butler improved the specifications of his vehicle over the years, but was prevented from adequately testing it due to the 1865 red flag act, which legislated a maximum speed for self-propelled road vehicles of 2 mph (3 km/h) in built up areas and 4 mph (6.5 km/h) in rural areas. additionally, the vehicle had to be attended by three people, one of whom had to proceed in front of the vehicle waving a red flag.