Abstract: A trolley travels in response to rotation of a winch along a main cable of a suspension bridge having a tower and support cables extending along and substantially parallel to the main cable. The trolley includes a support assembly engaged with the support cables, first and second enclosures suspended from the support assembly, each enclosure located at a laterally opposite side of the main cable, and a tugger cable engaged with the winch and connected to the support assembly for pulling the enclosures along the main cable toward the tower and/or allowing the enclosures to move along the main cable away from the tower.