Let me rephrase. Every loco and self propelled railcar ( i.e., our version of the tube) has sand reservoirs with pipes that deliver the sand right in front of the driving wheels on top of the rail, and can be turned on and off by the driver while moving. Works in forward and reverse too. A photo is worth a thousand words!
http://www.railpictures.net/viewphot...333925&nseq=65

Presumably, if you're moving at 90+ mph you don't have a traction problem.