I-43 begins in
Rock County as the eastern leg of a
T 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 suburban residential areas 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 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. In
Elkhorn, I-43 junctions with
WIS 67,
US 12, and
WIS 11. The freeway passes through
East Troy about northeast of Elkhorn and junctions with
WIS 20 and
WIS 120. It then enters
Waukesha County at
Mukwonago. I-43 crosses
WIS 83 at an interchange just southeast of the village. After about , the highway junctions with
WIS 164 just north of
Big Bend and then enters the city of
New Berlin where the freeway has interchanges with South Racine Avenue (CTH-Y) and South Moorland Road (CTH-O). It then turns east to enter
Milwaukee County. , traffic volumes range from 21,000 around Elkhorn to 35,800 in Waukesha County to 85,000 (2007 figures) at
WIS 100. The Beloit-to-Milwaukee portion (at the Hale Interchange with I-894) was given the name "Rock Freeway" because the freeway traverses Rock County and heads towards the cities in the
Rock River valley, including
Rockford, Illinois. However, the moniker generally only applies to the portion of the route in Waukesha and Milwaukee counties; freeway names in southeastern Wisconsin media are used interchangeably with Interstate numbers. The freeway is entirely four lanes from Beloit to New Berlin. A six-lane segment begins where
US 45 merges on the Interstate. The highway passes through mixed urban residential and industrial areas of the greater Milwaukee area, carrying six lanes throughout with the exception of near the Marquette Interchange where eight lanes of traffic exist. Up to 146,000 vehicles used this portion daily in 2007. This count decreased further north, with a count of 78,900 vehicles per day near WIS 100's northern terminus and 69,600 closer to the Ozaukee County border. As it passes through mixed residential and commercial zones north of downtown, the highway carries eight lanes of traffic downtown, six lanes of traffic north of North Avenue to WIS 60 in Grafton, and four lanes of traffic north of WIS 60 all the way to
Green Bay. WIS 32 leaves the freeway at
Cedar Grove and the Interstate passes
Oostburg to the east and
Sheboygan to the west. In Sheboygan, I-43 intersects
WIS 28,
WIS 23, and
WIS 42. I-43 enters Manitowoc County north of Sheboygan. , traffic counts in southern Ozaukee County peak at 66,900 vehicles per day—this value generally decreases further north. , the counts in Sheboygan County bottom out at 21,100 vehicles per day just south of the Manitowoc County line. I-43 passes
Cleveland on the county line. The highway continues to follow the lakeshore to straddle Manitowoc's westside, passing west of
Newton, Wisconsin, with a
weigh station for southbound truck drivers located midway between Newton and Cleveland. I-43 connects with
US 151 and WIS 42. WIS 42 north follows the freeway north to the interchange with
US 10. WIS 42 leaves to the east along with US 10 east, and US 10 west follows I-43 north to the interchange with
WIS 310 where it turns off to the west. The Interstate passes
Francis Creek and
Maribel (at
WIS 147) and turns northwestward into Brown County, with a
rest stop located just before the county line. I-43 in Manitowoc County has the least traveled portion of the highway with 17,400 vehicles passing south of WIS 147 according to 2005 results. These values increase further south. The Interstate passes
Denmark and meets the terminus of
WIS 96 north of the county line. The Interstate then continues another to
Bellevue where
US 141 begins. This interchange provides access to
WIS 29, a route the freeway crosses under later. At this point, the Interstate enters urban residential areas as it approaches Green Bay. I-43's lowest traffic volume in this county is at the southernmost entry with a 2006 value of 22,100 vehicles per day near Denmark. Values around Green Bay range from 34,600 to 42,200 vehicles per day. ==History==