Soon after opening, the company received complaints that vibration was felt in the buildings above the route. The Board of Trade appointed an investigating committee in January 1901, which reported in May that the problem was due to the large unsprung mass of the 44-ton locomotives, and the track. An experiment in August showed the vibrations could be reduced by rebuilding locomotives to reduce the unsprung mass to tons. The following month, after four of the carriages had been converted into motor cars and fitted with British Thomson-Houston control equipment that had been invented by Frank J. Sprague in Chicago, an electric multiple unit was tested.