King's Highway 4, also known as Highway 4, is a provincially maintained highway in the Canadian province of Ontario. Originally much longer than its present 100.8 km (62.6 mi) length, more than half of Highway 4 was transferred to the responsibility of local governments in 1998. It travels between Highway 3 in Talbotville Royal, north-west of St. Thomas, and Highway 8 in Clinton, passing through the city of London inbetween.

King's Highway 3, commonly referred to as Highway 3, is a provincially maintained highway in the Canadian province of Ontario which travels parallel to the northern shoreline of Lake Erie. It has three segments, the first of which travels from the Ambassador Bridge in Windsor to Highway 77 in Leamington. The second portion begins at Talbotville Royal outside of St. Thomas at Highway 4, and travels to the western city limits of Port Colborne. The road is regionally maintained within Port Colborne as Niagara Regional Road 3, but regains its provincial designation at Highway 140. Its third and final terminus is at Edgewood Park, within the Fort Erie town limits. From there, the road continues as Niagara Regional Road 3 to the Peace Bridge, where drivers can cross to the United States. The total length of Highway 3 is 258.2 km (160.4 mi), consisting of 49.2 km (30.6 mi) from Windsor to Leamington, 187.9 km (116.8 mi) from Talbotville Royal to Port Colborne and 21.1 km (13.1 mi) from Port Colborne to Edgewood Park.