Transportation Statistics and Microsimulation

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5Chapter

Common Probability

Distributions

5.1 INTRODUCTION

Inexperienced transportation professionals sometimes make the mistake

of thinking that all variables are deterministic; that is, they have a known

and constant value. For example, in most introductory classes engineers

are exposed to the fundamental equation of trac ow, which relates ow

(vehicles/time unit), q, to density (vehicles/distance unit), d, and velocity

(distance unit/time unit), v. at is,

q = dv.

However, if one were to go measure any of these parameters in the eld

it would quickly become obvious that there is considerable variability in

the observations. is is true ...