Team-BHP - Road Intersection Management Algorithm?

Hello BHPians,

A friend of mine is working on a image processing based intersection management project where the lights at an intersection are timed by the amount of traffic and traffic density, instead of a fixed time. This is for a 4 way intersection, with all 4 directions being 2 way.

What he wants to know is how the current traffic algorithm works? Meaning that how is traffic controlled right now.

Is one direction of traffic allowed to pass through all 3 directions, while the rest of traffic is stopped? The problem with this algo is that if each direction takes 120s maximum, one signal's traffic will have to wait upto 360s.

There are two methods I have seen been deployed in traffic junctions across Indian cities:
Method 1:

a. (1) and (3) move straight ahead simultaneously
b. (1) and (3) take right turns simultaneously
c. (2) and (4) move straight ahead simultaneously
d. (2) and (4) take right turns simultaneously

This is typically used at large junctions where two opposite stream have sufficient place to take right turns without obstructing the opposing traffic.
Usually the left turn (for 1, 2, 3, 4) is also kept free in such cases. (Except Mumbai)

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Method 2:

a. (1) is allowed to move straight ahead as well as take a right turn
b. (1) continues moving straight ahead but right turn is stopped, simultaneously (3) starts moving straight ahead
c. (1) is stopped completely and (3) starts taking right turn also
d. (3) is stopped completely and the same sequence is followed for (2) and (4)

This is usually done on small junctions where simultaneous right turns of opposing stream can cause obstruction. In addition this is also used when the roads are quite narrow and you wish to drain them completely before focusing attention to other roads. Left turn can also be clubbed with merging straight movement [i.e. (1) left turn + (4) straight]

Incidentally, most traffic policeman also implement this method.