Biting cold gripped north India on Tuesday while dense fog caused several accidents, leaving three people dead and 40 injured and prompting affected states to take steps like suspending night operations of buses, reducing speed limit in some areas and changing school timing. Dense to very dense fog engulfed the Indo-Gangetic plains, including Delhi, for the second morning on the trot on Tuesday, lowering visibility to 50 metres in the city and affecting road traffic and train movement. Taking note of the dense fog and accidents due to it, the Uttar Pradesh government on Tuesday evening stopped plying of state roadways buses at night.