Glossary

Bus Factor

The bus factor is the number of people who would have to be lost — "hit by a bus" — before a project stalls because critical knowledge or access went with them. A bus factor of one means a single person is a single point of failure. Raising it is a core goal of good ownership and delegation.

The bus factor (sometimes "truck factor" or "lottery factor") is a blunt but useful measure of key-person risk. It asks: how many people would your project have to lose before it grinds to a halt because the knowledge, access or relationships they held aren't shared? The idea began in software engineering, where researchers have since tried to measure it formally — one study of GitHub projects found that a large share of popular repositories had a truck factor of just one or two developers.¹

A bus factor of one is the danger zone — one person holds something nobody else can pick up. It is extremely common and rarely noticed until that person is on holiday, off sick, or has left.

Why it matters

A low bus factor is a hidden form of drift: the work looks healthy right up until the one person who understands it is unavailable, at which point a routine task becomes a crisis. It also quietly traps the individual, who can never fully hand work over or take a real break.

How to raise it

You raise the bus factor by treating knowledge-sharing as part of the job, not an extra: documenting decisions, rotating who handles key tasks, and delegating outcomes so more than one person has carried the work. Good ownership increases the bus factor rather than hoarding it — a sign someone is leading a system rather than being the system.

Avelino, Passos, Hora & Valente, "A Novel Approach for Estimating Truck Factors," IEEE International Conference on Program Comprehension (2016).

Frequently asked

What is a good bus factor?

Higher is safer. A bus factor of one means a single person is a single point of failure, so the practical goal is at least two or three people who can each pick up any critical area. There is no universal target; raise it until losing any one person would slow the work rather than stop it.

How do you calculate the bus factor?

Informally, you ask how many people would have to disappear before a project stalls for lack of knowledge, access or relationships. For codebases, researchers estimate it by tracing which authors hold the knowledge of each file and finding the smallest set whose loss would orphan most of the code.

What's the difference between bus factor and single point of failure?

A single point of failure is any one element whose loss breaks the whole; the bus factor applies that idea specifically to people and knowledge. A bus factor of one is, in effect, a human single point of failure.

Guide

How to Delegate Outcomes, Not Just Tasks

To delegate an outcome rather than a task, hand over four things together: the outcome the person owns, the standard it must meet, the constraints they must respect, and the check-ins you'll use. Task-handing tells people what to do; outcome-handing makes them responsible for whether it actually works.

Guide

How to Stop Being the Bottleneck Your Team Waits On

You become the bottleneck when too many decisions and too much context route through you alone. The way out is to make your expectations predictable, push decision rights down with clear guardrails, and let people act from their remit rather than waiting for instruction — so work moves when you're not in the room.

Topic

Delegation: How to Hand Over Work So It Actually Holds

Effective delegation means handing over an outcome — not just a task — with a clear standard, sensible constraints and the right check-ins, so the work comes back finished rather than bouncing back to you. Done well, it raises a team's capacity and lowers the manager's role as bottleneck.

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