How many vehicles were involved in the crash?

这次撞车事故涉及多少辆汽车？

《牛津词典》

How many vehicles were involved in the accident?

这次交通事故涉及多少辆汽车？

youdao

How many vehicles are required?

一共需要多少辆这种交通工具？

youdao

Determining how many vehicles, and what kind of vehicles, will cross a bridge on a daily basis is not merely academic.

NPR: Bumper to Bumper: Predicting Traffic Flow

They say that for too long, Chrysler has allowed its marketing decisions to be driven by manufacturing concerns--how many vehicles can a factory churn out to maximize efficiency?

FORBES: Chrysler: Dealers' Turn For Pain

Nobody can tell how many of these vehicles come from Albania's notorious stolen-car market.

ECONOMIST: The market-minded Kosovars