sentences:  On October 9, 2016, OPTO was successfully implemented on the heavy-rail Sheppard line, which uses four-car sets of Bombardier Toronto Rockets.According to a 2016 presentation, OPTO is "one of the TTC's key modernization efforts" as a cost-saving measure.The Toronto Rocket trains were altered to include a train door monitor system uses cameras to display a clear view of train doors while maintaining unobstructed views of the track and signals.