Question

The stoplights on a street are designed to keep traffic moving at 22 mi/h. The average length of a street block between traffic lights is about 80 m. What must be the time delay between green lights on successive blocks to keep the traffic moving continuously? There are 1.609 × 103 m in a mile. Answer in units of s.

Answer 1

The time delay between green lights on successive blocks must be 8,134334 seconds.

Explanation:

The idea in this problem is to know how long it takes to drive through each block at a speed of 22 mi/h. At that speed, it would take 8,134334 seconds to complete the distance from a green light to the next.

First you need to convert the 22mi/h to m/h. The equivalence presented in the question is wrong, actually it is: 1609,34 m = 1 mi. Then we have:

1 mi ---> 1609,34 m

22 mi --> ?m

(22 mi x 1609,34 m)/1 mi = 35405,48 m

22 mi/h is equivalent to say 35405,48 m/h

Second, considering the equivalence 1 h = 3600 s, you can replace this value in the speed previosly calculated:

35405,48 m/ 3600 s = 9,834856 m/s

From this you now know that in one second, at the specified speed, you drive 9,834856 m

But you need to know how much time you need for driving in a distance of 80 m between green lights, so:

1s ---> 9,834856 m

?s ---> 80 m

(80 m x 1s)/9,83485556 m = 8,134334 s

You drive the 80 m between green lights in 8,134334 s