Adults can use some power-assisted bicycles on shared paths.
The power assistance is limited to 200 Watts, which restricts maximum speed capacity to approximately 25 kph, the announcement from Bikewest said.
The bicycles are classified as power-assisted pedal cycles.
PAPCs were frequently used by older people and those with health issues who had limited mobility and could not ride a standard bicycle, the Bikewest announcement said.
People under the age of 16 are still banned from engaging the power assistance on a bicycle equipped with it.
The new regulations were announced in the Government Gazette on August 30.
Other regulation changes were for child carrier seats, front lights, the colour of rear mudguards and the width of handlebars.
Child carrier seats can now be attached in front of bicycle handlebars provided that the rider has an uninterrupted view to the front of the bicycle. This type of child carrier seat is on sale in WA.
A flashing or steady white light clearly visible for at least 200 metres in front of a bicycle must be used when it is ridden at night or in reduced visibility conditions. There is no change in the regulations for rear bicycle lights and reflectors.
The requirement that rear mudguards must be either white or silver has been removed from the regulations.
The minimum width for handlebars has been reduced from 200mm to 180mm.