Transportation Statistics and Microsimulation

70    ◾    Transportation Statistics and Microsimulation

plots that as λ gets larger, all else being equal, the distribution becomes

more symmetric.

Example 5.2

The arrival rate at a pedestrian crosswalk is known to be 0.2 arrival per

minute—in other words, a pedestrian arrives every five minutes on average.

What is the probability that there will be no pedestrian arrivals in the next

minute? What is the probability there will be more than two arrivals?

In this case, the number of pedestrian arrivals per minute at a crossing can

be modeled by a Poisson distribution having an arrival rate of 0.2 (i.e., λ = 0.2).

Let X be the number ...