LUCKNOW, Dec. 18 -- As dense fog blanketed many parts of Uttar Pradesh on Wednesday, the India Meteorological Department (IMD) issued a red alert for 20 districts and an orange alert for several others till December 20 while the state government was considering halting traffic on expressways and National Highways during spells of extremely low visibility after a series of fatal accidents. Fog also led to the India-South Africa T20I match, the fourth game of the series, being abandoned without a ball bowled. The toss was delayed as a blanket of fog enveloped the ground, and following multiple inspections, the umpires eventually abandoned the match. Also, air traffic was severely affected in Lucknow, causing cancellations, diversions and significant delays. The Lucknow administration revised school timings, directing Classes 1 to 12 to start at 9 am or later from Thursday until further orders, district magistrate Vishak G said. Bareilly reported zero visibility, while Lucknow saw visibility dip to around 50 metres during early hours. Bareilly also recorded the lowest maximum temperature at 13.4degC, followed by Shahjahanpur (13.8degC) and Muzaffarnagar (15.2degC). Lucknow recorded a maximum of 17degC and a minimum of 10degC. Kanpur was the coldest at night with 6degC. The IMD attributed the prolonged fog to an inversion layer in the lower troposphere. For their part, the authorities were examining the possibility of traffic restrictions on expressways and National Highways during fog on the lines of suspension of train and flight operations due to poor visibility. The transport, home and law departments are examining legal and operational aspects of the move. Meanwhile, two flights were cancelled, one had to be diverted while several domestic and international flights operated hours behind schedule, said officials in the state capital....