Track diagnostics - FMK 004 track geometry measuring car

Measuring systems


Self-propelled car measuring railway track geometry.


  • Instant measuring diagram
  • Automatic evaluation
  • Statistical record
  • Railway qualification
  • Repeated procession of test results

Measured characteristics:

  • Gauge
  • Alignment
  • Superelevation
  • Twist
  • Surface
  • Curvature
Simultaneously with the measurement the measurement diagrams and reports are produced.

The report comprises:

  • the exact figures of the errors exceeding the dimension limit
  • the index- and qualification numbers concerning to the qualification sections
  • statistical records prepared by each 1 km.
The measuring diagram and the evaluating report have a header including the main ID parameters of the measured line.

The following details are automatically marked in the diagram:

  • Distance (by each 100m)
  • Dimension limit
  • Curve detection
  • Speed (by each 100m)
  • Measuring numbers and qualification number (by each 500m).
The operating staff records information about level crossings, points, signals, bridges, tunnels and stations in the course of the measurement. The longitudinal scale of the diagram is adjustable.

The evaluation report comprises:

  • the measuring- and qualification numbers of the qualification sections as well as statistical records
  • list of errors exceeding the dimension limit, with the name, location, length, maximum, place of maximum and limit of the characteristics.
The Hungarian State Railways (MÁV) uses a multilevel dimension limit regulation (A, B, C), which is observed by the computer system of the measuring car. This measuring system is suitable for testing new railway tracks after maintenance or in operation.

At the present the following dimension limit classis are used by MÁV:

  • "A" construction (new material)
  • "Ah" construction (used materials)
  • "B" maintenance
  • "C" operation
The EM-120 measuring car performs track geometric measurement on a 20000-21000km long gridiron (tracks) per year.

Technical data:

Length:15,0 m
Axle load:130 KN
Max measuring and travelling speed:100 km/h
Signal detection:mechanical / with measuring wheels
Signal transmission:mechanical / electronic
Signal recording:computer controlled / Flash card


Measuring Principle:

The most important element of the measuring system is the telemeter – that includes the rotating laser –, which can be easily transferred from the FMK004 measuring car to the trolley.
The system works according to the theory of laser distance measuring: the rotating laser source deflates laser flows that are reflected from the objects. The telemeter detects the reflected laser-flows and - using the time of reflection -, it can calibrate the distance from the centre of the track and the height above rail level of the objects.

The rotating frequency of the laser source is 100 Hz that means that it takes 100 turns per second. The maximum speed of the vehicle is 100 km/h. As the laser detects one point in one definite section, the measured data are served like a spiral. This means that the vehicle runs a definite distance during measurement with a length that is obviously dependent on the speed. This length is 278 mm with a speed of 100 km/h, therefore only those objects can surely be detected that are wider than this value.

In order to find the narrower elements (e.g. signals) as well, speed reduction is necessary in front of them. The information about the required places of speed-reducing is served for the engine-driver by the system automatically. The system deals with the data of the mechanical track geometry system so that the clearance system receives the radius data, which is essential for the calculation of curve supplement, that are necessary at the curves with R≤4000 m radius. If the measuring is taken by trolley (manual measurement), the radius data have to be added to the system manually, whereas it only measures the gauge and superelevation. The null-point of the coordinate system of the telemeter is defined by the intersection of the rail levels (“X”) and the centre of the track (“Y”). In addition, the system can calculate the curve supplement transition and it is also able to define the distance from the center of the adjacent track.

Besides the mentioned telemeter, another laser is mounted to the bottom of the vehicle with cameras as well. These equipments deliver necessary geometry data to the system (e.g. gauge). These elements work without contact, so they can be considered as a more developed and modern measuring method in comparison with the original mechanical one. The system is able to handle the same database that is applied by other diagnostic measuring systems of the MÁV Central Rail and Track Inspection Ltd. With this mode of data transmission the evaluation process is supported by technical data-channels (e.g. railway-lines, sectioning, stations, speed, track-system, switches, bridges, tunnels, etc.). The localization of the vehicle – like previous practice - is accomplished by an encoder, so that the taken distance is calculated from the diameter of the wheels and the number of turns. The encoder calibration is required to be completed before every measuring periods. At the process of purchasing of the new clearance gauge measuring system, a new GNSS receiver equipment was installed that makes possible to provide the measured objects and local faults with GNSS localization data as well.

The identification of the obstacles that reach the analyzed clearance profile is possible by the video system that is mounted above the vehicle. With the infra-red cameras the system is capable of operating independent on the time of day.

Testing and calibration:

The test-run with calibration was coordinated in cooperation with colleges of the Italian Tecnogamma company. After the installation of the vital softwares, the calibration of the encoder and the verification of the measuring accuracy were executed. The supervising consisted of static and dynamic tests. While the location of the static accuracy-checking was at Rákos station, the dynamic test-run was completed on the railway line section between Soroksári út and Soroksár stations more times with different speeds. The required accuracy of ±10 mm at the diameter of the measuring range was confirmed in comparison with geodesy measurements that were executed by the colleagues of MÁV Track Establishment Co.


This clearance gauge measuring system and the well developed official evaluating software that were taken into operation by the MÁV Central Rail and Track Inspection Ltd. provide vital support for the operators of the railway tracks with their speed and accuracy. The accurate definition of the surrounding objects serves necessary input data for the planning of special consignment delivery. / CC BY 3.0