Is the limit still 255 ?You can edit openttd.cfg to change the max for each player. It is bytes, so there are a limit of 255. Nowever setting it to 255 allows more than 255 trains and the next will be number 0. I will not recommend that people do that since the code is not made for that and it most likely will have sideeffects
Set it to 254 if you want as many as possible
Would be nice to be able to build more than 255 road vehicles, and now with bigger maps the limit really needs to be changed
But this may require a change in the save game format ?