What's the origin of "throwing someone under the bus"?

What's the origin of the phrase "to throw someone under the bus" or "so-and-so threw me under the bus?" (in the sense of betrayal)? It seems like a very specific phrase not to come from some specific incident.

Wikipedia provides the origin:

Its first use was by General Manager Joseph M. Kelly, who said he was considering ending a network affiliation. "I'm thinking about putting The Source under the bus," Kelly said in early 1988. The phrase was picked up by station employees, and often used to describe political intrigue at the station,

Also used in this:

In Septuagenarian Stew (The Life of a Bum), published in 1990, the Charles Bukowski character Harry pushed his friend Monk in front of a bus, and then stole Monk's wallet while Monk lay unconscious and probably dying in the street. After taking the wallet, Harry went directly to a bar and, using Monk's money, bought himself two double whiskeys. Later, Harry went to the Groton Steak House and, again using Monk's money, bought two beers and two Porterhouse steaks with fries ("go easy on the grease").

Thus, as you said, it came from a specific incident. It wasn't coined that long ago either, 1988.

I worked at a restaurant called Casa Bonita in Colorado in the mid-80s that was used by tour companies and it was not uncommon to see 10-20 or more busloads of tourists in a day. From time to time a late tour would call ahead and ask us to keep the restaurant open. Needless to say this did not make night shift employees very happy.

In the summer of either 1985 or 1986 a group of employees who regularly met for beers after work were discussing the practice and decided that keeping the restaurant open for late tours was just like throwing all of the employees under the bus. From that night forward, it was common to hear Casa Bonita employees talk about being “under the bus” or being “thrown under the bus”. Being “Thrown under the bus” had the similar meaning as it does now. Being “under the bus” meant to be behind and struggling to catch up.

In The North Middlesex Magazine for November 1879, in the section "Pickings by our own Gatherer", I find:

A poet sings "And I covered her up with the kiss I gave." He must have been a coachman and put her under the 'bus.

Note: a "kiss" can mean "a glancing blow"; a kiss from a bus is easily enough to kill.

I'm not going to claim that this instance was the forerunner of today's common usage... but I will say this: it didn't take a brain surgeon to coin this phrase. Buses are large and hard to stop, and quite a lot of people are killed by them every year; add to that the (apocryphal) legend of the Juggernaut, and you had the ingredients for a catchphrase. I'm not surprised that it caught on; I'm only surprised that it didn't catch on sooner.

The term is rather interesting, but its origin is somewhat shrouded in mystery:

The earliest solid example of “throw under the bus” found in print so far is from 1991, although a 1984 quote from rock star Cyndi Lauper where she uses the phrase “under the bus” (without “throw”) may or may not count as a sighting...

The exact origin of “thrown under the bus” is, unfortunately, a mystery. Slang expert Paul Dickson, quoted by William Safire in his New York Times magazine column, traces it to sports, specifically the standard announcement by managers trying to get the players to board the team bus: “Bus leaving. Be on it or under it.” The phrase does seem to be popular in sports circles, but few of the citations I have seen from sports publications carry the same overtones of casual, callous betrayal that one finds in non-sporting uses.

I personally believe the origin is not necessarily sports-related. I hear it in business usage mostly, to speak of sacrificing someone to an oncoming destructive force — to throw someone under that "bus" in an attempt to propitiate the malevolent power.

I think it probably comes from the ethical thought experiment known as the "Trolley Problem." See http://en.wikipedia.org/wiki/Trolley_problem.

One way of phrasing the problem is you can push the large man onto the track to stop the trolley and save a crowd of people.

Just a guess.