Congestion is a bit like cholesterol – if you don’t have any you die.

A World Bank study on Cairo’s traffic problem in 2010 revealed that the annual cost of traffic in the greater metropolitan area was about 50 billion Egyptian pounds – four per cent of Egypt’s entire GDP. Compared to Jakarta, which is as densely populated as the Egyptian capital and famous for its traffic but only loses 0.6 per cent of Indonesia’s GDP to traffic costs.

It’s not the same story worldwide however – many American cities with the worst congestion also have the largest economies. If nothing else, a lot of traffic is a sign that a lot of people have jobs to get to. For example, during the US government shutdown of 2013, congestion in the Northern Virginia suburbs of Washington noticeably declined.

As John Norquist notes, “Congestion is a bit like cholesterol – if you don’t have any you die. And like cholesterol, there’s a good kind and a bad kind.”

In a study of the economic effects of traffic, Matthias Sweet found that higher levels of congestion are initially associated with faster economic growth. But, above a certain threshold congestion starts to become a drag on growth. It seems that job growth slows when congestion gets to be worse than about 35 to 37 hours of delay per commuter per year (or about four and a half minutes per one way trip).