History of Secondary Highway 550B:
Secondary Highway 550B was a short business route in the Sault Ste. Marie, which extended from Highway 550 into downtown. The highway is believed to have come into existence in the Fall of 1962, when a new route of Highway 550 was established through Sault Ste. Marie. The entire route of Highway 550B was under the jurisdiction of the City of Sault Ste. Marie, and was therefore not an assumed portion of the provincial highway system. It should be noted that there remains a lot of uncertainty about the status and exact route of this highway over the years. The highway was sometimes marked as Highway 550 (or omitted entirely) from the Official Ontario Road Map in many years and was also inconsistently described in Department of Highways of Ontario (DHO) mileage tables and other documents.
I've interpreted the conflicting information about Highway 550 and Highway 550B as follows, based on the typical DHO route marking practices used at that time. Initially, Highway 550 went into Downtown Sault Ste. Marie from the intersection of Second Line and Korah Road, via a Municipal Connecting Link which was established in January, 1962. Highway 550 came to an end at the intersection of Huron Street and Wellington Street (Highway 17B). In the Fall of 1962, a "new" route of Highway 550 was established via Second Line, while the "old" route of Highway 550 established in January, 1962 became Highway 550B. This theory is further supported by the fact that the route of Highway 550B was described as such in the DHO's mileage tables for 1970. It is also consistent with the information found in a very detailed 1966 DHO document, which contains the earliest confirmed reference to Highway 550B. Until other evidence comes to light, this description of the routes of Highway 550 and Highway 550B will be presumed to be correct, despite how these highways are marked on some Official Ontario Road Maps during the 1960s. The route of Highway 550B was shown for the first time on the 1968 Official Ontario Road Map. The mileage given for Highway 550B in the 1970 DHO mileage tables was 1.4 miles, which matches the length indicated for Highway 550B in the 1966 DHO document.
After making an appearance on the 1968 Edition of the Official Ontario Road Map, the route of Highway 550B was then only marked intermittently on the Official Road Maps issued up until the late 1970s. Highway 550B disappeared entirely from the 1969-1972 Editions. A highway matching the route of Highway 550B was shown on the 1973-1976 Editions, but no route number was indicated on the maps. Highway 550B reappeared on the 1977 Edition, but was only signed along Huron Street between Wellington Street and Cathcart Street. The remainder of the route was marked as Highway 17B. This shortened route of Highway 550B was similarly shown on the 1978-1979 Edition. On the 1980-1981 and subsequent editions of the Official Ontario Road Map of the 1980s and early 1990s, Highway 550B is shown as entering downtown via Korah Road, Lyons Avenue and Wellington Street. Two spurs of Highway 550B extended from the intersection of Huron Street and Wellington Street due to the presence of a one-way street system. One spur extended southerly along Huron Street to Cathcart Street while the other extended southeasterly to Cathcart Street/Gore Street via Wellington Street. The last MTO mileage table showing the route of Highway 550B is dated 1989, where the mileage for the highway was listed at 3.7 km. The route of Highway 550B was not marked on the Official Ontario Road Map after the 1997 Edition.
It should be noted that during this entire period (1960s onwards) the route of Highway 550B remained designated as a Municipal Connecting Link. In fact, the highway continued to be marked as Highway 550B in MTO documents right up until 2006. A Minister's Order was signed on March 29, 2006, which formally revoked the Municipal Connecting Link designation from the route of Highway 550B. That said, the route of Highway 550B was definitely not being signed as such by the Year 2000, based on my personal field observations. It is quite probable that the City of Sault Ste. Marie discontinued signing Highway 550B around 1997, even though the Highway 550B designation was still technically in effect right up until its revocation in 2006.