Distributed power question

[Anonymous]

Could someone explain the concept of distributed power engines on the back of the coal trains Im seeing? Just recently I have noticed alot of BNSF coal trains in my area are using the DP's and never seemed to in the past. What power does this provide these long trains? When they go passed it seems that they are really not working but more like they are "tagging" along.

[Anonymous]

Thanks, M.W., that explained my question to a T!