You should not start to pass if you are _________of a hill or curve.

Explanation

At 55 mph, you need about 10 seconds to pass. If there is an oncoming vehicle in the passing lane, your vehicle and the oncoming vehicle will close a distance of over 1,600 feet (one-third of a mile) in 10 seconds. To be able to avoid a head-on collision, you have to be able to see that far ahead. Therefore, you should not start to pass if you are within one-third of a mile of a hill or curve where your visibility would be restricted.