Reimpose the 55mph speed limit!?

My little Honda Civic doesn’t get above 3000 RPM until I hit 75. Does this mean that the law doesn’t apply to me?

As long as you’re not one of the people with a big wing spoiler on it, sure?

None of the laws have ever applied to you. Didn’t you get the memo?

It did before, dunno why it won’t again.

I would guess there would be fewer traffic fatalities at 55 than 65.

but millions will be late!

Actually, while the evidence is somewhat mixed, it appears likely that the 55mph speed limit increases accidents. When 55 is imposed, the mean speed drivers choose falls but the variance increases, cops spend more time on interstates and thus less on other roads, and high-risk speed demon types are more likely to choose roads other than interstates. All of these effects work to increase the fatality rate, even though it is at the same time true that, other things being equal, if everyone drove slower the fatality rate would decrease. This influential paper found that the net effect of the 1987 switch from 55 to 65 in many States was a 4% or so reduction in fatalities.

Not only does 55 really piss Sammy Haggar off and make millions late, it’s deadly, too.

Why safety measures are not equal to safety.

A few years back the maximum speeds at points of our highway system was raised from 68 MPH to 81 MPH and even though the government tried to bury it a recent report slowed that the death toll clearly had risen on the freeways after the change.

But of course what Skedastic writes is true, if police are busy reinforcing highway speed limits to the cost of other roads you might just switch the danger - but that hasn’t happened here to my knowledge. Freeways are still safer than cities (where limits are 31 MPH except for few speedier roads and of course freeways feeding into the city).

The problem with speeding is simply relative speeds. The problem with a 55mph limit is someone passing you at 75 – it’s impossible to enforce, but if you could make sure that no one passed another car going more than a few MPH faster, it would probably make a big difference.

That was a good read.

I know that Europeans making fun of Americans and stupid signs like “Do not put dog in microwave” is as stupid a cliché as Americans not knowing the first thing about geography or history (plenty of posters here can school me in both subjects), but:

The four-way stop weakens the force of all stop signs by muddling the main question drivers need to answer, namely: Which road has priority? And indeed, American drivers have apparently become confused enough by this question that some communities are now beginning to affix another sign to the poles of stop signs that aren’t four-way, warning cross traffic does not stop.


Our traffic regulation is like the UKs he mention. Not many signs, full stops are very rare (I know the sign, I wouldn’t know where to drive to show one in the wild) and we always know the speed limits on a given road with no signs - signs are only used for conditions out of the ordinary. And we have quite q few signs that aren’t rules but warnings to show caution.
(Ie a sharp turn might have a recommended speed of 28 MPH, but you are allowed to go almost twice that… but if somethings happens you automatically take full responsibility and might face a charge of recless driving especially in adverse conditions).

That’s not to say that we’re better drivers. I don’t know the statistics, but having only acquired my license recently, I really notice how many don’t know/follow the rules and have troble with concepts like right of way, so I can see how frustrated regulators might think that more signs are the solution - I personally want more police and higher fines (one of the few cases where I think fear of punishment does have the desired effect).

You were probably kidding about this, but I don’t see how having to drive slower will make people late. People are generally late because they are bad at estimating how long it will take to get somewhere (assuming they care about being on time to begin with). If they can drive faster, they’ll just assume they can leave for their destination later.

If you’re referring to the report discussed on this page, that’s not how I would interpret the findings (although I couldn’t find an online version of the actual paper). Apparently the study found that accidents increased 8% on roads on which the limit was increased to 130 and fell 49% on roads which stuck to a limit of 110.

There are (at least) two related problems with interpreting that evidence as indicating the higher speed limit cost lives. First, as discussed in the paper I cite above, it’s plausible that the decrease on the 110 roads was because of the increased limit on other roads. Speed demons who used to drive on the 110 roads switch routes and now take the 130 roads, which increases accident rates on the 130 roads and decreases them on the 110 roads. The net effect may be to reduce overall accident rates, and that would not be inconsistent with the report’s findings (I guess).

Second, the wording implies the authors may have used a common statistical technique called “difference in difference” regression, which in this context amounts to estimating the effect of the change in speed limits by comparing the change in accident rates on roads which switched to 130 with roads that stayed at 110. Basically, the model assumes that the roads that switched would have behaved like roads that didn’t switch if none of the speed limits had been changed. So when we observe rates decreasing 49% on roads that didn’t switch and increasing 8% on roads which did, this method tells us that rates on roads that switched are actually 8 + 49 = 57% higher than they would be if the limit hadn’t changed.

If it is true that drivers dangerous drivers sorted onto the 130 roads after the change, this method’s mathematical assumptions are violated in such a way as to dramatically overestimate the increase in accidents caused by the increase in the speed limit. I suspect this is the case because with only about 10 fatal accidents per year I don’t think that the estimates would otherwise obtain even weak statistical significance, ie, the report would’ve just said we can’t say with any degree of certainty whether the change in the speed limit made accident rates go up or down.

Of course, it’s plausible that changes in speed limits have different effects in different places and different times, but this report doesn’t seem to me to be very credible evidence that this particular change in limits actually caused higher accident rates. Of course, I would have to, you know, actually read the study to see if it’s credible.

I didn’t bother linking because I didn’t think anything was avaliable in anything but Danish. So nice Google.

I’m sure you’re right in the statistical stuff, but for a few things.
It’s a small country so nowhere do people who like to drive fast have the option to pick between a 110 route or a 130 route. They get to pick between driving 130 on the freeway or speeding on paralell smaller and more winding roads with 80 km/h limits.

So I don’t think the change in speed has changed the road usage pattern. People needing to go from a to b were using the 110 freeway and are now using the same freeway but driving 130 on some stretches.

I’d love to link you to the study since you’re the statistican, but since neither of us have it, let me just say that going from that same short article, I’m more willing to trust a supposedly non-biased part of the actual ministry in charge of the roads than a politicians “own set of data”. Especially knowing the politician in question, but of course you’d have to take my word on that (which isn’t likely).

Oh, I found the report… but only the summary is in English.

Suppose drivers do sort onto motorways in the manner described in the study I cited. If some motorways increase speed limits and others do not, we should expect to see speeds on the motorways on which the limit was not changed go down.

Motorways on which the limit changed from 110 to 130 saw mean speeds increase trivially (and probably not statistically significantly) from 120 to 121. On the other hand, roads on which there was no policy change saw more marked decreases in mean speeds. It seems likely that some combination of sorting of drivers across roads and changes in enforcement explains these differences.

Changes in the variance in speed are at least as important as changes in mean speed, but changes in variance appear to be ignored in this study.

130-motorways had 9 percent more personal injuries per year in the after period compared to the before period. Contrary to this, on the 110-motorways – including motorways in the Greater Copenhagen Area – a decrease of 40 percent of personal injuries was recorded. Compared to the number of personal injuries on other roads outside urban areas the development in personal injuries was 33 percent higher on 130-motorways and 27 percent lower on 110-motorways.

This is simply not evidence that the increase in speed limits caused a net increase in accidents. The study does not appear to report estimates of the effect on total accidents, and we would have to know the absolute numbers rather than percentage changes to calculate the effect on total accidents. But large decreases on some roads and small increases on others seem likely to translate into decreased overall accidents.

Note that I am not repeating what some politician said. I don’t think the politician’s comments make much sense. You might try searching Danish blogs and such to see if any statistician-type people have made comments on the report. It doesn’t appear to me to be methodologically compelling.

I drive 55 to save on gas.

simply quoting homer simpson when arguing against the 55mph speed limit when he and marge were at debate club.

Our 96 GT has the same mileage profile. We just got back from our big cabin road trip. On the way out we filled up right before getting on the highway. We had gone 360 miles and still had an eighth of a tank left when we filled up. We averaged 70 - 75 mph on the NYS thruway and Masspike (up / down large hills etc, breaking only for tolls). I tried to drive pretty steady - no punching the accelerator (if possible) - it worked pretty well.

I don’t think I could do 55… I have too much of a need for speed. However, most of the traffic was going much slower this week. The average speed on 495 in Mass was approx. 70 mph— unheard of.

I may be wrong, but I think that car’s are tuned towards maximum fuel economy at whatever the speed limit is set at. So, I don’t think 55mph would necessarily be the ideal fuel economy speed, especially for cars built in the 20 years since that limit was relaxed. I find it hard to believe that my car, which exceeds highway fuel economy ratings at 70, would be much if any better at 55.

Does that work? Have you tested it? It takes you longer to get where you are going. Does the overall usage really balance out? Let’s make up some numbers:

Driving 50 gives you 35 mpg in your car.

Driving 70 gives you 30 mpg in your car.

Now it seems like the simple math is just dividing your distance by the number of mpg you get to find out how much gas you used. But I’m wondering if the increase in time (2 hours, if you were driving 350 miles) is a factor. Even idling uses some gas, so presumably 2 more hours of the engine running would use more gas as well. When we test our miles per gallon, most of use a simple algorithm of topping off the tank, driving for a while, topping off again to get gallons used and comparing it to our mileage. But that doesn’t take into account extended trips or use over time.

Does anyone know if that’s a factor? I sincerely don’t know, which is why I am asking.