It’s deja vu all over again, reading Alex Steffen’s The future of cars is slow in Medium. He is looking at the future of the self-driving car, or autonomous vehicle (AV) and makes some good points, concluding that The optimal speed for a self-driving car is slow.
This is a point discussed on TreeHugger years ago, long before AVs were much more than science fiction. At a time when people were talking about slow food and slow travel, I proposed slow cars very much like the post-war Isettas, (which kind of look like Google cars) suggesting that it would save fuel, that they would be smaller and lighter (lower impact standards), would reduce wear on bridges and infrastructure, and promote innovation in urban design. I wrote:
Perhaps, like the slow food movement, we need a slow car movement, a radical lowering of the speed limit so that the private car can survive in an era of peak oil and global warming, simply by being smaller and slower. We don't need hydrogen cars and new technology, we just need better, smaller designs, lower speed limits and no big SUVs on the road to squish them.
I did not anticipate the move to electric cars, and most importantly, the impact of the AV, which changes everything. As Alex notes, slow cars are a lot safer.
The danger drivers pose to pedestrians, other drivers and themselves is largely a function of how fast their vehicle is traveling. An eighteen wheeler nudging you gently at 1 foot per minute is an inconvenience; one hitting you at 45 miles per hour is probably a death sentence.
I wouldn’t have used the 18 wheeler as an example; research by Brian Tefft of the AAA foundation for traffic Safety shows the direct correlation between speed and death rate. On Pro-Publica they built a great interactive graph that shows the difference a few MPH can make. And the effect of speed is far more pronounced among older people.
Alex also mentions reaction time and stopping distance, as TreeHugger did in More reasons why twenty is plenty (or 30 is enough for metric types).
He digs up some interesting research in favour of slow speeds:
It’s been demonstrated that lowering speed limits in urban areas can actually move more vehicles more smoothly through a city’s streets. Slow-moving cars can actually increase capacity.
This is due to reaction times; slow cars can follow the car in front more closely. His linked study notes that “The capacity of a given lane depends on the time-intervals between successive vehicles. The slower the leading car drives in front of a queue, the closer follows the next car.”
AVs can follow even more closely, moving even more cars. And since it is likely that they will not need stop signs or perhaps even traffic lights, they will get you there in less time even though they are slower.
I have perhaps two points of disagreement with Alex; He suggests that driverless cars are best in compact cities noting “The travel-time difference between 20 and 45 m.p.h. doesn’t really matter much when you’re going a mile.” In fact, studies show that in the UK, 78 percent of trips of less than a mile are done by walking, and a third of trips less than five miles. So perhaps investment in making walking safer and easier would be wiser, and perhaps AVs are not really needed in a compact urban environment. (But slower cars sure would be nice for that)
He also suggests that “driverless cars will disadvantage the suburbs, not save them.” I really disagree with that; if you can sit back in your AV with an iPad and a martini, who cares if it is slow. And the average commute in the San Fernando Valley now travels at 17 MPH; it won’t take any longer in a slow car.
But I totally concur with his conclusion:
Smart streets in future cities — it looks to me — will likely be built not for hurtling suburban SUVs but for happy people and the slow robots that take them where they want to go.