Don’t be fooled into thinking that wayside signals work like traffic lights and speed limit signs are regulatory. Engineers and even conductors are responsible for knowing the railroad, in quite a bit of detail, before they’re qualified to operate that district—that’s why a conductor was riding in the cab of the Cascade that crashed. They’re responsible for knowing the authorized speed for every part of the run; the wayside signs are just redundant reminders.
As for wayside signals, it’s also not quite true that there’s no redundancy. Almost all rail signaling systems show the permission to occupy the next block of track, and also indicate the situation with the block beyond that (some show two blocks beyond). If the distant block isn’t also clear, you typically must reduce speed to be able to stop within half of the distance at which you can spot another train ahead. Railroads also typically require the two people in the locomotive cab to call out and repeat to each other the signal aspect as it is passed. The Japanese put some value on pointing to signals as another way to help move the information into the conscious brain, and I think the practice has spread to some rapid transit systems in North America.
Railroads have had 150 years of trial and error, and have developed pretty elaborate protocols around signaling, track authority, and safety. But they also have many thousands of miles of track, with lots of varied conditions.