Tandem in the tunnel.

A special feature of the 2-way vehicles converted by ZAGRO is the possibility of coupling the Unimog in an emergency, thereby almost doubling the tractive force. This means that, in an emergency, a metro train 120 m long and weighing approx. 200 t can be towed effortlessly even on a gradient of > 4 %, such as when exiting a tunnel.

“In this tandem operation the Unimogs are coupled both mechanically and electronically and can thus achieve optimal tractive performance by precisely matching the engine speeds,” explains Matthijs Bokma of the KOKS Group, ZAGRO's Dutch sales partner. Only the leading Unimog is crewed; the control of the coupled Unimog is taken over automatically by the control system developed by ZAGRO.

To achieve this tractive performance, both Unimog U 423s are equipped from the factory with a torque converter shifting clutch and the necessary electronic interface. Propulsion on the rails via the Unimog's wheels also provides sufficient tractive force, and ZAGRO's rail guidance ensures secure tracking. Of the M52's total length of 9.7 km, 7.1 km run underground; therefore equipping the Unimogs with environmentally friendly Euro VI engine technology was an important aspect for GVB.

According to Gijs Brink, the GVB project manager, coupling the Unimog into a tandem in an emergency will, however, hopefully be necessary only very rarely. Therefore, the Unimogs are designed as flexible work vehicles that can also be used individually for a wide range of tasks on the GVB's rail infrastructure. The Unimog U 423 delivered in 2017, fitted with a loader crane and a wagon brake system for 400 t, proves its worth every day during the metro's operating pause and is used, for example, to renew switches or to tow rail-mounted work machines.

The Unimog U 423 handed over to the GVB at the RailTech Europe trade fair in March 2019, with a box body, a wagon brake system and hydraulic rail-lifting devices, is also flexibly deployable for the GVB.