Pennsylvania prohibited pushing against an occupied caboose with more than 3500 horsepower in diesel days. That's two GP9's. The rear end crew had to ride the helper.
It wasn't so much as railroad rules as individual state laws. I know Ohio was late to forgive the pushing of occupied cars. Pennsylvania law was prohibited to push wood frame cars/cabins that was occupied. West Virginia was the all steel cabin. Some of the PRR cabins later had the I beam collision posts. Those were not so much for protection from shoving but actual rear end collisions. Some divisions also had different rules for pushing occupied cars.
Pete.
As stated each railroad had different rules about shoving against steel underframed cabooses but, some railroads required they be vacated by the rear end crew in such situations.
Wood framed cabooses need to go behind the engine.
Generally, steel framed cabooses do not. Individual railroad rules apply but on most railroads a helper can shove a steel caboose.
Dave H. Painted side goes up. My website : wnbranch.com