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Speed Kills (your pocketbook)

I'm back from the New Partners for Smart Growth conference in Denver but am headed back out on the (snowy) road (3-6 inches) today for a Curbside Chat in Northfield, MN. I'm also prepping for a podcast tomorrow with Ian Rasmussen where we are going to discuss the arguments in this video:

I've been making arguments like this for years and years. Ian doesn't see it the same way. Understanding that most people agree with Ian -- and he is intellectually a very worthy opponent -- I thought it would be an interesting conversation.

Th video is meant to be provocative, but what is your reaction to the underlying argument: that posted speed and roadway design have little to no relation to each other?

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Reader Comments (9)

Really good video, Chuck.

Just restating the point since I caught myself ignoring it a few times: This video is just about roads and highways, not streets with lots of pedestrians. Different strategies (downgrading design speed to match the low speed limit) are required where we want people to drive slower. On roads where we want people to move fast, speed limit should match the high design speed.

February 17, 2014 | Unregistered CommenterTim


You guys are the same, really. You are both data driven.

The difference: Your focus is towns and places for people, and the road geometry that makes them safely compatible.

His is about rural highways that are built with the geometry for safe high speed travel, but have political constraints placed on them by the nanny state.

This isn't a debate unless he is a proponent of stroad retail corridor development . You guys should get along well. I look forward to the podcast.

February 17, 2014 | Unregistered CommenterAndy

I'd be interested to hear both of your thoughts on streets that become bridges, as that was a major highlight of the video, and are common "speed trap" locations (at least in Minneapolis). Yes, bridge design could be changed to induce slower/safer speeds, but they lack the adjacency to land-uses that help frame the street. By that, I mean even 10' lanes will still be surrounded by an unavoidable clear zone (unless you're on Ponte Vecchio). In cold-weather climates, bridges (or over-passes) freeze and ice much easier, meaning the design speed (even if 20-25 mph, similar to streets on land) may still be unsafe. For the most part, I agree that design drives speed, not random signs.

February 17, 2014 | Unregistered CommenterAlex

I'm interested in what Ian's argument is…Does he think signage (mandated speeds) are more important than design? Or is it that the design speed should follow the mandated speed? I agree with the latter, but it is essentially the same argument that this video is making: design speed is the real determinate of how fast drivers go, therefore design speed and signage should be in synch (or else it's a death trap or extortion).

February 17, 2014 | Unregistered CommenterSkyler Yost

“Generally, the posted limit should be set near the 85th percentile speed.”

A 1986 study by McCormick, Walkey and Green found that 80% of participants in a driving study evaluated themselves as being above the average driver.[1] Therefore, the above quote says speed limits should be set by people who are poor at estimating driving ability. There must be a better way.

“Higher limits meant fewer crashes.”

This makes sense for the reasons given in the video. But more important than the number of crashes is the number of injuries and fatalities. Kinetic energy says that higher traffic speeds result in more injuries and fatalities per collision. Therefore, raising speed limits to the 85th percentile speed may reduce collisions but increase injuries and fatalities. Please ask Rasmussen whether the tradeoff is acceptable.

February 18, 2014 | Unregistered CommenterDerek

From what I've heard, the basic premise -- that speed limits have little influence on actual driving speeds -- is true. There are also big problems with law enforcement priorities and methods. However, I have a few problems with the arguments in this video.

The video argues that the speed limit should be set to match what most people think is the maximum safe speed under normal conditions. This might not be the status quo in British Columbia, but it is the status quo in Massachusetts (and probably other states in the United States), except that there are overriding speed limit limits, one for interstate highways and a separate one for other highways. I disagree with this standard. The speed limit should be set to an objectively determined maximum safe speed under normal conditions. The general motoring public should not be trusted determine what is and isn't safe, because they usually get it wrong. For example, most people choose a speed that might be safe as long as nothing unexpected happens, but an important reason to limit your speed is so that you can react safely when something unexpected happens.

The video cites the Solomon Curve. The Solomon Curve does not have a sound scientific basis, and the uneventful experience of many cyclists driving among high-speed motor traffic suggests that it is false. A traffic engineer who has done a lot of research into the history of his field informs me that the Solomon curve is based on a single, small study, and one that is limited in scope and flawed in interpretation. For example, in many of the crashes in the Solomon study involving a vehicle going slower than average, the vehicle was preparing to turn, so the low speed was probably not its traveling speed. The Solomon study also did not account for factors like impairment, which could separately cause both low speed and unsafe driving. Moreover, the Colorado interstate highway study suggests that lowering driving speeds reduces crashes substantially. In this study, police officers drove on a particular stretch of highway at regular intervals. The drove side-by-side and at the speed limit so that it would be impossible to pass them and hence impossible to speed.

So I agree the idea the speed limits are ineffective at limiting travel speeds, but I disagree with the idea that higher speeds or higher speed limits can reduce crashes.

February 18, 2014 | Unregistered CommenterEli Damon

This entire video is just a bunch of excuses for why it's acceptable for drivers to routinely break the law. Crashes that occur at higher speeds are more likely to be deadly. Reducing speeds saves lives, and in the long run, saves money.

February 19, 2014 | Unregistered CommenterAlan

I agree with the basic premise that speed limits and roadway design should match. The problem is that for decades engineers have been using "design speeds" that are much higher than actual speed limits. This impacts the radii of curves, sight distances, and a host of other design elements. So, of course it feels safe to drive faster, because the road was designed to make you feel safe driving faster. What we really need to do is start designing roads for the speeds we want cars to go. That will save us all a bunch of money in the long run.

February 19, 2014 | Unregistered CommenterJustin

This entire thing comes back to the important difference between a road and a street.

@Eli....the Solomon curve does work - on HIGHWAYS. When you have a stroad or a street you are, by definition, going to have randomly slowing traffic because of all the accesses and intersections. That doesn't work with high speeds. But cycling doesn't work on automobile highways where speeds are 55+. If we want intercity or interplace travel by bike (and I agree that we do), those need to be separate facilities for everyone's safety. Within cities, mix it all up but then design it to move slow.

@Alan...while I believe you would have the consensus viewpoint among Americans, I disagree. I think this video does a decent job explaining why people speed (it isn't because they are deviants) and why speed limits and enforcement have not and will not change that. Yes, higher speeds are dangerous. Yes, higher speeds kill. You don't reduce speeds by lowering the posted speed limit.

@Justin....you are right on. Design the road/stroad/street for the speed we want people to go. Amen.

February 19, 2014 | Registered CommenterCharles Marohn
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