The train services across the northern railways were affected due to low visibility.

The Northern Railway, a unit of Indian Railways, cancelled 55 trains while 25 trains remained partially cancelled and at least 11 trains were delayed on Friday as dense fog enveloped several parts of the national capital, reported Press Trust of India (PTI). The situation, however, was much better this year because of 'Fog Pass', a safety device that was provided to railway zones worst affected by fog, railway officials were quoted as saying in the PTI report. A total of 6,940 devices were provided across the railway network with 2,648 in the northern railway alone.

Here are 5 things to know about Indian Railways train services on Friday:

1. The Puri-New Delhi Purushottam Express, Howrah-New Delhi Poorva Express, Malda-Anandvihar Express, Mumbai-Amritsar Express and Farakka Express Malda-Delhi were among the trains that got delayed by several hours on Friday, the agency noted. Most of the affected trains were running late by two to three hours.

2. The train services across the northern railways were affected due to low visibility. However, operations were not affected at the Delhi airport.

3. At 5.30 am, visibility at Palam and Safdarjung was zero and 400 metres respectively. The visibility was 50 and 400 metres at Palam and Safdarjung respectively at 8.30 am.

4. The minimum temperature, meanwhile, settled at 7.1 degrees celsius in the national capital on Friday.

5. On Thursday also, 55 trains were cancelled while the frequency of 25 trains were reduced due to dense fog. Two trains remained partially cancelled across northern railways on Thursday, PTI reported citing official figures.