Perhaps I'M missing something, but the tool tip for the concrete road tunnel gives a max. weight of 16t while the built tunnel has only 14t, making it impassable for the later heavy trucks.
Thank you for the report. I cannot reproduce this with the latest development version; are you using the latest release version (11.35) or a self-compiled build from devel-new?
Unmodified vanilla 11.35 + Pak from a year ago.
The first screenshot shows the tile between the tunnel entrances. It's the one causing the trouble. Newly built tiles (screenshot 2) are correct, although when dragging the tunnel the old tile isn't "upgraded".
Ahh, in which case, hopefully this will be fixed in the next major release. Thank you for your patience!