ITS vehicle to vehicle demo at ITS World Congress

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.) On its own, even the enthusiasts now agree that decent market penetration is not too likely. The only course to quick adoption is a regulation requiring the systems. And that's in play in the USA. The DoT is conducting a trial in Michigan by equipping 3,000 cars of workers at a hospital with the transmitters. This will create a local zone with decent penetration. If they like the results, in 2013 NHTSA will consider making a regulation requiring the radios. At the speed at which car vendors move, that means it's the 2019 model year which is the first to have the radios standard. Then, over several years, penetration goes up, so that in the mid 2020s you have a decent chance that a car will have the radio.

Robocars (and human drivers) could never depend on such radios as their only way to detect a car. Even with near-100% penetration they will sometimes break or fail. Indeed, as penetration gets high there is a real risk that human drivers would come to depend on the system, figuring they don't need to check their blindspot any more, causing more reckless driving and creating some collisions. Robocars at least won't do that. On the other hand, for the robocars, extra information on the road is generally valuable, particularly information about cars which can't be seen or detected directly by sensors.

Traffic light transmission is also useful to all. Cars can know to not race up to a light that's going to be red, and rather coast and always get a green. (Though this could also be done over the wide area network with synchronized clocks and lights on predictable timers.) It is also planned to let emergency vehicles get signal priority using these radios -- though that interferes with planned timing. Another minor application allows cars to tell signals they are coming, so that the signal does not have to wait for you to go over the magnetic loop to be detected. Late at night that might let you breeze through lights without being an ambulance.

At the ITS congress, there were several demos of this technology. One, done at the Disney speedway by a coalition of most major car vendors, showed the basic functions above in actual operation, with cars from many makers.

In this video I shot, we're in one car following another. We can't see it, but a 3rd car has stopped ahead on the road. The car we're following swerves around it at the last minute, but we get a warning about its presence before that swerve, before we can even see the stalled car.

In some other videos such as this one of a DENSO test you can see an attempt at doing a map with a green band to show where to drive to get a green. Also of interest in this video is the two DSRC equipped cars driving around our bus, shown on the screen. One thing that may concern you is the way they dance around -- GPS is not very accurate, and in fact not even accurate enough to be entirely sure what lane another vehicle is. They've had to work to avoid that causing false alarms, and they still happen. One way they could fix that would be to have the radios share GPS solution data, so you can be sure both GPSs used the same algorithms and satellites for their solution. In that case the relative error of GPS is much smaller, and you can tell if another car is in your lane or the next one. They are not doing that at present.

Here are some of the other problems they face:

  • Security is a big issue. They have a plan to digitally sign transmissions, and a PKI for these signatures. But the internet hasn't got its own PKI for TLS working perfectly after 20 years and these guys won't do much better.
  • Even if you can certify the messages, you have to seal and certify the whole system. What if bored teenagers send out signed messages from a fooled GPS that says a car is stalled in the middle of the highway, and everybody gets a collision warning, or worse, their cars auto-brake?
  • Even without malice, I am not sure how well the system handles a car parked on an overpass, transmitting the truth about where it is. (Altitude accuracy in GPS is much lower.) And of course there is no GPS in tunnels and many urban canyons.
  • Many of the current radios just don't link-up fast enough or over long enough distances to really be good for safety applications.

All in all it's a tough problem. It would be nice to see this happen but as yet it's hard to see how that comes to be.

Where were the robocars?

One thing that surprised me about the ITS congress was the general absence of robocars and discussion of them. Oh, the keynote from GM predicted them and GM had their autonomous EN-V doing demos in the parking lot. And a few papers out of a thousand talked about autonomous vehicles and related technologies. Most were unaware of the progress in robocar technologies and sensors or placed the technology many decades out. That's an issue because many of the safety systems aimed at assisting drivers are much less important if fewer people are driving, particularly the ones who are early adopters of fancy safety systems.

Today's safety systems are another matter. Known as ADAS (Advanced Driver Assist Systems) many of these technologies are precursors for robocars. What began with radar based adaptive cruise control (ACC) now has blossomed, and things like blindspot warnings, lane departure warnings, collision detection and pedestrian detection can be found in high-end cars from most vendors, though overall penetration is still quite low. It is extensions of these technologies -- combining lane-keeping with ACC that is behind the announcements from several car vendors of their plans to have limited self-driving in highway or stop-and-go situations just a few years from now.

AISIN, a Japanese supplier of advanced in-car technology, described a system I found quite interesting. They have worked hard to make systems for getting more accurate locations for cars. GPS is just not accurate enough or reliable enough for many applications. AISIN's system starts with GPS but uses a map of the road and turning sensors to place the car in specific locations when the car turns. It then counts the stripes on the road combined with the odometer to figure out just how far the car has gone since the last identified turn to get a good handle on where the car is to within a meter or two along the road. Then it does something I discussed a while ago -- shares information about problems with the road. If one car hits a pothole, it uploads the location of the pothole to the cloud. Other cars download it, and when they are approaching the pothole, the car softens the suspension. It also detects positions in on-ramps and off-ramps and tells the automatic transmission to shift differently based on that knowledge.

More benefit from low adoption

These tools might do better if they see what they can do with low adoption. For example, many cars, not just robocars, are gaining sensors to detect other cars and pedestrians for various purposes. If those cars have DSRC radios and transmit their own view of the world, suddenly you don't need to have nearly as much penetration to get safety benefits -- if you can trust the other reports. One car ahead of you might sense several cars around it and tell you about all of them, and suddenly it's like a lot of cars are broadcasting.

This is also true for traffic signals. Each traffic signal should broadcast not just its own timings but those of the signals around it. For close signals, that means you don't need to wire them all up. For more distant signals, each one still needs a transponder in theory, but you could learn about upcoming signals much further away than you could with a direct connection.


Another big theme in the ITS world is traffic management. And they are starting to see the role of automated driving here, even if it's only ACC. To my surprise, 60% of congestion on Japanese highways is caused by "sags." Sags are stretches of highway through a gentle depression, so that the cars go down for a bit and then up for a bit. In gentle sags, the drivers aren't really paying that much attention but they slow down as the up-grade section starts, and this slowdown causes a shockwave back through the traffic and a tie-up. The use of ACC avoids this, because the ACC maintains speed on the upgrade. (On steeper sags, the drivers notice and accelerate when they hit the climb.) This research points to something I have intuitively believed for some time: That robocars will cause major improvements in congestion because they avoid a variety of human driving behaviours. They will not just maintain speed, they won't pause to look at accidents or distractions on the road, and they will perform more orderly merges. And of course they will cause fewer accidents. These together are the major causes of congestion. The other big cause is simply having more demand than there is available roadspace, and I have detailed other solutions for how robocars can solve that.

Congestion currently costs $100B per year and burns 1.9 billion gallons of gasoline. At the conference, it was stated that in a few years this will climb to $130B and 2.5 billion gallons. They hope to solve that with ITS, but robocars will do an even better job.


Hi Brad.
I have been driving from Cleveland to New York City almost every weekend.
I get a feeling of belonging when I am in Manhattan and the crowded streets are filled with cars and taxis with people who drive just like me!

Dean Buonomano makes an interesting point in his book "Brain Bugs". Over 40,000 people per year have been dying in car accidents. Very few people are killed by spiders or snakes. Yet many people are very afraid of these creatures but feel very comfortable behind the wheel of a car.

If they are ever looking for a beta tester for a robot car, count me in. No question I will be much safer.

Best regards.

Aside from the issues of deployment, where if you mandated them in cars today it'd be a decade or more before you had a high enough density that it could possibly make a difference, the big problem I see with V2V communications is the problem of silent failure: So the transponder in my car fails, how do I know, and what's my incentive to get it fixed? Do we deploy some sort of enforcement mechanism, that watches for vehicles that aren't transmitting location and mails them tickets? How widely do we deploy these sensors? What do we do with the crowd carrying pitchforks and torches when one of these verification machines goes bad?

Not to mention the fact that you'll never get the wildlife or the kid chasing a ball into the street to carry a transponder.

You make a good point on security, too: Building an encryption system means nothing if teenagers bored of stealing catalytic converters decide to yank a transponder and drop it in a pothole or put it up in the bridge girders where it'd take a concentrated search to find.

Given that interoperability is an absolute necessity, and that there's no way to force the world to replace the existing infrastructure any time soon, my money's on reading existing traffic signals optically, and simply encoding something in those lights that gives you timing information that may improve traffic flow.

Yes, I have also wondered if it might make sense to encode data in the optical output of traffic lights. While sometimes in close quarters lights of different intersections will be close together, the pulses would tell you which intersection they are for. Data rates might not be super high if you want to read from far away but probably should be enough.

Actually, there were presenters at ITS talking about pedestrians and cyclists carrying small transponders. Not all of them of course, just ones who feel at risk and would like the knowledge that some fraction of cars would work harder to avoid them. The disabled and elderly for example. And kids, given by their parents. Put the here-i-am in a cell phone and you would get wide deployment -- and also lots of privacy nightmares.

The V2V crew, I should have pointed out, have been thinking about the privacy issue but I am not sure they have it solved.

For cell phones to do this, it would be a big battery suck right now (though they could be clever enough to only broadcast when walking near streets.) But even leaving GPS on all day is expensive. There are many other apps that would like that though, so I expect work to be done on making that a lower power function.

With a bit of cleverness you probably could develop a transponder that only transmitted when you were next to roads. If you did, it is possible that parents would buy it for their kids, that's probably the biggest market, though the very safety conscious would eventually buy it too. Parents will buy things they don't really need to assure child safety.

My impression is that the Google cars, and I assume pretty much all the other folks who have autonomous vehicle behaviors are already using video cameras and figuring out which signals go to which lane (and what the state of the signals is.

Heck, since I believe that even this year's Ford Focus is reading street signs now, I have no problem with the notion that you can read highly directional information off of the same cameras that are in place doing LDW and street sign reading. You have to encode the data such that a 30 or 60Hz camera can read it, but that puts it in a place where failure can be easily detected, retrofits are cheaper and easier, and a whole lot of multi-path and positioning problems go away.

Asking pedestrians and cyclists to carry transponders is like asking women to dress more conservatively. And still doesn't address wildlife. I think that V2V will be necessary for relaxing safety requirements, like you might find in cooperative intersection behavior or platooning, but it can only be for relaxing safety requirements, not for providing safety.

I think the V2V folks understand they can only enhance safety. For a robocar, other sensors will always be needed, and for human drivers, they will need to keep their eyes on the road. The V2V thrust is that if they can get high penetration (a big if) then they will prevent some accidents, and preventing some accidents is a worthwhile goal. Of course, some may wish to look at the cost of the system and the number of prevented accidents and calculate a trade-off. The "vision zero" folks of course do not.

Same with the peds. Of course most peds will never carry a transponder. They hope that some (elderly, disabled, kids) might carry them, and that this will reduce accidents. It's hard to see regular people carrying them in any numbers, but it's not impossible to see paranoid parents insisting the kid carry one. After all, 75% of kids get driven to school because of paranoid parents already.

Information can be transmitted through the visible light emitted from the traffic signal with lifi. No need for a radio transmitter.

Yes, the products that have been announced so far from BMW, VW etc. have been products for highway driving and stop-and-go highway traffic driving.

The decision of where to go first is not a slam dunk though. As I have written in my earlier essays, slow driving on streets is much more complex but there is less kinetic energy involved, and the stopping distances are much shorter.

Re: In gentle sags, the drivers aren’t really paying that much attention but they slow down as the up-grade section starts, and this slowdown causes a shockwave back through the traffic and a tie-up. The use of ACC avoids this, because the ACC maintains speed on the upgrade. (On steeper sags, the drivers notice and accelerate when they hit the climb.)

Maintaining speed up hills is the exact opposite I've been told to do to enhance fuel economy. I realize that this wrecks havoc on the flow of traffic, but if every car is doing it, then its effect might be less severe.


Obviously it takes more energy to climb uphill, and if the car downshifts it may use even more. But that energy is stored in the vehicle as potential, and mostly regained when the vehicle goes down again, I would imagine.

If everybody slowed in concert it would not cause a jam I suspect, but what happens is that somebody slows, and the next guy sees him coming up fast so hits the brakes and overcompensates (wasting even more energy -- any braking is a big waste in a non hybrid) and the shockwave goes back.

I was surprised that this was so important in Japan, I don't know if it is as much of a factor here.


According to, driving at a near constant speed on the flat while slowly decelerating on an up-hill is the most efficient.

Here's the relevant section:

56) Drive with load (DWL)

AKA "target driving". Put most simply, this technique is accomplished by choosing a "target" rate of fuel consumption and ensuring you don't fall below it on hills (or in very strong winds, or any conditions which cause load to vary for a given speed).

In other words, you will back off the accelerator and lose speed (possibly also downshifting) as you climb, and gain that speed back on the descent.

It's far more efficient than pressing the accelerator more and more to maintain speed on the way up a hill and then releasing it down the other side.

DWL is how an efficiency minded person can greatly outperform cruise control in hilly terrain.

Obviously the ability to use this technique without adversely affecting other drivers depends on the traffic situation.

As well, fuel economy instrumentation is required to DWL/target drive to the maximum extent, though it can also be done using a vacuum gauge, and to a much lesser extent by the seat of the pants.

While I certainly can see it would be more efficient -- it's always more efficient to go slower on the highway -- I don't think it would be far more efficient, and more to the point, based on the congestion that this causes, it is in fact far less efficient for the total highway if you cause a traffic backup. Slower is better, but stop and go is worse.

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