May 16, 2016

Costs of driving and Associated Press article

I received an email this morning in response to an Associated Press article that ran in the New York Times and some other outlets, citing our work on the energy impacts of self-driving cars.

The person took issue with my claim about the costs of driving:

In today’s piece “Will robot cars drive traffic congestion off a cliff?” it is unfortunate that the AP printed “But the biggest cost of car travel is drivers’ time, said Don MacKenzie. …” and nothing of what you said about the societal costs of climate change. … Worsened green house conditions will lead to even more violent weather, crop failure, water shortages and ultimately war as an overpopulated world struggles over these limited resources, not to mention the intangible cost of lost natural systems and their diversity.

This comment highlights two points worth clarifying here. First, in the context of this article, I was referring to the private costs of driving. While the costs of carbon emissions are very real, they are mostly not felt by the individual driver, and will not figure into the travel decisions of most people, unless policies such as a carbon tax force consumers to “internalize” those costs.

Second, and perhaps more importantly, even if we consider the social cost of carbon, the cost of the driver’s time remains the largest single cost of driving a car. Consider the following estimates of the social cost of carbon, compiled by the Energy Collective:

Suppose we believe that even the highest of these estimates is too low, and that the true social cost of carbon today is one the order of $500 per tonne of CO₂. Assuming an average fuel economy of 25 miles per gallon and GHG emissions of 11 kg CO₂-equivalent per gallon of gasoline, the social cost of carbon emissions from a mile of driving amounts to

 

($500 / tonne) * (0.011 tonnes / gallon) * (1 gallon / 25 miles) = $0.22 per mile.

As we showed in our article, the costs of the driver’s time average out to about $0.50 per mile, or $0.31 per kilometer.

Clearly, the costs of carbon emissions from driving are significant, but they are not the main driver of the total cost.