Complex sentence: Back of the Hill is the least-used MBTA station, averaging only 35 riders per day by a 2011 count; it is one of only four MBTA stations to average fewer than 100 riders per day.
Split into simpler sentences: Back of the Hill is the least-used stop on the MBTA subway system, averaging only 35 riders per day by a 2011 count. It is one of only four stops to average fewer than 100 riders per day.