Speed limit based on 85th percentile: is it really the safest?

That certainly matches my experience as an ordinary driver in the pre-55mph limit era, the 55 era, and immediate post-55 era, up through now while driving and living all over the country.

Around here now though the speed of traffic on arterial surface streets is limit plus 15. It’s limit plus 20 on the freeways & toll roads. The folks I see pulled over are the ones that passed me a few minutes ago by 15 or 20 mph when I was already going limit plus 20 like everybody else.

As the “going rate” of routine everyday speed exceedance just keeps going up, I think we’re gonna need those self-driving cars pretty soon as a way of stuffing that genie back in the bottle. Once 15 or 30 percent of drivers simply don’t give a hoot what the limits are, the situation will be beyond the ability of even dedicated police forces to contain.

We here in California have a two lane road (Hwy 12) running from central Cal toward the SF Bay Area. Traffic is constantly bumper to bumper going 40-50mph interspersed with long stretches of open road. After mile after mile of trying to stay awake some people are going to try to pass several cars at once. That’s when horrendous headon crashes occur and plenty of less serious ones too from inattention, following to close etc. How does this happen? There is always somebody who insists on driving 35-50 mph and do not care how many cars are lined up behind them even if they do look in the rear view mirror. When most of the drivers are forced to drive way below the speed they feel comfortable at they will bunch up, its practically a law of nature. As is the impatience that builds resulting in a certain number trying to pass and getting into trouble. The road is perfectly capable of carrying the volumne if they would all have a minimum speed of around 65-70 mph. When another death occurs the papers are full of “speed kills” warnings when the fault is really these people who are driving too slowly. Of course the Highway Patrol is out looking for people speeding in order to pass rather than ticketing those who are the real cause.

Those are certainly factors, as are anti-lock brakes (though many drivers don’t understand how they are supposed to be used), stricter enforcement of drunk driving laws, and so on. But the benefits of those things do not diminish the fact that the wrong conclusion was derived at in 1974. When gasoline tripled in price people simply drove less, especially on the nations highways. Less people driving less miles in the period of 1 year is going to result in a drop in fatality rates. It’s hard to get killed on the highway when you’re not there!

Today more people and more vehicles are driving more miles at [legally] higher rates of speed and the fatality rate trend is downward.

If the limit in areas that are posted at 65, 70, 75, etc where all posted at 55 tomorrow and strictly enforced you would not see a noticeable drop in fatality rates. The reason being is that divided multi-lane freeways were built for higher speeds in the first place. A large chunk of vehicle accidents occur on roads posted at below 55 MPH.

The 55mph speed limit was all about saving gas during the OPEC oil embargo in the 70’s.

Where exactly did you hear this inane argument? Of all the debates that went on over the double nickel in the 70’s & 80’s I never, ever heard this.

55 was initially imposed to reduce fuel consumption. A year later it was discovered that highway fatality rates had dropped during that time. As I explained before the wrong cause/effect conclusion was drawn and after the energy crises had passed the national speed limit continued through 1995, though raised a bit in '87.

What a lot of people don’t realize is how much money and effort was wasted trying to cram 55 down the nations collective throats. The feds and the states spent BILLIONS on studies, speed enforcement devices, police overtime, etc., all for a benefit that was the emperors clothes. The agency I worked for took federal grant money to buy radar guns and we had to fill out these stupid matrix forms about average speeds, coogin, accident rates, fatalities post accidents, and so on. It was all crap. The “55 saves lives” mantra was a lie.

In some places, this is definitely the case. I recently changed jobs, and on my new route, there’s a section of relatively flat, straight road with a limit of 35. But inexplicably, there’s a part where it drops to 25 for about 500 ft stretch where it is perfectly straight with no intersections or merges. The only thing special about it is that it dips down a small hill just inside this limit from both directions. Also interestingly, this is the only spot on my entire commute with a speed enforcement camera, and it’s ALWAYS snapping pictures. I see at least one a day, sometimes two or three in a row. I can’t imagine any motivation for it other than knowing they could get easy money by reducing the speed limit right before a hill.

For my old commute, there was something similar. A stretch of road with a limit of 45, and a section of 25 that lasted about 500 ft. Admittedly, there was a small side road in that stretch, but there’s plenty along the whole road and that one seemed even less busy than some. Yet, there was ALWAYS a cop there during my morning commute in the last days of the month.

My experience is that there’s a fairly large cohort of people who for whatever reason really do view the speed limit as an absolute upper bound. They will not exceed the speed limit in sustained driving for any reason, and typically drive somewhere between 5 and 10 miles under the posted limt. Usually law & order, extreme rule-follower types.

The other main cohort seems to be the crowd that sees the speed limit as particularly milquetoast or absurd, and habitually exceeds it by at least 10, if not 20 mph.

If you drive an interstate (speed limits in my example are for Texas) and you don’t fall into either group, you’ll be caught in a tug-of-war between the two groups- one group wants to drive 90 in the left lane, while the other group wants to go 68 in the right lane. So if you want to actually go the 75 mph speed limit (or even over at 80 mph), you’re doomed to weaving back and forth between lanes constantly, sitting at the turtle speed, or intentionally screwing the 90 mph crowd.

I don’t know how you figure this into percentiles but my “safe driving seed” usually goes up significantly along with my familiarity with the road. If I don’t know what’s around the next bend, I’m more cautious and slow. When I know there isn’t any surprise around the bend (except for the traffic around me) I’m much bolder.

The problem isn’t the people who want to drive at, or even below, the speed limit, if they stayed in the right lane. If they stayed in the right lane, faster traffic could pass on the left. The ones mucking up the works are those who get in the left lane and stay there, at any speed, either below or above the speed limit. I don’t really want to have this thread change to one about lane discipline, so I’ll leave it at that.

As for people always wanting to drive over the posted limit, no matter what it is, there are some who do. But the majority of drivers want to drive at a reasonable, safe, prudent, efficient speed, and many speed limits are set below that point. My state raised the highway limit to 70 MPH last year. To the chagrin of the “speed kills” crowd, cops are finding that most drivers are no longer driving 10 or 15 MPH over the limit, but are driving right around 70-75 MPH. And accidents are not going up. The new limit seems to be about right for most drivers, and speeding (from a legal sense) and accidents seem to have both decreased, even as actual speeds have edged up a bit.

I would argue that an attentive driver in a modern, road-worthy car could safely drive quite a bit faster than 70 MPH, at least in dry weather in the daylight. And all of those factors come into play when deciding what speed is safe - weather, visibility, vehicle, attentiveness, sobriety, alertness, traffic volume and even driver skill. So, it is silly to think that one speed limit figure is reasonable for all times, conditions and drivers.

Knowing where the typical speed traps are definitely increases my average speed; for example, there are stretches of I-45 between Houston and Dallas that I have never seen a policeman or state trooper on, in probably 100 trips back and forth, so as a result, I pretty much fly along those stretches, and slow down to the speed limit where there are typically speed traps.

Nowadays, I just fire up Waze on my phone, and watch for speed traps that way.

Both of these demonstrate that the real error is ever building a long-haul highway with only two lanes in a single direction. Particularly once you add trucks (and for states other than Texas these mysterious things called “hills”) you really need more than two lanes to handle the disparity of speeds. Three works, barely, but four is better.

IF traffic densities are very low, one lane for cruising and one for passing is logically defensible. Once density picks up to the point that the faster traffic would be pulling back and forth every 30 seconds as they come upon yet another slower car ahead it becomes impractical not to use both lanes for cruising, albeit at different speeds.

I haven’t seen a stretch of rural interstate where two lanes per direction is adequate in probably 20 years. Admittedly I don’t frequent I-80 in NV; it might still get by with two. IMO/IME, “keep right except to pass” is a 1950s solution to a 1950s problem that’s largely inapplicable since the 1980s, much less today.

After 25 years I retired but took a part-time gig with another agency to maintain my law enforcement certification in this state.

In this jurisdiction there is a stretch of street here (city street) that is divided 4 lanes, almost like a freeway. But the posted limit is 25. The reason is, there is a park on the west side of the street. I’ve been a patrolman here since I retired from full time in mid-2007 and hardly anyone frequents that park. Not kids, adults, or squirrels! it’s a large park, yet empty. Even in mid-day during the summer! That stretch of street should be at least 35 if not 40. 2 miles later the limit goes up to 40 and then, 2/10’s later, to 45.

I do my job, make more stops, write more cites than anyone else minus one officer. But no way am I writing for less than 45 on that 25 stretch. It’s not reasonable!!! And it’s not the departments fault. The DOT let the local street dinks set the limit.

Plenty of rural highways are perfectly adequate with two lanes in each direction, if people do indeed follow the keep right rule. The only time there ever seems to be much of a slowdown on the highways here in Maine is when one slow vehicle overtakes another.

Incidentally, keep right except to pass signs are posted even on three-lane highways here. I don’t see how it is obsolete. In fact, I’d say it’s quite orderly, because when everyone follows it, even in “heavy” traffic (by Maine standards), there is a clear progression from slowest to fastest as you move left, and much less passing on drivers’ blind sides, since people move out of the way when they’re safely clear.

The point wasn’t that all highways should be multi-lane, but that most interstate highways have enough traffic and large enough speed deltas to warrant a third lane.

The “keep right except to pass” is basically what causes the weaving back and forth that I mentioned in my post- you stay right, until you come on some farmer driving his turnip truck (or ancient geezers in Buick land barges, or timid mousy drivers, etc…) at 55 on the 75 mph interstate… at which point you jump out into the left lane, stomp on the gas, and hope the assholes going 90 don’t rear-end you as you speed up. Then get back over once it’s clear, and repeat the whole cycle ad-nauseam until you get where you’re going, or the freeway gets larger, and you can find a lane where you can just drive.

It’s a problem; since I really DGAF, I usually just drive 75 in the left lane until there’s a LARGE open stretch in the right lane, at which point I’ll get over.

You’ve also obviously never driven on a European highway. There’s lots of super congested rural highways there but traffic generally flows much smoother than a similar US Interstate precisely because drivers don’t dawdle in the left lane. Congested rural highways are where lane discipline is absolutely critical.

I’ve driven all over the US and I’ve rarely seen a rural insterstate that needs more than 2 lanes. 4?? T’s so every precious snowflake can keep their ever-so-special personal favorite speeds.

I-95 in the Carolinas definitely needs 3. The laws must be different there because there are a lot more trucks in the Carolinas that park in the left hand lane going 1 mph (or less!) more than the traffic in the right hand lane, even compared to other 2 lane regions of I-95.

I have driven about 2000 miles on interstate highways within the past month, and left lane campers, left lane hogs or whatever you want to call them are what gum up the works. Lane discipline is horrendous, which impedes traffic and creates backups. People who drive in the left lane and who won’t move over are my biggest frustration. I think some are completely ignorant of lane discipline, that they should move into the right lane. Some, like a couple of poster here, know they should move right but misguidedly think they are OK in the left lane. And others are just being purposefully vindictive, petty and are pretending to be cops for a day - the “if I’m going the speed limit, I don’t need to move over, as nobody should be driving faster” crowd. I’ve seen all of them recently, including the numbskulls who drive mile after mile in the left lane and then move over a half mile before they get off at an exit.

Flashing your headlights, as is done in Europe, just seems to tick off the left lane bandits. So, I started using my left turn signal, thinking this is a friendlier, gentler suggestion. 80 percent of the time, this doesn’t work either. Many left lane hogs are simply passive/aggressive twits who don’t care about other drivers.

Oh, and BTW, I am not one of those drivers who is going 90 mph, or who is aggressively tailgating. I usually drive 5 to 9 mph over the limit. I am glad to move over to the right to let a faster driver through. It doesn’t upset me in the least.

95 may be an exception as the only major road up and down the east coast. I’s been at least 10 years sice I’ve been on it, but I agree it was always crowded, pretty much everywhere.

OTOH, I’ve spent a lot of time on both I80 and I70, and neither of them needs a 3rd lane let alone a 4th except near and through large cities.

Well, no. They’re a symptom of a bigger problem, which is the fact that there is a huge speed differential between the two lanes. If one lane’s going 90, and one’s going 60, there’s no middle ground for anyone who wants to go any other speed, UNLESS we want to weave in and out of traffic, or go one of the two other speeds.

If traffic isn’t heavy, then it’s not a problem - I’ll stay right and go roughly the speed limit (usu. a little over), and just change lanes when I occasionally come upon a turtle going slower than me.

But on say… I-45, between Houston and Dallas, or certain stretches of I-35, it’s sort of a 90 or 60 option because the traffic is heavy enough to where you’re literally going back and forth every few miles, and I more or less refuse to go either of the other speeds. So the 90 mph contingent loses out.