Take the Road Train, Revisited

I’ve written here before about some of the work being done to develop “self-driving” cars, including Google’s tests of a fully-autonomous vehicle, and Volvo’s work on developing “road trains”, essentially convoys of semi-autonomous vehicles that follow a lead vehicle with a human driver.  Volvo’s  work is part of the European Union’s Project SARTRE (Safe Road Trains for the Environment).

The New Scientist site has an article reporting on a recent demonstration of the road train technology.  This approach probably has the higher likelihood of practical application in the near term, because it is largely based on technology that is already present, at least in some high-end cars.

Almost all the sensors and actuators that keep me from flying off the road now come as standard in most new Volvos (and other manufacturers for that matter). They are the exact same ones that enable cars to stay in lanes and avoid hitting other cars and pedestrians.

In contrast, completely autonomous cars, like those being tested by Google, require a considerable amount of added equipment to function.

Both approaches have the potential to provide significant improvements in safety.  The autonomous “driver” will not drive while sleepy or intoxicated; nor will it be distracted by sightseeing, fiddling with a cell phone, or turning around to smack the kid in the back seat.  An automatic system can also react more quickly than a human driver.

That faster reaction time means, in practice, that cars, particularly in a road train system, can follow one another much closer than would be safe or legal with a human driver  .  In the test reported in the article, the following distance at a speed of 90 km/hour [56 mph] was about 6 meters [19.7 feet].  By comparison, with a driver reaction time of 500 milliseconds, about 80 feet of additional separation would be needed at the same speed.  Putting vehicles closer together, with fewer speed fluctuations, should help reduce road congestion.  Obviously, all this assumes that the lead driver is highly competent.

The ability to follow other vehicles more  closely also might improve fuel economy, by the phenomenon that cyclists everywhere know as “drafting”.  As speed increases, the amount of power required just to overcome air resistance increases as the third power of the vehicle’s relative air speed (that is, taking into account any head- or tail-wind).   At a speed of 15 mph on level ground, for example, most of a cyclist’s power is used just to make a hole in the air. [Source: Bicycling Science, 2nd Edition, by Frank R. Whitt and David G. Wilson; Cambridge MA: MIT Press, 1997].  The effect is not so pronounced for cars, since they are typically more streamlined (that is, have a lower drag coefficient), but it is still significant.

Vehicles driving in such tight formations with fewer speed fluctuations should dramatically reduce congestion, says Erik Coelingh, Volvo’s senior technical specialist who is heading the research near Gothenburg. The reduction in drag could potentially cut fuel consumption by as much as 20 per cent, he says.

The technology is certainly interesting, and seems to have a good deal of potential.  Whether the legal and cultural obstacles to its adoption can be overcome remains to be seen.

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