Tuesday, May 06, 2008

The Deadweight Loss of Speed Limits

After driving a lot over the last few days, and obeying the traffic laws a bit more than I'd prefer due to a recent two-speeding-tickets-in-one-hour situation, the concept of speed limits tends to come to the surface. How worse off am I since these laws exist? Let's count the ways:

- I get to my destination slower. The little anti-speeding charts that show the marginal discrepancy in travel time for arriving at destinations at different speeds are largely correct...at short distances. Speeding around town does nothing but pacify an impatient attitude. There's a sizable impact for driving 5 or 10 miles an hour faster over a long distance-- the difference between 65 and 75 is over an hour from Morgantown to Chicago.

- People like to argue that the existence of speed limits leads to less accidents. I wholeheartedly disagree. People driving faster will pay more attention to what they are doing, and I'd say that it is getting distracted/bored while driving that causes the lion's share of wrecks, not inability to handle a car at a high rate of speed. But with regards to that...

-...I'd also say that speed limits cause more wrecks to be with other cars. At face value, cars able to drive faster are able to separate themselves more. (Think long range driving.) It's getting cars clumped together that want to be going faster that create the dangerous scenarios. I believe on net you'd have less accidents without speed limits, but as a proportion of wrecks, I'd also say that wrecks involving other cars would be lower without speed limits.

- Good laws are clearly written and strictly enforced to the letter. Speed limits are not a good example of this. There is a lot of uncertainty in how these laws are enforced, from how far over the limit yields a citation to uneven enforcement throughout the hours of the day. With uncertainty comes reduction in welfare.

(I'm curious: What's the most minor speeding violation anyone has received, in terms of least miles per hour over the posted limit?)

- Speed limits may protect pedestrians a bit more; but do pedestrians feel more comfortable around roads now because of speed limits? Would roads be more like train tracks without speed limits? Certainly not in neighborhood areas, but in more commercial areas this mindset may develop. If all speed limits were to be eliminated, I could see those in shopping/commercial areas informally hanging around while higher speed zones would see them drop from the radar almost immediately.


Unknown said...

I agree with this in general, and I think there are data out there investigating this. I'm thinking in Montana, or the autobahn maybe.

However I think there are certain areas where speed limits need to remain. Around schools, for example.

Justin M Ross said...

What is a street with cars driving 100mph? A street I don't try to walk across.

What is a street with lots of pedestrians walking across? A street I drive really slowly on.

It's all about property rights.