Abandoned National Road
Eastbound. West of Clark Center, the old National Road is made of concrete. US 40 is on the left.
One thing that strikes me as odd is that the brick road tended to meander a little bit, while the concrete road is as straight as an arrow. Look at an aerial map, and you can see how west of Clark Center the old road ends and then begins again a bit later, but on a slightly different trajectory, and running perfectly parallel to US 40.
This section is only quasi-abandoned, as it provides access to a farm on the right. But I find it unlikely that the state maintains it, and it's my group, and I get to stretch the rule.