SARTRE “Road Train” Project: Everything Has Been Figured Out, Except How to Drive

This entry is the latest in a Worldwatch blog series on innovations in the climate and energy world.

This SARTRE at least provides an exit

Have you ever seen The 6th Day? It’s a forgettable Arnold Schwarzenegger movie about human cloning, and the one thing I remember from seeing it a decade ago is that it imagines a future of not just “6th day violations,” but automated cars as well.  I can’t speak to human cloning, but a group of scientists and engineering in Europe is now attempting to move us one step closer to self-driving vehicles.

The Safe Road Trains for the Environment (SARTRE) project, a partnership of companies based in the U.K., Spain, Germany, and Sweden, is tasked with examining the viability of vehicle “platoons” as a method of future highway transport. The concept is relatively simple: a lead truck or bus operated by a professional driver guides a coordinated ‘train’ of cars and other trucks/buses along a highway, sharing the road with vehicles driven manually. Each vehicle in the train would be outfitted with equipment to wirelessly track and mimic the movements of the car in front of it. Cars would have to constantly gauge the distance between themselves and the forward car, as well as that car’s speed and direction, using a combination of cameras, drive-by-wire technology, and car-to-car communication.

Once attached to the train, drivers wouldn’t have to control their cars with hands or feet, leaving them free to safely eat, talk on the phone, and apply makeup—and even to read the newspaper, watch TV, and check email. Drivers would be able to take full control of their cars in an emergency and would be able to signal when they wish to leave the platoon. The program could theoretically be profitable or at least revenue-neutral, as drivers would pay for the convenience and fuel savings that platoons provide.

Does it pass the laugh test?


Let’s say it’s 2025. You pull onto an autobahn or Japanese expressway (because, let’s face it, road trains don’t seem like an American kind of thing) and see a five-car platoon in front of you. You’ve never joined a platoon before but you know that your car is properly equipped and you’re curious. You pull up behind the last car and press the button to notify the platoon operator that you would like to join. You feel your car’s speed adjust to the speed of the convoy as you take your foot off the gas and realize it’s not so different from using cruise control. You know you’re supposed to take your hands off the steering wheel, too, but there’s a turn coming up—can you let go?

Any road train program will face a monumental marketing challenge, far bigger even than China’s proposed straddling bus. It will take a Herculean effort to convince the public that platoons are safe, and one accident early in implementation could scuttle the entire concept. In essence, it will come down to precisely this question: will drivers be able to take the leap of faith to let go of the steering wheel? And even if they are, will the feeling of riding in a platoon, though perhaps disconcerting, be considered worthwhile?

Does it have that WOW factor?


Maybe I’m just a sucker for autonomous driving schemes. I geek out over the lot of them, from Google’s driverless car to the partnership between Volkswagen’s Vehicle Innovation Lab and Stanford University (Go Card!), which recently taught its car how to powerslide.

What does it bring to the table?

A safer, more relaxing commute, with a side of fuel savings.

Properly designed, road trains could make the roads safer by taking human fallibility (at least partially) out of the equation. One U.S. National Highway and Traffic Safety Administration study found that 80 percent of crashes involved driver inattention, while a U.K. Department of Transport study determined that 65 percent of crashes were due entirely, and another 30 percent partially, to drivers.

If it works for cyclists…

Drivers in the platoon would also get to enjoy some downtime while driving, potentially making daily commutes less stressful and/or more productive. And because platooning involves keeping cars closer together than they otherwise safely could be, it would slow the formation of congestion events and speed their dissolution.

Road trains would likely bring environmental and economic benefits as well. Aggressive driving, characterized by speeding and high rates of acceleration and braking, lowers gas mileage by as much as 33 percent at highway speeds. Joining a platoon guarantees that you will be driving in the speed range of highest fuel efficiency, between 55–60 mph, and will be accelerating and decelerating gradually.

Platooning itself comes with its own fuel-efficiency benefits. A 1990s research project by the Partners for Advanced Transit and Highways Program analyzed the fuel savings of platoon driving and found that drag is reduced both with the size of the platoon and the more closely packed the cars can be. The closer the cars get, however, the more complicated controlling the platoon becomes. It is also worth considering that energy would be expended both in the central management of a road train system and the computing power necessary to keep the platoon itself running. This would eat into the fuel savings of a platoon to some degree. The extra energy required per car would decrease with the uptake of platooning, however, and fuel savings would become more significant.

To many, road trains may seem like a pie-in-the-sky alternative to public transportation, which is a proven way to save energy and transport large groups of people over long distances. Platoons have two significant advantages, however. First, while they may require years of research (with all the investment that entails), platoons would have nowhere near the development cost of public transportation infrastructure. They would require no significant infrastructure improvements and could operate on many existing highways. Second, road trains would allow drivers to drive straight to their destination, a very important consideration for many who eschew existing commuter rail or bus systems.

How close is it to commercialization?


The SARTRE development teams tested their road train systems outside a simulator for the first time this past month, with a single car following a lead truck. The test went well, but it was done in a very controlled environment on the Volvo Proving Ground.

Everyone agrees it will be at least 10 years, and probably much longer, before platoons are on public highways. Myriad technical issues obviously need to be resolved in terms of how the road train would operate, how it would interact with other vehicles on the road, how to ensure that proper back-up systems are in place, and how to design emergency procedures to give drivers full control of their cars when appropriate. But even more importantly, preventing panicked drivers from making matters worse will be a significant challenge.

How scalable is it?

Eventually, quite.

Even once road trains begin operating, it will be a while before they can capture a large customer base. Upgrading existing cars will likely be financially prohibitive, and adding in the necessary equipment would add noticeably to the cost of new cars as well. This, combined with inevitable public skepticism of platooning, would mean that any company (or government) initiating a road train scheme would have to expect a long period of low usage. But there are no technical barriers to widespread use of platoons, save for the need for multi-lane highways.

What is the biggest obstacle to success?

Redefining the rules of the road.

Let’s set aside the many significant technical hurdles for a moment. The bigger challenge may be making road trains work in the real world. The existing rules of the road have been crafted and tweaked over the long life of the automobile, updated to reflect inventions and innovations such as turn signals, headlights, cell phones, and HOV lanes.  But to incorporate something as alien as a road train into both the legal framework of the road system and the collective understanding of proper driving technique will require a more significant overhaul. The presence of platoons would likely frighten many drivers, and it would be a struggle to establish new norms.

It is easy to think of ways in which the presence of road trains would alter the road environment. Merging onto highways and negotiating exits would become more challenging. Also, how would a platoon deal with a car traveling significantly below the speed limit in its lane? Presumably a platoon could never change lanes, so it would be stuck. Minimum speeds might need to be more strictly enforced on roads with platoons. Vehicles not joining the platoon would also presumably need to stay farther behind a platoon than would normally be the case, to allow other cars to join the platoon from the rear. This might need to be codified in some way as well.

The final word(s):

It sounds good now…

In the abstract, it sounds like a great idea. Though many might rather see money invested in public transportation, the R&D budget associated with a project like SARTRE is small potatoes compared with developing new infrastructure, and it by no means precludes new public transit funds.

The bigger issue is that we are only starting to understand how drivers would behave in and around platoons. Recent SARTRE research using simulators found that drivers on average felt uncomfortable at nearly 17 meters behind the car in front of them in a platoon and pressed an emergency button to immediately dissolve the platoon at 7.5 meters. When asked to rate their own comfort subjectively, however, 73 percent said a 10 meter distance was adequate, and 55 percent said the same for 7.5 meters. Clearly visualizing a platoon and actually being in one are not the same. So the question remains: when the time comes, will you be able to let go?

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