In the early days of the American automobile, interstate travel was a challenge to even the most daring motorists because there were no highways, few maps or any other motorist services. In 1912, Carl G. Fisher, of Indianapolis, Indiana, proposed a stone-paved highway that would reach from coast to coast. "Let's build it before we're too old to enjoy it!" he toasted. In 1912, his dream came to fruition in the Lincoln Highway, that traveled from New York to San Francisco.
The Lincoln Highway inspired others to create named highways, such as the Yellowstone Trail, the Harding Highway, the Jefferson Highway and many, many more, all of them administered by private organizations. The roads were marked with color stripes on utility poles and by the 1920s, there were over 250 named highways, with a myriad of signs and colors. With no central administration, it was easy for unscrupulous promoters to relocate a route by repainting signs, far out of the way of the most direct route, in order to direct unsuspecting motorists into other municipalities.
In the 1920s, it became painfully obvious that a simplification of route naming and a central administration was becoming necessary. In 1926, the US Bureau of Roads, under the guidance of Thomas Harris MacDonald, put a set of rules into place. Named highways were banned, as was the myriad of signage.
Federal highways would all be numbered, following a model that was put into place by the State of Wisconsin in 1918. Federal numbers would follow a simple model, even numbers would travel east-west, odd numbers would travel north-south. The numbers would be assigned sequentially, with the lowest even numbers being in the north and succeeding higher numbers moving southward. The lowest odd numbers would be in the east with succeeding numbers moving west.
Numbers that ended in 0 were to be major highways that traveled coast-to-coast. Numbers that ended in 1 or 5 would be major routes that traveled from the Gulf of Mexico, or the Mexican border, to Canada. The strength of politicos was in evidence here. It explains why US 6 is out of the numbering sequence, all because a certain senator thought his state was important enough that it should have a single digit number - which, by the way, is why some Interstate Highways are, today, numbered out of sequence.
US 45 was one of those major north-south routes designated in 1926. Initially, it only traveled as far north as Des Plaines, Illinois from its origin in Mobile, Alabama. In 1934, it was extended north through Wisconsin to the shore of Lake Superior in Ontonagon, Michigan.
Another major highway is US 41, routed from Miami to Copper Harbor, Michigan. US 41 and 45 were signed concurrently through much of southeastern Wisconsin and the Milwaukee area, but northwest of the city, they spilt with 41 following the route of the old Yellowstone Trail for several miles. 41 and 45 ran concurrently, split off, and ran concurrently again all the way to Menasha for many years. US 41 was slated to become a divided expressway with an eventual upgrade to freeway, in fact, early Interstate Highway plans called for it to be designated an Interstate corridor. (That never happened. There was some talk of upgrading 41 to an Interstate Highway in 2005 but that is likely on the back burner now.)
In 1953, US 41 split off from the US 45 corridor in Germantown, with 41 following a northwesterly route toward Slinger, the corridor that it follows today. US 45 continued north, along its old alignment, toward West Bend. It was part of an upgrade of 41-45 to expressway status from the Milwaukee County line to this split.
At that time, a new interchange (of sorts) was built at this location. At the same time, two bridges were built to carry US 45 across Cedar Creek, part of the upgrade to the corridor. In the mid 1970s, a new interchange was built here, relegating the old alignment of 45 to local road status. If you stand on the bridge and look south, you can see how the northbound lanes of modern US 41-45 come straight for your location before veering in a northwesterly direction into the freeway interchange, with 41 following the corridor toward Slinger and Fond du Lac while 45 continues north to West Bend, then to Fond du Lac.
Today, the Shadow Lane bridges are a part of the original alignment of US 45, pretty much the way they were built in 1953. While small, these two bridges are well preserved examples of post-war bridge and highway designs, with concrete decks cast in place over steel stringers, curbing and steel guard rails. Other than the addition of modern guard rails, the bridges appear as they did in 1953.
For more about US 41 and US 45 in Wisconsin, see Christopher Bessert's Wisconsin Highways website.