Otherwise the intensity parameter (accident rate) would not be constant over the entire time period.

Otherwise the intensity parameter (accident rate) would not be constant over the entire time period. If the three assumptions hold, then the probability that there are accidents during a time interval of length will be given by (1), where is the average of expected number of accidents per unit time. Example 26.2 During the busy period from 4:00 to 6:00pm on weekdays, accidents occur along a stretch of highway at the average rate of 3 per hour. What is the probability that there will be more than 6 accidents in a 1-hour period? What is the probability that there will be at most 2 accidents during the 2-hour busy period on a particular day?