Accessible, comfortable, maintainable
The case for articulated rolling stock on the UK network
Introduction
On a fairly regular basis, I take my son to the National Railway Museum. He’s three. It’s free
(donations always welcome), provides plenty of things to look at, and there are plenty of
buttons to press. However, I always approach one area with trepidation: the Bullet train. The
lead car from one of Japan’s 1976 built 0 series Shinkansen sets is rightly in the museum to tell
the story of high speed rail, but every time I go in I hear comments such as “why can’t we have
trains with this much space?”. I just grit my teeth and get out quickly, trying not to mutter
about Brunel…
The truth is though, British trains are small, and by current trends getting smaller. This can’t be
right. In the modern age we want bigger and better, and yet on the railways better seems to
mean smaller and better only for the railway system. It is as if we, the industry, have forgotten
what the railway is there for. It is as if we need reminding of what our mission statement for
passenger rail should be – enabling any passenger to access the railway to travel from A to B
safely, in comfort, within a socially acceptable timeframe, arriving on time.
As we head further and further into the rail harmonisation across Europe, we see the influence
of each member country having an impact on other parts of the community. Our standards are
converging, our signalling system, so we are told, will be interoperable, our latest UK high
speed trains are a standard European design built to European standards, including the
loading gauge, and our freight trains run across the length and breadth of Europe; other
examples will occur to readers. Yet, despite all this, one aspect which has been common on
mainland Europe for some time, which helps to achieve the mission statement of the
passenger railways above, has, with a few notable exceptions, failed to make an impact on
British railways, namely articulated rolling stock.
This article examines some of the presumed barriers that have prevented wide-scale
introduction of articulated rolling stock in Britain, and argues the case for its use.
Articulation
Going back to basics, articulation is the means by which a fixed formation train shares a single
bogie between two carriages. This type of bogie is often called a Jakobs, or Jacobs, bogie
(named after its inventor, Wilhelm Jakobs).
To cover quickly the few notable UK uses of articulated rolling stock, in metro and light rail
circles the Jakobs bogie is a fairly standard item, appearing on many vehicles including the
Manchester Metrolink T-68 trams and the Tyne and Wear Metro units.
Heavy rail articulation is much less common, although there have been some attempts to
introduce it. One was Sir Nigel Gresley who was Britain’s leading designer of articulated rolling
stock of the 20th Century. His first carriages appeared in 1907 and his designs ran to twin, tri,
quad, and quintuple articulated sets and included the Silver Jubilee and Coronation train sets
and the Quad-Art sets built for the Great Northern Railway, one of which has been preserved
at the North Norfolk Railway.
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In 1966, JF Thinng, presenting a paper to the Institution of Locomotive Engineers on the
engineering aspects of high speed trains, noted that “…to complete the picture of stability, it is
suggested that methods of connecting cars together will require serious review… If progress is
to be made and aerodynamically clean exteriors, including undersides, are to be used, and if
peripheral coupling plus a greatly improved gangway connection and probably electropneumatic control of bolster levels are to be incorporated, the only position for the bogie is
between cars, that is articulation… behaviour of articulated bogies at high speed…will be one
of the key factors in deciding the layout and configuration of the train of the future.”1
By the early 1970s that suggestion was a reality with articulated bogies used on the Advanced
Passenger Train (APT) project, on the research test bed, the “POP” train, the APT-E gas turbine
experimental train, and the APT-P electric Class 370 which entered service in 1983.
The final use of the articulated bogie in the UK is on the Eurostar Class 373s introduced in 1994
which run on High Speed 1 and have also run on the East Coast Mainline during the reign of
GNER. The Eurostar is based on the successful first generation TGV design, first introduced in
1981, but built to the constraints of the UK loading gauge2.
The Alstom TGV design has consistently used the Jakobs bogie design, ever since a world
speed record was set by a prototype model in December 1972. The current world speed
record of 574.8 km/h set in 2007 was achieved by a specially adapted TGV Duplex fitted with
experimental Jakobs bogies fitted with traction motors.
Casting the net wider in mainland Europe, articulated electric and diesel multiple units are
used in many countries. Bombardier has successfully used articulation for both the Talent
DMU in Germany and the Spacium EMU in France.
Yet despite all this, articulation is still the exception in the UK. Why is this?
Axle loading
Axle loading is often mentioned negatively when discussing articulation, but is it really that
bad? The perception appears to be that because there are “half as many” axles, the loading
will be significantly greater than conventional rolling stock. However, it isn’t that simple as
articulated trains can in many cases be lighter overall3, and generally have shorter vehicles so
if we take the example of the Alstom AGV, a 200m unit has 11 vehicles with a total of 24 axles,
while the equivalent length train using conventional 23m stock has 9 vehicles with a total of 36
axles, which makes the difference a third, not a half.
On shorter, commuter trains, the difference is nearer three quarters, and hence axle loads
tend to be similar between articulated and conventional stock. Table 1 compares the axle
loading of different modern multiple units, using Bombardier’s articulated EMU, the Spacium,
1
The engineering aspects of high speed trains, No.2 Passenger rolling stock, JF Thhing CEng AMIMechE, Journal of the Institution
of Locomotive Engineers, March 1966; 56 (310), page 200-202, Downloaded from sagepub.com at IMECHE on 16 June 2015
2
TGV Handbook, Brian Perren, 2nd ed, Capital Transport Publishing, date unknown
“Articulated twin sleeping cars having one attendant’s compartment and berths for 20 passengers were completed in 1926; the
weight of the articulated vehicles being 63.25 tons compared with 74.75 tons for two single cars conveying the same number of
passengers.” The development of LNER carriage and wagon design 1923-1941, Paper read before the Institution by N. Newsome,
Associate Member, on 10th March 1948 in London, May 1948; Journal of the Institution of Locomotive Engineers, 38 (203),
Downloaded from jil.sagepub.com at IMECHE on 16 June 2015
3
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and DMU, the Talent, for comparison with UK EMUs and DMUs and two current UK
locomotives.
Table 1: Axle loading of multiple units by heaviest vehicle
EMU axle loads (Tonnes)
DMU axle loads (Tonnes)
Bombardier Spacium
13.3
Bombardier Talent
12.8
Siemens Cl450 Desiro
12.15
Bombardier Cl172
Turbostar
10.4
Siemens Cl444 Desiro
12.83
Bombardier Cl222
Meridian
13.2
Bombardier Cl387
Electrostar
11.05
Siemens Cl185 Desiro
13.85
Alstom Cl390 Pendolino
13.9
Alstom Cl175 Coradia
12.68
Hitachi Cl395 Javelin
11.68
Alstom Cl180 Adelante
12.85
As shown, axle loads aren’t significantly an issue. The Talent has lower axle loads than the
Cl185s and Cl222s and is nominally the same as the Cl180s. Although the Spacium has a
nominally higher axle load than its rivals, it isn’t a large degree of magnitude different.
Ride quality
Ride quality of articulated sets is good. Ever since the introduction of articulated trains in the
UK, ride quality has been reported as “exceptionally smooth riding and a previously unattained
ease of walking through the gangway between vehicles”.4
Articulation brings the added benefit that each vehicle can be used to help stabilise and steer
the next, as has been demonstrated over many years on the TGV. The shared bogie enables
suspension components to link the two vehicles together, which reduces bodyshell roll and
hunting, and ensures longitudinal alignment in the event of a collision, although this does
bring with it the added requirement of more energy absorption in the leading vehicle5.
Maintenance and spares
Historically, articulation has caused inconveniences due to the need to split a fixed formation
unit for maintenance6. When a split is required, an ambulance bogie needs to be introduced to
support the vehicle which is detached from the Jakobs bogie.
This issue has largely been mitigated with the introduction of full length jacking systems,
enabling an entire train to be lifted as one – the Class 390 Pendolino fleet being one such
4
The engineering aspects of high speed trains, No.4 Permanent Way, Journal of the Institution of Locomotive Engineers, JC Loach,
CEng AMICE MIMechE Comment made by Mr T Henry Turner MSc in the discussion following the reading of the paper, March
1966; 56 (310), Downloaded from sagepub.com at IMECHE on 16 June 16, 2015
5
Qualitative comparison of the characteristics of articulated and non-articulated trains and their effects on impact, X Xue(1), S
Ingleton(2) , J Roberts(3) ,and M Robinson (4), (1) School of Computing and Mathematical Sciences, University of Greenwich,
London, UK, (2) NEWRAIL – University Rail Research Centre, Newcastle University, Newcastle upon Tyne, UK, (3) Bombardier
Transportation, Crespin, France, (4) NEWRAIL – University Rail Research Centre, Newcastle University, Newcastle upon Tyne, UK
Proc. IMechE Jan 11, Vol. 225, Issue 1, Part F: J. Rail and Rapid Transit, Downloaded from pif.sagepub.com at IMECHE on June 16,
2015
6
“Consideration has been given to articulation. It was not proceeded with due to lack of flexibility of a train of this type.”
Experience with the new rolling stock on London Transport Railways, G S Ringham, MIMechE MILocoE and J G Bruce, BSc MIEL
MILocoE MInstT. Journal of the Institution of Locomotive Engineers, September 1965; 55 (307), Downloaded from sagepub.com at
IMECHE on 16 June, 2015
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example where an entire 11 car unit can be raised in one action. Further, bogies tend to be
regarded as a rotable spare item in the modern maintenance facilities, and so with the aid of a
bogie drop, an articulated bogie can be changed to enable maintenance to take place off the
unit. This technique is employed at Temple Mills Depot on the Class 373 Eurostars.
Additionally, articulation usually reduces the number of bogies required. This is not definite as
it depends on the configuration of the vehicle but (for example) as described above, the
Alstom AGV is a 200m unit with 11 vehicles and 12 bogies, while the equivalent length train
using conventional 23m stock would have 9 vehicles with 18 bogies. This means the spares
pool can be reduced. Similarly, given the reliance on braking by regeneration or rheostatic
resistor banks, the brake components are not given any significantly heavier burden and so
that spares pool can also be reduced in line with the bogie reduction.
Traction
An argument against the use of articulated bogies was the additional difficulties with applying
traction to the wheelsets. Although both the gas turbine TGV prototype and APT-E used
articulated power bogies, until recently, production articulated trains used conventional
bogies on a power car (such as the TGV, Eurostar, and Class 370 APT-P), or on the lead,
conventional, bogie of a multiple unit (such as the Spacium and Talent).
However, the Alstom AGV uses articulated power bogies. This has been achieved by using
permanent magnet IGBT motors which are small enough to be bolted to the bogie frame.
These were sufficiently developed to be used under the TGV Duplex which broke the world
speed record in 2007 as mentioned in the introduction, and are now in revenue service on the
AGVs in use with the Italian open access operator NTV.
Platform gaps
Until relatively recently, accessibility-for-all on trains has been seen as a “bolt-on” extra rather
than an integral part of rolling stock design. The mandatory compliance with the PRM TSI, and
RVAR before that, has changed this, and opportunities exist to improve the accessibility of our
trains for those less mobile. It seems to me though that those in our society who are
unfortunate enough to be in wheelchairs are better catered for when accessing trains than
those who still walk, but with limited mobility. This is not implying our solutions for wheelchair
users are always adequate; one only has to look at the dreary “guard’s van” feel of the
wheelchair accommodation on the Trans-Pennine Express Class 185s to know that isn’t the
case. However, people who walk with an aid can find the process of getting on or off a train a
real challenge, especially as it is unlikely that railway staff will deploy the ramp for them, which
may actually be the better solution. Accessibility is key for on-time running, though one which
is all too frequently ignored.
The key issue for accessing the train is the horizontal and vertical platform gap7. The vertical
platform gap generally is determined by the height of the platform and then the height of the
vehicle floor which is often set by the designer’s desire to ensure the compression loads of the
vehicle is transmitted along the floor line, providing greater strength.
7
On higher speed routes, at curved platforms, track cant can also account for changes in both vertical and horizontal platform
gaps, but being relatively constant, platform positioning can be designed to mitigate this to a certain extent.
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The horizontal platform gap, however, is determined firstly by whether the platform is on
straight or curved track, and then secondly, when on curved track by the parameters of the
train design, namely the position of the doors relative to the bogies, the bogie position on the
vehicle, and the width and length of the vehicle.
With HS2 currently in the planning stages, there is no excuse not to have straight platforms
with level boarding (i.e. no vertical platform gap), and reduce the horizontal platform gap to a
minimum, enabling persons of reduced mobility unassisted access to the train (i.e. no carer or
member of railway staff required to assist). It should be considered a failing by our industry if
we do not achieve this.
The existing railway is more of a problem as there are already constraints in place. Much has
been done, however, in the past to improve platform gaps by such means as raising platform
heights.
As mentioned above, the horizontal gap on curved platforms is determined by door position,
bogie position, and width and length of the vehicle. Two of the worst stations for platform
gaps in the region where I live are York and Newcastle. Both stations are on fairly severe
curves and the platform gaps are significant. It is most noticeable on the 23m stock with the
passenger doors at the ends of the vehicles (such as HSTs, Mk4s, Class 220/221s, 158s and
153s).
The new IEP class 800/801 units are 25m in length, but with the doors inboard of the toilets,
so will be in a similar position to the doors on a current intercity train. However, rolling stock
longer than 20m has to be narrower than the C1 loading gauge to accommodate the extra
length within gauging parameters, and as a result, the new IEP units have to be significantly
narrower than current stock. In fact, the new IEPs will be the narrowest vehicles on the
network. This has the effect of making the platform gap at various stations, and most notably
at York and Newcastle, worse than currently. Given the current integration of accessibility as
standard practice across all design and engineering disciplines, it seems incredible that this
decision was ratified. As such, it is to be hoped that IEP is a one off, and future rolling stock
orders should ensure accessibility is totally integrated within the design process.
One of the benefits of articulated rolling stock is the consistent improvement in platform gaps
(whether on convex or concave curves) and passenger comfort that can be introduced due to
being able to have a bodyshell that maximises the loading gauge restrictions. An articulated
vehicle has no “end throw” which is the critical constraint on vehicle width, and generally
articulated vehicles are shorter (nominally 13m) which reduces the “centre throw”. The only
vehicles with end throw are the driving vehicles and those can be narrowed at the end beyond
the bogie as the cab does not need to be full width.
The data in Table 2 and Table 3 shows the platform gap for different types of train at
Newcastle station compared with an articulated train.
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Table 2: Platform gaps at Newcastle station for different electric rolling stock
Width
Centre
Throw
End Throw
Inside
Platform
Gap (e.g.
Platform 3)
Outside
Platform
Gap (e.g.
Platform 2)
Rolling Stock
Length
Door from
C/L
Bombardier
Spacium
(articulated)
13.24
4.62
2.96
1.607
1.477
0.114
0.117
Siemens
Cl450 Desiro
20.40
5.10
2.70
1.548
1.518
0.306
0.423
Siemens
Cl444 Desiro
23.57
10.29
2.74
1.495
1.509
0.452
0.133
Bombardier
Cl387 Electrostar
19.08
4.50
2.80
1.515
1.630
0.159
0.453
Alstom
Cl390 Pendolino
23.90
11.55
2.73
1.553
1.593
0.559
0.192
Hitachi
Cl395 Javelin
20.00
5.00
2.81
1.550
1.552
0.198
0.348
Mk4 Carriage
22.86
10.43
2.79
1.583
1.588
0.456
0.199
Hitachi
Cl800 IEP
25.00
10.43
2.70
1.495
1.661
0.501
0.320
C1 loading gauge
20.00
2.82
1.558
1.554
Outside
Platform
Gap (e.g.
Platform 2)
Table 3: Platform gaps at Newcastle station for different diesel rolling stock
Width
Centre
Throw
End Throw
Inside
Platform
Gap (e.g.
Platform 3)
Rolling Stock
Length
Door from
C/L
Bombardier
Talent
(articulated)
13.46
4.73
2.96
1.612
1.477
0.117
0.119
Bombardier
Cl172 Turbostar
23.27
5.82
2.69
1.533
1.552
0.284
0.487
Bombardier
Cl222 Meridian
23.00
10.00
2.73
1.556
1.560
0.460
0.260
Siemens
Cl185 Desiro
23.75
5.94
2.84
1.608
1.643
0.213
0.425
Alstom
Cl175 Coradia
23.03
10.02
2.79
1.583
1.593
0.431
0.230
Alstom
Cl180 Adelante
23.03
10.02
2.79
1.583
1.593
0.431
0.230
Mk3 Carriage
22.86
11.03
2.79
1.583
1.588
0.494
0.160
C1 loading gauge
20.00
2.82
1.558
1.554
It clearly demonstrates that an articulated vehicle would significantly help to improve the
platform gap issue at Newcastle, and similarly would do so at York, and other stations on the
network. To illustrate this point further, a concept vehicle was also run through the
calculation. This was developed using vehicles nominally half the length of current UK rolling
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stock at 12m, aiming to maximise the potential width. As demonstrated in Table 4, the
platform gaps are kept to a minimum while achieving a maximum width of 2.90 m,
significantly wider than existing rolling stock, and a full 200 mm wider than the future Class
800/801 IEP units. This has been achieved while keeping the centre throw of the vehicle the
same as that achieved by the C1 loading gauge profile. This is however outside the nominal
static outline of the C1 loading gauge, and so gauge clearance proving work would be required
for a vehicle wider than 2.82 m, as would have been completed for the Class 185s.
Table 4: UK articulated train platform gaps
Rolling Stock
Length
Door from
C/L
New articulated
train for UK
12.00
4.00
C1 loading gauge
20.00
End Throw
Inside
Platform
Gap (e.g.
Platform 3)
Outside
Platform
Gap (e.g.
Platform 2)
1.558
1.451
0.124
0.136
1.558
1.554
Width
Centre
Throw
2.90
2.82
Further, by having no end throw, the platform gap at the corridor connection is removed, and
the short vehicles minimise the platform gap along the length of the vehicle, not just at the
doors. This assists with removing the potential for incidents of passengers falling between the
platform and the train either through being partially sighted, losing their footing, or
intoxication, as was tragically demonstrated at James Street station on the Merseyrail
network.
Interior comfort
The fact that articulation enables a wider bodyshell results in a more spacious interior. This is a
positive step and will be appreciated by passengers who have recently come to rely on
modern trains with cramped environments, such as the Class 390 Pendolino.
Further, articulation usually results in shorter vehicles (as mentioned above), which means
fewer people per vehicle, and produces more of a compartmentalised feel which helps to
reduce the numbers of people disturbed by an antisocial passenger.
As Mr T Henry Turner noted8, articulation provides “a previously unattained ease of walking
through the gangway between vehicles”. This is certainly demonstrated on the TGV vehicles
where if it wasn’t for the doors, it would be difficult to realise you were passing between
vehicles, so stable is the gangway, placed as it is, on the bogie bolster.
Concluding remarks
In Ian Walmsley’s article on the replacement of Pacers9, he takes a brief look at articulation,
and then concludes with “But sadly articulation in the UK just isn’t worth doing”. I think this
remark should read “Articulation of two car sets to replace the Pacers just isn’t worth doing”.
That statement is certainly true, but as trains get longer, so the case for articulation gets
8
The engineering aspects of high speed trains, No.4 Permanent Way, Journal of the Institution of Locomotive Engineers, JC Loach,
CEng AMICE MIMechE Comment made by Mr T Henry Turner MSc in the discussion following the reading of the paper, March
1966; 56 (310), Downloaded from sagepub.com at IMECHE on 16 June 16, 2015
9
Blame it on the bogie, Ian Walmsley, Modern Railways, June 2015 Vol 72 No. 801, Key Publishing, Stamford, UK
7 of 8
stronger. Certainly articulation should be considered where three or more conventional
vehicles are being proposed. The benefits provided by using articulated trains have been
recognised in many areas of the globe and should be recognised here in the UK. On a railway
system blighted by a small loading gauge, many platforms on curves, and yet needing to
accommodate the ever increasing demands of a mobile society, articulation solves many of
the issues that can not be improved in other ways. This article has demonstrated that the
barriers to articulation are insignificant. The question should not be if we will see a native UK
fleet of articulated trains, but when.
Bibliography
Newsome N, The development of LNER carriage and wagon design 1923-1941, Journal of the
Institution of Locomotive Engineers, 38 (203), Downloaded from sagepub.com at IMECHE on
16 June 2015
Perren B, TGV Handbook, 2nd ed, Capital Transport Publishing, date unknown
Ringham GS and Bruce JG, Experience with the new rolling stock on London Transport
Railways, Journal of the Institution of Locomotive Engineers, September 1965; 55 (307),
Downloaded from sagepub.com at IMECHE on 16 June, 2015
Thhing JF, The engineering aspects of high speed trains, No.2 Passenger rolling stock, Journal
of the Institution of Locomotive Engineers, March 1966; 56 (310), page 200-202, Downloaded
from sagepub.com at IMECHE on 16 June 2015
Turner T Henry, comment made in the discussion following the reading of the paper, Loach JC,
The engineering aspects of high speed trains, No.4 Permanent Way, Journal of the Institution
of Locomotive Engineers, March 1966; 56 (310), Downloaded from sagepub.com at IMECHE on
16 June 16, 2015
Walmsley I, Blame it on the bogie, Modern Railways, June 2015 Vol 72 No. 801, Key Publishing,
Stamford, UK
Xue X, Ingleton S, Roberts J, Robinson M, Qualitative comparison of the characteristics of
articulated and non-articulated trains and their effects on impact, Proc. IMechE Jan 11, Vol.
225, Issue 1, Part F: J. Rail and Rapid Transit, Downloaded from sagepub.com at IMECHE on 16
June, 2015
Chris Hoskin
Chris is a Chartered Rolling Stock Engineer, a Fellow of the Institution of Mechanical Engineers,
and a Member of the Institution of Railway Operators. He started his career in 1998 designing
railway condition monitoring equipment based in Derby, then moved to consulting in Australia
and New Zealand, returning to the UK in late 2013 to take up his current role as Head of
Rolling Stock at Steer Davies Gleave, the leading transport consultancy. His area of expertise is
in the procurement and refurbishment of passenger rolling stock, starting from early strategy
through to service entry, particularly specialising in the development of rolling stock
specifications. He is married, has two children, and lives in York.
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