Class 37s were subject to several modifications during their time in service. One short-lived experiment involved 37 175 receiving CP5 'self-steering bogies' designed to reduce excess wear and noise on the tightly-curved West Highland line to Fort William and Mallaig. This however, proved too expensive to be practicable. Some Inverness allocated Class 37s received 'car lights'; these were essentially spotlights that made them more visible on the sharply curved Scottish branches, especially to users of level crossings. These were eventually either removed or superseded by the modern 'sealed beam' lights that became compulsory from 1993. Other classes fitted with these or similar lights were Class 24s, Class 26s, Class 47s and a solitary Class 86 86 225.