Monday, September 7, 2009

Public Safety vs. Public Safety

"A minute is a long time to wait if you're not breathing."

I tried it out while researching this post, and concede that the fire chief who made this comment has a point.

It's a concern that comes up frequently in debates over installing traffic calming devices on streets where high speeds hinder pedestrian safety. Pedestrian advocates argue that slowing down traffic improves walkability and reduces pedestrian injury. Fire departments contend that in a life-threatening emergency every second matters, so it's counterproductive to introduce obstacles to vehicle travel.

So who's right? Good question.

Research on emergency response times has centered on cardiac arrests, as there's reasonable consensus that time is of the essence when your heart has decided to stop beating. In general this research shows that response times under five minutes produce the best results in terms of survival (not to depress you, but this does not necessarily mean the survival rates are high when a victim is reached within the five minute window--just better than they would be otherwise). Many fire departments set a goal of responding to 90 percent of life-threatening calls within five minutes, and the LAFD appeared to be achieving that goal--at least prior to its recent budget cuts.

While there hasn't been much investigation of how traffic calming measures impact emergency response times, the work that is available (summarized in this report by Reid Ewing) suggests that speed humps and traffic circles slow down emergency vehicles by 3-14 seconds per measure. The biggest delays are to the largest vehicles, so an ambulance won't be slowed as much as a ladder truck.

By these estimates, a series of traffic calming measures along an emergency route could conceivably delay responders enough to be problematic--at least for cardiac events. But only if emergency response times were right at the cusp of five minutes, or if vehicles were confronted with a whole slew of traffic calming measures in a row. Given this, it doesn't necessarily follow that all traffic calming is a bad idea; in areas with high pedestrian traffic the benefits of improved pedestrian safety might outweigh the costs of slower response times.

I don't mean to downplay the importance of timely emergency response, but it's important to recognize that rejecting traffic calming measures based simply on blanket assertions instead of case-by-case evaluation could actually harm public safety. I'm hoping decisionmakers are sophisticated enough to recognize this...but I won't hold my breath.


  1. Good post. I would also assert that, when traffic is calmed, it gets at the root of the problem that those emergency responders are responding to.

    When traffic slows, then there won't be quite as many serious collisions that responders need to get to. If people drive less, then they're less stressed and there's less gunk in the air, which are both causes of those cardiac arrests.

  2. I wonder that if by introducing these measures traffic is lessoned and by that effect emergency vehicles can make the trip faster even with calming devices...

    and even without surly the slower speed, greater safety for pedestrians, motorists (yep they benefit too) and cyclists cant but help reduce 911 calls