3 ms·

This topic comes up, and people really love the "people don't follow the speed limit", but I remember seeing a couple studies that were very explicit. Places ra

by rtpg 9y ago

This topic comes up, and people really love the "people don't follow the speed limit", but I remember seeing a couple studies that were very explicit. Places raised the speed limit, and fatalities spiked upwards. People focus on whether the speed limit will be respected and not on what the full consequences up. (Right now I can find a couple studies, but they're mostly from... insurance lobbyists? I feel like the interests are aligned there but lobbyists so...)

ubernostrum 9y ago
In a vacuum, the safest speed to be driving is one close to that of other traffic around you. Outside of some specific situations (sharp curves, ice on road, etc.), absolute speed does not cause accidents: speed differential causes accidents, and does so in both directions. In other words, a car traveling significantly faster than surrounding traffic is a danger, but so is a car traveling significantly slower than surrounding traffic. The intuitive explanation is to consider that every instance of passing or being passed is an opportunity for a collision, and increasing the number of instances (either by being faster and passing many vehicles, or by being slower and being passed by many vehicles) will inevitably catch up to you the longer you do it. Meanwhile, there is a lot of well-done research around this. But several factors get in the way of doing the ideal thing (which is usually to put the speed limit either at the design speed of the road segment, or at the 85th percentile of observed traffic speed). The biggest problem is political forces causing a road to have a posted limit significantly lower than its design speed; many people will, unless they're laser-focused on the speedometer, end up driving around the design speed of the road regardless of posted limit, because they'll take their cues from the road (width, length of curves, length of turning and merging lanes, etc.) rather than from infrequently-placed signs.

by rtpg 9y ago

ubernostrum 9y ago

In a vacuum, the safest speed to be driving is one close to that of other traffic around you. Outside of some specific situations (sharp curves, ice on road, etc.), absolute speed does not cause accidents: speed differential causes accidents, and does so in both directions. In other words, a car traveling significantly faster than surrounding traffic is a danger, but so is a car traveling significantly slower than surrounding traffic. The intuitive explanation is to consider that every instance of passing or being passed is an opportunity for a collision, and increasing the number of instances (either by being faster and passing many vehicles, or by being slower and being passed by many vehicles) will inevitably catch up to you the longer you do it. Meanwhile, there is a lot of well-done research around this. But several factors get in the way of doing the ideal thing (which is usually to put the speed limit either at the design speed of the road segment, or at the 85th percentile of observed traffic speed). The biggest problem is political forces causing a road to have a posted limit significantly lower than its design speed; many people will, unless they're laser-focused on the speedometer, end up driving around the design speed of the road regardless of posted limit, because they'll take their cues from the road (width, length of curves, length of turning and merging lanes, etc.) rather than from infrequently-placed signs.