Driverless cars are somewhat in the news this year, with Ford investing $1bn to meet their objective of launching a fleet of autonomous cars in 2021. Coincidentally, the July 2017 issue of 'Scientific American' features an article extolling the virtues of a driverless future in modern cities. The article is written by Carlo Ratti and Assaf Biderman, who work for something called the 'Senseable Lab' at the Massachusetts Institute of Technology.
A number of the claims made in the article are worth reviewing. Let's start with the following:
"On average, cars sit idle 96 percent of the time. That makes them ideal candidates for the sharing economy...The potential to reduce congestion is enormous...'Your' car could give you a lift to work in the morning and then, rather than sitting in a parking lot, give a lift to someone else in your family - or to anyone else in your neighbourhood or social media community...a city might get by with just 20 percent the number of cars now in use...fewer cars might also mean shorter travel times, less congestion and a smaller environmental impact."
A number of thoughts occur in response to these claims:
1) Ride-sharing would reduce the number of cars, not the number of journeys. Every journey which currently takes place would still take place, but in addition would be all the journeys made when a car needs to travel from the point where one passenger disembarks to the point where the next embarks. At present, each journey contains a passenger; with the proposed ride-sharing of driverless cars, there would be additional journeys in which the cars contain no passengers at all. All other things being equal, that would increase congestion and pollution, not reduce it.
2) The modern technological world, including the GPUs and artificial neural networks which have created the possibility of driverless vehicles, has been built upon the wealth of a capitalist economy. Such an economy is driven by, amongst other things, the incentivization of private ownership. In particular, people like owning their own cars. It's not clear why a technological development alone, such as that of the driverless car, will prompt society to adopt a new model of shared ownership.
3) Not everyone lives in cities. Universities tend to be located in cities, hence many academics fall into the habit of thinking that everyone lives and works in cities. Many people live outside cities, and drive into them to their places of work. They drive into the cities from different places at the same time each morning. For such people, there needs to be a one-to-one correspondence between cars and passengers.
4) People like the convenience and efficacy of having a car parked adjacent to their home or place of work. If you're a parent, and your child falls ill at home, or there's an accident at school, you want to drive there immediately, not wait for a shared resource to arrive.
5) If cars are constantly in use, their components will degrade in a shorter period of time, so maintenance costs will greater, and the environmental impact of manufacturing new tyres, batteries etc. will be greater.
So that's just for starters. What else do our MIT friends have to say? Well, they next claim that "vacant parking lots could be converted to offer shared public amenities such as playgrounds, cafes, fitness trails and bike lanes."
Unfortunately, most car parks are privately owned, either by retail outlets or employers. If they become redundant, then those private companies will either extend their existing office space or floor space, or sell to the highest bidder. Car-parks are unlikely to become playgrounds.
The authors then claim that current traffic-light controlled intersections could be managed in the style of air traffic control systems:
"On approaching an intersection, a vehicle would automatically contact a traffic-management system to request access. It would then be assigned an individualized time, or 'slot', to pass through the intersection.
"Slot-based intersections could significantly reduce queues and delays...Analyses show that systems assigning slots in real time could allow twice as many vehicles to cross an intersection in the same amount of time as traffic lights usually do...Travel and waiting times would drop; fuel-consumption would go down; and less stop-and-go traffic would mean less air pollution."
Sadly, this is a concept which seems to imagine that cities consist of grids of multi-lane highways. Most cities in the world don't. And in every city, the following 'min-max' principle of road-capacity applies:
For a sequence of interconnected roads, given the capacity (i.e., the maximum flow-rate) in each component, the capacity of the entire sequence is the minimum of those individual capacities.
Hence, even if the capacity of every multi-lane intersection in a city is doubled, the capacity of a linked sequence is determined by the component with the lowest capacity. In many cities, multi-lane highways taper into single-lane roads, and it is the single-lane roads which limit the overall capacity. Doubling the capacity of intersections would merely change the spatial distribution of the queues.
So, all in all, not a positive advert for driverless cars.
One quibble: Indeed, doubling the capacity of intersections may not increase the capacity of the system. However, it would decrease journey times and prevent inefficient fluctuations in speed. I think this is the point they are making.
ReplyDeleteEliminating queues at traffic lights, and the dead time which occurs when the flow from one direction has been stopped by a red light, but the flow in another direction hasn't received a green light, would eliminate one type of inefficiency.
ReplyDeleteHowever, the result is that you deliver the cars more quickly to the other limiting points in the system capacity, so the queues and the delays are longer at those points. It wouldn't necessarily decrease journey time.
The benefits of self-driving vehicles will vary depending on the type of location. It's most likely that the biggest benefits will occur in cities, so your arguments about less-populated areas don't really apply.
ReplyDelete> People like the convenience and efficacy of having a car parked adjacent to their home or place of work.
Not in a city. Many people in large cities forgo their own car because it's a lot of trouble to find parking at your destination, and when you do find parking, it costs you $$$, and you also would probably pay $200 or so for the privilege of parking at your apartment.
Also, when buying a car you necessarily have to compromise between the small car you'd use every day, versus the SUV you use once in a while for that skiing trip or hardware store. It would be more appropriate to choose a vehicle that is better sized for that particular journey.
> 5) If cars are constantly in use, their components will degrade in a shorter period of time, so maintenance costs will greater, and the environmental impact of manufacturing new tyres, batteries etc. will be greater.
That doesn't follow. The components may degrade faster, but not faster-per-passenger-mile. Maintenance costs will not be greater.
1) Ride-sharing would reduce the number of cars, not the number of journeys.
All other things being equal, that would increase congestion and pollution, not reduce it.
Self-driving cars could improve things beyond just pure journey counts. For example, often in cities we lose two lanes of traffic due to on-street parking, but usually some idiot is double-parked with their flashers on because they are waiting for someone. Self-driving cars could make more efficient use of the roads we already have, for example by avoiding stopping in an intersection (avoiding gridlock), reversing travel direction of one-way streets, better signal management. These things are not necessarily functions of the self-driving vehicle. Blocking intersections is illegal, but rarely are people cited for it. So, that is a case where enforcement is too costly for the benefit. Coding the desired behavior into self-driving vehicle software would improve compliance.
With respect to Automated Intersections, Peter Stone's group at UT Austin has done a significant amount of research on this topic and I encourage you to read his papers:
http://www.cs.utexas.edu/~aim/
"It's most likely that the biggest benefits will occur in cities, so your arguments about less-populated areas don't really apply."
ReplyDeleteMy arguments were not about less populated areas, they were about the fact that many people drive in and out of cities to and from their place of work, so the arguments do apply.
"The components may degrade faster, but not faster-per-passenger-mile. Maintenance costs will not be greater."
That conflates driverless cars with ride-sharing. With driverless cars there would be less cars, but more journeys, hence components would degrade faster, and without ride-sharing they would degrade faster per passenger-mile.
Driverless cars do not entail ride-sharing. Conversely, ride-sharing of taxis is already feasible without driverless cars. The Scientific American article draws attention to a study which concludes that taxi sharing in New York would reduce the number of cars by 40%. The fact this hasn't happened suggests that people generally don't want to ride-share. That would still apply with driverless cars.