Why do traffic police switch off the lights during peak hours?

Actually it is not a good practice but is in-evitable due to inadequate capacity of junctions. There are the situation when road is not able to take the entire volume of traffic and tail of traffic ahead does not get cleared even till next green phase. Now if the lights are not switched off, vehicles will block the junction and make it impossible for even cross traffic to move thus creating a grid-lock. It is lose-lose situation for all. At this juncture policemen take over the signal and regulate it according to clearance and relative volume. However, this practice is largely reduced and will disappear soon due to increased capacity of roads and junctions. Switching off also becomes inevitable during acts of nature like water logging, cracks in road and man-made situations like strikes, rasta-rokho and VIP movement, when one or more roads become unavailable for traffic. In all such situations mannual operations are resorted to. This practice is, however not encouraged.