The Bay Freeway was a proposed facility that was to have run roughly parallel to the I-94/East-West Freeway through the northern portion of the Milwaukee metropolitan region, north of STH-190/Capitol Dr. The Bay Freeway was to have begun at I-43/North-South Freeway and continue westerly in the CTH-EE/Hampton Ave corridor to an interchange with the proposed-but-never-built Stadium Freeway in the area of the Hampton Ave & N 60th St intersection. It would have then turned northwesterly to follow the Fond du Lac Freeway for a short distance before departing to the west again via the CTH-E/Silver Spring Dr corridor, bypassing Timmerman Airport to the north. The Bay Freeway would have then dipped slightly to the south to intersect the US-45/Zoo Freeway south of the Silver Spring interchange before continuing westerly through the southern portion of Menomonee Falls, intersecting with the proposed-but-never-built Belt Freeway in the southwestern part of that city. It would have then continued along the northern limits of the City of Pewaukee north of Lindsay Rd before merging into the present-day STH-16 freeway halfway between the CTH-KF (Exit 186) and CTH-KE/North Shore Dr/Jungbluth Rd (Exit 184) interchanges. The Bay Freeway was then planned to continue westerly through Hartland and Nashotah to Oconomowoc.
In "Greater Milwaukee's Growing Pains, 1950-2000: An Insider's View," Richard W. Cutler states it was "politically active residents" who "persuaded legislators at state, county and local levels to pass resolutions opposing the Bay Freeway." On December 23, 1969, the Milwaukee County Expressway Commission removed the Bay Freeway from its various plans and maps. The state legislature even went to far as to enact a statute disallowing the construction of this freeway anywhere in Milwaukee County.
The one portion of the originally-proposed Bay Freeway that was actually constructed now comprises part of the STH-16 freeway in Waukesha County. The portion of STH-16 that had been realigned as a two-lane highway between Hartland and STH-190/Capitol Dr in Pewaukee in 1953 was converted to full freeway in 1974, while the segment connecting Capitol Dr with I-94 a four-lane, divided "expressway" with at-grade intersections. The STH-16 freeway was extended through Hartland to the eastern boundary of Chenequa in c.1977 and by 1980 the highway from that point westerly to Okauchee was converted to a four-lane, divided highway. Then, by 1983, the STH-16 freeway had been extended westerly through the CTH-C interchange at Nashotah and through the CTH-P NORTH interchange (Exit 176) by 1991. Meanwhile in the 1983–94 timeframe, the portion of STH-16 between STH-190/Capitol Dr and I-94 was converted to full freeway standards, connecting the "orphaned" portion of the completed Bay Freeway with the East-West Freeway.