(rail transport) A term generally applied to main-line railways, but this varies from country to country. It has no relation to the weight of the rails used.
2019 October 23, Andy Coward, “New acclaim for Oldham Loop”, in RAIL, number 890, page 63:
As with all Metrolink routes on the network, the Oldham-Rochdale line is performing well. Passenger usage is now considerably higher than when it was in use for heavy rail services, [...]
2022 November 30, Paul Bigland, “Destination Oban: a Sunday in Scotland”, in RAIL, number 971, page 75:
This section of line is a rarity, with heavy rail passenger and freight services sharing tracks with the Tyne and Wear Metro as far as Pelaw, where the Metro services run onto dedicated tracks.
heavy rail on Wikipedia.Wikipedia 