The average arrival rate, λ is 240 veh{/}h or 1/15 vehicles per second. According to poisson distribution, P(n)=
(λt)ne−λt
n!
Where, P(n)= probability of having n vehicles arrive in time t. λ= Average vehicle flow or arrival rate in per unit time t= duration of the time interval over which vehicles are counted e= base of natural logarithm