Geometry of the road

Doesn't the proverb say: "Look before you start"? This certainly applies to planning and building the road network on our layout. Nothing is more annoying than having to conclude afterwards that certain vehicles cannot drive on part of the road network because that one corner is just too tight ......

Geometry, sizes and dimensions.

During the planning of the road network, we should ask ourselves what dimensions we should use for the roads, what is the minimum radius of bends, the minimum width of the road, etc. We also have to determine, as in reality, which vehicle type is allowed to drive where. Example: a long trailer with a semi-trailer will not drive through a winding one-way street where cars are parked on both sides.

The dimensions therefore partly depend on the vehicles that drive over it. In order not to make it too difficult, I use roads that all types of vehicles must be able to drive over.

A vehicle is maximum 3 cm. wide. For a single lane straight section, a width of 4.5 to 5 cm is therefore sufficient. With a double carriageway this will therefore be 9 to 10 cm. This size applies to straight tracks and very gentle curves.

Better cornering

In bends, things get considerably more complicated because we have to deal with the scissoring of, for example, buses and trailers with trailers. The sharper the corner, the greater the scissor at which an oncoming car will collide at some point. For buses and older types of trucks we also have to deal with scissors from the front to the outside because the front axle is located a little further back. You already understand that it is very difficult to come up with a standard solution here, because for every radius, shape and length of the bend different sizes apply ....

What I have done is to purchase:

The longest vehicle with the most cut-out inwards: a trailer with trailer

A vehicle that extends far outwards: a bus with the front axle far back

A small vehicle, for example, a delivery van with a small towing magnet to see whether this is still realistic in model practice

This allows you to determine by trial and error what the minimum width of the road must be at a bend of the desired radius and length. This has shown me that with the long vehicles it is better not to 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 options for achieving more realistic road behavior. In reality, a driver of a long truck combination will pick up the corners. He will take the bend wider so that his trailer will extend less far. This can also be achieved in model with an extra contact wire / 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 carried out automatically, this requires extensive steering of the vehicles. After all, you have to distinguish between long and short vehicles. These must be detected and with that the relevant route will have to be selected. This is of course technically quite a challenge to realize ...

Downhill on downhill

Another question is what slope percentage can be used for slopes. Practice has shown that it is better not to make more than 7% slopes. A steep slope means significantly higher power consumption and therefore a significantly shorter driving time. Especially the smaller vehicles that have a low capacity battery are sensitive at this point. As with trains, the ramp should run smoothly.

In summary, it boils down to the fact that every situation is different and that no standard dimensions can actually be given. In my opinion, the best and fastest is to try out a test setup first. If there are mathematicians among you who see an opportunity to make it possible to calculate everything in a simple formula form, then I keep heartily recommended.