It is possible to "fake" a tramloop using overlapping tiles.
I've made a quick setup (with no actual rails under it) to show the graphics you could make:
Tramloop01.png [ 33.83 KiB | Viewed 526 times ]
There are a couple of issues though (besides the obvious graphic glitching you always get when using overlapping tiles):
- There has to be a tramstop placed on the outer part of the loop (to force the tram to use the visible track)
- The catenary of the actual track will still be visible (so you'll have a powerline with no track under it next to the powerline with visible track under it), but this might not be that big of a problem or could be used in combination with fake inner loop graphics.
- The tramstop will still look like one for double track. However you could make a small switchyard, so there is only double track at the stop (of which one line will never actually be used)
Regarding the waypoint issue, in OpenTTD you can set the order of the tram to non-stop-via for that tramstop. It will then take the route you want, without stopping there (so no need then for the train waypoint solution Wallyweb suggested)