the reduce/increase figures are lacking a baseline for the comparison, ISTM
I find the reduced emissions most questionable. I am told engines are designed for peak efficiency at higher speeds than 20mph
also, if 20mph made little difference to travel times, why would people bother to make and fly airplanes, choppers and the like?
I mean, I believe the figures make sense under a number of other unstated assumptions, from comparison baseline to urban traffic patterns, but without them, the claims come across as blatantly false propaganda, which is IMHO a disservice to the likely good goals behind them