Proponents of driverless cars often suggest the technology will make all sorts of significant changes to transport. Gone will be car ownership with people just hiring a car when they need one, like taxi’s only easier and cheaper. As such they say gone too will be the need for public transport, especially when you take away some of the benefits PT currently has like being able to do other things such as work, read, use a phone or even sleep. Further congestion will also be a thing of the past with these smart vehicles able to better work together rather than the randomness of humans. Of course the biggest and likely most accurate prediction will be safety as for a start these cars will obey the road rules so no speeding, no running red lights or any of the other bad habits human drivers have.
That all sounds wonderful however an article from CityLab highlights research showing that at least for some time driverless cars could actually make things worse on the roads.
A new simulation-based study of driverless cars questions how well these two big secondary benefits—less traffic and more comfort—can coexist. Trains are conducive to productivity in large part because they aren’t as jerky as cars. But if driverless cars mimic the acceleration and deceleration of trains, speeding up and slowing down more smoothly for the rider’s sake, they might sacrifice much of their ability to relieve traffic in the process.
“Acceleration has big impacts on congestion at intersections because it describes how quickly a vehicle begins to move,” Scott Le Vine of Imperial College London, who led the research, tells CityLab via email. “Think about being stuck behind an 18-wheeler when the light turns green. It accelerates very slowly, which means that you’re delayed much more than if you were behind a car that accelerated quickly.”
For their study, Le Vine and colleagues simulated traffic at a basic four-way urban intersection where 25 percent of the vehicles were driverless and the rest were standard. In some scenarios, the driverless cars accelerated and decelerated the way that light rail trains do—more comfortable than, say, riding in a taxi, but still a little jerky at times. In other scenarios, the cars started and stopped with the premium smoothness of high-speed rail.
Within these broad scenarios the researchers also tested alternatives that reduced speeds but improved smoothness, such as longer yellow lights or following distances. All told they modeled 16 scenarios against a baseline with all human-driven cars. The researchers then ran each simulation for an hour, repeated it 100 times, and calculated the average impact that scenario had in terms of traffic delay and road capacity.
In every single test scenario, driverless cars designed to create a comfortable, rail-style ride made congestion worse than it would have been in a baseline scenario with people behind every wheel.
So cars with fast acceleration and deceleration are obviously easy to make but that’s not what people are likely to want if you’re also trying to do some of the other activities mentioned earlier. Regardless traffic generally moves at the pace of the slowest vehicles so all it takes is one slow driver or driverless vehicle and many others will be slowed down too. I bet they won’t say that in the marketing brochures.
I suspect this isn’t the only aspect of driverless cars that could create congestion. As an example the driverless taxi model that most people say will happen, is likely to result in a lot more vehicle movements as cars reposition themselves to pick up additional fares. That means that where roads are generally congested in one direction only, with driverless cars congestion could occur in both directions.