Brian D. Taylor: "A typical freeway lane can handle up to 2,000 vehicles per lane per hour, but in really bad traffic that throughput can be cut in half; just when we need the most out of our road system, it performs at its worst. So heavy traffic is not only 
irritating, it’s also really inefficient. Second, traffic delays are non-linear, which means that when traffic rises to certain levels it becomes unstable. Add just a few too many cars at the wrong time and fast-moving traffic suddenly slows to a crawl; take just a few cars off of the road at the right time and traffic speeds and throughput can both increase dramatically. If we can find a way to keep some cars from crowding onto already congested roads at certain times and places, many more people will get through the system overall, and at higher speeds to boot."
"Keeping drivers from crowding onto roads at the wrong times and places is not easy, and could entail a heavy-handed role for government. This is where pricing comes in. Road space is scarce and valuable, so why not use prices to allocate it like we do for almost everything else, including food, housing, and utilities?"