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Digital Twin

Punctual, reliable and convenient transportation to work, school, friends and back home: These are the expectations passengers have of public transportation systems. To ensure that these are fulfilled every single day, depots have to ensure maintenance on time and the deployment of the required vehicles, among other things. A sophisticated software and a real-time locating system make an important contribution here.


The ÜSTRA busses and trams transport around 500,000 passengers in all directions through the city – every single day. 

In Hanover, the state capital of Lower Saxony in Germany, around 500,000 passengers rely on the services of the ÜSTRA Hannoversche Verkehrsbetriebe AG day in and day out – and when large events take place at the Hanover Fair grounds, the figures are notably higher. To meet these demands the company has a fleet of 325 light rail trains and 137 busses that operate in a transportation network of more than 700 kilometers. Another factor in the smooth operation are the five depots which handle the cleaning, maintenance and deployment of the vehicles. Minor or major repairs are also carried out in the depots and the associated workshops.

Complex tasks in the depot

The management of the depots is, however, more complex than it would appear at first glance. On the one hand the deployed vehicles have different properties that have to be brought into line with the requirements placed by the timetable: from bicycle compartments over so-called counting vehicles for passengers statistics up to the latest railcars of the type TW 3000 that can only run on lines with high-level platforms. The situation is similar for the busses in their depots. On the other hand the configuration of the trains is often changed to optimize the capacity and the mileage: For example, train carriages that run as double-traction trains during rush-hour traffic are parked during the daytime at the terminal stations, and then coupled to a different train in the late afternoon. And finally, the timetable has to be modified constantly – for example due to construction work or road closures, the need for additional trains during trades shows or school holidays.

To ensure that ÜSTRA can transport its passengers rapidly, reliably and comfortably, the latest technology is used in the depots. 

The utilization of a sophisticated software solution (Depot Management System, DMS) that, like a digital twin, manages all data related to vehicles and operational processes and makes it available to other systems is vital to the depots. Extensive interplay and interleaving with other programs is of enormous importance here. For example, the vehicles inform the DMS by radio signal about the current mileage and any defects so that when they enter the depot they are guided directly to the workshop, to the stations for topping up fuel and operating materials, or to a parking area. Through integration into the workshop management, for example, the required work can be planned and prepared in good time. The timetable system also passes its data to the DMS, thus allowing the vehicle deployment for the next day to be carried out automatically.

Automatic synchronization

A decisive factor for how the DMS functions is the continuous synchronization with the actual situation on the tracks. This is due to a particularity of the light rail system: In contrast to the “large” railroad system, the switches are set by the light rail driver and not in a signal control center. In addition, unpredictable states can always occur, for example, because the repair work takes longer than originally planned. This synchronization between software and reality is the task of the radio locating system (Realtime Locating System, RTLS) that acquires the position data of all vehicles in the depot in one-second intervals and transmits this information to the DMS. Small transponders are installed in the vehicles – small radio transmission devices that can transfer a unique vehicle identifier and, if required, further data – are installed in the vehicles. The antennas are located on the roof of the vehicle, well-protected from the influence of weather.

RTLS anchors deliever the actual position of any vehicle within seconds

In the depots the corresponding counterparts (so-called anchors) are mounted on masts outdoors or in the building. These anchors receive the transponder signals, process them and transfer them to a server. In addition, RTLS also supports automatic acquisition of performance indicators, for example, by recognizing the passage of a vehicle through the washing system and evaluating this information to determine service quality.

Exact parking position locating

ÜSTRA as the user and VAB Verkehrsautomatisierung Berlin GmbH as general contactor and integrator made a decision in favor of Simatic RTLS – this is the name under which the locating system from Agilion GmbH has been marketed since it was acquired by Siemens in April 2018. Simatic RTLS offers decisive advantages. For example, the transponders do not require their own batteries but can be connected to the on-board electrical system of the trains and busses instead. Locating accuracy can be scaled simply though the number of anchors used. In the depots this allows implementation of zones with exact parking position locating or with only rough position location, which optimizes the costs for the position location system. At the main workshop, for example, a single anchor is sufficient to detect the entry and exit movement – exact position locating is not required here in view of the operational procedures.

Well prepared: When arriving at the depot, the maintenance-relevant information are already processed by the DMS.

A further advantage is the simple commissioning. For example, the experts from Chemnitz were able to set up and commission a functional test installation in Hanover in just two days. The integration into the DMS software called VABdepot was also realized rapidly thanks to the existing software interfaces. A final aspect is that Simatic RTLS has proven to be particularly reliable even when the antennas are covered in snow in the winter. The acceptance by employees who have to rely on Simatic RTLS every day is correspondingly high. At ÜSTRA, Simatic RTLS is now being used in all depots, workshops and vehicles.

Higher quality at lower costs

With the combination of DMS and Simatic RTLS, ÜSTRA was able to achieve its goals of achieving leaner and less expensive organization of the procedures in no time. While the notation of parked trains used to be carried out manually in the past, it is now carried out continuously and fully automatically. Maintenance and deployment is now much faster and with fewer errors. In addition, the system has also improved the quality of the procedures. Thanks to the automatic deployment, the timetable requirements can be fulfilled reliably. Any changes can be accommodated rather quickly. The digital twin for trains and buses thus saves money and increases passenger satisfaction.

Read more on Simatic RTLS: http://www.siemens.com/rtls

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