What's the effect of road maintenance?

I know what road maintenance does IRL. But I see no mention of it's impact in the game on the transportation index or anything else in the transportation department.

So what happens in this game if I just run a deficit of road and rial maintenance?

You will find roads and train tracks closed.

You will also have a drop in your supply index which effects welfare and all sorts.

You will also lower corp welfare and so production with a lower transport index.