Almost 6,300 pedestrians were killed in 2018 in the United States, the highest number since 1990, federal officials said this month. Collision-avoidance systems on many new vehicles could reduce that toll, but there are significant differences in how well they work, according to new tests.

Such systems scan the road ahead — sometimes with a camera, radar or lasers. If an object is detected, a computer can issue a warning and ultimately apply the brakes.

“We think these kinds of systems — as they become more prevalent in the fleet — will make a difference in reducing pedestrian fatalities,” said David Harkey, the president of the Insurance Institute for Highway Safety, which conducted the tests.

But the tests, conducted on 16 midsize sedans, found a wide range of abilities among the systems. Some cars stopped before the pedestrian dummy could be hit, others were slower to react. In one case, the vehicle did not reduce its speed and hit a child dummy.