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Why we fight about black spots
  1. P L Jacobsen
  1. Correspondence to:
 P L Jacobsen
 2771, 14th Street, Sacramento, California 95818, USA; jacobsenp{at}medscape.com

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Injury prevention—need for a consensus between epidemiologists and traffic engineers

In this issue, Morency and Cloutier1(see page 360) report that, over a 5-year period, motorists injured pedestrians at exactly one quarter of all intersections in central Montreal. Those of us alarmed over unsafe streets will not be surprised by this finding. But I suspect that many of those setting traffic policies will be.

That is because the roads agency in Montreal operates under a policy of fixing collision “black spots”, where a “black spot” is an intersection with eight or more collisions in a 5-year period. Amazingly, seven motorist–pedestrian collisions in 5 years—that’s one in every 260 days—is not enough to brand an intersection as dangerous. The black spots approach fixes only 1% of the intersections where a motorist hits a person.

The unspoken premise of this policy seems to be that a high frequency of collisions is evidence of design problems unique to that intersection. However, Morency and Cloutier’s report suggests that faults in the road design are not site-specific but are nearly universal.

PERSPECTIVE

Morency and Cloutier approach the data from the perspective of epidemiologists and present the data in terms that make the problem particularly vivid: one quarter of all intersections were the site of a collision over a relatively short period of 5 years. By contrast, traffic engineers identify 22 black spot intersections for fixes.

These two different presentations may result from the different perspectives of the different professions. …

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