US route endpoint in
Louisville

...but during the early years, routes were often overlapped to a more centrally-located junction.  This 1928 photo shows that traffic heading east on Broadway from 2nd Street (US 31) was reassured with two US route shields.  Unfortunately the numbers themselves were not visible, but nevertheless that gives further support to the idea that US 60 and 168 were overlapped between 2nd and Barret.  This route log (from the 1929 official state highway map) suggests that the route actually terminated at 5th and Jefferson.  In one sense that is plausible (considering that the courthouse is located there), but on the other hand it is odd that inset maps from that timeframe illustrated neither 5th nor Jefferson:

With very little to go on, my conclusion at this point is that US 168 may have ended at the courthouse during the 1920s.  This photo was taken looking to the west on Jefferson, with 5th being the crossroad.  In the foreground is the courthouse, and City Hall is visible in the next block:

At the time neither US 60 nor US 31E followed the same routings they do today, so it would have made sense for US 42 to end right downtown at its junction with US 31 (specifically on Main Street at 2nd Street).  And according to the preceding photo (since Market is the eastbound counterpart to Main) US 168 probably ended there as well.  This shot was looking west on Main at 2nd: