Scrapers can be very efficient on short hauls where the cut-and-fill areas are close together and have sufficient length to fill the hopper. The heavier scraper types have two engines ('tandem powered'), one driving the front wheels, one driving the rear wheels, with engines up to 400 kW (550 horsepower). The First Motorised Scraper was invented by LeTourneau in the 1930s by adapting a pulled scraper for one-man operation, from the pulling tractor, by use of electric motors. Two scrapers can work together in a push-pull fashion but this requires a long cut area.