on most ICE cars, the most fuel efficient speed is the minimum speed where you can get into the highest gear without lugging the engine. frictional losses from

on most ICE cars, the most fuel efficient speed is the minimum speed where you can get into the highest gear without lugging the engine. frictional losses from spinning the engine at a higher rpm tend to be larger than losses from air resistance. on most modern cars, this is around 50mph, which is very slow to drive on the interstate. my car can get well over 40mpg at this speed, which drops down to the mid 30s when I travel at 80mph. on most EVs, there are no gears, so efficiency increases asymptotically as speed approaches zero. what I'm getting at is that fuel efficiency for an individual car should not be the only optimization target for traffic laws. we are willing to make at least some tradeoffs in efficiency to get where we are going faster. most speed limits in the US have not been increased since the 60s, and since then cars have become much more efficient, capable, and survivable in the case of a crash. I'd say at least a modest increase in speed limits is warranted. plus, a bunch of ICEs crawling in stop-and-go traffic is pretty much the worst case scenario for fuel efficiency. if this new policy can actually reduce gridlock, it is likely to have net gains in emission reduction.