Basically, let's say there is a highway going through the city. How do I avoid the city spawning city roads and houses along the highway? I remember pak128 in normal simutrans had some graphics for railway tracks that made them look like fences or something. Is there such a workaround in this pak? Or would you suggest something else? Maybe some download somewhere?
The only workarround I know of is building public player owned roads.
Don't confuse public player owned and unowned roads.
One solution is introducing of a noise_barrier_t wayobj. That makes the road fix the top speed. However there's no wayobj for that currently in this pakset, and it doesn't avoid to build any buildings next to the way.
I am not even sure if the city speed limit would not apply to such roads.