It was revealed earlier this month that NHTSA wishes to mandate vehicle to vehicle radios in all cars. I have written extensively on the issues around this and regular readers will know I am a skeptic of this plan. This is not to say that I don't think that V2V would not be useful for robocars and regular cars. Rather, I believe that its benefits are marginal when it comes to the real problems, and for the amount of money that must be spent, there are better ways to spend it. In addition, I think that similar technology can and will evolve organically, without a government mandate, or with a very minimal one. Indeed, I think that technology produced without a mandate or pre-set standards will actually be superior, cheaper and be deployed far more quickly than the proposed approach.

The new radio protocol, known as DSRC, is a point-to-point wifi style radio protocol for cars and roadside equipment. There are many applications. Some are "V2V" which means cars report what they are doing to other cars. This includes reporting one's position tracklog and speed, as well as events like hitting the brakes or flashing a turn signal. Cars can use this to track where other cars are, and warn of potential collisions, even with cars you can't see directly. Infrastructure can use it to measure traffic.

The second class of applications are "V2I" which means a car talks to the road. This can be used to know traffic light states and timings, get warnings of construction zones and hazards, implement tolling and congestion charging, and measure traffic.

This will be accomplished by installing a V2V module in every new car which includes the radio, a connection to car information and GPS data. This needs to be tamper-proof, sealed equipment and must have digital certificates to prove to other cars it is authentic and generated only by authorized equipment.

Robocars will of course use it. Any extra data is good, and the cost of integrating this into a robocar is comparatively small. The questions revolve around its use in ordinary cars. Robocars, however, can never rely on it. They must be be fully safe enough based on just their sensors, since you can't expect every car, child or deer to have a transponder, ever.

One issue of concern is the timeline for this technology, which will look something like this:

1. If they're lucky, NHTSA will get this mandate in 2015, and stop the FCC from reclaiming the currently allocated spectrum.
2. Car designers will start designing the tech into new models, however they will not ship until the 2019 or 2020 model years.
3. By 2022, the 2015 designed technology will be seriously obsolete, and new standards will be written, which will ship in 2027.
4. New cars will come equipped with the technology. About 12 million new cars are sold per year.
5. By 2030, about half of all cars have the technology, and so it works in 25% of accidents. 3/4 of those will have the obsolete 2015 technology or need a field-upgrade. The rest will have soon to be obsolete 2022 technology. Most cars also have forward collision warning by this point, so V2V is only providing extra information in a tiny fraction of the 25% of accidents.
6. By 2040 almost all cars have the technology, though most will have older versions. Still, 5-10% of cars do not have the technology unless a mandate demands retrofit. Some cars have the equipment but it is broken.

Because of the quadratic network effect, in 2030 when half of cars have the technology, only 25% of car interactions will be make use of it, since both cars must have it. (The number is, to be fair, somewhat higher as new cars drive more than old cars.)

Forms of Connected Car

There are 3 other ways I have proposed for moving data to and from a car. These are:

1. The mobile data networks -- 4G today, and some "5G" form in the 2020s. This is already widely deployed in cars (and basic mobile connections are mandated in all cars in some locations for emergency services.) These are very widespread and are being developed without any demand from the automotive sector. In addition, protocols could be established for low-latency "urgent" messages on the mobile data networks, either relayed to other clients or to the global network.
2. A special stream on an ATSC-M (Digital TV for Mobile) spectrum, allocated from a local TV channel, combined with the mobile data networks which act both as a backup, and a means to send information to the network for broadcast in the stream. This stream would report all traffic signal timings, traffic data and special events seen by cars on the road.
3. A point-to-point protocol built into cell phones (Ph2Ph,) said phones either simply carried by drivers, or slotted into a standardized holder in the cars. Cell phone generations are less than 2 years, and volumes dwarf car sales, allowing a rapid pattern of innovation. Expect tech in smartphones to be 10-20 years ahead of tech in cars, based on past history.

To contrast DSRC with these other methods, the following factors stand out:

• DSRC and Ph2Ph offer low latency, the mobile data network offers the risk of high latency.
• As part of cars, generations are long and the innovation cycle is slow. To match other technologies, the DSRC module must be built so that frequent field replacement is the norm. That's expensive and not usual thinking in the car world.
• DSRC provides a mostly line-of-sight protocol. The 5.8ghz signals are capable of going around corners and vehicles, but less reliably. ATSC-M is a long-wave protocol that goes through buildings and transmits with very high power. The mobile data protocols are a middle-ground but the infrastructure is so widespread and market forces so strong that it's available everywhere as well.
• DSRC and Ph2Ph would be able to do V2V even out in rural areas where there is no digital TV or mobile data
• As a dedicated safety protocol, DSRC is likely to use more reliable equipment
• The centralized ATSC-M approach fails for everybody if the TV station goes down. This can be mitigated somewhat with backup TV-station availability, as well as use of the mobile data networks as a more expensive backup.
• The introduction of a low-latency protocol into mobile networks combined with ATSC-M could provide for a broadcast protocol of low latency and high penetration
• Reworking the 500,000 US signalized intersections for DSRC is a very expensive proposition for which there is no money available. Many traffic signals already report their data back to HQ over mobile data modems with longer latency, and modifying older signals to do this is comparatively inexpensive. DSRC antennas must be put high for line-of-sight, but mobile data modems can be put anywhere there is cell signal.
• Mobile data equipment is already present in many cars, and will continue to be, and it's also in all phones. ATSC-M is not yet present but as a consumer technology it is quite cheap. Even $150 TV sets have ATSC decoders.
• Mobile phones can do all the methods. They could do a DSRC-like protocol to cars and other phones. They all have mobile data. Many will also integrate ATSC-M as it becomes available to let you watch TV on your phone.

Unlike the DSRC timeline above, a timeline for Ph2Ph might look like this:

1. In 2014, the FCC and NHTSA together announce that the DSRC band will be open to unlicenced use, provided all mobile handsets which use it support a Ph2PH protocol
2. In 2015, phone chip designs start supporting this protocol
3. In 2017, new smartphones all support the new band and protocol
4. In 2019, most people have a device supporting the protocol and carry it with them everywhere they drive, walk or bicycle. (Though in the latter cases, battery life restricts use moderately.)
5. In 2020, 90% of cars are talking Ph2Ph. New versions of the protocols are being deployed and will spread within 2 years. Meanwhile, on the DSRC timeline, the first cars are now being sold with the technology.

It should be noted that without an authenticated GPS in the phone (as tall an order as authenticated V2V,) messages from phones would be informational only and not to be trusted.

Do we need the latency and reliability?

DSRC's main advantages are latency and reliability, but its main disadvantage is non-deployment. So the question becomes, just how important is the low latency.

The answer, surprisingly, is not that much.

• Traffic signals never change instantaneously. They always know they will change with a few seconds notice, even when doing a change due to an emergency vehicle.
• Hidden stalled cars are there for many minutes, low latency would only be needed when the car is in the process of stopping. In that case, sensors will reveal this and are a better choice.
• Hidden cars running red lights (one of the prime applications for DSRC) may still not be detected due to lack of line-of-sight. Cameras on the lights themselves may do a better job (and can turn the light red for all cars, not just those with radios.) The short 100ms latency of DSRC is superior here, but the 500ms latency of a low-latency mobile data plus ATSC protocol is not much different, and even the 2 second latency of mobile data will catch most problems.

Curiously, reliability, while seen as a "motherhood" issue may be a distraction as well. Because DSRC doesn't work at all if the car is not equipped with it, it turns out that a 99.9% reliable system found only in 50% of cars is not as good as a 95% reliable system found in 90% of cars. The latter actually helps in more events.

I think the right answer is to put everything into mobile phones, and start establishing a generalized rough standard for a mobile dock. The mobile dock would be a simple slot featuring wireless charging and a secured data channel to the car to receive information from the car like speed, brake and turn signals. For security reasons, the phone would not be able to control the car (like hit the brakes) but it could give alerts to the driver to do so. The dock could either be in the ceiling (for best antenna visibility) or it could be lower if there is a way to boost the external antenna signal with an analog signal booster that works over all present and likely future bands. This hardware, should it exist, should be modular so it can be replaced as mobile phone and radio standards change, but it would of course include the DSRC bands, wifi bands, mobile bands and ATSC bands.

Will it work?

All this discussion presumes that V2V can be made to work. Unfortuantely, there are still many unresolved issues:

• DSRC still need to sync up, which can cause latency and range issues, and it is still mostly line-of-sight
• GPS simply isn't reliable enough to tell what lane a car is in, or if it's on the shoulder or in a lane, or if it's on a bridge or on the road. V2V planners hope to fix that with maps and tracking the history of GPS readings.
• People might lie to you, so the protocol has to be secured, with a certificate system and a certificate revocation system -- something challenging in a protocol meant to work offline. We have not managed to properly secure TLS on the web in 20 years, so having cars do it is a tall order.
• Further of that, it is suggested a popular application for a pirate V2V radio would be to tell all cars ahead of you there is an obstacle in their lane, so they all change lanes and get out of your way. (Though some might brake, defeating the purpose.)

So what is it good for?

There are a few applications that make sense, but they aren't always the ones talked about.

• Some V2I technology is already used for toll collection and for management of congestion charging. Because all cars in Singapore have such a system, you can usually pay at parking lots with it as well.
• Robocars could eventually use it (decades from now) to cooperate on the road to pack the roads more densely.
• It has been tested to do cooperative adaptive cruise control, to keep vehicles more in sync.