• May 15th, 2014

This article is to explain the rationale for the following statement that is made in the 2010 Crash Facts Book:

Based on 2010 data, if you are a typical driver in Alabama, there is greater than a one in three chance that you will be involved in an injury or fatal crash while driving an automobile over your lifetime. The probability of your being in a crash of any severity is greater than 98%. The following web page gives a recent count of the number of licensed drivers in Alabama:

Number of drivers in Alabama = 3,598,034 from the above website.

Assuming that each crash involves a different driver, the CARE results from Driver-Vehicle dataset are as follows:

Number of drivers involved in injury crash 2010 = 26,978 drivers involved in injury crashes.

This leads to the calculation of the following probabilities:

Pr (crash in one year for any driver) = 26,978/3,598,034 = 0.007498

Pr (any driever not being in an injury crash) = (1-0.007498) = 0.992502

The “driving life” of any driver is estimated to be 60 years (76-16 = 60). This assumes that the average life span of an Alabama driver is 76, and that most will obtain their drivers license at age 16 and retain it for the rest of their lives.

Pr (any driver not being in a crash over 76-16 = 60 years) = 0.992502 ** 60 = 0.636625

Pr (being in a crash over 60 years) = 1 – 646625 = 36%

This is used as the basis for the “greater than a one in three chance,” since a one in three chance is 33.33%.

Similar techniques were used to estimate the probability of being in any type of crash over a driver’s lifetime.