History of King's Highway 20A (Thorold):
There have been four different routes in Ontario numbered as King's Highway 20A. This section of Highway 20A ran from Allanburg to Thorold, just south of St. Catharines. Three other discontinuous sections of Highway 20A existed north of Stoney Creek, west of Elfrida on Hamilton Mountain and south of Bismarck.
On June 4, 1930, the Ontario Department of Highways (DHO) assumed the road from Thorold to the Highway 20 Junction in Allanburg as a new provincial highway. However, it has not yet been confirmed if this route was signed as Highway 20A. Some sources suggest that this highway may have in fact been a part of Highway 3A. However, it should be noted that the date of assumption of the Allanburg to Thorold road matches the date that Highway 20A was assumed from Bismarck to Wellandport. In light of this fact, and given that both of these routes served a similar purpose providing a link from Highway 20 to nearby towns, it is quite probable that the Allanburg to Thorold route was numbered Highway 20A as well. The length of Thorold's Highway 20A was only 4 km. The entire route was paved in 1930. In 1937, the entire route of Highway 20A from Allanburg to Thorold was renumbered as Highway 58.
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