Autonomous vehicles and urban mobility

A discussion of the potential impacts of autonomous vehicles on urban transport.

There has been much written about Google, Inc’s recently announced forays into autonomous vehicles, including the recent decision by the Legislature there to legalize operation of the vehicles. While Google’s efforts are still in the experimental stage, they appear to represent a significant advance in the state of the art, and have inspired much discussion on What It All Means for urban mobility in the future.

Some transit critics see the autonomous vehicle, whether privately owned or operated as driverless taxis, as displacing public transit–Randall O’Toole was quick to predict that the technology would make rail transit obsolete. Others see it as providing transit an opportunity to expand its operations. While it’s too soon to make any firm predictions, it’s an interesting subject to discuss.
Railroads and automatic operation

In ground-based transportation, use of automated or centralized systems to assist with vehicle operation has long been most prevalent on the railroads. Trains, especially long freight trains, have long had a fundamental safety issue: the safe stopping distance frequently exceeds the driver’s line of sight. This is true both because of the length and weight of many consists, and due to the low coefficient of friction between rails and wheel. Unlike road-based vehicles, which can more or less proceed safely based on local observation, trains cannot safely operate at speed in this manner.

The earliest way of preventing train collisions was a simple one: the timetable. In addition to the other benefits of scheduled service, railroad schedules ensured that no more than one train would be in the same section of track at a time. Other crude signalling mechanisms, such as explosive charges deposited on the rails, were employed to deal with breakdowns and such. Track reservation by timetable was highly unreliable–accidents were common–and inefficient.

As technology improved, mechanical and later electric wayside signals were developed to permit finer-grained mutual exclusion of train segments. As communication technologies improved, central monitoring of signalling (and centralized operation of switches) became commonplace. Many freight systems, and much of MAX, use a modern version of this approach known as Automatic Block Signalling. In addition, MAX trains are equipped with safety devices which will stop trains that attempt to proceed past a red signal, for example. (MAX FAQs is a great resource for those wondering about MAX signalling).

ABS has its limitations, however, and some railroads go further and deploy more advanced command and control technologies, which go by such names as Automatic Train Control (which replaces wayside signals with cab signalling, and the fixed blocks of ABS with continuously-moving blocks around trains) and Positive Train Control (think of it as automated air traffic control for railroads).

None of the above technologies replace the train engineer, however. A few transit systems have gone further and implemented various types of Automatic Train Operation, which takes over some or all of the duties of the driver. In systems such as the Washington Metro (which featured automatic operation until the 2009 accident that killed 9 people), ATO was used as a capacity-enhancement measure and only during rush hour; drivers are present on the trains at all times. Vancouver’s SkyTrain, on the other hand is completely driverless; under normal circumstances there are no crew members aboard. SkyTrain vehicles even lack cabs; passengers may sit in the trains’ nose should the choose.

Both the Metro and SkyTrain’s ATO systems are limited in many fundamental ways, however. They lack the capability to detect obstacles (or potential obstacles) on the track, and thus require segregated rights-of-way. (Both use third-rail power, as well; making the tracks unsafe for trespassers even if no train is around). And neither is capable of autonomous operation–both require constant communication with the ATC system.

Autonomous operations

An important detail of the technology being developed by Google is that it is autonomous; Google’s driverless cars do not require any special infrastructure outside the car, other than ubiquitous services such as GPS. Cameras and other sensors, backed by complex image processing, detect the location of the pavement, the presence of obstacles or other vehicles, traffic control devices, and such–the onboard control system functions much as a human driver would. More reliable interfaces are possible, such as car-to-car and car-to-signal communications, but these aren’t required for operation–the autonomous cars can navigate ordinary roads.

Some have suggested that assuming the technology becomes widely available, that the importance of public transit (specifically, large vehicles like busses or trains designed to carry dozens or hundreds of passengers) will be diminished. To test that claim, it is useful to examine the disdvantages of cars (for passenger travel), and see how driverless operation will change things. Disadvantages of driving (both for motorists and for society) include:

  • Driving itself is inconvenient. Some motorists are auto enthusiasts–they love driving, and working on, automobiles, and often purchase cars based on their “style” or on their handling and performance characteristics, rather than on more functional criteria. For most motorists, though, driving is a pain in the butt–a chore which is an often-ignored cost of car ownership. Who enjoys sitting in rush hour traffic with their foot riding the break? Who enjoys a twelve-hour drive to Sacramento? Who enjoys circling a block looking for parking? Also, there are some people who cannot (legally) drive, due to physical disability, lack of license, or revocation of the privilege by the law.
  • Cars are dangerous. Automobile collisions kill tens of thousands of people every year in the United States, and injure thousands more. In most cases, driver error is to blame. In addition, automobile traffic, particularly high-volume or high-speed traffic, is detrimental to the pedestrian environment; highways, in particular, act like walls which pedestrians are unwise to cross.
  • Cars are expensive. Owning or operating an automobile costs a lot of money–they are expensive to purchase, expensive to fuel, expensive to maintain, and expensive to insure. In some locales, they are also expensive to license, operate, and park. Likewise, arrangements by which one can use an automobile without owning are either expensive (car rental, taxis) or inconvenient (informal carpools).
  • Cars consume a lot of space. A single-occupant vehicle (SOV) requires, on average, about 100 square feet of real estate (including some margin outside the vehicle’s footprint) to carry around the person it contains. That’s a 100-square-foot patch which must move down the streets at speed, while avoiding encroaching on any other 100-square-foot patch, and which must then be parked when not in use. This consumption of space is a major problem in dense urban areas; and a common solution–less density–makes things inconvenient by spreading everything out further, requiring cars (or other mechanized transport) for trips that might otherwise be easily accomplished on foot.
  • Cars consume energy and produce pollution. Along with the area consumed by cars, they weigh a lot. A 150-pound commuter lugging around a 3000-pound automobile simply to get to work is a profound waste of energy. And given that most cars today are powered by internal combustion engines, this results in a lot of filth out of the tailpipe.

Well-used public transit addresses each of these issues. Transit passengers need not operate the vehicle; transit is operated by professional drivers, and some transit already is automatic (accidents still occur, but it is rare for transit passengers to be killed about a transit vehicle); transit rides are available at low cost (and a transit pass is far less than the annual cost of owning even a beater car); and well-used transit requires a lot less space and weight per passenger. (That said, walking or biking does even better than transit on these last two issues).

What about driverless cars?

  • Driverless cars solve the “driving” problem completely–rather than driving to work, one simply rides to work, and can use the time for more productive pursuits than operating a motor vehicle.
  • Assuming that the technology reaches its potential, driverless cars ought to be much safer than human-driven ones–for passengers, pedestrians, and other motorists. Computers have much faster reaction times than do humans. Computers don’t get drunk or tired or have bad days. Computer control systems won’t engage in antisocial or aggressive behavior (assuming proper programming), and don’t suffer from the need to demonstrate their machismo behind the wheel. And computers can easily be programmed not to disregard traffic controls, in particular speed limits. While automatic vehicles won’t eliminate accidents, automated cars should reduce this carnage. In addition, if and when driverless vehicles become commonplace, it may become practical to build lanes or roadways on which manual operation is restricted (commercial license holders only) or prohibited altogether–and maybe manual car operation itself might be greatly restricted, with only highly-trained professional drivers being permitted behind the wheel.
  • Driverless cars probably won’t reduce the expense of car ownership; and may increase it, depending on how much of a premium is charged for the control system. Insurance rates will likely go down for cars operated only in automatic mode, but other expenses are not likely to be greatly affected. However, driverless cars may make it far easier for persons to have access to cars without owning one. Taxis, presently, are notoriously expensive (and often hard to find), due to the need to pay the driver. (And taxi drivers, despite the high fares, generally earn a pittance). Driverless taxis, on the other hand, will likely become ubiquitous, and arrangements such as “share taxis” might become more practical. Driverless automobiles will also make other arrangements such as car rental and car-sharing more practical. The delivery problem (how to get the car from the garage to the user) will go away, as might concerns about liability and insurance (again, assuming that manual operation of shared cars is not permitted) which presently frustrate car rental. (That said, Hertz will still try and sell you worthless collision damage waivers…)
  • Driverless cars will help greatly with the parking problem, even for unshared vehicles, simply by permitting parking to be relocated away from the home or jobsite. (Shared vehicles might not need to be parked at all, other than overnight). Rather than having distributed parking all over the place (with valuable street real estate consumed for on-street parking, and each business with a parking lot intended to handle their individual peak loads), parking could be centralized at an out-of-the-way location. When someone goes to work, they are dropped off at the office, then the car travels to a central garage for storage (having already reserved a parking space electronically); at the end of the day, the car is summoned, picks up the commuter, who then heads home. The effects of driverless cars on congestion are a bit less clear. If a roadway is reserved for driverless cars only, the carrying capacity of the road will increase significantly; and by solving the parking problem one also solves the circling-the-block-looking-for-parking problem. However, the need to travel to and from central garages might increase congestion, particularly if centralized parking is concentrated in a particular space.
  • Addition of control systems shouldn’t materially change the weight of vehicles; however fuel efficiency should improve for several reasons. Reduction of congestion and of aggressive driving habits (which often waste fuel) will improve fuel efficiency assuming no changes in the fleet; and anything that can be done to encourage carpooling will have a corresponding reduction in fuel consumption and pollution.

    A more important advantage might be greater fleet specialization. Right now, many commuters get to work in large vehicles such as SUVs which are particularly inefficient at transporting single occupants (with minimal, if any, baggage) to and from locations on the improved street network. However, these commuters may have hobbies or other circumstances which require ownership of a large vehicle–and at that point, it’s more cost-effective to drive the Expedition to work than it is to purchase an additional vehicle for the commute. By reducing the barriers to car-sharing, it may become more practical for more motorists to deploy appropriate vehicles for differing circumstances: a family could own a small, fuel-efficient (or electric) car for commuting, and then rent the gas-guzzling SUV for trips to the lake or other circumstances where the greater power, size, or clearance is needed.

How will this affect transit?

Many transit critics assume an auto-normalized environment–that the natural state of affairs is for low-density, auto-centric development, and that transit is only useful or effective for specific exceptions to the norm (high density, transport for the poor), often as a result of government interference. A common assumption is that people intensely dislike both high-density living, as well as travel in large communal vehicles–and that any way in which automatic cars can alleviate the problem with driving, will result in a mode shift away from transit back to the automobile.

For some people, this is certainly true–and I expect that certain applications of transit will become less prevalent. In particular, the express bus–which appeals to commuters who dislike driving in rush-hour traffic (though don’t mind being stuck on it while riding a bus), and/or wish to avoid parking downtown, but prefer to user personal cars for trips other than the commute–may disappear. Most transit agencies won’t consider this a great loss–express bus is an inefficient service to provide. (One concern might be a loss of political support for transit from suburbanites). Likewise, other arrangements may become practical for the frequently-empty social service routes through suburbia–again, a service which is inefficient to provide.

However, in dense urban areas, where stowing and parking a car is frequently expensive and difficult (regardless if manual or automatic), I don’t expect automatic cars to displace transit, simply due to the space aspect. A collection of small cars, even all running on autopilot (and packed onto the roadway like sardines), simply lacks the people-moving capacity of a rapid transit line.

More importantly, autonomous operation will provide advantages to the transit system as well.

Autonomous vehicles can reduce or eliminate the “last mile” problem associated with transit. Rather than needing to build park-and-rides to attract suburbanites (who live in neighborhoods ill-suited to quality bus service) to rapid transit, one can simply ride to the train station, get on the train, and have the car return home (where it can then be used by other members of the family); and repeat the operation in reverse for the commute home. This not only reduces the need to consume real estate to store cars during the day, it can reduce the number of cars a household needs. (And easier carsharing can eliminate the temptation to have a “spare” car on hand in case one breaks down).

But the most important factor to consider is this: Transit vehicles may become autonomous as well.

Right now, the biggest expense for transit systems in the developed world is labor. TriMet’s service levels are not presently limited by the amount of rolling stock or by the capacity of the infrastructure–the agency has plenty more busses and trains in its garages than it currently operates, especially at non-peak times. They’re limited by the agency’s ability to pay for drivers. If that factor is eliminated; we could easily have frequent service throughout the entire network, making transit a more realistic option for a larger number of people. (Obviously, this will require throwing hundreds of drivers out of work–a factor which should not be overlooked in these discussions).

Furthermore, and this should make the libertarians happy, autonomous transit may actually become a profitable enterprise rather than one which requires a public subsidy; with the result that private operators and not TriMet or C-TRAN run many (or even all) of the mass transit services in town.

Final thoughts

The production and deployment of autonomous vehicles, including mass transit vehicles, may bring about significant changes to how transport is arranged. It may increase the number of SOV trips (albeit making them more efficient) by eliminating some of the disadvantages of driving and vehicle ownership; but at the same time it might actually reduce the size of the vehicle fleet. It may result in a shift away from inefficient transit services, and better service in the urban environments where transit thrives. It may even result in a fundamental shift of who provides transport services to the public.

My suspicion, however, is that widespread use of autonomous vehicles will be a net win for sustainability–even if fundamentally alters, or even eliminates, the current ways that public transport is provided. When couples with the pressure of rising energy prices, autonomous vehicles may shatter some currently-held assumptions that presently abound in middle-class American society, such as the belief that households need one car per driver; and it may make urban living more attractive and available as the size of the fleet is reduced. It may end up greatly reducing public transit as we know it today–perhaps limiting it to operation of high-capacity corridors which require extensive infrastructure. But speaking for myself–my interest is not in defending the turf of TriMet, or of any other particular agency. My interest is in providing efficient and sustainable mobility to the people, and in particular in alternatives to the SOV.

But my crystal ball is probably no more clear on this topic than that of anyone else.


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