The problems here are a bit deeper, since this still brings several challenges:
We need to keep in mind every single kind of situation, where this type of road interacts with something else. Be it other types of roads, railways, canals, bridges, buildings, ... Not only from a visual point of view but also regarding the game logic (considering when talking trams, people usually expect a gameplay element connected to it).
Having two types of transport with their own logic share a system would most likely make it worse and not better ;)
Generally, the topic of new street types etc. is something we will have another look at regarding technical feasibility, but there are certain challenges connected to it which makes it tricky to implement in the current system.