It immediately became the primary route between Toronto and Ottawa, via Highway 2, and as such saw many improvements and realignments carried out over the next three decades.

Former portions of Highway 16 can be followed north from Johnstown, through Spencerville and Kemptville to the Rideau River along Leeds and Grenville County Road 44.

For example, the 1918 DPHO Annual Report noted that in North Gower Township, the road "was in places very narrow and the sides grown up with brush and small trees.

"[5] Work began immediately to clear, widen, grade, and gravel the route, which was in many cases only 10 m (33 ft) wide between the overgrown fence lines.

[6] Paving began in 1922, starting at the Central Experimental Farm in Ottawa, and progressing in a southerly direction for approximately 6.5 km (4.0 mi).

This left unpaved segments south of Kemptville (except through Spencerville), and from the Rideau River to the village of North Gower.

[11] Premier Howard Ferguson officially opened the completed highway on October 7, 1929, at a rail overpass south of Kemptville.

[15] This route, dubbed "Highway 16 New",[16] was designed to easily accommodate the eventual upgrade to a freeway when traffic volumes necessitated.

[16] The project was completed in 1983,[13] merging into the original route of Highway 16 northeast of the present Prince of Wales Drive overpass.

[19] With the completion of Highway 16 New, there was sufficient right-of-way to construct interchanges and the southbound lanes in order to create a full freeway corridor.

[21] Immediately after crossing over a Canadian National track, the route encounters an interchange with Highway 401 at Exit 721B.