‘ Every car engine has a sweet spot in terms of efficiency, typically when running at 55 mph. Beyond 60 mph, engine efficiency plummets because of higher temperatures. In addition, three other factors that affect gasoline consumption become more significant at higher speeds: tire resistance, wheel bearing friction and air drag. What all that means is that for the average car, cutting the speed from 75 mph to 55 mph improves fuel efficiency by roughly 25%.This would save 1 billion barrels of oil per year - more than US imports from the Persian Gulf. Former President Carter endorsed a 55 mph limit in the oil crisis of the 1970s but the public kicked him out. Lowering the speed limit did reduce demand and help cut gasoline prices. But there are some arguments for again trying such a policy:
- Reducing the limit to 55 mph just broadens the sense of public good to include conservation.
- For most people a reduced limit would not add greatly to travel times and those who it would harm – e.g. long-distance truckers - would spend less money on gasoline - they would save more than 50 cents per gallon at current prices.
- There would be fewer serious traffic accidents.
A flaw in the plan is that consumers alone pay. President Carter forced US car makers to establish an average fuel efficiency standard - the Corporate Average Fuel Efficiency (CAFE) standard - across their fleet of 27.5 miles per gallon within a decade. This has been fixed since though it too could be tightened to 33 miles per gallon today – higher targets than this have been suggested by the Sierra Club. With this change the US would save a further 2 million barrels of oil a day and there would be incentives too for car manufacturers to improve an engine's sweet spot to make it run more efficiently at 75 mph.
The Slakey plan is worth examining. The cost savings in fuel bills and the reduction in traffic damage accident costs need to be assessed against the value of increased travel time valued at some function of real wages. A good thesis topic for an economics student once the core science is checked out – my reservation is only that fuel economy in vehicles I drive is better on long-distance trips when I drive faster than when I drive around town - due I assume to more stop-and-start driving in urban areas. I have always believed (falsely?) that increased fuel consumption was driven by the need to accelerate a vehicle but that it would be low if one is travelling at a relatively high speed but not accelerating.
Of course, if the argument is correct, one can individually reduce fuel bills by slowing down! The advantage of a law is the macroeconomic effects of induced lower oil prices.