High speed testing on WCML in the 70's

In late 1970 and early 1971, a series of high speed running tests was undertaken using various forms of traction primarily to evaluate their reaction to "dipped joints". The information evaluated included measurements of sleeper baseplate loads and the tests were conducted over a specially constructed dipped joint just north of Cheddington Station on the West Coast Main Line.

The object of the tests was to measure the loads exerted on the track at an irregularity, by a modified AL6 locomotive with Flexicoil secondary suspension at speeds up to 125 mile/h and to compare these loads with those produced by a Deltic,  an AL5 locomotive and an AM9 EMU plus an AL6 locomotive with conventional secondary suspension.

The first Class 86 locomotive to be fitted with 'Flexicoil' suspension was affectionately known as 'Zebedee' after a spring-mounted puppet in the popular 'Magic Roundabout' children's programme of the time, and was tested with and without a glass-fibre nose cone during the series to assess its aerodynamic affect.

Proposed increases in main-line running speeds, first to 110mile/h with existing locomotive types and subsequently to 125 mile/h with new, yet conventional designs posed a number of questions of mechanical, electrical and aerodynamic performance.

An important consideration was the possibility of very high loads being induced in the track due to features such as crossings and rail joints. Accordingly the Chief Civil Engineer, BRB, and the Chief Mechanical & Electrical Engineer, BRB, requested that an investigation into track loadings at high speeds be included in a series of tests which were being planned to examine other aspects of high speed running.

The primary objective of the tests was to compare the loadings induced at a given track feature by a number of vehicles running at various speeds. This would enable the effect of high speeds to be assessed in conjunction with a comparison of various types of suspension and motor mounting. Absolute measurement of track forces was by comparison a less important but still desirable objective. The comparison of vehicles would be unlikely to be affected by the precise nature of the feature tested, whether a crossing, joint or weld, etc.

Not only were the tests used to monitor the vertical track forces imparted by the locomotive over an instrumented dipped rail joint but also to check turbulence caused by trains passing at 125 mile/h.

Fitted to Mk2 coach No:E5625, one of the passenger coaches involved, was the then new 'DOC2' bogie. These runs were also used to assess the high speed riding qualities of this revolutionary bogie. This was the forerunner of the BT10 Mk3 bogie and was fitted with coil springs on its primary suspension with radial arms and secondary suspension airbags, quite a novelty after the 'BR1', Commonwealth and 'B4' bogies which preceded it.

Our train was hauled by E3173 'Zebedee' with Test Car 4 and E5625 and was confined to the Down line. The train would start its test run just to the south of Linslade Tunnel and the southbound train would start from Leighton Buzzard. At a pre-arranged and synchronised signal both trains would start off and run at controlled speeds to ensure as far as practicable that the trains passed just to the North of Cheddington station.

The other train was hauled in turn by another standard class 86 or by a Deltic class 55 locomotive with another short formation. An AL5 locomotives and  an AM9 EMU were also used at one time or another.

The specially installed 'dipped joint' was in the Up fast line just north of the station where vertical track force measurements (P2) were recorded as the Up loco traversed the joint at high speed. Aerodynamic probes were also installed on the trains and alongside the track to measure the effects of turbulence inside and outside the trains when they passed.

Total possession of the Up and Down Fast lines was taken on three consecutive Sunday mornings (16th, 23rd and 30th May 1971) between Leighton Buzzard and Tring for the purpose of the testing to allow the trains concerned to set back 'wrong road' to the starting positions after each run.

I remember that we were based at Bletchley depot and had to leave there at around 05.30 on the Sunday morning. We had breakfast on the Test Car but at lunchtime the trains would stop and set back to Cheddington where food was especially provided and served in the Down platform waiting room.

It was during these tests that Test Car 4 (a GWR Hawksworth coach with GW bogies and plain bearings) was hauled at 130 mile/h!

E3173 was later re-numbered 86204 and even later was named 'City of Carlisle'. It was scrapped in 2003 but in 1975 it was in the news again being involved in the Watford accident.

Click on the picture for a bigger image - photos are the author's unless otherwise indicated

E3173 at Cheddington on the test series of October 1970

Alan Betts

E3173 at Cheddington on the test series of October 1970

BR Official courtesy David Campbell


E3173 is pictured near Tring in an earlier test series in October 1970, when it was fitted with the streamlined nose cone.

C T Gifford

E3173 One of the test trains stabled at Bletchley depot with E3173 - this is probably from early 1971.  The author was not involved with these particular tests.

Note the grille over the windscreen of the loco and the ex-LMS Dynamometer car (now known as Test Car 3) and a couple of Mk1 coaches in the train

Authors collection


The instrumented Faiveley pantograph on E3173 viewed from inside the depot at Bletchley on an early test in 1971 - how this monstrous pantograph behaved at 125 mile/h is lost in the mists of time!

Authors collection

Tea break In this very poor quality picture (Boots slide film) the Mk2 coach E5625 fitted with the prototype Mk3 bogies is shown in the Down Fast platform at Cheddington in May 1971 Note the wasp stripe rear door cover with air horn on the top and the viewing window all of which were fitted to facilitate propelling during the tests.

over 120mph

The speedometer on the Western Region Dynamometer Car (Test Car 4) is off the clock in this view

BR official

Slow Lines open This shot looking back from the test train on the Down Fast shows Cheddington station with all lines occupied. Normal traffic is confined to the Slow lines and the other test train is still in the Up Fast platform. 


Later re-numbered 86204 this is 'Zebedee' at Carlisle in the 1980s showing its Flexicoil suspension    


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