To answer Nancy's second point (in part) compliance to the 55 mph was
always a problem, there are various studies showing quite high levels
of noncompliance although levels do fluctuate. Similarly states
implemented the 55mph limit to greater or lesser degrees so
enforcement regimes varied considerably.
So any safety benefit from the 55 mph has to be seen in the context of
routine violations of procedure as James Reason would put it. And
those violations in the context of varying organisational compliance
On Oct 11, 2011, at 22:11, Nancy Leveson <leveson.nancy8@xxxxxx> wrote:
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> I know nothing about road safety. But there seem to be a lot of issues not
> mentioned so far that might (or might not) be relevant:
> 1. Controllability: Is a driver more likely to lose control at higher
> speeds? if a driver loses control at a higher speed or if something goes
> wrong in the car, is there more likely to be an accident? What about
> weather, e.g., wet and slippery roads?
> 2. Enforcement: posted speed limits may not have much impact on how fast
> people drive but instead the number of tickets that are given in that area
> or on that type of road may be more of a factor.
> 3. Design of automobiles: I think cars are designed to pass collision tests
> so that, for example, the force may be taken by the bumper instead of the
> passenger compartment (the bumper crumbles) up to a certain speed. What
> about at higher speeds? Are such designs actually more dangerous at higher
> 4. Design of roads: the design of the roads will affect the number of and
> lethality of accidents.
> 5. Amount of traffic: On lonely, straight highways in very rural areas, is
> it safer to go fast? Or is there more likely to be a deer or farm equipment
> that suddenly crosses or pulls onto the highway?
> 6. Condition of the roads: Are they well maintained, pot-hole free, etc.?
> 7. Distance between cars when impact occurs: Is there more tailgating at
> higher speeds because those ignoring the speed limits come up close to try
> to intimidate the driver in front into letting him/her by? Or perhaps it is
> a matter of relative speeds.
> 8. Relative speeds: the German autobahns used to be the most dangerous road=
> in the world (although I think I read the death rate has improved). One of
> the reasons was the very high speed limit on two lane highways where the
> trucks were going very slowly in the right hand lane while cars were
> whizzing along at extremely high speeds in the left lane. I once rented a
> car with very little power in Germany and greatly regretted it. I tried to
> pass the very slow trucks in the right lane, but had difficulty getting up
> enough speed to avoid cars on the left that were going so fast they were no=
> visible before I started changing lanes before they were suddenly up on my
> tail. In addition, do lower limits make people drive at relatively equal
> speeds (i.e., do the slower drivers slow up or is it more likely that the
> faster ones slow down). Is it harder to pass safely (or to judge the
> distance required to pass safely)?
> 9. Psychology: Do people drive more recklessly at higher or lower speeds?
> (e.g., fantasies of being a race car driver)
> 10. Weather: what about areas where there is likely to be fog and other
> weather conditions that often lead to massive pileups?
> 11. Probably a lot more I forgot or don't know about. As I said, I know
> nothing about road safety. But I don't think that arguments involving
> kinetic energy are going to answer the question.
> Simply using statistics, when the things being compared are very different
> and the sample size is not large enough to account for the differences (suc=
> as terrain, straight versus curvy roads, weather, etc.), is not enough for =
> safety analysis. In addition, there is a need to compare the actual speeds
> limits involved, for example, people might be more likely to be killed at
> higher speeds but have more accidents at lower speeds. Basing these
> decisions simply on statistics ignores too many other factors that need to
> be considered in a safety analysis.
> On Tue, Oct 11, 2011 at 6:17 AM, <michael.ellims@xxxxxx> wrote:
>> Part 1 of who knows how many... (apologies this has raised my interest)
>> The question on changing the speed limits in the USA is interesting,
>> because it is counter-intuitive AND the effects of the changes were
>> incorporated within the meta-analysis I mentioned before.
>> So far I have tracked down a single paper on-line, IMPLICATIONS OF THE
>> 65-MPH SPEED LIMIT FOR TRAFFIC SAFETY, DAVID J. HOUSTON
>> The headline is that on the roads effected, the rate of accidents increas=
>> i.e. "Based on the analysis reported above, there is evidence to suggest
>> that higher speed limits have had negative safety consequences on those
>> roads directly affected by the change in posted speed limits=94.
>> There is of course an =93however=94 i.e. =93states have experienced a red=
>> in fatality rates on other types of roads <snip> reductions in fatality
>> rates are enough to offset the increase experienced on rural interstate
>> And why? The author suggest =93that riskier drivers will be diverted on t=
>> the rural interstate highway away from other more dangerous roads, follow=
>> a change in posted maximum speed limits to 65 mph=94 and as the interstat=
>> roads are safer be design... e.g. more Armco...
> Dr. Nancy Leveson
> Professor, Aeronautics and Astronautics
> Professor, Engineering Systems
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Received on Wed 12 Oct 2011 - 10:58:36 BST