It is not a binomial distribution, but a geometric distribution, which refers to the number of repetitions when an event occurs for the first time in an independent repetitive test.

For this problem, when the number of intersections passed by the first stop is less than 3, it conforms to the geometric distribution, qi- 1p, while the number of intersections passed for the first time is 4: 00, which does not conform. It's time to stop, because it's the first time, and the first three intersections didn't stop, that is, they all met the green light, P4=(3/4)3=27/64.