Question

Average speed of traffic advancement is $5\text{m/s}$ when green and red lights remain open for same duration. To avoid traffic jams at peak hours, duration of opening green light is doubled keeping red duration same. What is new speed of traffic advancement in $\text{m/s}$ is

Answer 1

Say, n is number of cars, x is the average length of a car, and t is the duration of each light.
Then the average speed of the traffic is,
$\frac{nx}{2t}=5$ ...(1)
The duration of the green light is increased to $2t$. This implies,
$v=\frac{2nx}{3t}$ ...(2)
By (1) & (2)
$v=\frac{2}{3}\times 10=6.666$