Network Rail and Balfour Beatty are fined a total of £13.5m following fatal Hatfield train crash in 2000.
Balfour Beatty has been fined £10m for breaching health and safety regulations over the Hatfield train crash, which killed four people.
Network Rail, formerly known as Railtrack, was fined £3.5m, and both firms were ordered to pay £300,000 each in costs.
The accident was caused by a cracked section of a northbound section of track near Hatfield.
In July a jury cleared three Network Rail executives and two Balfour Beatty executives of charges under Section 37 of the Health and Safety at Work act 1974. The five were cleared of manslaughter charges while a corporate manslaughter charge against Balfour Beatty was also dismissed.