The new vehicles are being ordered as part of the Durchmesserlinie project to connect the Trogen - St Gallen and St Gallen – Appenzell lines with a 700m tunnel beneath St Gallen town centre. Construction is due to start this year on the link, which is expected to boost AB ridership by around 50%.

The Tangos will seat 133 passengers in second class and 12 in first class. The vehicles will be assembled at Stadler's Altenrhein plant in St Gallen canton and are due to be delivered in time for the opening of the St Gallen tunnel in 2017. The contract includes the provision of spare parts.

The introduction of new LRVs will allow AB to abandon rack operation on the Trogen branch.