[ohwp]

Other answer: with a lot of model trains: https://www.youtube.com/watch?v=vC-dmKHiCnY#t=445

[Luc]

According to the video about 100 kg tractive force is enough to get the locomotive moving. That's a lot less than I expected (though I've seen a video of a strongman called John Massis pulling a loc by his teeth).