The Surprising Impact of the SUV

In New York, the congestion pricing that kicked in on January 5th appears to be working. Raking in close to $100 million since it began, toll revenue exceeded projections. And anecdotally, I can say that traffic is much lighter.

However, there is one other (surprising) reason for congestion.

Traffic Congestion

Most large and midsize American cities report more traffic in 2024. While the usual culprits are sprawling populations and inadequate mass transit, a recent study adds one more cause to the list. Because of its “loop sensors,” Minnesota is able to collect data on the number and kind of vehicles on its Twin Cities road network. As a result, they calculated that the number of vehicles passing through lanes–the throughput, declined.

SUVs

SUV purchases are up from one in four to four in five between 1970 and today. Called “car bloat,” more SUVs mean less room for other cars. Between 1995 and 2019, the freeway lanes near Minneapolis and St. Paul lost 9.5% of their capacity. Blamed especially on SUVs, but also on other trucks, and tractor trailers, the actual decrease was approximately from 24 to 19 vehicles per kilometer per lane between 1995 and 2019. Because SUV volume rose by a whopping 1043.62% during those 25 years, much more than all other trucks, it played a far larger role in reducing throughput.

As you might expect, a longer vehicle diminishes throughput. More compact Honda Civic Hatchbacks (178 inches) can drive down a lane then Cadillac Escalades (211 inches). In addition, needing more space to stop, the heavier SUV might create more distance between it and other cars. Or, the compact car might just give the trucks more room.

This directed acyclic graph illustrates trucks (SUV included as a truck) and autos impact on throughput:

Our Bottom Line: Externalities

Defined as the unintended impact on a third party, an externality can be positive or negative. Education and vaccines typically create positive externalities. Both can benefit others beyond the direct recipients. Similarly, spewing the harmful smoke that affects neighbors with whom it has no relationship, factories initiate negative externalities.

For traffic congestion, the irony is that the people that make it worse also bear the burden of the externality.

My sources and more: Thanks to my Bloomberg City Lab email for looking at the congestion impact of the SUV. From there, a TOM TOM report came in handy as did this academic report about throughput. And finally, Gothamist had the congestion pricing update.