Are Driverless Cars the Answer? Putting Your Car On A Diet

Many people anticipate that Driverless Cars are the future of transportation.

In subsequent posts I’ll describe my joyous experiences with the autopilot features in my Tesla Model S. And of course the joys of never stopping at a gas station, or needing an oil change. Suddenly, highway driving is almost relaxing, instead of being an exhausting challenge. So don’t get me wrong; driverless cars are an excellent innovation and a good start.

However, I believe we need to go far beyond just Driverless Cars, and fast.

My friend David got me started thinking about the potential advantages of Autonomous Vehicles almost a decade ago. We investigated how efficient they could be. My conclusion was that although Autonomous Vehicles could potentially improve transportation efficiency by a factor of 3-5, that wasn’t enough. Instead the number of trips would increase so much it could potentially require even more energy overall. That’s when I started looking for better alternatives.

To help visualize the changes we’ll be talking about, here’s a sketch of a typical car, with the major sub-systems identified, and the 4,000 pound weight.

So let’s start with the potential efficiency benefits of fully Autonomous Automobiles.

Obviously, we could get rid of the expensive controls and displays, which would make the passenger compartment more comfortable, reduce the weight somewhat, and save a lot of money. But Autonomous Vehicles require extensive sensors and all the control systems to integrate them into safe navigation. So we might achieve a weight advantage, but not necessarily much of a cost advantage.

One potential source of efficiency for Autonomous Vehicles is improved traffic flow. They can safely travel closer to each other, and at higher speeds than human-driven vehicles. That could substantially increase the capacity of highways. Autonomous Vehicles could coordinate among each other, speeding flow through intersections. In cities and even in suburbs, we could experience faster travel due both to higher speed limits, and to eliminating stops and congestion. Reducing stops significantly improves fuel efficiency, except possibly for hybrids.

Unfortunately, those advantages aren’t attainable if there are human driven vehicles around. Let’s ignore that for the moment and see what we could achieve because Autonomous Vehicles don’t crash – I’ll address the problem of human-driven vehicles crashing into them in the next posts.

If there are no crashes, we could remove all of the safety equipment: airbags, safety belts, bumpers, crumple zones, heavy frame, reinforced doors and roof, and heavy seats. This is a significant fraction of the weight and cost of a car.

Having removed all that weight, we can get by with a smaller engine and drive train. Now we can get by with a lighter suspension system and tires. This is a virtuous cycle: reducing weight in one component allows us to make other components lighter. In the next figure I’ve guesstimated these weight savings at about 80%, but as you’ll see, this intermediate result does not need to be precise.

Perhaps you start to see why some of the new cars on the road are so tiny – perhaps you thought it was just a fad.

Next we’ll see how much going to electric motors helps.