If all the hype over self-driving cars has left you wondering what true automotive autonomy would mean for traditional, centralized mass transit systems, you are not alone. After all, when we can all hail an autonomous taxi that comes right to our door and drops us where we need to go, won't all the subways, light rail systems and bus routes start to feel a little old-fashioned?

It's something I've been pondering.

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My community in North Carolina is in the process of trying to develop a light rail route between Durham and Chapel Hill. Much of the inevitable and predictable public debate has focused on localized impacts, property values and tax dollars, but I've also heard neighbors question whether centralized light rail makes sense in an emerging era of autonomous vehicles and car sharing. It's a question that deserves some consideration.

It turns out that this is a hot topic in transit- and planning-focused circles. Urban planner Antonio Loro has an excellent, balanced piece over at Human Transit looking at how improvements in vehicle autonomy might impact our transit mix.

Here are some of the main takeaways:

  • In some cities, based on road capacity alone, it would be technically feasible for autonomous vehicles to replace both private car use and mass transit, but the number of vehicle miles traveled would go up considerably. (A lot of empty taxis would be moving about from place-to-place to pick up riders.)
  • In order for this to happen, autonomous taxis would need to make use of currently underused road space — meaning that less-traveled side roads, currently spaces where people walk, play, bike and... errrm... live, would become busy thoroughfares for these autonomous pods.
  • Vehicle-to-vehicle communication might help ease congestion — for example by allowing much more efficient use of intersections than current stop light systems, or clumping vehicles into closely packed "platoons" — but doing so would presumably require almost complete separation of non-automated vehicles like bikes, pedestrians and regular driver-driven cars.
  • In cities where road space is already at a premium, such a move to automation would be even more challenging. Wherever large numbers of people need to move through restricted space, simple geometry suggests some form of mass transit and/or walking and biking will most likely win out.

Rethinking our cities and streets

In other words, in all but the densest cities, it might be technically feasible to create a world of fully automated vehicles zipping us about from point-to-point, but doing so would mean an almost complete rethink of what our cities and streets are used for. Given that many communities have been rethinking car-centric development patterns, and rediscovering the joys of dense, mixed-use communities where you can walk, bike and perhaps even talk to your neighbors, it would be a shame if the driverless car suddenly pulled us back into our bubbles of isolation.

It's worth noting that Antonio Loro's post does not suggest we reject autonomous vehicle technology. As with most debates around innovation and development, this does not have to be an either/or scenario. Instead, suggests Loro, we should use automation where and when it makes sense, but we should do so with a plan that is focused on overall well-being. A few ways that this might happen:

  • Automated buses and light rail, on specific routes, could greatly improve the frequency, economics, reliability and convenience of mass transit routes. (Especially when combined with the benefits of smart phones, et cetera.)
  • Autonomous taxis, especially shared autonomous taxis, could help take care of "last mile" transportation to and from mass transit routes, coordinating their timing to reduce wait times and ease transfer.
  • By reducing the demand for car ownership, such systems could actually boost walkability by freeing up parking spaces, and encouraging biking and walking as options — calling on taxis only as and when needed.
  • Self-driving cars may also offer huge benefits for seniors and folks who are less mobile.
  • And finally,suburbia probably isn't going to disappear so automated cars and taxis in less-dense areas could help to mitigate the worst impacts of car-dependency.

Keeping mass transit

And one more thing that we should not forget: I, and many other people, really like riding on trains, buses and other forms of mass transit. When they run well, they are not an imposition or a sacrifice. They are a delightful amenity where one can relax, get some work done and perhaps even make contact with other people. In fact my kids — who admittedly spend too much time in cars — view riding on the bus as an unmitigated treat, a treat that rivals a trip to the theme park.

Let's not allow ourselves to get hooked into another mistake of building our communities around the needs of a technology. Instead, let's reflect on what it is we want our communities to look like and then harness the technologies we need to get it done.

From slashing dangerous air pollution to the health benefits of more walking, rethinking our cities could be a huge boost to our well-being. Autonomous vehicles can play a part in that evolution.

But they should not be seen as a panacea.

Why self-driving cars won't replace mass transit
Even if self-driving cars could replace mass transit, it would be a very bad thing.