26 February 2018

The SIMGAB Project : Clearance gauge simulation

Interview: SIMGAB Project

With thanks to Frederic DESGACHES and Romain HIRON for agreeing to answer our questions.


  • What exactly is SIMGAB?
    SimGab stands for “SIMulation GABarit” (or Clearance gauge simulation in English). The aim of the project was to develop a tool, using a code-based rail dynamics calculation model (SIMPACK), for identifying the actual displacement of a vehicle on the track and assessing the risks of contact with structures encountered along the line. This method offers a more accurate appreciation of the phenomena involved, by contrast with the “traditional” gauge-based approach, in which blanket values are taken for vehicle displacement, thereby making allowance for situations unlikely ever to occur.


  • What motivated the project and what was its purpose?
    Since the project concerns both SNCF Mobilité and SNCF Réseau, it was therefore jointly developed by I&P (Engineering & Projects) and the CIM (Rolling Stock Engineering Centre). The purpose was to establish margins for manoeuvre with regard to cases of apparent non-compliance with clearance gauge requirements. With a tool like SimGab, it will be possible to eliminate rogue cases of non-compliance, since the system will be able to rule out the risk of physical contact between rolling stock and infrastructure.


  • What tests and measurements have been performed?
    Tests are required to confirm the validity of results obtained with the tool, which basically operates by establishing vehicle displacement in relation to the track (vertically and laterally). These consist of running a vehicle under various regularly encountered railway operating configurations (on straight sections at maximum speed, in curves, over turnouts) and of measuring vehicle body/bogie, bogie/axle, and axle/track displacement. The findings of these tests are then set out in a report giving measurement results, a description of the instruments used for the purpose and interpretations of specific situations. The numerical data obtained is then used to establish the correlations between the test results and those produced by the tool.


  • What resources were deployed for the project?
    To characterise all the movements occurring in a Corail coach during the test campaign, a large number of measuring points (94 sensors) were required. For measuring factors such as lateral displacement of the bogies in relation to the track, contact-less technologies (laser scanners, cameras) and image processing algorithms came into play. And specific mechanical assemblies had to be produced by our design office for instrumentation purposes.


  • Did the project have any special features?
    The main innovation of the test campaign was dynamic measurement of the lateral displacement of the bogies in relation to the track at speeds up to 140 km/h.


  • When were the tests carried out?
    First feasibility tests were performed in April and June 2017, followed by complete instrumentation in July 2017 and line tests in August 2017.


  • Where?
    Feasibility tests were carried out on the AEF site in Vitry-sur-Seine. Line tests were conducted between Vitry-sur-Seine and Montereau (Seine et Marne), where a wide range of running conditions similar to those likely to be encountered by the rolling stock in practice could be found.


  • Which teams contributed to the project?
    We would have been unable to fulfil all the client’s requirements, had we not had been able to count on the combined support of AEF (Dynamics and Structures Unit) and LEM (Mechanical Engineering Unit), whose complementary skills and resources proved invaluable.


Frédéric DESGACHES is a National Bogie and Running Gear Advisor and a Scientific and Technical expert in the SNCF – SYNAPSES network of the Rolling Stock Engineering Centre (CIM)

Rémy DRON is a Dynamic Calculations and Structures Advisor and a Scientific and Technical expert in the SNCF – SYNAPSES network of the Rolling Stock Engineering Centre (CIM)

Louis POMMIER is a Track gauge and Alignment expert in the Engineering & Projects Division

Romain HIRON is an Engineer specialising in Railway dynamics at the Railway Test Agency (AEF)

Thierry LEMARECHAL is a Test Engineer at AEF

Mathieu GREGOIRE is a Test Engineer at the Test and Measurement Laboratory (LEM).


Members of the Eurailtest EIG

AEF: Railway Test Agency, SNCF

CIM: Rolling Stock Engineering Centre, SNCF

LEM: Test and Measurement Laboratory, RATP