Doesn't the saying say, "Think before you start"? This is certainly true of planning and building the road network on our model runway. Nothing is more annoying than having to find afterwards that certain vehicles cannot drive on part of the road network because that one bend is just too tight……
Geometry, size and dimensions.
During the planning of the road network we have to ask ourselves what dimensions we should use for the roads, what is the minimum radius of bends, the minimum width of the roadway and so on. We also need to determine, as in reality, which vehicle type is allowed to drive where. Example: a long trailer with semi-trailer will not drive through a winding one-way street where cars are parked on both sides. The dimensions therefore depend in part on the vehicles that drive over them. In order not to make it too difficult, I start from roads that all types of vehicles should be able to drive over.
A vehicle is up to 3 cm. Wide. For a single lane straight section, a width of 4.5 to 5 cm is sufficient. In the case of a double roadway, this will be 9 to 10 cm. This size applies to straight sections and very bland bends.
The better cornering
In corners, things get considerably more complicated because we have to deal with the shearing of buses and trailers with semi-trailers, for example. The sharper the bend, the greater the shearing where an oncoming car will collide at some point. With buses and older types of trucks we also have to deal with the shear from the front to the outside because there the front axle is a bit further back. You already understand that it is very difficult to propose a standard solution here as different sizes apply to every radius, shape and length of the bend….
What I've done is purchase:
The longest vehicle with the most inward clearance: a trailer with semi-trailer
A vehicle that travels far out: a bus with the front axle far back
For example, a small vehicle a van with small sled magnet to see if e.g. still realistic in model practice
This allows you to determine the minimum width of the roadway for a bend of desired radius and length. This has shown me that with the long vehicles you should not go under a radius of 15 cm because otherwise you have to use very wide lanes that no longer correspond to reality.
However, there are technical possibilities for a more realistic road behaviour. In reality, a driver of a long truck combination will pick up the bends. He will take the bend more broadly so that his trailer is less far-range. This can also be achieved in model with an extra thread/magnetic tape that ensures that the longer vehicle takes the outside bend while the shorter ones take the normal route. You already understand that if you want to have this done automatically, you want to have this in full control of the vehicles. After all, you have to make a distinction between long and short vehicles. These must be detected and therefore the route in question will have to be chosen. This is of course technically quite a challenge to realize…
Mountain on mountain
Another question is what percentage of increase can be used for slopes. In practice, it has been shown that it is better not to make more than 7% gradients. A steep slope means significantly higher power consumption and therefore a significantly shorter driving time. Especially the smaller vehicle that has a low capacity battery are sensitive at this point. As with trains, the ramp will have to have a smooth run. In summary, therefore, every situation is different and no standard dimensions can actually be given. The best and fastest is m.i. e.g. first in a trial setup. If there are mathematicians among you who see chance to e.e.a. in a simple formula form to make it accountable then I wholeheartedly like recommended myself.