Bus factor

The Truck Number ( sometimes also bus' factor ) is a measure used in Extreme Programming for estimating software project risks. With the value of the number of employees is described in a project that can fail without jeopardizing the project.

" How many or few would have to be hit by a truck (or quit) before the project is incapacitated? "

The Truck Factor is a standard proposed by Kent Beck value that describes the probability of failure of a project in absence of an employee and is a real number between 0 and 1

The worst value is 1, because it says that each team member is an indispensable specialist and so the failure of one ( any ) team member brings the project to failure. To avoid the risk or mitigate the Collective code ownership is used in Extreme Programming, in which each team member can change any part of the source code and take it.