Actually they are, but use is limited to a couple of sightseeing trains.
https://www.roaringcamp.com/
They're infrequent, don't move too quickly, you can hear them from a mile or more away, and since you're on a mountain bike, any need to escape (wildly unlikely) is not only easy, but potentially really fun. There's a huge shoulder as well, it's really not an issue. There is a 100 feet of bridge a bit further up, but it only takes a few seconds to cross.
Some of the trails coming off the steep side of UCSC dump about a quarter mile north of the trail back up. The options are to ride down Highway 9 with no shoulder and a fair bit of not-too-bike-friendly-traffic, or drop into a really fun little descent to the tracks, and ride the tracks back to the climb. It's fun, scenic, and a nice little diversion from the climbing and steep-as-heck descending.
Still wondering what the guy we captured off in the distance is up to. Mildly creepy.