Up to the minute bus arrival times have been appearing on many of the message signs at RapidRide A Line stations with caveat message “Testing is in Progress”. The displays show times for the A Line and any other Metro route serving that stop, though other routes may not be accurate because they aren’t equipped with GPS yet.
I was watching the sign at S 176th St/SeaTac station. I arrived at the station seeing 5 minutes to the next bus and about 5 minutes later the bus arrived. The sign changed from “1min” to “due” as the bus became visible in the distance. It’s quite accurate, with buses arriving within 1-2 min of the predictions, though some stations showed an arriving bus as 2 minutes away. There was one case where it predicted around 3-4 minutes and the bus arrived 8 minutes after the previous one. I’m not expecting clockwork here, just a general idea of how long the wait is. One Bus Away seems to be using the tracking data as well.