Traffic enforcement makes the roads safer

In case you were wondering, Michael Makowsky and Thomas Stratmann report:

Traffic accidents are one of the leading causes of injury and death in the U.S. The role of traffic law enforcement in the reduction of accidents has been studied by relatively few papers and with mixed results that may be due to a simultaneity problem. Traffic law enforcement may reduce accidents, but police are also likely to be stricter in accident-prone areas. We use municipal budgetary shortfalls as an instrumental variable to identify the effect of traffic citations on traffic safety and show that budgetary shortfalls lead to more frequent issuance of tickets to drivers. Using a panel of municipalities in Massachusetts, we show that increases in the number of tickets written reduce motor vehicle accidents and accident related injuries, and that tickets issued to younger drivers have a larger effect in reducing accidents. The findings show that failure to control for endogeneity results in a significant underestimation of the positive impact of law enforcement on traffic safety.

Here is the paper.


Why not take the subject even further and say that budgetary shortfalls lead to less accidents?

Or, to extend Brian's point further, why not sum up as: government revenue increases lead to more traffic deaths.

Headline version: High taxes kill!


Budgetary shortfalls correlate with economic slowdowns, meaning lowered employment, meaning lowered driving, meaning lessened traffic congestion.

Lower traffic congestion leads not only to fewer accidents all by itself, but it also yields more opportunity to speed and therefore more tickets written.

I don't have time to read if they controlled for any of this.

Ridge was governor, nor grocer of PA.

'There is absolutely no evidence that the public finds current traffic safety to be objectionable.'

Right, they're too busy being worried about terrorist attacks and airplane crashes.

The public is really, really bad at estimating risk. Let's not defer to their inexpertness on the subject.

I know, I know: people are rational, the wisdom of crowds, markets work well, etc. But people favour skewed funding and regulation for safety measures not because they believe dying in an air crash is a thousand times worse than in a traffic accident--it's because they get risk assessment wrong. Sometimes you can't just defer to the market.

@Luca My argument wasn't strengthened by my flippant reference to the public's risk calculations. I wasn't trying to bring up diffuse costs vs. direct benefits, obviously a huge problem in democratic (all?) societies.

Of course I can't disagree with your point. I would happily trade 1/4 of the existing public funding for air travel and nuclear plant "safety" towards improved driver training and traffic flow.

I still think that we should be trying to reduce traffic congestion by increasing speeds while holding injuries fairly constant. It doesn't make sense to slow everyone down just to make them safer unless you hate suburbia.

Interesting because according to 2 sources the death and injury rate on the autobahn which has no speed limit is lower than on USA highways which are speed limited.

From my wife who is a highway safety researcher and has done studies in MA.

"Did you actually get to read their paper? The reason I ask is because there is a large crash problem with MA data. We discovered this in our advance street name signs. There are huge dips in and around 2001 , 2002, 2003. Depending on the years they use, it could definitely look like there was an effect."

Not sure they didn't catch this but this is the problem you can sometimes get when people cross fields. They can potentially miss very simple things that people who regularly study the field know about.

BTW, she does not believe speed and safety are highly correlated based on her reading of the literature and research. What is correlated to safety is the variance in speed. Some people going fast others going slow.

A similar paper by Ben Hansen, a UCSB student on the job market, can be found here:

@Luca, I think you mean we can't differ to democracy. When mass irrationality exists, democracy doesn't work.

floccia, I do not believe that speed, in and of itself, is necessarily accident-prone. The conditions (especially visibility) play a huge role.

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