New Delhi: As dense fog enveloped several parts of the national capital Friday, 55 trains were cancelled, 25 remained partially cancelled and at least 11 delayed across northern railways due to low visibility, officials said.

The minimum temperature settled at 7.1 degrees Celsius Friday, normal for this time of the year. 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.

Puri-New Delhi Purushottam Express, Howrah-New Delhi Poorva Express, Malda-Anandvihar Express, Mumbai-Amritsar Express and Farakka Express Malda-Delhi were some of the trains which got delayed by several hours, the railways said.

Most of the affected trains were running late by two to three hours due to very low visibility, they said.

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, they added.

A Global Positioning System-based portable device, the Fog Pass serves as an aid for the crew during low visibility conditions through an audio-visual alarm whenever a landmark comes within its geo-fence range.

A total of 6,940 devices were provided across the railway network with 2,648 in the northern railway alone.