Typical uses of the word collision are:
automobile collision, two cars colliding
mid-air collision, two planes colliding
ship collision, two ships colliding
ATROPELLOS, GOLPES O CHOQUES CONTRA VEHÍCULOS could be something like
- (INJURIES SUSTAINED IN ) COLLISION WITH WITH VEHICLES
- BUMPS, KNOCKS OR COLLISIONS INVOLVING VEHICLES

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Note added at 6 hrs (2012-06-24 13:00:11 GMT)
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Al tratarse de una cabecera, me parece que "lo breve, cuánto más breve, mejor"
"BUMPS, KNOCKS OR COLLISIONS INVOLVING VEHICLES" works fine for me in the context.


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Note added at 10 hrs (2012-06-24 17:40:19 GMT)
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NB: to anyone remotely still interested, I think that as the context is a heading, nominal (not verbal) forms are indicated. Since the next heading down is (24) ACCIDENTE DE TRÁFICO, you could maybe use: (23) MINOR VEHICLE INCIDENTS / MINOR INCIDENTS INVOLVING VEHICLES . This would include forklifts and other rolling equipment on site and in factories, etc., and distinguish these incidents from traffic accidents per se.