Diesel locomotive break down. Hydraulic transmission for locomotives was developed in Germany. There is still debate over the relative merits of hydraulic vs. electrical transmission systems: advantages claimed for hydraulic systems include lower weight, high reliability, and lower capital cost. By the 21st century, for diesel locomotive traction worldwide the majority of countries used diesel–electric designs, with diesel hydraulic designs not found in use outside Germany and Japan, and some neighbouring states, where it is used in designs for freight work. In Germany and Finland, diesel–hydraulic systems have achieved high reliability in operation. In the UK the diesel–hydraulic principle gained a poor
Electro-diesel locomotive have exhaust restrictions. Once out of the tunnels, the engines are started and operation is as a normal diesel locomotive. With modern electronics, it is much easier to construct (or adapt) an electro-diesel locomotive or multiple-unit which is equally at home running at high speeds both "under the wires" and under diesel power (e.g. SNCF Class B 82500, Bombardier ALP-45DP). These will normally operate under pure electric traction where possible, and use the diesel engines to extend the journeys along non-electrified sections which would not be cost effective to electrify. They may also be used on long cross-country routes to