The Reddy Analytics team members were instrumental in providing irrefutable evidence from signal system data that demonstrated the dramatic and immediate impact of recalibrating “grade timers” on one of the busiest rapid transit systems in the nation. At the time, there was a debate internal to the transit agency regarding specific minutiae of signal system design that had taken on a very high profile after press reports that the system had been slowing down for many years. “Grade timers” are a form of approach control, where a more restrictive aspect would be displayed to the train operator than was absolutely necessary based on the block occupancy states of the tracks ahead, to essentially enforce a permanent speed restriction and ensure that the operator has the train under control. Traditionally, they were used in locations with steep down gradients, but over time has evolved to become a primitive form of train speed control. We were tasked to investigate the issue and found that, based on knowledge of our signal specialists, that the number of timed signal devices had been increasing, and their calibration had become more restrictive. The addition or adjustment of “grade timers” was often done in response to critical incidents, or in conjunction with signal upgrade projects or track layout changes. However, the signal team making the adjustment had responsibility only for collision avoidance and not necessarily for journey time performance. Our analysis revealed that the journey time impact of these devices were significant and immediate, essentially confirming quantitatively what was common knowledge within the rapid transit operations directorate. This analysis triggered a systemwide review of all such approach control locations, and where it was safe to do so, timing devices or signals were recalibrated, relocated, or redesigned to improve the journey time performance while still ensuring that trains could not approach permanent speed restriction sites at unsafe speeds. The work continues today under an interdisciplinary “Train Speed & Safety Task Force” at the agency.
