Explanation: There are four general types of co-ordination of signals for road network: Simultaneous system:In this system all the signals along a given road always show the same indication (green, red etc.) at the same time. As the division of cycle is also the same at all intersections, this system does not work satisfactorily. Alternate system: In this system, alternate signals or group of signals show opposite indications in a route at the same time. This system is also operated by a single controller but by reversing the red and green indicator connections at successive systems. This system is generally considered to be more satisfactory than simultaneous system. Simple progressive system: In this system, the signal phases controlling “Go” indications along this road is scheduled to work at the predetermined time schedule. Flexible progressive system: In this system it is possible to automatically vary the length of cycle, cycle division and the time scheduled at each signalized intersection with the help of a computer. This system is most efficient among all four systems.