First off, one-way-two-lanes would be a big relief for players who need to supply a pharmacy or a gas station in a downtown with all those traffic jams. I sometimes ended up building a railway to supply those small markets in the towns because buses and trucks used to lock the streets. But.... a railway here doesn't make some much sense.
But would these classes be inherent to the road object (in dats) or simply triggered by signals?
I prefer by object, because player would intuitively try to build an one-way lane instead of placing a sign.
For now, considering the people's ideas (and Issac's too), these are the possibilities I could think of that could be combined depending on the need:
I) Number of lanes:
- Two lanes: both lanes have traffic
- One lane: one lane is used, and the other is unused (where grass or white strips could be painted).
II) Directions:
- Two-direction
- One-direction
III) Overtaking:
- Allow
- Disallow
IV) Player vs. Citycars:
- Free traffic: player vehicles and citycars can use both lanes freely.
- Separate: player vehicles always drives on main lane, and citycars always drives on second lane. (
i.e. main lane = right lane in U.S. and left lane in U.K)


I hope the former, but how could you set the direction of the road?
Player could. The direction could be set by the clicks:
1st click -----------> 2nd click
Therefore, traffic goes W -> E
2nd click <--------- 1st click
Therefore, traffic goes E -> W
Now, how would the player see the directions of the way after he's done?
1) The graphics, depending on the pakset theme, he can distinguish by colors and strips.
2) Likely "Show/Hide reserved blocks" and "Show/Hide station coverage", Simutrans could use visual cues (arrows and colored tiles) to show the player directions, type of road and ownership (if the road belongs to him, someone else, or public service).