A Psychological Speed Limit

On aver­age, vehi­cles seri­ous­ly injure or kill some­one in New York every two hours; last year, 173 pedes­tri­ans were killed. Last week Gov. Andrew M. Cuo­mo signed a bill allow­ing New York City to enact a city­wide default speed lim­it of 25 miles per hour as part of its “Vision Zero” cam­paign to reduce traf­fic deaths to nil.

When the speed at which a car strikes a pedes­tri­an ris­es a mere 10 m.p.h. — to 40 m.p.h. from 30 — the chance of the pedestrian’s dying ris­es to 85 per­cent from 45. The real ques­tion is not absolute speed but appro­pri­ate speed.

There are two sure­fire ways to reduce speed: the speed bump which costs lit­tle and is effec­tive in a blunt, lim­it­ed way. The oth­er, though still rel­a­tive­ly rare in the Unit­ed States, is ubiq­ui­tous else­where in the devel­oped world: the speed cam­era.

• Unlike most traf­fic enforce­ment, cam­eras work because they are vis­i­ble and pre­dictable.
• Install them, and give dri­vers warn­ing, and speeds will drop.
• Ran­dom enforce­ment pro­vides a very weak feed­back sig­nal — when a strong sig­nal is need­ed to curb habit­u­al behav­ior
• Dri­ving fast with­out being caught or crash­ing — deter­mines “how your brain decides whether to remem­ber a habit for the future.”
• Speed cam­eras have been shown to reduce crash and fatal­i­ty rates.
• A major­i­ty of peo­ple sup­port speed cam­eras when they are used in school zones, on roads with a his­to­ry of crash­es or where many dri­vers vio­late the speed lim­it.
• The use of cam­eras does raise legit­i­mate issues about pri­va­cy, trans­paren­cy and accu­ra­cy, but sim­i­lar con­cerns exist with any form of enforce­ment.

In any case, enforce­ment — whether by cam­eras or cops — can­not deliv­er “Vision Zero.” To alter dri­ver behav­ior on speed­ing, a city like New York will need more than a catchy slo­gan, a tech­ni­cal fix or ramped-up enforce­ment. Enter “psy­cho­log­i­cal traf­fic calm­ing.”

This approach relies on the sug­ges­tive pow­er of con­text: Dri­vers tend to go at a speed that feels appro­pri­ate for the road they are on. For instance, does your street have a cen­ter divid­ing line? If so, add a few m.p.h. to the aver­age traf­fic speed. Is it one-way? Add some. Does it have well-marked bike lanes? Cut a few m.p.h. Trees on the side? Drop some.

The effect of psy­cho­log­i­cal traf­fic calm­ing seems con­ta­gious and pain­less. Dri­vers can be nudged out of their worst instincts.

Read the orig­i­nal arti­cle in its entire­ty.


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