The series 598 and 599 are tilting three-car diesel multiple units for medium distances. 21 sets of the series 598 were built by CAF in 2004. Each end car has two 338 kW (460 hp) MAN diesel engines which power one axle each via a Voith hydraulic transmission. The middle trailer contains two smaller diesel engines for heating, air conditioning and other auxiliaries. Originally, this type of trains and also the services it provided were marketed under the name “Nexios”.

In 2008, CAF built 50 sets of the successor series 599. They are known as TDMD or “Tren Diésel de Media Distancia” (Medium-Distance Diesel Train). They are also composed of three cars, but the middle one has a low-floor section for accessibility reasons. In this case, the auxiliary diesel engines are located in the roof.

The power of the traction engines had been increased to 382 kW (520 hp) and the weight had been decreased, leading to better acceleration and higher curve speeds. The undercarriage has been designed with enough spare space for the future installation of gauge-changing bogies which allow the trains to run on standard gauge high speed lines. The series 449 is basically the electric variant of the series 599.