If it's about waybills for future movement of the cars they may not want people to know exact times when they're moving hazardous material so protesters or terrorists wouldn't be able to try to block derail or sabotage the train.
Some communities around the country have tried to pass laws requiring railroads to let police and fire officials know when hazardous cargo is coming thru and the railroads have used the secrecy requirement to prevent those laws from being passed or enforced