Gridlock May Not Be Constant, but Slow Going Is Here to Stay

New York Times article Gridlock May Not Be Constant, but Slow Going Is Here to Stay (March 23rd, 2010) makes a causal claim it does not have identification for. Relaxed drivers on the weekend due to faster traffic is cointegrated with it being the weekend itself. The Times ignores this.

Small changes in speeds also seem to have an outsize psychological impact on impatient New Yorkers. On weekdays, when few people expect a trip to go quickly, speeds in east Midtown average about 6.3 m.p.h. in the daytime. On Saturdays, the average speed is about 8.5 m.p.h. — not an enormous difference, even though drivers report feeling more comfortable on weekends.

We expect traffic to be lighter and therefore faster on days when people are less rushed (therefore less stressed). It is unclear whether or not there is a third cause (less weekend responsibility) that confounds the causal conclusion offered by the Times.