Cost-Effectively Protecting Old U.S Bridges from Depreciation Caused by Extreme Weather

The New York Times has published a very interesting piece that raises more questions than it supplies answers. The Times argues that America is filled with old bridges that play a key role in our transportation system and these old bridges are depreciating even faster because of climate change.

I am not an engineer. I am an economist. This article raises several economic issues that are not discussed in the actual article!

Throughout this short column, I define “bridge depreciation” to be the probability that a team of Civil Engineers deems a given bridge in a given year to have more than a 2% chance of collapsing. An alternative definition is whether the bridge literally collapsed in the last year. Here is an example of such data.

#1 How do we test the statistical hypothesis that extreme weather events such as heat and flooding have a causal impact on accelerating bridge depreciation? In any causal statistical study, there needs to be a control group. Would the statistician conduct a survival analysis where each bridge in the United States has an annual checkup to see what quality the bridge is in? Over the first 50 years of its life, do any “die” and collapse? As the bridge ages AND it is exposed to extreme weather , does the probability of a collapse rise?

#2 An economist asks; “what is the marginal increase in the probability of a bridge disaster collapse brought about by extreme weather?”

#3 Building on #2, the economist then asks; what is the marginal cost of repairing the bridge to reduce this risk?

#4 An economist would also ask; will the bridge collapse be a sudden shock with cars driving on it or will it be gradual so that the local authorities can shut the bridge and work on it? In the latter case, nobody will die due to the bridge decline.

#5 If wild weather has large causal effects on depreciating bridge infrastructure and if infrastructure is such an important part of the local economy, then why aren’t elected officials investing more in maintenance and getting ahead of the problem? Are these issues only salient after a bridge collapses? Are the leaders facing financing constraints? Do voters not prioritize these issues?

#6 The article claims that climate resilient infrastructure is more costly to install. Why is this the case? Does the Buy America Act bind here so that infrastructure cannot be built by foreigners but instead is built by U.S unions? Who is overseeing the work here ot make sure that cost-overruns do not occur such that the U.S taxpayer “over pays” per new bridge?

I raise these points because there will be more and more discussion of the necessary infrastructure we need to adapt to climate change; airports that don’t flood, highways, bridges, water treatment systems. I believe that localities should pay for their own infrastructure and there should be national civil engineering inspections that certify the quality of these investments. Localities should use their own $ to pay for local public goods. Sunshine laws can be used to certify the relative quality of such infrastructure. Bridge collapses are rare events so it is difficult for people on their own to figure out the risk associated with a given piece of infrastructure.

To wrap up, I like the NY Times piece but I see no crisis here. Instead, I see a nation that is always updating its capital stock and we face tradeoffs in deciding how much to spend to update our bridge capital stock. There are alternative uses for that $!

UPDATE: Here is the National Bridge Inventory Database . In this age of Machine Learning, a young data scientist could geocode local weather over the last 20 years and rank these bridges with respect to which of them is at the greatest risk. Governors in these states could be informed about these risks and they would have to face their voters and newspapers to explain why they aren’t using their own state public funds to repair them. This is how data science increases government accountability!

Finally, let’s not forget comparative advantage and specialization. As more cities need to invest in more resilient bridges, competitive suppliers will gain experience here and learn how to make these bridges at a lower cost. Competition between these suppliers will lower the price to tax payers and this competition would be even more fierce if foreign firms could bid on these contracts.