As everyone probably knows, there’s talk of reinstating the 55mph national speed limit. Although somewhat unfairly with respect to individual cars, drivers, and driver habits, it’s common wisdom that driving more slowly can bump up your mpg.
Without going into all the pros and cons–I may open a GD thread for that later–I have a question for planners, traffic engineers, or anyone else who has some expertise on roads and traffic.
If we lower the speed limit from 65 to 55mph, then that means it now takes about 10 minutes longer to cover a 65-mile stretch of road. It also means that any given car is on the highway for that much longer. More cars on the road at a time means more congestion. Isn’t it possible that some drivers could lose mpg due to more time spent stuck in traffic? Has it ever been worked out mathematically, or is it possible to do so, to find at what speed the cost of congestion outweighs the economy of slower driving?
Sen. John Warner (R-VA) has proposed that the speed limit be set back to 55. Senator Warner must have gotten a hell of a contribution from his local Fraternal Order of Police, because all this will do is create more opportunities for revenue generation. States can set their speed limits at whatever speed they want to, they don’t need the Feds to jump in.
In fact, the last time I went down I-81 through Virginia, all 323 endless miles of it, the speed limit was 55, and I never saw a cop because they were too busy getting someone else for speeding. It was 70 in West Virginia and 65 in Tennessee, but not in Virginia. Oh, and radar detectors are banned there, too. Think that state makes some money on speeding tickets?
I wonder if the cost of gas combined with the increased length of long road trips would cause a significant spike in rail and air travel if such a restriction were put into effect.
BTW–States are afraid to lower the limit, because they think truckers/tourists will choose another route. I’m in my State’s DOT, & this is the line we’re getting.
Seriously, it’s just too damn slow for me. I physically have a hard time staying at that speed because I feel like a snail. Unless of course I’m doing 55 in a 40, then I’m good.
Talk about increasing speeding ticket revenues!
And yeah, VA sucks ass about their radar detector laws. They have radar detector detectors, I do believe.
Strangely enough, when certain British motorways have particularly heavy traffic (i.e. a lot of the time), they impose lower speed limits - usually 60mph but sometimes 50mph. The theory is that traffic actually flows more smoothly at lower speeds: above a certain speed the flow becomes “turbulent”* as drivers have to brake which causes chain reactions to propagate down the flow.
they actually do model the traffic as a fluid IIRC.
See here. Supposedly the slower speed limits actually reduce journey times when traffic is heavy.
Cars are safer these days, I’m not convinced a 55mph speed limit would save a non-negligible number of lives and damages. I would be curious to see if a given trip is actually more fuel efficient at 55mph than 65mph and 75mph. Incidentally there’s nothing magic about 55mph. I’m guessing that car designers could optimize a cars engine tuning and aerodynamics to be most efficient at about any speed.
This would also slow down trucking. That’s going to cost.
If every state did it, for myself, It would also cause me to take another day or two on the roads to get to Wisconsin and back in September. Not may choices for the route.
Or, I may make my driving day longer. That’s what I did when Carter imposed this. I’m not a trucker, but do use the roads in fly over country. Imposing a 55mph limit on roads and vehicles that can easily handle 75 is a bad idea IMHP.
Is that necessarily true? I’ve heard that the reduction in accidents caused by the lower legal speed limit is outweighed by the increase in accidents caused by people driving at a wider actual range of speeds.
As to the OP, traffic engineers model this sort of stuff using computer simulations but I don’t if anyone has ever examined this specific question in a place that is publicly available. Driver behavior and traffic movement is complex so I doubt there is a straightforward equation where you can just plug in speed x and speed y and find out which one is more cost-effective.
In CA at least the maximum speed limit for trucks is 55. Not that they stick to it, and not that the CHP actually enforces it, but that’s how it is in theory.
You also have to remember to value the lost time. Somehwere in Mr Roadshow he figuered it as around $5 per hour you’ll be “paid” if you drive 55. Is your time worth only $5/hr? Mine isn’t.
Colophon is right. As a former fast driver I hate to admit it, but they lowered the speed limit on the freeway I take home from work and I don’t even tap the breaks anymore, whereas it used to be stop and go about 3/4ths of the way. It cut my 40-45 minute commute down to 20-25 minutes.
Yeah, but you can get a radar detector detector detector. It detects the radar detector detector and shuts off your radar detector before it can be detected. Juts hope the cop doesn’t have a radar detector detector detector detector.
I don’t have a whole lot to add, but as an Australian, it is truly strange to hear American folks talking about this matter this way.
Maximum speed limits here on interstates and local freeways is 100 or 110km/h (62 or 68 mph). It is drummed into us from birth, every day, in every media, at every opportunity that “speed kills”, and failure to observe speed limits is just-fucking-stupid thing to do (drinking and driving is similarly treated, not sure which one kills more people, tho?). There are fixed speed cameras on many roads, every cop has one in their car, and compared to the US, there’s very little speeding (I have spent a total of 12 weeks driving around US interstates, ~350 miles each day, so I have a realistic understanding).
Presumably, the research is right - on purely economic grounds, it’s cheaper to spend a bunch on ads and whatever ripple effects of things moving slower, than it is to spend a bunch on hospital care for people who crash cos they were going too fast, let alone the pain and suffering, let alone the innocents who are killed or injured.
Speeding here is perhaps kinda like using incorrect words in social discourse for African Americans; it happens, but not many people are down with it.
I like that the dope can highlight these differences in society.
