Bus Factor


Source: 5 Whys Published: May 2019

Bus Factor

Circulated: June 17, 2020

The “bus factor” is the minimum number of team members that have to suddenly disappear from a project before the project stalls and is at risk of falling apart. We prefer the optimistic phrase of “won the lottery” instead of “hit by a bus.”

A factor of 1 means that there exists a single source of failure. A factor of 5 (on a 5 person team) means the risk of the project is low because team members know enough to carry on in the case some of them would quit the project.

You can increase the bus factor by:

  • Sharing knowledge (e.g., daily huddle meetings, documentation, project email updates)
  • Cross-training to develop skill redundancy (e.g., AWS certifications, team lunch and learn sessions)
  • Peer-reviewing (e.g., code reviews, editing a teammate’s PR/FAQ)