 Stephenson's design convinced the backers of the proposed tramway to appoint Stephenson, who had recently built the Hetton colliery railway, as engineer.Traffic on the Stockton and Darlington Railway (S&DR) was originally intended to be horse-drawn, but Stephenson carried out a fresh survey of the route to allow steam haulage, and the Act was amended to allow the use of steam locomotives.The railway was also empowered to carry passengers in addition to coal and general merchandise.