as a passenger unit was the Santa Fe 167 four unit set in February 1945. Learning from that, EMD offered an optional steam generator on all later F unit models. It was mounted at the rear of the carbody; steam-generator equipped locomotives can be recognised by the exhaust stack and safety valves protruding at the rear of the roof. The F units were popular passenger locomotives on mountain grades (where they were recommended by EMD), because a four-unit set had more motored axles than a trio of E-units of equivalent power (sixteen versus twelve) and thus had less chance of overloading the traction motors. Additionally, that 4-unit F set had all its weight on driven wheels and was thereby capable of greater tractive effort. The AT&SF Super Chief, CB&Q/D&RGW/WP California Zephyr, and GN Empire Builder all used F units on their Chicago-West Coast routes in the 1950s. The F7 was also popular for commuter lines and other passenger service where the trains were short. Options There were several options that could be specified by customers, such as type and mounting location of horns and bells. Dynamic brakes Dynamic brakes were an option on F units ordered by railroads operating in mountainous terrain and with steep grades. Passenger or freight pilot Either a passenger or freight style pilot could be ordered. The passenger pilot, similar to that standard on EMD E units, sloped smoothly down from the bottom of the nose, making a single slope all the way down from the headlight. The coupler was retractable with concealing doors. The result was a very attractive appearance that enhanced the impression of a powerful and speedy machine. The freight pilot curved inward a little way below the bottom of the nose before sloping out again, to give more clearance to the coupler and hoses. The coupler was fixed and protruded through a rectangular opening in the pilot. See also CF7 - A rebuild of an EMD F unit by the Atchison, Topeka and Santa Fe Railway. References External links Railpage - Australian implementation of the F7 B-B locomotives F North American streamliner trains Diesel-electric locomotives of the United States Locomotives with cabless variants Standard gauge locomotives of Canada Standard gauge locomotives of the United States Standard gauge locomotives of Mexico Standard gauge locomotives of Saudi Arabia Diesel-electric locomotives of Canada Diesel-electric locomotives of Mexico Diesel-electric locomotives of Saudi Arabia