The principle is sound, but the ants actually obey the rules whereas (in the UK at least) a small contingent of human drivers will ignore the limits, speeding up and slowing down between enforcement cameras. This concertina effect from just a small number of drivers is enough to slow the entire flow of traffic.
It would have happened anyway after a certain density of vehicles is exceeded, since each car and truck had different accel/decel rates. Especially if there is an incline anywhere.
yes, speed reduction on the Paris belt was also done in order to reduce traffic jams. The argument was "peak speed is slower, but apart from night/holidays situation with empty road, you'll actually get faster to where you're going because of less jams"
