Non DCC stop and go switch?

[Anonymous]

I went to a county fair in northwestern Iowa last year where they have a pretty big HO layout in a glass encased booth.
There was a snowplow up in the mountian that sped up and slammed into a snow pack that was blocking the track, it waited a few moments and then backed up, waited a few moments and sped towards the snow pack again. I asked one of the helpers there how that was done, nobody knew, they just knew which switch to throw to make it go.
What is the mechanism called that does this and where can I get it?
I have heard rumor that MR had an article on building it years ago, but have not found it yet.

[Anonymous]

You could do it with an infrared sensor between the ties. Ive built crossing signals that operate that way.

[Seamonster]

Try this site: [code]http://home.cogeco.ca/~rpaisley4/CircuitIndex.html#63[/code]
He's got a couple of automatic reversing circuits that could be adapted for this use.