http://usa.streetsblog.org/2015/05/27/compelling-evidence-th...
But to get that tiny bit you're still paying the entire cost of slowing vehicles down. It takes longer to get where you're going, including for emergency vehicles. The most fuel efficient cruising speed for most vehicles is at or above 40MPH, which you're diverging from.
You're paying full costs for fractional benefits. You would be better off putting some cops on the side of the road with an EMP cannon to disable any cars that show up. Sure, it sounds crazy, but it improves safety by slowing people down so we should do it, right?
Except that there are other, better ways to improve safety. Like building sidewalks, and making sure there is enough capacity on the highways that people don't come down to surface streets to avoid it, and improving mass transit so there aren't as many people driving to begin with.
And now you're doing something different than the data and will plausibly get a different outcome. If the opposing traffic is not closer together then maybe people don't slow down as much or at all anymore. And you're pushing the cars closer to the pedestrians.
> To wit, this conversation revolves around residential neighborhoods, where cars frequently park on the street, where the speed limit is likely not 40MPH.
Yet that may nonetheless be the prevailing traffic speed, and the speed that emergency vehicles can reasonably travel when not impeded by "traffic calming" measures. That you didn't expect people to get the efficiency you're taking away from them doesn't mean you aren't taking it away. Moreover, fuel efficiency is a curve with an inflection point somewhere above 40MPH. That means 40 is better than 30, but it also means 35 is better than 25 and 30 is better than 20.
> Making the lanes narrow is meant to get people to follow the speed limits, I'd say at 30MPH or less.
Except that the speed limit is generally supposed to be set at the 85th percentile traffic speed (and is generally set ~10MPH below that for reasons of politics and revenue generation), so slowing down traffic will lead to a reduction in the speed limit.
I still can't understand this logic of "let's make the roads safer by making them more dangerous" as if the only factor is how fast people are going. Wouldn't it be better to make roads that are safe at the speeds people want to drive? Build sidewalks so pedestrians don't have to be walking in the street etc., and let bicycles use them because a bicyclist is clearly more like a pedestrian than a car?