I do not believe killing trains has any affect on how slowly anything comes up..
An ex squaddie tried it one time..the tracks were right next to a fuel depot..he sat at the end and killed the train every time it was in his sights..Unless the train has to be killed a certain length away,and he killed many of them,.within a certain amount of time,it was all popping back up..an hour max I believe..TRY it..
Kevin