The MBTA partnered with BostonBRT to pilot all-door boarding on Silver Line routes 4 and 5 (Washington Street) from May 24th to June 6th, 2017. The goal was to measure how service improved when passengers could board at each door instead of lining up at the front door. Before the pilot began, the MBTA and BostonBRT identified several different metrics on which the SL 4/5 was expected to improve during the pilot, including reliability, reduced dwell time, and customer satisfaction.
For the MBTA a key improvement would be a reduction in the variability of the time it takes the bus to make a trip, whether that is due to dwell times or traffic. Since the MBTA schedules buses to take a certain amount of time, large variance in the time it takes a bus to complete a trip can either cause unreliable service or extra time at terminals to account for the occasional longer trip. Since we are interested in variability, in addition to the median we often look at the difference at the 90th percentile.