The Structure Gauging Train (SGT)

The ability to move a railway vehicle and its load along the railway tracks depends on the height and width profile, known as the loading gauge, of the route concerned. A railway vehicle must comply with the route loading gauge to ensure that it passes clear of all structures, principally over-bridges and tunnels but also features such as station platforms, canopies and overhead or lineside equipment.

The high tech laser and light technology of the Structure Gauging Train (SGT) provide a superb picture of such infrastructure. The laser beams reflect back to the train, and should the distance that the laser travels be too small, an alert isactivated. The train also measures the distance between pairs of tracks ensuring that passing trains will not foul the loading gauge
The recent SGT had its beginnings in the mid-1970's. Several experiments were carried out utilising the four-wheeled Wickham self-propelled laboratory (sometimes known as the Elliott Track recording car owing to its equipment being supplied by Elliott Automation Ltd) and also as the 'Yellow Peril'. Using a dual-triangulation system  with lights and cameras this optical method was a big improvement over the existing ways of gauging. It was trialled at the Old Dalby test track.

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Wickham car

This is view of the Wickham car with the solebar-mounted equipment was taken at Old Dalby

Author's collection

SGT early Here's a close-up

Author's collection

The work pioneered at Old Dalby with the Wickham Car led the way for the building of the special Structure Gauging Train in the early 1980's. It was completed for the Director of Civil Engineering in the summer of 1986, the project having been in the development stage for many months.

A specially-built four wheel structure-gauging optical vehicle, ZXQ DC460000 based on a steel carrier chassis, was formed as the middle car of a 3-vehicle formation. The two outer coaches were RDB975081 (formerly Test Coach Hermes converted to a driving trailer vehicle and re-numbered DB975081) and RDB975280 - (formerly Test Coach Mercury) became DB975280 and housed computer data collection and staff facilities. The two vehicles had previously been used extensively by the Train Control Group at the Mickleover test track and elsewhere from the early 1970's. 

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Early days

The SGT on trial at the Old Dalby test track in 1985 with DB975081 nearest the camera, then DC460000 and DB975280 at the back. Note that the leading vehicle is fitted with Commonwealth bogies

BR Official

SGT Nov 85 The SGT pictured behind 47305 near Stenson Jcn in November 1985

Phil Eames

Driving trailer

A close up of 'Hermes' DB975081 in the RTC yard - note the class 24 'Experiment' in the background - still fitted with Commonwealth bogies

D Bower

Calibration The train is shown here being calibrated under the gauging rig in the yard at RTC in 1991

Author's collection

Optical car

A closer view of the optical car

Author's collection

SGT June 92 The SGT pictured in December 1992 in the newer livery passing Elland being propelled by 47976 - now fitted with B5 bogies

Phil Eames

Following major changes within the Research Division in the late 1980's the SGT was transferred to the DM& EE and then to Railtest and finally to Network Rail.

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Mixed Serco 1988

Here it is at Old Dalby heading south in the company of other Serco test coaches after a publicity shot in 1998


Inside Stanton tunnel The SGT at work in Stanton Tunnel in the late 1990's - this time in Serco livery - showing its radiating lights gauging system to good effect



The SGT in the yard at the RTC in 1999 showing the optical car in black


Derby The new version consisting of locomotive 31233, DB975280, DB97508, DC460000 and DBSO 9708 and 31459 on the rear pictured on the Goods Road at Derby on 19th September 2008


A close up of DB975081 formerly Lab 18  'Hermes' now no longer a driving trailer. Optical car

Another close up of DC460000 - the optical car - now using laser technology

DB975280 A close up of DB975280 formerly Test Car 'Mercury' DBS 9708 The latest edition to the SGT is this ex-Anglia DBS driving trailer - not 'Open' anymore.

New developments

The SGT was operated by DB Schenker on behalf of Network Rail but the original Mk 1 coaches and optical car that formed it were withdrawn in 2013. The latest development is a laserflex system (nicknamed 'dusty bin') which was trialled on the optical car but has now been fitted to the end of a Mk2 coach (977985) and this will run (via an extended coupling) with another Mk2 (977986). This new SGT has superseded the original which is now stored in the RTC yard awaiting its fate.

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DB975081 formerly Lab 18  'Hermes' stored in RTC yard on 23rd January 2014

Last seen at York Klondyke Sidings on 22 July 2017

Andrew Royle

DB975280 DB975280 formerly Test Car 'Mercury' stored in RTC yard on 23rd January 2014

Last seen at York Klondyke Sidings on 22 July 2017

Andrew Royle

DC 460000 The optical car DC460000 stored in RTC yard on 23rd January 2014

This vehicle was scrapped at Sims Metals, Beeston in February 2015

Andrew Royle



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