In Espee days, the oil cans ran with manned mid - train helpers over Tehachapi. The tank cars were, at the time, only connected in strings of 13 ??? cars, so placing helpers mid - train was fairly simple. The manned helpers often ran through to Taylor or even Delores Yard. I'm guessing the current configuration is similar: due to the extreme length of the train it would be difficult to pump heavy crude through all the cars.