Speed Limits, Revenue, and Road Safety

Tuesday, September 20th, 2011

Interesting post from the National Motorists Association about a highway in Massachusetts where state officials are keeping the speed limit artificially low, despite plenty of evidence that doing so makes the road more dangerous.


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28 Responses to “Speed Limits, Revenue, and Road Safety”

  1. #1 |  Chad Olsen | 

    But why is going the speed limit dangerous? Because other drivers have decided to go faster than the speed limit? I’m not so sure raising the speed limit would fix this. As I was growing up there was a push to increase the speed limit to 65 from 55. One of the arguments was that people were already going the 65 and it would put them in compliance. Now people ignore the 65 and do 75-80. Yes the road is rated higher, but that doesn’t mean that doing a faster speed will make the road safer.

  2. #2 |  Radley Balko | 

    . Yes the road is rated higher, but that doesn’t mean that doing a faster speed will make the road safer.

    Traffic fatalities have consistently fallen since Congress suspended the nationwide 55 mph speed limit. They’ve fallen overall, and they’ve fallen dramatically in proportion to miles driven.

  3. #3 |  Chad Olsen | 

    But the technology in cars to help reduce fatalities has also increased substantially in those years. I’m reluctant to believe that an increase in speed is the cause of less fatalities.

  4. #4 |  Zargon | 

    Sure. And if there was a nationwide speed limit of 5 mph with 100% compliance, traffic fatalities would be zero.

    One study after another has shown that most people drive about what a road is rated for, regardless of the posted speed. That’s why every person who knows anything about traffic knows the best known way to set speed limits is using the 85th percentile, and they know why that method works.

    In ideal fantasy-land where people all drive the speed limit, sure, lower the speed limit and reduce fatalities. Back in the real world, setting the speed limit too low (and too high) increases the variance in traffic speed, which increases fatalities.

  5. #5 |  EH | 

    But why is going the speed limit dangerous? Because other drivers have decided to go faster than the speed limit?

    Yes. You get fewer fatalities if everybody’s speeds are closer together.

    I’d be curious to hear of your citations saying that increased speed limits increase fatalities.

  6. #6 |  SJE | 

    Fatalities have decreased per miles driven because of
    (a) improved safety technology in cars
    (b) a tendancy to drive bigger cars
    (c) seat belts and less DUI
    (d) roads being designed for maximal car speed.

    However, while DRIVERS are safer than ever, it is a different story for everyone else: pedestrians, cyclists, motorbike riders. A big reason that municipalities want to slow speeds is because speed is the single biggest factor determining death of a struck pedestrian, and making it safer for pedestrians is important if you want to have cities etc that are not just freeways and parking lots.

  7. #7 |  H. Rearden | 

    I took a transportation engineering class in college. When doing capacity calculations of a highway, it is usually assumed that a driver’s speed on an uncongested roadway is 75MPH. This same speed is used when designing the degree of banking in turns.

    There’s a small town in WV well known for it’s speed enforcement tactics. 10-18 thousand tickets per year written in a town of less than 4,000. Trip advice websites warn travelers and suggest an alternate route. A number of years ago a local businessman was so fed up with the police tactics that be bought a billboard to warn motorists. It’s been a while since I’ve traveled through there. I don’t know if it’s still there.

  8. #8 |  Brandon | 

    Speed limits shouldn’t be anything more than recommendations anyway. Cops should concentrate on finding and stopping actual unsafe drivers, ie drivers who can’t stay in one lane around a curve, drivers who are clearly distracted or not able to control their vehicles, people who don’t check their blind spots before changing lanes, etc, rather than sitting and waiting for someone to go by exceeding an arbitrary number to raise revenue. But of course that would never work, because then we wouldn’t need as many fat, useless thugs on the public dole. The unions and the pols would never go for it.

  9. #9 |  Highway | 

    Chad, the fatalities have fallen more ‘in spite of’ higher speeds, rather than ‘because of’, but the fact remains that fatalities have fallen, and that higher speeds have not caused a bloodbath. Higher speeds almost certainly contribute to more fatalities, but not enough for drivers to make the decision to drive slower. And that’s fine.

    People drive the speed that’s comfortable for them. Given the current technology in cars, that speed is higher than it used to be, for the same roadway conditions. Every car sold now is probably more capable in every way than the best car from the 70’s, or maybe even the 80’s. So people feel comfortable going faster. And when you set a speed limit too low, then you are intentionally making people uncomfortable while driving, which contributes to increasing the accident rate.

    H. Rearden, the banking in curves isn’t necessarily set for 75 mph. It’s set for whatever the design speed of the roadway is, and if a curve requires a smaller radius, then the superelevation will be set for whatever the radius is. Sometimes it requires a reduction in design speed, because of other factors.

  10. #10 |  Chad Olsen | 

    “Yes. You get fewer fatalities if everybody’s speeds are closer together.

    I’d be curious to hear of your citations saying that increased speed limits increase fatalities.”

    Speed limits are designed to group peoples speeds so I fail to see your point? Increased speeds do cause fatalities. That’s a matter of physics and biology.

  11. #11 |  Peter H | 


    This is the speed limit for a limited access highway, not an avenue or residential street. Pedestrians and bicycles are explicitly prohibited from entering. You may oppose the existence of freeways, but this one exists, and the freeway speed limit should not reflect speeds designed to protect non-existent pedestrians or cyclists.

    As to motorcycles, they are inherently dangerous, and anyone who rides one knows (or ought to know) that they’re taking their life in their own hands.

  12. #12 |  Chad Olsen | 

    Highway, I understand your point. But setting it higher can also make some uncomfortable with the increased speed. The faster your car is moving, the more braking distance you need, the faster your reaction time needs to be, and the handling of a car decreases in regards to turning and other avoidance maneuvers. Would it be better for faster people to drive slower and be uncomfortable or for slower people to be forced to drive faster safety wise?
    I’m not saying speed limits need to be decreased, but I really don’t see why because of fast drivers, a speed limit should be increased. If people doing the speed limit are cited as a cause for dangerous driving then are we not justifying the actions of those breaking the law? I fail to see how speed limits are an affront against personal freedom.
    And besides, just because a road is made for 75mph, doesn’t mean traffic conditions, neighborhoods, location ect justify 75 miles an hour. There could be other factors that are not being presented.

  13. #13 |  Chad Olsen | 

    I stand corrected as the last part of my above. I’ve forgotten that this is a limited access highway.

  14. #14 |  Highway | 

    Chad, that’s where the 85th percentile speed comes in. Most people are going to drive around that speed (it is defined as the speed that 85% of people are driving). People who do not drive up to the 85th percentile speed naturally are 1) few and far between and 2) should consider that they perhaps shouldn’t be driving on that road, or at all. The confounding factor, however, is the black and white sign, and the black and white *car* that is going to pull you over with the red and blue lights. Many of the people who are currently ‘uncomfortable’ going closer to the 85th percentile speed are made uncomfortable because of the knowledge of possible sanctions. Remove those sanctions, and that differential speed goes away.

    Speed limits may have been intended to group people’s speeds when they were first introduced. At that time, there were many vehicles which were not capable of going those speeds. Also, there was much tighter enforcement of limits: no ‘8 mph buffer’ or anything, if you’re going 46 in a 45, you get stopped. This is no longer the case. Any modern vehicle that cannot go a reasonable speed should be either marked and/or escorted, or shouldn’t be on the road.

    The only grouping of speeds that speed limits do now is to make everyone drive uncomfortably slow.

  15. #15 |  Highway | 

    Also a note on design speed. All factors go into the design speed of the road. A collector or arterial will have access limitations as necessary for the design speed, but also people realize what the dangers caused by other factors are, and slow down accordingly.

    What is the design speed of a straight grade 12 foot lane divided roadway? The answer is that you can’t say, because it’s dependent on so much other stuff. Physically, it could be over 100, but nobody would drive that (safely) because of the houses on the sides, or the business entrances, or the lack of shoulders.

  16. #16 |  SJE | 

    Peter H: Thanks, I had not realized that it was limited access, although I did not see where it is stated.

    I do stand behind my comment, however, regarding the decline in vehicle fatalities due to factors that shift risk to those other than occupants of the vehicles. These are numbers based on all roads. While limited access roads make sense, they are also used far too often IMO. Putting a highway through a community and declaring it for cars only doesnt stop the fact that people may have to cross it.

  17. #17 |  awp | 

    traffic engineering is, at its heart, about human psychology, statistics and tradeoffs.

    appropriate (or naturalish) speed limits limit the likelihood of accidents occurring. If everyone going the same direction is going the same speed they are less likely to run into each other.

    higher speeds increase the likelihood of fatalities if an accident occurs. Physics/Biology.

  18. #18 |  H. Rearden | 

    #15 | Highway –

    I was not trying to imply that all roadways and banked curves are designed for 75MPH. I was speaking of superhighways where conditions permit. Thanks for pointing that out.

  19. #19 |  MassHole | 

    I’m quite familiar with Rt. 3. It’s 3 lanes wide in both directions. When I travel it early AM on weekend snowboard runs, it’s easily navigated at 80 mph. There are only two issues I have to worry about on that road:

    1. Cops out to raise revenue.

    2. Morons that don’t understand drive right, pass left.

    I would bet good money that actively enforcing #2 would save more lives than all the speeding tickets combined on that stretch of road. I hate passing on the right, but self absorbed idiots force you to.

  20. #20 |  Highway | 

    Lane Discipline would certainly go a long way towards making the roads of the United States safer and more enjoyable. There is pretty much no excuse for anyone to be driving along a road without somebody or the shoulder on their right. If you are passing someone, pass them on the left, and *get it over with.* Don’t go 2 MPH faster than someone else, and take a mile and a half to pass them, or worse just waffle around the same speed as they do. If people are passing you on the right, you’re in the wrong place, get over to the right when you can.

    Don’t be a left lane camper (some people use the phrase bandit, but I think camper is far more appropriate). If someone wants to go faster than you, let them. Even if you think they are going too fast. Besides, if you think they are unsafe, do you really want them right behind you?

  21. #21 |  SJE | 

    I just returned from Oregon, where it is the LAW that you must move to the right unless passing. Oregon drivers are pretty good with it.

  22. #22 |  Stephen | 

    I hate the “civilian speed limit enforcers” that create a rolling roadblock at or under the speed limit. I have a tendency to pass them on the right shoulder and hit the brakes.

  23. #23 |  Steamed McQueen | 

    Okay, one more time people. Speed does not kill. Running into things kills.

    If speed alone killed then everyone who ever drove on dirt track, NASCAR or the Indy 500 would be dead.

    It is my opinion that while the introduction of all manner of safety equipment from seat belts to airbags to collision-avoidance radar has made vehicles safer, it has also made drivers more complacent. All this safety gear has made modern drivers feel invincible Good grief they have cars that can actually parallel park themselves now.

    You want safer roads? Get off the phone, turn down the music enough so you can hear what’s going on around you, take your eyes off the video screen and pay attention to the damn road!

    THAT’S how you achieve safer roads. Everything else is revenue generation

  24. #24 |  MassHole | 

    If you spend a lot of time on the highway dealing with poor drivers, I highly recommend a set of these:


    Much louder than stock horns and really get peoples attention on the highway. They also work great on jerks, as the guy in the boxster that cut my wife off in traffic the other day found out.

  25. #25 |  c andrew | 


    I remember reading about a road in Wisconsin where they had problems with fatalities back in the mid-70’s. They did the 85 percentile thing and accidents and fatalities dropped. Unfortunately, so did ticket revenue, so they re-instated the former speed limit.

    I’ve never been able to find that article again. It’s possible that I’m mis-remembering the state. I was curious if you had ever run across this story.

  26. #26 |  Highway | 

    c andrew, I haven’t heard of that one, but I did read about this study in Michigan:


    The perfidy of government with respect to roadway safety is abominable. It is completely unconscionable that governments do not do *every single thing in their power* to make roadways as safe as possible. Imagine the outcry if a private roadway owner made the safety reduction choices that governments seem to routinely make – lowered speed limits, shortened yellow times, inconsistent enforcement. There would be a tremendous backlash if they did these things, just on their own. Now imagine that they do those things [i]to raise their profits![/i] The wailing and gnashing of teeth would be terrible to behold! Yet, people accept the government doing exactly that, and even encourage it!

    People continually ask for horrible ‘solutions’ like speed humps, unwarranted stop signs and signals, excessively low speed limit signs, and surprise ‘gotcha’ speed traps. They want these things out of a mistaken belief that it makes their roads safer or lowers speeds. They don’t. And at the same time, they want their roads to be extra wide, off street parking, longer curves. The very things that encourage drivers to feel more comfortable driving fast!

    So many tools for safety have been irredeemably ruined by the political greed for more money to buy votes with. Red Light cameras could have been a tremendous force for reducing accidents: put the cameras up, tell people they’re there, make the signal as safe and predictable as possible, and still fine people who blow through a red light. But instead they turned them into a sleazy money grab.

    It’s enraging to me.

  27. #27 |  c andrew | 

    Thanks, Highway.
    That was an interesting article.
    I think that you are correct; particularly when jurisdictions are caught cutting the yellow time and increasing the accidents. It’s too bad they’re never charged with reckless endangerment under color of law. ’cause that is what it is.

  28. #28 |  » lobbying for speed. pop bytes | 

    […] explicitly recommended raising the speed limit.” — National Motorists Association via The Agitator Byte off a […]