What is the tunnel theory?
What is the tunnel theory? A theory of fluids is described based on a 'tunnel' model, in which lines of molecules are pictured as moving almost one-dimensionally in tunnels or fine capillaries, the walls of the tunnels being formed by neighbouring lines of molecules.
How far are you allowed to reserve?
You are allowed to reverse as far as necessary but no further. This is because what is necessary will vary on different roads. For example, on single-track lanes, you may need to reverse a long way to find a suitable passing point. You are also permitted to reverse in order to turn your vehicle around.