Apparently the two-minute warning is the best we’re going to get without infusion of money technology. Via ST spokesman Bruce Gray:
By contract [with GE Transportation Systems] we only provides a 2-minute warning and a train arriving message. We do not have plans for continuous count down arrival clock.
The rest of the explanation below the jump.
… many properties have tried and some have struggled with delivering accurate feedback of the arrival time. These systems require that the vehicle’s position and speed be known so that updates to the arrival clock can be made in real-time. In order to get the position and speed of the vehicle we would need either GPS or vehicle telemetry sent back in real-time. Since we operate in tunnels in both Downtown and Beacon Hill this would make GPS unusable until the trains exit the tunnels and reacquire the satellites. As for sending the data back we do not have a data radio on board the vehicles. We are operating on the KCRS [King County Radio System] trunk radio system which provides us with voice only radio. We do not have an easy way to get the telemetry data back from the vehicles to recalculate the arrival time and make the appropriate updates. Yes many other technical solutions exist but they all come at a cost that was not in the original scope or budget.
We picked an approach that triggers our message based on track circuits, train schedules, and departure times from previous stations with an adaptive algorithm that provides the 2 minute warning and train arriving message. We want to give our patrons the most accurate information that we can.
Decent digital radios (or more sensors) would solve a lot of transit problems. They would provide better real-time arrival information for both buses and trains. In principle they could also fix some signaling problems associated with the current system. Sounds like a good project for an enterprising UW grad student!