I think turning loops are something as train fuelling with water towers and maintenance depots – really not needed, but adds some immersion. It is my personal wiew, I am not trying to force it to anybody.
Why there are main connection in game at all? Because people start driving cars from town to town. If you delete a road, the only way to reach their destination (without motorway connection) is your railroad. That’s no fair play. But if there is any road, may be even small country road, and very long, it makes an alternative way for citizen to reach another town.
In reality, there is no town, where you can reach only with railroad, because CEO of railroad company destroyed the only road to town to force people to use his trains. Yes, there are places difficult to reach. But there is always a small road or a path (free of charge, for pedestrians and some others). If you, as CEO, bribe the city major and destroy this road, local people make another road. I am not talking about places that can be reached only with helicopter. So, if ANY another road is exist – you could delete another one, but only if other way is exist.
About segments of long parts – it is just my wiev to flying/digging vehicles. It is not gamebreaker at all, but it can make visuals looks a little more satisfyingly. And yes, you are right: a minimum segment lenght should be checked.
