Why are traffic jams so bad on Mondays?

9th January, 2010

Dear Economist,
I have always been curious about two things. First, why are traffic jams always heavier on Mondays than on other weekdays? Second, I wonder why traffic is heavier when it rains. I know drivers get more cautious on rainy days, but even when it rains so little that I can hardly feel the raindrops, the traffic gets a lot heavier than on sunny days. Why?
Confused commuter, South Korea

Dear commuter,

I began by checking the data, and they surprised me. Inrix, who supply data to in-car satellite navigation systems, reports that the worst mornings of the week – in the US, at least – are actually Tuesday, Wednesday and Thursday. Monday and Friday are low-congestion mornings. Friday evenings are bad, but Monday evenings are particularly quiet. My guess is that Monday is a popular day to take a holiday or call in sick.

As for data on rain, two Australian academics have found that the heavier the rain, the lighter the traffic in Melbourne. You are asking me to explain two illusory phenomena.

So what is going on? One possibility is that things are different in Korea, but I am not so sure: I think that Australians, Americans and we Brits all share your perceptions that rainy days and Mondays are bad for traffic. And we seem to be wrong.

I think we need to turn to psychology for our answers. Norbert Schwarz – a psychologist who is well known to economists thanks to his work with Nobel laureate Daniel Kahneman – has famously showed that if you want people to tell you that their lives are a wreck, just ask them on a rainy day. There is also some psychological evidence that Monday mornings depress us, too.

In short, rainy days and Mondays always get you down. You’re living in a Carpenters song, but please don’t blame the traffic.

Also published at ft.com.

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