determine the overall line capacity. Short loops Long and short trains can cross at a short loop if the long train arrives second but leaves first. It is best if all crossing loops are longer than the longest train. Two long trains can cross at a short loop using a slow so-called see-saw process, which wastes time. Right- and left-hand traffic Countries generally have a principle on which side trains shall meet, either on the left or on the right, generally the same for the whole country. But this is generally valid only on double track. On passing loops this principle is not necessarily used. Often the train that shall not stop uses the straight track. See also Right- and left-hand traffic. Gallery Accidents at crossing loops Other names and types crossing loop or crossing place passing siding (US) refuge loop - used on double track lines A run-around loop enables a locomotive to change ends when a train has reached a terminus station. Spirals are sometimes called loops. Balloon loops are sometimes called loops. See also Glossary of North American railway terminology Lists of rail accidents Refuge siding Siding Train meet References Railway sidings