 During the 1970s , NSB started the process of finding a replacement for the El 9 . New locomotives would cost NOK 20 million , and the company saw it as unrealistic to invest so much in a marginal branch line . NSB had also concluded its away @-@ with @-@ the @-@ steam program , and therefore had a lack of locomotives in general . If a new class of locomotives was to be built , it would have to satisfy more than the requirements for the Flåm Line , so NSB instead started investigating whether any of the older models could be used . Tests were performed in 1971 and 1973 with El 11 , built between 1951 and 1964 , and El 13 , built between 1957 and 1966 . Neither was considered optimal : El 11 allowed the train weight to increase to 100 tonnes ( 98 long tons ; 110 short tons ) , but the train had the steps for the voltage regulator and the commutation set for too high speeds . El 13 had rheostatic brakes , which were not suitable for the gradient ; the locomotives were also better suited for mainline service and would therefore not be prioritized for branch lines . 
