Nevada DOT recently posted 80 mph on part of I-80, leaving most of the highway posted 75. This was a political compromise. The legislature had asked for 80 as a general speed limit but the governor’s people didn’t want any of it.
The order went out last year to collect speed data on part of I-80 and look for excuses not to post too much 80. The National Motorists Association obtained the engineer’s report.
Speed limits should be a bit above the average speed of traffic. The average speed on I-80 is 73, down to 68 over one mountain pass and up to 80 on the plain. The 85th percentile speed, which is the specific “bit above” measure generally accepted, is about 7 mph higher.
I-80 was divided into 27 segments, of which 24 had speed measurements. On every segment the measured 85th percentile speed was over 75. Two segments they avoided studying — Lovelock and Elko where the boss said not to raise speed limits — are not significantly different in design or operation from the rest. The third excluded segment includes Reno and might have slower traffic.
So 350 miles, maybe more, of I-80 should have been posted 80. Less than half if it was.
The report looked at two alternatives to using the 85th percentile method for speed zoning. One was the USLIMITS2 excuse generator. It had a perfect excuse: speed limits should never be higher than 75 under any circumstances. That must have seemed a little too obviously defiant of the legislature. The other was a method called “minimum study analysis”. The only version I know of that method doesn’t allow speed limits so high either; Nevada must have found a different one or made its own version. Consistent with its name “minimum” consistently recommends a speed limit 1-3 mph below the 85th percentile rule. Great when the boss doesn’t like the 85th percentile rule but can’t completely ignore it.
There is no reason to post a speed limit below the 85th percentile. This is the best case you can get for speed zoning.
I-80 east of Reno is generally flat and straight. Only three short mountain passes have curves and grades steep enough to slow trucks. Eastbound and westbound roadways are widely separated. Interchanges are widely spaced.
Traffic volume is low, around 8,000 vehicles per day.
The accident rate is low. Only over the three mountain passes does the accident rate rise to normal. The most dangerous summit has 1 accident per million vehicle miles traveled, comparable to an average freeway in New York state.
Possibly the 8 mile section over Pequop Summit could use a more detailed study to find why it has an average accident rate. If accidents are related to fast cars passing slow trucks, reducing the speed differential is worth considering. If accidents are weather-related (mountain passes get more snow in winter), that’s not a speed limit problem.
Speaking of speed limit problems, why does this highway even have a speed limit? The literal answer is, because state law requires one, the governor wants one, and police want excuses to make pretext stops. But rural Nevada didn’t have speed limits 50 years ago, when 80 mph was fast and the Interstate wasn’t finished. It doesn’t need speed limits now.
Quoting the 1967 state highway map,
SPEED LIMITS — Unless otherwise posted, Nevada’s highways do not
have maximum speed limits. You must drive at safe and reasonable speeds,
however. Use your good judgment, taking into consideration road and
weather conditions, visibility and traffic. Reduce your speed through
urbanized areas according to posted limits. Slow down, also, as you approach
ranches or other settled areas regardless of size. Some of these may not
have posted speed limits but you should be prepared to stop.
If you were in the country you were responsible for your own speed.
Believe it or not, only half the state troopers I saw last trip along I-80 were running speed traps. The other one was picking debris off the highway.
Time to get all of the Highway Patrol doing honest work.
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