lane width and car width

[mindstalk]

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.

Comments

[mtbc]

I was quite happy driving a Ford Crown Victoria on an American road to find that when someone pulled out right beside / in front of me and there was a car in the adjacent lane so I couldn't escape to that, I could actually fit between the two!

[mindstalk]

Hmm. Two lanes would be 20-24 feet. A Victoria is huge, 6.5 ft wide, but even three of them are 19.5 ft, so could just squeeze in 2 10-foot lanes. With smaller cars and the bigger lanes, yeah I can kind of see it, if the other cars are enough to the far side of their own lanes.

buses

[elusiveat]

Maybe you can shed light on a recent change in how an intersection near my Somerville house is painted.

Following some recent road work they moved the stop lines much further back from the intersection. Following my total inability to correctly estimate what fraction of our lot is occupied by the house, I'm not going to guess at distance, but it's far enough that you really can't get a view of traffic on the cross street, *and* it makes me nervous as a bicyclist to be in front of the line of cars for a left turn lane because the bike is slow enough to accelerate that I know the longer distance without being able to turn out of the way is going to slow every body down, and I really try not to do that. I was mystified and annoyed by the new setup. Sometimes they post traffic cops, who don't always make the most helpful calls, too.

For a while, I was kind of rolling my eyes at the whole situation, and when taking a left turn from the higher traffic road onto the lower traffic road would pull up to where the stop line used to be. Then one time as I was doing this, a bus pulled up from the cross street on the left and leaned on its horn. My first reaction was "WTF", and then I gradually realized that it needed to turn right (onto the street that I was trying to turn left from), and that somehow, with the way the intersection is laid out, I was occupying the space that the bus would need to sweep through as it turned. So I picked up my bike and moved it. I guess that's why they moved the stop lines so far back?

Anyway, now I can't figure out how the intersection worked previously, and also I continue to be frustrated by being forced to stop so far back from the actual intersection. Are you at all familiar with this kind of change in how the streets are paint? Any context you can provide?

Re: buses

[mindstalk]

Nothing substantial, sorry. If they'd painted it differently I could see moving the cars back to provide a 'bike box' for bikes, but you don't mention that. I think I had seen "far back stops" when I was there; to make life easier for buses sounds plausible, or for fire trucks in one place (I think there's a place on Somerville itself where if cars went up to the corner they would be blocking a fire station.) As for how the intersection worked before... I have dim memories of seeing cars have to back up for a turning bus, so maybe they had just relied on low levels of traffic and thus conflict?