The buses use 40% less electricity even when compared to an electric trolley bus, mainly because they are lighter and have the regenerative braking benefits.
Those three were converted to electric trolley bus (trackless trolley) operation which survives to this day; diesel buses were substituted on some other routes.
The inflexibility of the trolley bus system and a desire to standardise on diesel buses led to the decision to withdraw the trolley buses in the 1950s.
The objective was to determine how trolley buses would perform on such terrain, though not intending to actually convert the route to trolley bus operation.