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Are road speed limits based on safety?

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Re: Are road speed limits based on safety?

#11

Post by mannykannot »

readthenotes1 wrote: post #4
credit_guy wrote: post #3

They can't be just based on safety. If they were, then 5 mph is safer than 10 mph, and 2mph is safer than 5 mph. Road speeds need to be a tradeoff between safety and convenience. Unfortunately, in our mind safety and convenience are not just quantitative things, they carry moral connotations. Safety is good, convenience is at best neutral. Until people develop a good framework to express this tradeoff, speed limits w…

One of the things I think you are labeling under convenience is efficiency/productivity. Until we can all work from home and use replicators to create our stuff, transportation will be a huge part of the production side of society. Speed limits affect that directly.

In the places where the speed of road transport has most influence on productivity, the speed limits are largely moot because of traffic congestion at the times when most commuting happens. In places and at times when congestion is not a problem, speed limits rarely have much effect on productivity.

Re: Are road speed limits based on safety?

#12

Post by dsfyu404ed »

dazc wrote: post #8
credit_guy wrote: post #3

They can't be just based on safety. If they were, then 5 mph is safer than 10 mph, and 2mph is safer than 5 mph. Road speeds need to be a tradeoff between safety and convenience. Unfortunately, in our mind safety and convenience are not just quantitative things, they carry moral connotations. Safety is good, convenience is at best neutral. Until people develop a good framework to express this tradeoff, speed limits w…

There is a road on my route home that switches from 50mph to 30mph for no other apparent reason than it is slightly residential. Fair enough, but there are many similar examples where this isn't the case - the limit is uniform regardless. What people miss about this is that there is also a slightly awkward bend at mid-way point and it isn't unusual to see a car lodged into the fence that runs alongside. Sometimes the…

Other than facilitating smug "we know better" commentary from the peanut gallery why not throw up chevrons?

It's long since been established that alerting drivers to specific hazards at or before those hazards is far more effective at reducing the hazard than dropping the speed limit or slapping up a "windy road" sign far in advance.

Re: Are road speed limits based on safety?

#13

Post by v01dlight »

dazc wrote: post #5
xipix wrote: post #2

The implicit point here is that speed limits should be based upon safety, or they should be abolished. This article fails to mention that there are important reasons for speed limits other than safety. For example, noise, pollution and climate. Mobility and freedom of those without a car, especially the young and very old. Speed limits are a tool that can be used to help boost the health, fitness and quality of life…

The point of all of these arguments is always that speed limits should be increased when all evidence suggests they should be lowered. Evidence, in this case, being number of deaths.

Did you read the article? The first evidence it examines is roadway deaths vs speed limit, and the author concludes "there is little correlation". I'm not saying I agree with the article's conclusions, but it's easier to trust someone who shows some evidence than someone who just suggests that evidence which supports their conclusions exists.

Re: Are road speed limits based on safety?

#14

Post by v01dlight »

mannykannot wrote: post #11
readthenotes1 wrote: post #4

Earlier quoted context omitted.

One of the things I think you are labeling under convenience is efficiency/productivity. Until we can all work from home and use replicators to create our stuff, transportation will be a huge part of the production side of society. Speed limits affect that directly.

In the places where the speed of road transport has most influence on productivity, the speed limits are largely moot because of traffic congestion at the times when most commuting happens. In places and at times when congestion is not a problem, speed limits rarely have much effect on productivity.

I think the point about productivity is less about people's 'burbs to downtown commute and more about say, the trucking industry. Trucks drive at or near the speed limit for much of their long highway routes, and over those distances, a slight difference in average speed can mean a big difference in arrival time, and throughput of the whole system.

Re: Are road speed limits based on safety?

#15

Post by pc86 »

dazc wrote: post #9
dsfyu404ed wrote: post #6

This article bakes in some false assumptions about compliance. You can't just set a 40mph speedway on a limited access highway because "tHaT's WhAt'S sAfE gUyZ". Drivers will ignore it. Except that one guy with a dead hooker or brick of cocaine in the trunk or some other specific reason to be very cautious about complying with the law. He'll do 40. And safety will have been reduced because you have increased the vari…

People who obey speed restrictions have a dead hooker in the trunk, who knew?

No, people with a dead hooker in the trunk obey the speed limit.

Completely different thing and an important distinction.

Re: Are road speed limits based on safety?

#16

Post by curiousgibbon »

scrlk wrote: post #7

> In the UK the 60mph country roads in particular shouldn't be trusted to provide a safe speed at all times. Especially on country roads, you shouldn't view the 60 mph speed limit as a speed target - drive at the speed appropriate to the road and conditions.

There's a big cultural difference between the US and UK driving signage. In the UK there are fewer signs and it's generally upheld that the speed limit is a limit, and that what constitutes lawful driving may require driving much slower. You're doing to have a hard time suing anyone if you lose control of a car on a tight and narrow bend on a country road but were doing 59mph (i.e. within the limit).

Contrast the US where little yellow signs on every bend suggest a speed at which it's safe to go around, usually a conservative one. I think something missing from US road signage is the idea that more is worse: drivers are trained to ignore signs and speed limits because there are so many verbose and pointless signs around. It's much harder to trust the installers of the signs when they're obviously silly. In the UK it's more as if signs likely indicate some legitimate hazard that a driver will find out about very soon.

Re: Are road speed limits based on safety?

#17

Post by dazc »

dsfyu404ed wrote: post #12
dazc wrote: post #8

Earlier quoted context omitted.

There is a road on my route home that switches from 50mph to 30mph for no other apparent reason than it is slightly residential. Fair enough, but there are many similar examples where this isn't the case - the limit is uniform regardless. What people miss about this is that there is also a slightly awkward bend at mid-way point and it isn't unusual to see a car lodged into the fence that runs alongside. Sometimes the…

Other than facilitating smug "we know better" commentary from the peanut gallery why not throw up chevrons? It's long since been established that alerting drivers to specific hazards at or before those hazards is far more effective at reducing the hazard than dropping the speed limit or slapping up a "windy road" sign far in advance.

There is actually signage alerting people to this hazard, as is the norm, in addition to the lower limit.

Ironically, there is a low bridge a mile before this bit of road with huge signs alerting truck drivers that it is quite a bit 'lower' than they might be reckoning on.

Guess what, it still gets hit - so much so there is now flashing light signage in addition and, thus far, this has also proved ineffective.

I'll save the red traffic light signal example for later...

Re: Are road speed limits based on safety?

#18

Post by curiousgibbon »

dsfyu404ed wrote: post #6

This article bakes in some false assumptions about compliance. You can't just set a 40mph speedway on a limited access highway because "tHaT's WhAt'S sAfE gUyZ". Drivers will ignore it. Except that one guy with a dead hooker or brick of cocaine in the trunk or some other specific reason to be very cautious about complying with the law. He'll do 40. And safety will have been reduced because you have increased the vari…

This logic can only make sense based on the axiom that almost nobody can be coerced into compliance. Sure, if fixed cameras are somehow impossible and the best hope for enforcement is "no more than 10 over no matter how bad the conditions" this may be the case. But in some countries other than the US these are solved problems.

Re: Are road speed limits based on safety?

#19

Post by dazc »

v01dlight wrote: post #13
dazc wrote: post #5

Earlier quoted context omitted.

The point of all of these arguments is always that speed limits should be increased when all evidence suggests they should be lowered. Evidence, in this case, being number of deaths.

Did you read the article? The first evidence it examines is roadway deaths vs speed limit, and the author concludes "there is little correlation". I'm not saying I agree with the article's conclusions, but it's easier to trust someone who shows some evidence than someone who just suggests that evidence which supports their conclusions exists.

I just take 'little correlation of deaths v speed limit' as an argument against speed limits in general. Otherwise, what is the point of raising the issue?

Also, he says: '10 times as many people die on UK country lanes than on motorways. This furthers our evidence that motorway limits have less effect on deaths than other roads..'

Comparing country roads to motorways? A country road could be one car width or two car widths at best, with vehicles driven, often, erratically in both directions with little warning of obstructions or oncoming traffic.

A motorway is 3 or 4 lanes of vehicles travelling in the same direction with virtually zero chance of anything coming the other way, usually clear visibility and advance warning of obstruction, etc

You don't see a problem here?

Re: Are road speed limits based on safety?

#20

Post by kybernetikos »

v01dlight wrote: post #13
dazc wrote: post #5

Earlier quoted context omitted.

The point of all of these arguments is always that speed limits should be increased when all evidence suggests they should be lowered. Evidence, in this case, being number of deaths.

Did you read the article? The first evidence it examines is roadway deaths vs speed limit, and the author concludes "there is little correlation". I'm not saying I agree with the article's conclusions, but it's easier to trust someone who shows some evidence than someone who just suggests that evidence which supports their conclusions exists.

My memory of years ago is that comparing the survival rates of someone hit at 30mph vs someone hit at 50mph was a part of every driving test. And unless my memory is very wrong, there is an extreme correlation there.
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