Congestion on the roads has a variety of sources. These include accidents of course, reductions in road capacity, irrational human driving behaviours and others, but most of all you get congestion when more cars are trying to use a road than it has capacity for.

That's why the two main success stories in congestion today are metering lights and downtown congestion charging. Metering lights limit how fast cars can enter the highway, so that you don't overload it and traffic flows smoothly. By waiting a bit at the metering light you get a fast ride once on the highway. Sometimes though, especially when the other factors like accidents come into play, things still gum up.

Now that more and more cars are connected (by virtue just of the smartphone the driver carries if nothing else) the potential will open up for something else in congestion -- finding ways to encourage drivers to leave a congested road. Of course, people often will try to exit off clogged freeways if there is a surface street route that they think they can use. It rarely is a win due to the much slower speed of surface streets, so not that many do it. But one thing that is true is that some people on the highway are in more of a hurry than others. Some are really in no hurry at all, but have no particular reason to leave the highway to make it flow more smoothly for the others who will stay on it.

Today man corporations sign a deal when they buy electricity that gives them cheaper energy because they agree that, in a brown-out or shortage, they will power off. It's a risk they take. (Some of them have generators to make up for this.) What if there were a way to say, "Those you you not in a hurry, here's an incentive to leave the road right away." Many people might take it. Even people on the way to work might take it if they could park, pull out their laptop and phone and do some work in the car. (You could even direct them to wifi-enabled parking lots set up for that purpose.)

In the power deals, they get the cheaper power and shutting down is not an option. Often a year goes by when they never have to shut down, and it's a win for them. It's a win for the power grid too because it doesn't have to build more peak capacity. You can have different incentive structures if you have people who have the option to leave the road, and those who must. (Handling those who must requires they have privacy-invasive tracking, though there are designs that can do this after the fact without taking the data out of your hands.)

Incentives could be plain old cash (which is still cheaper than building bigger roads just for the peak) or a gas tax rebate. It could also mean access to the carpool lane when you aren't agreeing to leave the road as a payoff for doing so when told.

This might also be a way to run a carpool lane. Initially, many people, including solos could use the carpool lane. The minute it slows down, a signal would go out to cars in the lane that some, or all of the solo drivers must leave the lane. In the event it is still congested, you could even have some or all 2 person carpools leave, or simply those carpools who elected that they would leave when ordered in exchange for some incentive. This is good because it makes full use of the carpool lane. (Some studies show that because only a modest number of extra carpools form due to carpool lanes, they often make traffic worse rather than better because of the wasted capacity. No wasted capacity while retaining the incentive to carpool is a win-win.) In this case, enforcement again has to be via tracking if you want it to be based on who made the agreement, because cops can only (barely) tell if there are 2 people in the car.

In the future robocar world, this sort of approach could be so rapid that congestion might never last more than a very short time. When a road becomes congested, enough cars would be asked or ordered to leave the road and get put onto other routes so that the congestion would vanish. Who gets to use the resulting fast road could be whoever is paying the most, winners of a lottery or some other test.