GERMAN Rail (DB) is typical of many railways where much of the infrastructure dates back to the 19th century. This makes DB's 33,000km network, which includes around 27,000 bridges and nearly 800 tunnels, increasingly costly to maintain and repair while it also faces increasing demands for upgrades to cope with rising traffic volume and higher speeds.

A sensible approach to managing track possessions is to use automated systems to collect and manage spatial information about existing track and structures. This has two important benefits. First, automated solutions can quickly capture and record detailed information on track and structures, which directly reduces the length of possessions needed for surveys and inspections. Secondly, the amount of information that can be gathered creates a comprehensive picture of existing conditions, so that design, engineering and construction can become faster and more efficient. GI-Consult, Germany recognised this and is using automated approaches to collecting and managing geospatial information in the rail industry.

HohenzollernbruckeGI-Consult carries out surveying, railway geometry processing and consulting in project conception, planning and construction. To capture spatial data on track and surrounding objects, the company uses a blend of technologies including Global Navigation Satelitte System (GNSS), total stations (which integrate an electronic theodolite with an electronic distance meter), trolleys and 3D scanning. Field systems are supported by office software for processing, data analysis and management.

In a 2013 report, DB noted that the average age of German railway bridges is just over 56 years, with many dating back to the 19th or early 20th century. The report identified 1145 bridges that needed to be rebuilt and another 6800 that required significant repairs. But maintaining Germany's diverse mix of bridge types, sizes and locations calls for detailed evaluation and planning.

The report noted that roughly 4000 bridges are built using steel girder technology. While steel construction is strong and cost-effective, many steel bridges require extensive maintenance and upgrades, which presents some unique challenges.

Rebuilding a steel bridge includes replacement of the sleepers. On a steel girder bridge, the wood or concrete sleepers are spaced roughly 60cm apart and are attached directly to the bridge structure. During the work, the old sleepers are removed and replaced with new steel sleepers. Each new sleeper is custom built to fit the girders, including drill holes for attachment. But custom fabrication requires extensive field surveying.

In order to enable design and fabrication, pre-construction surveys must measure each sleeper's size, location and attachments to the girders beneath it. For years, those surveys were a tedious, time-consuming process. But in 2013 and 2014, GI-Consult demonstrated a new approach that would radically reduce the time and cost of the surveys. The demonstration consisted of work on two historic structures scheduled for repairs: the Herrenkrug and Hohenzollern bridges.

Opened in 1911, the Hohenzollern Bridge crosses the River Rhine near Cologne. Originally built to serve as a road and rail bridge, it was damaged in World War II and subsequently rebuilt as a rail-only bridge. In 1989 the 409m bridge was modified to increase its capacity, so that it currently carries more than 1200 trains per day.

The Herrenkrug Bridge crosses the River Elbe near Magdeburg. The bridge was opened in 1873, destroyed in World War II, rebuilt in 1946 and again in 1979. It spans 480m and connects to a second 205m-long bridge crossing the Elbe floodplain. Like the Hohenzollern Bridge, the Herrenkrug structure was constructed using steel girder technology that dates to the late 19th century.

Each bridge has roughly 2000 sleepers supporting multiple tracks. To enable custom fabrication of new sleepers, about 10 different parameters need to be captured for each sleeper, including its height, length, and width, as well as connection points and distances between the sleepers. Additional 3D data is also captured such as track position, gauge and cant together with measurements of girders and other bridge components.

The similarities between the two bridges enabled GI-Consult to make meaningful comparisons between the projects. The Hohenzollern Bridge was surveyed using traditional methods, while work at the Herrenkrug Bridge would use GI-Consult's new approach.

To minimise disruption to passenger traffic, survey and inspection teams commonly work at night. "Generally only one track is taken out of operation, while the other tracks on the bridge are in use by heavy freight traffic all night long," explains Mr Thomas Zeidler, GI-Consult's managing director. "The cover panels, which are on the bridge for safety reasons, must be removed for the measurements. So it's easy to see how dangerous the surveying work is and how important it is to find solutions to reduce the work on site."

At Hohenzollern, crews used pocket tape measures and digital levels to measure the individual sleepers and girders manually recording more than 30,000 individual measurements onto pre-printed log sheets. Other information could be collected using GNSS or total stations, but still required slow, careful access to the entire structure. Working alongside DB safety teams, the GI-Consult crews needed 35 work shifts to gather the information, of which 30 took place at night. The five daytime shifts focused on project setup and connection to the reference framework.

GI-Consult regularly uses the Trimble Gedo system to capture existing conditions of track and related structures. One part of the system, the Gedo CE trolley, can collect data on track location, alignment, profile, gauge and cant. GI-Consult uses the information to document existing conditions and support work in track maintenance and repairs. A different configuration uses a 3D scanner mounted on the trolley. In both configurations, the trolley location can be determined by mounting a GNSS receiver on the trolley, or by a prism target for a total station. The data from the scanner is processed using Trimble Gedo Scan software.

GI-Consult frequently uses the scan system to collect point cloud data for use in clearance analysis, tunnel inspection and station design. Given its expertise in scanning and the large amount of data needed for the sleepers on steel bridges, Zeidler says that it made sense for GI-Consult to use 3D scanning to replace much of the manual measurement.

GI-Consult had to modify the Gedo trolley to handle the steel bridge needs. Working with Trimble, it relocated the scanner mount so that the scanner was positioned above one rail and tilted the scanner to enable it to "see" down to the sleepers and girders. The trolley could be easily moved along the tracks, taking only a few minutes to complete a full scan at each location.

At Herrenkrug, GI-Consult crews established a coordinate reference framework for the project. They mounted a Faro Focus 3D scanner onto the trolley and scanned each side of the track, rolling the trolley on the track and stopping to capture each scan. A Trimble total station measured the location of the trolley. In one night, they completed a round trip over the bridge, using each pass to capture complete data on a single side of one the bridge's two tracks. On the second night, they repeated the process for the remaining track.

The time savings in the field were remarkable. Instead of the 30 night shifts required at the Hohenzollern Bridge, the crews at Herrenkrug needed only two nights. Zeidler says they needed 10 daytime shifts at Herrenkrug, but much of that was spent in setup and testing for the new configuration. On future projects, he expects the setup time to be similar to the five days needed at Hohenzollern.

Some of the time saved in the field was offset by an increase in office time. Using Hohenzollern's manually-gathered data, office technicians needed six days to compile the manual field data and prepare the information needed by the fabricator. For Herrenkrug, the scanner data took 30 days to process, which included combining the scans into a geo-referenced point cloud and extracting tens of thousands of individual measurements into the fabrication forms.

Zeidler says that savings in the field easily compensated for the increased time in the office: "Costs to operate a survey team are higher than those for an office technician, so there is a cost benefit just from that aspect," he explains. "The overall direct savings to the client, which include reduced costs of safety personnel, are significant."

As the infrastructure manager receives a payment each time a train passes over its tracks, the rapid measurement provides additional financial benefits by greatly reducing track possessions.

The performance of the solution was confirmed when GI-Consult surveyed the Rügendamm bridge in northern Germany. Working under a total possession of the 540m-bridge, crews scanned it in roughly four hours. As Zeidler predicted, the time for preparation and checking at Rügendamm matched the five days spent at the Hohenzollern project.

Zeidler sees room for additional gains. "If we can automate the process of extracting the data for the fabricators, then we can realise large cost reductions in the office," he says. With the potential of thousands of bridge restoration projects on the horizon, the new geospatial technology should help DB to reduce the overall cost of the work.

* John Stenmark is a consultant and writer working in the geospatial, architectural, engineering, construction and associated industries. He has more than 25 years of experience in applying advanced technology to surveying and related disciplines.