In the 1920s, State Highway 315 also stayed within a single town, following today's Route 31 between US 44 and Route 32 in Coventry.

Today's Route 315 started out as SH 305 in the 1920s; and afterward became unsignposted SR 915. It served as a short but important connector between Route 10 in Simsbury and Route 9 (now Route 189) in Tariffville.

In 1959, after Route 9 was relocated to a new bridge north of Tariffville, SR 915 was moved from Winthrop Street (connecting to old 9) to Elm Street (which connects to new Route 9).

In 1963, SR 915 became signed route 315.

Plans: relocate highway, build new bridge

During the 1960s and 1970s, the town and state studied how to fix some deficiencies with Route 315. The one-lane steel girder bridge over the Farmington River, built in 1892, could no longer support trucks or emergency vehicles. Two sharp curves at Terry's Plain Road and Quarry Road were a safety problem. Studies were also done to examine relocating the highway from the center of Tariffville.

In 1966, the state announced plans to widen 1/2 mile of Route 315, starting at Route 189.

In June 1970, the state was planning to replace the steel bridge and relocate Route 315. Town officials wanted the new route to not split up Tariffville.

In August 1970, the steel bridge was closed two weeks for retrofitting. This was a temporary measure: after the work, the bridge was given a 10-ton limit, enough for school buses but not fire trucks.

In 1971, the prevailing plan would replace two old bridges, at Route 315 and Drake Hill Road to the south, with a new bridge leading from an extension of Owens Brook Boulevard across Route 10. An improved roadway would connect the relocated Route 315 to Route 185 to the south. This configuration would relieve some traffic on Route 10.

Tariffville citizens worried about the traffic impact of the relocation.

In 1974, the state still advocated one new bridge, a $3.7 million two-lane span, to replace the older bridges. Simsbury officials restated their desired for a relocated Route 315 as well.

By late 1977, the plan had changed: a new bridge would be built 200 feet north of the existing Route 315 bridge; and Route 315 would be straightened in the area between Terry's Plain Road and Quarry Road. This was done circa 1992.

In 1988, the Drake Hill Road bridge was also replaced. The old one was to be torn down, but fortunately some Simsbury residents had other plans. Since the bridge was historically important, connected to a 22-mile greenway trail, and could provide pedestrian access that the new bridge did not, the town council agreed the bridge should be saved. The bridge was restored, with rust and lead paint removed, and the roadway was replaced with wooden planks.

Each spring and summer, local volunteers place and water more than 100 varieties of flowers and 1,000 plants in boxes along the bridge, now known as the Old Drake Hill Flower Bridge.