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bus factor

Also called: truck factor

The number of people who would have to be suddenly unavailable before a piece of work stops. A bus factor of one, often the lead, is a risk to fix with documentation, pairing and rotating responsibilities.

The bus factor is the number of people who would have to become suddenly unavailable before a piece of work stops. The name comes from software teams and a grim thought experiment, but in practice the cause is ordinary: a vacation, an illness, a lost connection during a power outage, someone leaving. A bus factor of one means a single absence stalls that work.

It applies to more than skills. Count who can do the work alone today without asking anyone, and also who holds the access (accounts, passwords, payment tools), who holds the context (why a rule exists, what was promised to a partner) and who has the right to decide. A coordinator who knows how to handle a refund exception but isn't allowed to approve it doesn't raise the bus factor. Leads often find the most bus factors of one in their own work: the rota, the report to their manager, the relationship with another team.

Raising it is routine work: write down how things are done and have someone else follow the notes once; pair people on the task; rotate it; and give the backup the decision rights and real practice while the main person is still around to answer questions. The goal is a team where people can switch off on vacation, not people who can be swapped out. Building a role that only one person can do, as a form of job security, makes the team fragile and the person tired.

Example

August 2027. Before the lead's first two-week leave in October, Klasna's Support team lists who can do each piece of work alone today:

Work
Who can do it alone
Bus factor
Fix
Hard-ticket rotation
Olha, Taras, Maryna, Bohdan
4
none needed
Refund exceptions inside the policy
Olha only (she also solved 210 of the team's 355 refund requests, 59.15%)
1
Olha teaches Bohdan; Iryna agrees in writing that he decides exceptions when Olha is off; he decides two while she is still on shift
Summer rota and Iryna's monthly report
the lead only
1
Olha acts as lead during the October leave, with written limits: the rota is hers, refunds outside the policy stay with Iryna, contracts and hiring wait
Refund outside the policy
Iryna
1, by design
stays with Iryna; written in the handover note so nobody waits for the lead

Two bus factors of one, both held by the most experienced people, including the lead. Not a criticism of either, just a risk in a team where power and connection outages are part of normal planning. After the changes the refund exceptions have a bus factor of two, and the rota no longer stops when the lead is on a beach.

Common mistakes

  • Counting skills only. Access, context and the right to decide count too.
  • Documentation nobody has tested. Have someone else follow the notes once while you are still there.
  • A backup who never practises. Let the backup decide real cases before the absence, not during it.
  • Leaving yourself off the list. The lead's own tasks are often the biggest single point of failure.
  • Treating it as blame or as job security. It's a team risk to fix, not a judgment of a person.

Learn it in the course