 Widening of Highway 400 began in 1971. An additional lane in either direction was created by reducing the 9.1 m median by 6 m (20 ft) and using 1.2 m (4 ft) of the shoulder on each side. The first section to be widened was from Highway 401 to Finch Avenue, which was widened to eight lanes. Soon thereafter, the section from Finch to Highway 88 was widened to six lanes. A year later, the six lane freeway was extended 41.8 km (26 mi) north to Highway 11.
