Soon after the railway opened, complaints about vibrations from passing trains began to be made by occupiers of buildings along the route. The vibrations were caused by the heavy, largely unsprung locomotives which weighed 44 tons (44.7 tonnes). The Board of Trade set up a committee to investigate the problem, and the CLR experimented with two solutions. For the first solution, three locomotives were modified to use lighter motors and were provided with improved suspension, so the weight was reduced to 31 tons (31.5 tonnes), more of which was sprung to reduce vibrations; for the second solution, two six-carriage trains were formed that had the two end carriages converted and provided with driver's cabs and their own motors so they could run as multiple units without a separate locomotive. The lighter locomotives did reduce the vibrations felt at the surface, but the multiple units removed it almost completely and the CLR chose to adopt that solution. The committee's report, published in 1902, also found that the CLR's choice of 100 lb/yard (49.60 kg/m) bridge rail for its tracks rather than a stiffer bullhead rail on cross sleepers contributed to the vibration.