Often at my job when someone is becoming a single source of knowledge or otherwise has a skill that no one else on the team or the department has, a common expression is:

If John was hit by a bus, there would be no one that knows enough about what he does to take over.

I don't believe that this phrase is specific to my job as this also seems to be a common phrase in articles I have read online, for example:


My question, what is the origin of this phrase and is there any reason that it is phrased like "hit by a bus" instead of "in a plane crash" or something else entirely?

  • 1
    I've learned about it as the "truck factor" and I suspect that the phrase been coined in some book about project management (possibly about software project management specifically, but I'm not sure). Commented Oct 12, 2011 at 14:51
  • In my last workplace it was also referred to as "The Bus Test" as in "If John fails the bus test..."
    – Waggers
    Commented Oct 12, 2011 at 15:13
  • 4
    I've also heard "the bus factor" - eg "this project has a bus factor of 1", if it depends on one particular person not being sick. Commented Oct 12, 2011 at 16:08
  • It is more familiar to me as "knocked down by a bus" (as in the Conrad story people have quoted, or "goes under a bus".
    – Colin Fine
    Commented Oct 12, 2011 at 16:09
  • of course, you'd have to invent a bus in order to be hit by one...
    – JMP
    Commented Nov 6, 2017 at 16:56

5 Answers 5


People will use "heart attack", "plane crash", "fall off a cliff" as ways to describe that death might happen instantly, and the people left behind better be prepared in case that day happens.

This article talks about it: The Explainer Gets Hit by a Bus

Probably in the mid-20th century. The earliest instance the Explainer could find of a bus accident as a generic rather than literal example of misfortune is from Joseph Conrad's 1907 novel, The Secret Agent: "But just try to understand that it was a pure accident; as much an accident as if he had been run over by a 'bus while crossing the street."


To address "why a bus and not a plane" part of your question: most people have many more opportunities to be hit by a bus than to be in a plane crash, so "hit by a bus" implies a greater chance that this could actually happen (so you should plan for the possibility).


My colleagues these days prefer to use "hit by a lottery" as it's a more pleasant prospect for the one we might lose. (We still say "high bus factor" though, perhaps because it doesn't name names the way "what if Jeremy gets hit by a bus?" does.)

As for the prevalence of the phrase, a year or so ago a colleague of someone close to me was hit by the proverbial bus, and was killed instantly. There was indeeed a great disruption in her workplace. I think it's still a fairly common thing to happen. I don't know anyone (even indirectly) who was in a plane crash or who fell off a cliff. I know many people who were in car accidents, but most car accidents are not fatal.

The thing about "hit by a bus" is that it's sudden, possibly unpreventable (compared to say, having a heart attack), no warning signs (compared to deciding to work somewhere else) and complete. The employee is utterly lost to you without warning. But if you find it a little creepy, let me recommend "hit by a lottery" - it gets a smile every time.

  • I also prefer "winning the lottery" to getting "hit by a bus" for precisely the same reason (the more positive connotations). For extra smiles, add on "and sailing on a yacht." :-) Commented May 13, 2016 at 11:18

The phrase dates from at least 1907 - Joseph Conrad's novel, The Secret Agent: "as much an accident as if he had been run over by a 'bus while crossing the street."

In 1907 you were unlikely to die in a plane crash!

  • were planes safer back then? :P Commented Oct 13, 2011 at 6:02
  • 2
    @Jordaan - much safer, you never see a movie about one hitting an iceberg!
    – mgb
    Commented Oct 13, 2011 at 16:18
  • Except for when the Taliban called for a jihad on ice. And that's how global warming started. Commented Oct 13, 2011 at 22:01
  • Is this phrase in the context of organizational risk due to dependence on one person's skills or knowledge?
    – mattdm
    Commented Nov 6, 2017 at 17:51

This phrase seems most common in the software industry. The first instance I know of is this post on a Python programming language newsgroup

Subject: If Guido was hit by a bus?
From: Michael McLay
Date: Wed, 29 Jun 94 10:07:42 EDT

What if you saw this posted tommorrow.

> Guido's unexpected death has come as a shock to us all. Disguntled
> members of the Tcl mob are suspected, but no smoking gun has been found...

I just returned from a meeting in which the major objection to using
Python was its dependence on Guido. They wanted to know if Python
would survive if Guido disappeared. This is an important issue for
businesses that may be considering the use of Python in a product.

"Guido" is Guido van Rossum, the inventor and still leader of Python language development. Note that "bus" here is presented as one of a number of possible tragic scenarios. I think this is likely the first occurrence of this as a description of business risk.

It's a pretty vivid way of summarizing the problem, and quickly spread to other software projects, and apparently from there to the business world. I don't see any evidence of this having gone the other way around (although I suppose one could ask Michael McLay where he got the idea).

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