The first fog of the season affected the movement of Delhi-bound trains, leaving thousands of passengers in the lurch.
The condition will worsen in the coming days as dense fog is expected to envelop the north after December 10.
The average delay in the arrival and departure of trains shot up from six to 10 hours. The Met department expects dense fog in the weekend.
Services of 80 trains were affected on Friday as the dense fog forced the Railways to slow down the movement of showcase trains such as the Rajdhanis and Shatabdis.
More than 40 trains, including Rajdhanis and Shatabdis, ran hours late.
The routes most affected were the Delhi-Allahabad and Haryana-Punjab lines.
Around 15 trains were rescheduled, including a few Rajdhanis — Delhi-Bhubneshwar, Delhi-Howrah and Delhi-Sealdah — on Friday.
Thirty Delhi-bound passenger trains have already been cancelled and the number can go up.
Thousands of stranded passengers at New Delhi , Old Delhi and Hazrat Nizamudin stations parked themselves in the open and on railway platforms.
“In the coming days, there will be more delays and rescheduling of trains as the fog will get denser. After January 20, we are expecting the train services to improve,” a senior railway officer said.