The success of electric traction in large cities had been demonstrated but a few years when it was appreciated that the overhead wires of the trolley were unsightly and dangerous, especially in the case of fire or the breaking of the wires or supports. Accordingly a system was developed where the current was obtained from conductors laid in a conduit on insulated supports through a slot in the centre of the track between the rails. A plow suspended from the bottom of the car was in contact with the conductors which were steel rails mounted on insulated supports, and through them the current passed by suitable conductors to the controller and motors. This system found an immediate vogue in American cities, and though more costly to install than the overhead trolley, was far more satisfactory in its results and appearance. In certain cities, Washington, D. C., for example, the conduit is used in the built-up portion of the town and when the suburbs are reached the plow is removed and the motors are connected with the trolley wire by the usual pole and wheel. Perhaps the most important feature of the electric railway in the United States has been the development and increase of its efficiency. Wherever possible traffic conditions warranted, it was comparatively easy to secure the right of way along country highways with little, if any, expense, and the construction of track and poles for such work was not a particularly heavy outlay. It was found, as we have seen, that the current could be transmitted over considerable distances so that the opportunity was afforded to supply transportation between two towns at some small distance where the local business at the time of the construction of the road would not warrant the outlay. This led to the systems of interurban lines, small at first, but as their success was demonstrated, gradually extending and uniting so that not only two important towns were connected, but eventually a large territory was supplied with adequate transportation facilities and even mail, express, and light freight could be handled. Again the success of such enterprises made it feasible for the electric railways to forsake the public highway and to secure a right of way of their own, and gradually to develop express and through service, often in direct competition with the local service of the steam railways in the same territory. Here larger cars were required and power stations of the most modern and efficient type in order to secure proper economy of operation. The general character of machinery, both generators and motors, was preserved even for these long distance lines, and their operation became simply an engineering problem to secure the maximum efficiency with a minimum expenditure.