Fog enveloped the National capital this morning but flight operations at the Indira Gandhi International Airport remained unaffected. Airport officials said, the visibility is 200 metres which will further improve during the day. However, about a dozen of trains are running late due to fog. Departures of some trains have been rescheduled due to late arrival of corresponding trains.Nearly 70 trains were affected yesterday causing much inconvenience to passengers. As many as 30 trains coming from Orissa, Bihar, West Bengal, Assam and other parts of the country are running several hours late.Northern Railway spokesperson said in New Delhi that Railways have fully cancelled 24 trains and partially cancelled 12 trains due to the foggy weather condition. He stressed that passengers' safety is the main concern for railways, so the train speed would be restricted during the foggy weather.