A fleet of new trains for services running to Hertford East could be delayed for up to a year.
Greater Anglia were due to start introducing the 111 new trains earlier this year, replacing their entire fleet of aging commuter rolling stock.
The class 720 Aventra trains are being built by Bombardier in Derby.
Similar class 710 Aventra trains used by London Overground were introduced in May 2019 - a year later than originally planned.
Managing Director of Great Anglia, Jamie Burles, told RAIL Mazazine that the problem relates to the Train Control Management System (TCMS), which is similar to the 710s used by London Overground.
The new ten car trains will require the platforms at Hertford East to be extended. However, the siting of the listed Victorian signal box adjacent to Platform 2 means that any work would require the relocation of the structure. Planning permission to move the signal box was refused by the District Council earlier in the year.
The fleet replacement was part of parent company Abellio's bid for the East Anglia rail franchise, which runs from 2016-2025.
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