Originally posted by Mike
From I Civil Engineering perspective, I must disagree. Transportation Engineers do most of the practical setting of speed limits and are bound by efficiency and safety rather than monetary considerations as a matter of law. Real, engineering studies are used to determine how to run our roads.
I agree. The speed limit is not a political or monetary issue, it's a safety issue. The 70's oil crises and the change to 55-mph is the only exception, and these were changed back later on. That only effected interstate highways for a few years. The posted speed limit is primarily and engineering decision on almost all roads today.
What is being considered is the kinds of people who will potentially drive on the road (anyone from a teenage to a little old lady), and the reaction time of a driver. The calculated "site distance" is the main criteria for setting the "design speed". The greater the site distance (the minimum distance a drive can see an object on the road), the higher the allowable speed. The posted speed limit is usually about 5 mph lower than the "design" speed, so your in that window if your alert and have normal reflexes.
Also, for a given length of road, we don't want to the posted speed limit changing frequently. So while it may be safe to drive faster along a straight stretch, the posted speed limit may be lowered due to a gentle crest in the road ahead that limits the distance the drive can see when he gets a short distance further down the road.
I think the moral issue is not "the law of the land", but the intent of the posted speed limit - which is safety. And sometimes the posted speed limit is not necessarily the safest under some circumstances. For instance, when traveling a long straight section of interstate, with a post limit of 55 mph, if cars are passing you one after another, then you are actually increasing the danger to other drivers by going 55 mph. In that case, you do more to increase safety by driving in average speed of the other drivers (say 6o to 65 mph).
I try to keep a following distance of 2 seconds from the car ahead of me, regardless of the speed. But I know that when traveling the beltway around D.C., that keeping that much distance with heavy traffic - people would pull around me. And when I tried to drop back to the safer following distance, the next car behind me would do the same. I had to adjust reduce the following distance just to discourage other drivers from being stupid. When I'm driving in less congested areas, I go back to 2 or more seconds following distance.
So I think from a Civil Engineer's perspective, safety trumps the posted speed limit. Don't drive faster just because you
think you can. Consider the other drivers, and the fact that the posted speed limit is there to keep drivers who might be a little less alert from having accidents, or because much of the road your on does not provide enough site distance to drive 10 or 15 mph faster.
Whatever you do, don't drive a lot slower than the speed limit when everyone else is zipping past you. If your on a single lane and there's a 1/2 mile of cars right behind you, it might be a good to pull off at the next turn and let them by so they aren't tempted to pass you on a double-yellow line.
Bottom line, drive the posted speed limit whenever practical, considering that going a little slower or faster may increase your safety under certain circumstance. (And saving 5 mins on your drive to work is
not one of those circumstances.)
[Edited on 3-28-2006 by Civbert]