookup got 2.4-2.7 meters. So in round numbers of feet a bus lane would need at least 9 feet, preferably 10.
An obvious question is how this all relates to the width of vehicles. After looking at lots of Wikipedia pages, I can say that most cars are 1.8-1.9 meters, or 5.9 to 6.23 feet. The US requires clearance lights on vehicles wider than 80 inches, aka 6'8" or 2.03 meters. The old VW Beetle was 1.54 m wide, while an old Big Car like the Chevy Caprice was 2.02 m wide (as well as up to 5.7 meters long.) So a 7 foot lane is all you need if you're careful, and 10 seems rather luxurious -- thus the 45 MPH speeds.
Buses are another matter; Speck gives 8'6" as the typical width for buses, or 2.6 meters; my own lookup got 2.4-2.7 meters. So in round numbers of feet a bus lane would need at least 9 feet, preferably 10.
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