By how much is the number of fatalities expected to increase with a speed limit change from 55 to 60 mph?

Increasing the speed limit from 55 to 60 mph is associated with a rise in fatalities due to the increased risk and severity of accidents that typically occur at higher speeds. Research has shown that even a modest increase in speed limit can lead to a significant increase in fatality rates.

The choice of a 9% increase reflects findings from traffic safety studies which indicate that for every 1 mph increase in speed, the risk of fatality in a crash increases by approximately 4%. Therefore, changing the speed limit by 5 mph could reasonably lead to an estimated increase in fatalities of around 9% based on this relationship.

Higher speeds reduce the time drivers have to react and increase the distance required to stop, which contributes to an increased likelihood of collisions resulting in serious or fatal outcomes.