A quick note and idea on fuel efficiency...

...because it's been churning in my head since last Tuesday, and I haven't written it out yet.

When I was driving to South Carolina and back, I discovered I was going 80mph without pushing the car's engine much at all. (The amount of work I was asking the engine to do might have kept me going 55 or 60mph, normally. Maybe 65mph on the average downgrade on I-77.) It took me a while, but I finally came up with a plausible reason this happened.

I had merged onto the freeway, found myself embedded in a large pack of big-rigs semis, hadn't settled into traffic enough to set cruise, and had to move to get out of the way of traffic shifts to let another batch of traffic merge in. I signaled, changed lanes to the left and accelerated--and felt my jaw drop when I saw I was effortlessly going 80mph.

What I think happened was that the sparse pack of semis (and filler of smaller vehicles) spanning three lanes had caused the volume of air covering I-77 to be moving roughly uniform in line with traffic, not too far from the speed of traffic. In effect, the traffic had created its own wind tunnel, and you didn't have to be dangerously close to the back-end of a semi to get a drafting effect.

So what would happen if you took a long stretch of road (such as an under-river or through-mountain tunnel) and set up blowers pushing air in in the direction of traffic flow? Given the reduction in air drag, how much would you save on fuel economy? Would the energy involved in maintaining a 15mph tail wind in dense-traffic areas be greater than the aggregate saved energy in vehicle fuel? How much of an impact on local pollution would it have? By pulling energy from the electrical grid rather than car engines, you can move the atmospheric cost of energy generation away from areas where it could cause health problems. (Places with high pollution due to vehicle emissions might find that useful...)

Anyway, it was an interesting experience, and leads to a lot of interesting questions.