Trouble predicting auto trip rate distribution - Probability Question

Okay. We have a possible development that, according to the ITE Trip Generation Manual, 7[sup]th[/sup] edition, we expect will generate 1,347 automobile trips during the morning peak hour. I want to graph the density function, and get things like the standard dev. and how many cars can we expect to show up such-and-such percent of the time. (Like with a standard normal dist. where sixty-something percent of the observations will be w/in one standard deviation, or something like that.)

It’s my understanding that this will be a Poisson distribution with the density function P = e[sup]-1347[/sup] × 1347[sup]x[/sup] / x! because that’s the distribution that one uses for arrivals during some time period.

This doesn’t seem to be working out for me and I assume that I’m making some sort of mistake. Can you help me to figure out & graph a density function, get standard dev., etc., and cumulative function as well? Since I want to do more than the morning peak hour, e.g. do the same with the current traffic and graph out expected total traffic during the morning peak hour, please offer methods that I can use rather than just straight numerical answers.

Thanks much.