The new connector received the US 45 designation as that highway was transferred onto the freeway heading north. The first long segment was completed in 1969. It extended from the US 45 connector to CTH-F (now WIS 164) in Big Bend. After this segment was opened, the WIS 15 designation was applied. The next segment, to East Troy, was opened in 1972, the year the Highway 15 Committee had hoped the route would be completed in its entirety. It was extended to Elkhorn in 1973 in conjunction with the US 12 freeway construction, then to I-90 in 1976. I-43 signs were placed on the freeway by 1988 after designation in 1987, replacing WIS 15. I-43 was also mapped concurrently with I-94 and I-894 to link the two segments together. Even though exit number tabs were labeled according to the new mileposts, the mileposts themselves were not renumbered to coincide with the current length until 1991. The Marquette Interchange, which connects I-43 with I-94,and I-794, was completely reconstructed over a four-year span, beginning in October 2004 and ending in September 2008. This project eliminated left-hand exits and widened connecting ramps between I-94 and I-43. I-43 begins in Rock County as the eastern leg of a cloverleaf interchange with I-39/I-90 just east of Beloit. The highway becomes WIS 81 west of the interchange. The Beloit-to-Milwaukee segment of I-43 passes mainly through farmland situated on rolling hills, going around urbanized areas except for in the greater Milwaukee area—where the route passes through residential suburban zoning with some embedded industrial establishments. The Interstate bypasses Clinton to the north at WIS 140 and passes into Walworth County east of WIS 140. Daily traffic counts as of 2007 for Rock County range from 12,400 to 19,200 with the higher counts closest to Beloit. The interchange with I-39/I-90 accommodates 1,000–5,200 vehicles daily, with the most traffic on ramps connecting southbound I-39/I-90 to westbound WIS 81 and westbound I-43 to southbound I-39/I-90. I-43 passes north of Darien and crosses US 14 at that point, then junctions with WIS 50 south of Delavan. About 14,000–19,200 vehicles use this section daily as of 2006.