Each car has two sets of bogies (trucks), each with four sets of support tires, guide tires and backup conventional steel wheels. The motor cars' bogies each have two direct-current traction motors coupled to reduction gears and differentials. Montreal's Metro trains use electromagnetic brakes, generated by the train's kinetic energy until it has slowed down to about . The train then uses composite brake blocks made of yellow birch injected with peanut oil to bring it to a complete stop. Two sets are applied against the treads of the steel wheels for friction braking. Hard braking produces a characteristic burnt popcorn scent. Wooden brake shoes perform well, but if subjected to numerous high-speed applications they develop a carbon film that diminishes brake performance. The rationale for using wooden brake shoes soaked in peanut oil was health concernsthe use of wooden brake shoes avoids releasing metal dust into the air upon braking. It also reduces screeching noise when braking and prolongs the life of steel wheels.