Courtesy of Ricardo UK Ltd

Road trains — semi-autonomous highway platoons — recently completed a promising trial, but questions remain.

It's nearly at the point where using the word futuristic to describe autonomous cars verges on journalistic irresponsibility. Earlier this month the famous self-driving Google car received a (self-) driver's license from the state of Nevada. Computer scientists are cooking up ways for driverless cars to navigate busy driverless intersections. And last week the "road train" — a semi-autonomous highway platoon that follows the movements of a human-driven lead car — made a promising debut outside Barcelona.

The successful trial was conducted by the Sartre project, short for Safe Road Trains for the Environment. The five-car road train consisted of a lead truck followed by an autonomous truck and three Volvo sedans. (Volvo is a partner in Sartre.) The convoy traveled about 125 miles outside the city at speeds around 53 miles per hour while keeping a uniform 20-foot following distance between vehicles.  It was the first time a road train had operated on a public highway being used by other motorists:

A road train uses a combination of existing car sensors (radar, lasers, and cameras embedded in safety features) and wireless communication to stitch together a vehicle convoy up to 15 cars long. The cars follow the acceleration, braking, and turning maneuvers of a lead vehicle — call it a conductor car — driven by a professional driver. Meanwhile each vehicle monitors surrounding traffic and converses with the others to ensure a smooth, safe passage.

Once drivers find a road train through their navigation system, they can join it so long as their vehicle is equipped with the convoy's software program. Cars that join the train become autonomous until drivers manually detach from it near their destination. The main advantage of the concept, of course, is that drivers can do whatever they'd like while their car is part of the train: eat, read, talk on the phone — maybe even join the road train club, if the mood strikes.

The Sartre project has been going on for three years. During that time it's logged some 6,200 test miles. Among the project's main goals are reducing congestion (by limiting human traffic errors) as well as fuel consumption (by limiting air drag through close following distances). While fully autonomous cars may require expensive physical improvements — not to mention infrastructure changes — Sartre says participation in a road trains requires only modest upgrades to a car's software system and wireless communication network.

In a statement, project director Tom Robinson of Ricardo, another Sartre partner, called the concept an "improved driving experience." That's a bit of a misnomer, as Wired points out, but it wouldn't be far off to call road trains an improved commuting experience. Behavioral research tells us beyond a doubt that commuting is one of the least pleasurable parts of the average person's day. While road trains wouldn't make for a healthier commute from a physical standpoint, they might make for a less stressful one.

But the quality-of-life question is easier to answer here than the quality of urban mobility one. The folks at Sartre see the road train as the ultimate transportation compromise: the independent flexibility of a car with the efficiency of mass transit. Their online literature doesn't address the problems that auto-dependency and single-occupancy vehicles create for cities. Road trains may handle the highway part of the commute; they don't alleviate street congestion or driver-stress within the city itself.

Still other questions remain. Some of the obvious ones involve the conductor car. Accepting that road trains will decrease congestion and fuel consumption, will those savings significantly offset the increases made by lead vehicles, which wouldn't otherwise be on the road? And who would provide conductor cars anyway? The obvious candidate is an employer: but if a company is willing to send drivers into the suburbs to herd employees into the city, why not just carry them back in a luxury bus?

These are the types of things we should consider sooner than later, because later isn't as far off as it used to be.

Inset image courtesy of Volvo Car Corporation.

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