The Case that AVs Make Congestion Worse

Right now, there is huge debate raging in the long range planning community:

Are Autonomous Vehicles (AVs) going to make congestion better? or worse?

A lot rides on the answer to this question: each year planning organizations plan out millions of dollars in infrastructure (roads, signals, parking, etc..) to account for new growth, which brings along new drivers and new roadway traffic.  But, for pretty much the first time in the history of modern transportation, these organizations find themselves with a wildcard so spectacularly disruptive they cant rely on their 100+ years of transportation experience to plan the next 10 years, let alone the next 40 (and they have to plan out that far!).  If AVs make congestion better, suddenly they don’t need to plan to build so many new roads, or perhaps they can eliminate parking or perhaps the airport doesn’t need to be expanded and so on – all of these are multi million dollar decisions that need to be planned well in advanced.

So what IS going to happen to levels of congestion with the new age of AVs?

Well, the short answer is, we really don’t know, but there is a strong case that they are going to make congestion worse, and here it is:

There are two key factors that determine whether congestion gets better or worse:

  1. System Capacity Gains, and
  2. Vehicle Miles Traveled

System Capacity Gains are the benefits that will come from having vehicles that are driven by robots instead of humans and we discuss that here.  So maybe all this will get better, but lets look at the second factor: Vehicles Miles Traveled (VMT)

VMT is simply adding up all the miles that all the vehicles in an area travel in one day.  So if 10 vehicles each travel one mile, thats 10 VMT. On the other hand if 1 vehicle travels 10 miles, that’s also 10 VMT.  And, fortunately FHWA keeps track of these sorts of things for the US:


So, adding that up, there are over 230 Billion miles traveled each month in the United States – And, if youve ever driven a major urban route during rush hour – you know that are roadways are at capacity! Now, think about all the reasons people don’t travel, and lets think about what happens when AVs come around – and for purposes of this exercise, lets say that AVs are rolled out via ridesourcing services and rides become extremely cheap.

Reason People Don’t Drive #1: They Can’t Drive

Here are a few stats:

So we’ve just identified, lets say around 30 Million people who would like to be more mobile, that’s around 10% of the population of the United States. So if that were to translate to +10% VMT all of a sudden, we would be in trouble! remember, American roads are already at capacity during rush hour, any sudden increase would be disastrous.

Reason People Don’t Drive #2: They Drive Less Than They Could

Now lets think about the current population – what happens when rides become very easy and accessible? Do our social habits change? Here are some questions to play with:

  • Do we visit more people or take extra trips because they are easier? Think about your grandmother and how much she would love to visit all her grandchildren.
  • Do we make more long distance trips because we can replace airplane travel with an overnight autonomous ride?
  • Do our trips become longer? Would we go the extra 5 miles to the Whole Foods rather than shop at the local grocery store because we prefer the selection and the burden to get there is less?
  • What if trips in from the suburbs to work become really easy? Do we all move out to the country where land is cheap and houses are bigger? Do our commutes become longer?
  • What about instances when we are working in our car (or watching a movie even) and we arrive to our destination early? Would we just circle the block a few extra times?

All of this latent demand could drastically increase VMT! Think about how your life might change in these cases. I know I’d live out in the country and I’d be traveling to other cities every weekend!

Reason People Things Don’t Drive #3: They Can’t Drive

UberEats, Favor, Amazon Prime Now – there are now a ton of services that deliver food and goods within an hour or two from ordering.  But even beyond that, what about if we find that we forgot something at the house? Now we might just bear through the day without it, but what if we could send a car to pick it up and have it brought to us? Or what if we want to send our dog to the park but we don’t want to go?
Its easy to picture a time where we put the dog in the car and they go to an attended park without their owners.  Or perhaps we want to try on something from craigslist before we buy it – why doesn’t the seller just throw it in the car and send it over to us to look at first – if we don’t want it, we can just send the car back.

Unfortunatley, none of this is really measurable at this point in our history, and there is A LOT of opportunity for disruption of this (don’t count out drone technology to help a lot!).  But we are working on it very hard where I work and at numerous other fine research institutions in the US – and hopefully I’ll be able to share more info in the future!

until then,