Wow. Our experiment is off to a great start—let's see if we can finish it off sooner than expected.
How dangerous is it to live near areas of heavy traffic congestion? Janet Currie and Reed Walker of Columbia University have done a clever study to try to get a handle on this. They took a look at the incidence of low birthweight in babies born to mothers who lived near busy toll plazas before and after E-ZPass was introduced. Their idea was that E-ZPass reduced congestion, and therefore mothers living near toll plazas ought to benefit from it. And they did:
We find that reductions in traffic congestion generated by E-ZPass reduced the incidence of prematurity and low birth weight among mothers within 2km of a toll plaza by 6.7-9.1% and 8.5-11.3% respectively, with larger effects for African-Americans, smokers, and those very close to toll plazas....The results suggest that traffic congestion is a significant contributor to poor
health in affected infants.
As you can see from the chart, E-ZPass reduced the incidence of low birthweights by half for mothers who lived within a couple hundred yards of a toll plaza. The effect decreased with distance, and at about a kilometer out the effect went away, presumably washed out by the ordinary background traffic congestion in the area. Results are similar for premature births. The public policy conclusions are a little unclear here, aside from the fact that E-ZPass is good and breathing auto fumes is bad, but it's useful to put a number to this stuff.
(Via Austin Frakt, by email.)