Highway 37 is a 44.2 km (27.5 mi) road between Highway 401 at Belleville and Highway 7 at Actinolite that serves as a shortcut between Toronto and Ottawa.^[2][3] Lying entirely within Hastings County, the route travels parallel to the Moira River throughout its length. Outside of the communities that it cuts through, the majority of surrounding land use is agricultural, though forest is dominant near the Moira River.^[4][5] Traffic levels along Highway 37 taper gradually from south to north, and increase by approximately 144% in the summer months compared to winter months. On an average day, 9,150 vehicles travel the route immediately north of Highway 401, and 3,150 vehicles travel the route north of the village of Tweed. These represent the heaviest and lightest travelled portions of the route, respectively.^[2]

Highway 37 begins at an interchange with Highway 401 (Exit 544), south of which it continues as Cannifton Road into downtown Belleville. North of Highway 401, the route curves to the northeast, bypassing the communities of Cannifton and Corbyville. After travelling past Honeywell Corners and Thrasher's Corners, it crosses the Moira River on O'Brien's Bridge and curves east then north, bypassing the communities of Plainfield and Latta. At Roslin, the highway exits Belleville and briefly crosses into Centre Hastings, before straddling the boundary with Tweed north to Thomasburg. Bypassing east of the village, the route fully enters Tweed.^[4][5]

Highway 37 meanders northeasterly, bypassing the hamlet of Chapman. It approaches Stoco Lake and turns north into the village of Tweed, where it is locally known as Victoria Street.^[4][5] A 2.1 km (1.3 mi) segment through the village, between Jane Street and Hastings County Road 39 (Sulphide Road), is maintained under a Connecting Link agreement.^[2] Crossing the Moira River once more and becoming Moira Street, the highway continues north out of the village alongside the river. After venturing through farmland for several kilometres, Highway 37 parallels the Skootamatta River into Actinolite, ending at Highway 7.^[4][5]

Prior to the early 1930s, transportation between Toronto and Ottawa was limited due to the few roads that permeated the Canadian Shield between Lake Ontario and the Ottawa River; at that time the only option was via Highway 2 and Highway 16. The Ontario Department of Highways (DHO) set out to remedy this situation by extending Highway 7 east of Peterborough to Perth. As part of the ensuing depression-relief project, over 2700 men blasted rock, dredged muskeg and endured a constant barrage of blood-sucking insects in order to construct the new highway,^[6] which was opened to traffic on August 23, 1932.^[7]

During this timeframe, the DHO assumed ownership of several north–south routes to connect Highway 7 with Highway 2. On January 6, 1932, the Belleville–Actinolite Road was designated as Highway 37. The new route followed existing Hastings County roads.^[1] Originally, Highway 37 began at Highway 14 (Front Street) in downtown Belleville, and followed Station Street and Cannifton Road north through the communities of Cannifton and Corbyville.^[8] While this section was paved, the remainder of the highway was gravel-surfaced.^[9] It was paved from Corbyville to Roslin between 1942 and 1946,^[10][11] and from Tweed to Actinolite in 1945.^[12] The remainder of Highway 37, from Roslin to Tweed, was paved between 1951 and 1953.^[13][14]

Within Tweed, Highway 37 originally followed Bridge Street and Moira Street until Victoria Street was extended north across the river in 1937.^[15] O'Brien's Bridge over Moira River south of Plainfield collapsed in spring of 1945 when a truck struck it. Construction of a new bridge to the west of the old bridge as well as a 1.1 km (0.68 mi) diversion to connect with it began that summer,^[16] and was completed the following year.^[17]

The adjacent communities of Cannifton and Corbyville were bypassed by a new alignment that opened in October 1960.^[18] In 1968, a diversion around Plainfield and Latta was opened.^[19] The interchange with Highway 401 was built beginning in 1955 as a cloverleaf,^[20] and opened along with the section of that highway between Trenton and Marysville on October 7, 1958.^[21] The interchange was rebuilt in 1991 as a parclo AB, with the ramps on the west side of Highway 37 being removed.^[20]

The following table lists the major junctions along Highway 37, as noted by the Ministry of Transportation of Ontario.^[2][5] 

• Highway 37 - Length and Route from Google Maps
• Highway 37 Pictures and Information from Asphalt Planet