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.

I'm just back from the "ITS World Congress" an annual meeting of people working on "Intelligent Transportation Systems" which means all sorts of applications of computers and networking to transportation, particularly cars. A whole bunch of stuff gets covered there, including traffic monitoring and management, toll collection, transit operations etc. but what's of interest to robocar enthusiasts is what goes into cars and streets. People started networking cars with systems like OnStar, now known in the generic sense as "telematics" but things have grown since then.

The big effort involves putting digital radios into cars. The radio system, known by names like 802.11p, WAVE and DSRC involves an 802.11 derived protocol in a new dedicated band at 5.9ghz. The goal is a protocol suitable for safety applications, with super-fast connections and reliable data. Once the radios in the car, the car will be able to use it to talk to other cars (known as V2V) or to infrastructure facilities such as traffic lights (known as V2I.) The initial planned figured that the V2I services would give you internet in your car, but the reality is that 4G cellular networks have taken over that part of the value chain.

Coming up with value for V2V is a tricky proposition. Since you can only talk to cars very close to you, it's not a reliable way to talk with any particular car. Relaying through the wide area network is best for that unless you need lots of bandwidth or really low latency. There's not much that needs lots of bandwidth, but safety applications do demand both low latency and a robust system that doesn't depend on infrastructure.

The current approach to safety applications is to have equipped cars transmit status information. Formerly called a "here I am" this is a broadcast of location, direction, speed and signals like brake lights, turn signals etc. If somebody else's car is transmitting that, your car can detect their presence, even if you can't see them. This lets your car detect and warn about things like:

• The car 2 or 3 in front of you, hidden by the truck in front of you, that has hit the brakes or stalled
• People in your blind spot, or who are coming up on you really fast when your're about to change lanes
• Hidden cars coming up when you want to turn left, or want to pass on a rural highway
• Cars about to run red lights or blow stop signs at an intersection you're about to go through
• Privacy is a big issue. The boxes change their ID every minute so you can't track a car over a long distance unless you can follow it over every segment, but is that enough? They say a law is needed so the police don't use the speed broadcast to ticket you, but will it stay that way?

It turns out that intersection collisions are a large fraction of crashes, so there's a big win there, if you can do it. The problem is one of critical mass. Installed in just a few cars, such a system is extremely unlikely to provide aid. For things like blindspot detection, existing systems that use cameras or radars are far better because they see all cars, not just those with radios. Even with 10% penetration, there's only a 1% chance any given collision could be prevented with the system, though it's a 10% chance for the people who seek out the system. (Sadly, those who seek out fancy safety systems are probably less likely to be the ones blowing through red lights, and indeed another feature of the system -- getting data from traffic lights -- already can do a lot to stop an equipped car from going through a red light by mistake.)

Since getting involved with Google's self-driving-car team, I've had to keep silent about its internals, but for those who are interested in the project, a recent presentation at the intelligent robotics conference in San Francisco is now up on youtube. The talk is by Sebastian Thrun (overall project leader) and Chris Urmson, lead developer. Sebastian led the Stanley and Junior teams in the Darpa Grand Challenge and Chris led CMU teams, including BOSS which won the urban challenge.

Earlier I wrote about the transportation potential of walking robots-of-burden like BigDog. While these robots are not for the long haul, a whole range of options are opened up by a wheeled vehicle that can get to where the road ends, and then lower legs to walk along rough terrain, up stairs and up hills.

Boston Dynamics has gone even further with their latest model, AlphaDog