Prior to 1913, the BRT's rolling stock consisted of wooden cars with swing gates at each end, known as BU Cars. These cars were designed for use on elevated lines and were not permitted to operate with passengers on board in tunnels following the Malbone Street Wreck in 1918. Some BU cars were rebuilt in to Q Cars that had their ends enclosed and subway style sliding doors. The Q Cars operated for 66 years, making them the oldest rapid transit cars in New York history at the time of their retirement.