Swiss Federal Railways (SBB) returned the first rebuilt FV-Dosto double-deck EMU to regular passenger service on September 30, following operating approval from federal rail safety regulator BAV at the end of August. The trainset is the first of 62 to run with modified bogies that eliminate the WAKO passive tilt mechanism, whose poor ride quality has dogged the Bombardier-built Twindexx fleet since delivery.

SBB expects the modification programme to generate around SFr40m in savings over the fleet's lifetime. Removing the maintenance-intensive WAKO system simplifies bogie function, cuts depot workload and reduces the risk of technical failures.

The entire 62-trainset fleet will be modified progressively in Switzerland during scheduled overhauls, with completion planned for the early 2030s.

The FV-Dosto fleet was originally equipped with WAKO, a passive roll-compensation system intended to reduce the lateral acceleration perceived by passengers and permit faster running through curves. Unlike active tilt systems such as those on SBB's Alstom Pendolinos, WAKO used no motors or hydraulic actuators. Instead, specially designed suspension and kinematic elements exploited the bogie's behaviour as lateral wheel-rail forces increased in curves, inducing a controlled inward roll of the carbody. This altered the carbody's orientation relative to the combined forces of gravity and lateral acceleration, in theory supporting faster curve speeds without major increases in track cant.

In practice, the interaction between WAKO, the bogie and the suspension produced excessive rolling, jolting and vibration. The effects were most pronounced in curves, through pointwork and over worn track, and wheelset wear could aggravate them further. Track flaws were transmitted too strongly to the carbody, undermining the intended comfort benefits.

SBB decided in 2022 to abandon WAKO functionality. It worked with Alstom, successor to Bombardier Transportation as the trains' manufacturer, to develop an optimised bogie without passive tilt capability, with prototype development starting in 2023. The modified bogie was tested at the Velim circuit in the Czech Republic and subsequently on the Swiss network during 2025; test passengers reported reduced vibration and improved ride comfort. On December 5 2025, SBB approved modification of all 62 FV-Dosto trainsets.

A difficult procurement

SBB awarded Bombardier the contract on May 12 2010, following a 2009 tender. The order was worth approximately SFr1.9bn — at the time SBB's largest-ever rolling-stock procurement. It covered 59 trainsets for delivery in 2013-19, in four batches of EMUs in inter-city and regional express layouts and four- and eight-car formations. All were designed for 200 km/h operation and could be coupled to form trains up to 400 m long.

The programme ran into trouble early. Disability organisations challenged aspects of the design, including wheelchair facilities, triggering a lengthy legal dispute and substantial redesign work. The restaurant car also had to be modified to incorporate a PRM-compliant accessible toilet.

The first fare-paying passengers finally rode in February 2018, more than four years late. Bombardier compensated SBB for the delays by supplying three additional complete trainsets at no extra cost, raising the order from 59 to 62 units.

With BAV approval secured and the first modified trainset now in revenue service, SBB will roll out the remaining 61 conversions through scheduled overhauls, targeting completion of the programme in the early 2030s.