recent years, the issue of transport noise has become a high profile issue
and the industry has come under pressure to reduce operating noise. While
much has been achieved, the European Commission has become concerned that
the rail sector has not shown the same progress towards quieter operation
that rival transport modes have made. A Green
Paper from the Environment Directorate in 1996 underlined this concern,
and since then the Commission has contributed towards the funding of research
programmes aimed at cutting railway noise - especially in the movement
of freight where improvements have been least pronounced.
ago people living near railway lines had to put up with substantial noise.
The exhaust of steam locomotives, wheels hitting rail joints, brakes squealing
and clanking wagon couplings were all part of the background noise. Modern
railway operation has dispensed with many of these sources of noise. Quieter
diesel and electric traction has replaced steam.
welded rails provide a smoother ride, eliminating the 'clackety clack'
of wheels hitting rail joints. The close coupling of vehicles has done
away with the clanking of buffers. On passenger coaches, disc brakes make
vehicles much quieter than old tread-brake designs. However, substantial
sources of noise remain - particularly from freight vehicles, where brake
blocks operating directly on the wheel treads remain in widespread use.
railway operations most noise comes from the interaction between the steel
wheel and the steel rail, so the research has been directed primarily
at this area. On freight vehicles the problem is compounded by the continuing
use of tread brakes. By acting directly on the steel running surfaces
of wagon wheels, tread brakes can not only be noisy in themselves, but
can lead to noise-producing irregularities in the tyre surface.
Freight programme, co-ordinated by the European
Rail Research Institute (ERRI) in the Netherlands, looked at a
number of wheel designs with a view to cutting noise. A number of
manufacturers worked with ERRI on different designs, with ideas including
smaller wheels, perforations in the wheel, ring dampers, wheel shields
and tuned absorbers. Different combinations of these features were
tried. The use of ring dampers and wheel shields were seen to produce
some of the best results, while wheel shape optimisation had disappointing
Photograph of a train running along microphone
array site in Switzerland.
also co-ordinated the Silent
Track project. Here, both retrofitting existing track and a
new design of track optimised for noise reduction were studied:
The retrofitted section of track featured UIC60
rail - a heavy duty rail weighing 60 kg/m, which is approved by
Union of Railways (UIC) for use on high-speed lines - with
a stiff pad between the rail and the sleeper, and a tuned noise
The new section of track also used UIC60 rail,
with a 100mm wide foot on the rail, rail head support, a tuned
absorber and an optimised sleeper.
of the wheel and track designs were compared against wheels of a
standard 920-mm diameter on ballasted track with UIC60 rail and
soft pads. The overall objective was a 10dB(A) noise reduction,
which implies more than a halving of the noise from a freight train.
research results indicated that damping/shielding of wheels and
damping of track are necessary to achieve any reasonable reduction
in rolling noise. With the prototype designs developed during the
project, for damped wheels on retrofit track the upper limit of
noise reduction is approximately 7dB(A), while damped wheels on
the new track design gave an upper limit of about 8dB(A).
In addition to these measures, a bogie shroud manufactured within
international gauge constraints (168-mm gap to top of rail) was
tested in combination with low height trackside barriers (50mm above
top of rail); this gave a further noise reduction of 3dB(A).
research showed that, when the best noise reduction measures are
combined together, the 10dB(A) noise reduction target is achievable.
The testing demonstrated that hard rail pads produce no additional
benefit when used with damped track. The results of wheel shape
optimisation were also disappointing. This gave railway engineers
some indication about which ideas are not worth pursuing for noise-reduction
materials for brake blocks
showed that there are no easy answers in the field of brake block
materials. The aim of the Eurosabot project was to develop a brake
material for tread braking of freight vehicles that would suppress
the formation of wheel roughness, while still providing the required
braking performance. Netherlands national rail operator NS
was scientific co-ordinator on this project, with ERRI responsible
for project management, and railways, manufacturers and research
organisations from several countries helping in tests and contributing
in other ways.
iron is generally used for tread-brake blocks. This material has
many properties that make it suitable for brake blocks, but it causes
roughness on the wheel tread, and consequently a high level of rolling
noise. The phenomena involved in the generation of roughness on
the wheel surface were studied, mainly on the basis of dynamometer
tests. Thermo-elastic instabilities due to local heating of the
contact surface and material transfer between block and wheel, dynamic
instabilities and periodic wear were felt to be factors responsible
for the generation and growth of roughness.
series of computer-based models was developed, that were able to
reproduce qualitatively what had been observed in the tests. Together
with these models, rig test results were used to select promising
solutions from a large spread of ideas that were then tested in
researchers found that the results of the final tests were to some
extent disappointing. The project did not succeed in identifying
a 'low roughness' brake block material suitable for a simple retrofit
exchange of cast iron blocks. However, it did succeed in improving
significantly the understanding of the processes that are important
in wheel roughness generation. In addition, advances were made in
the modelling of thermo-elastic instability, combined dynamic-thermal-wear
instability and brake squeal.
research on Land Transport and Marine Technologies
is focussing on reducing rail noise of rail transport, particularly
looking at ways to make freight vehicles quieter,
looking at ways to make the track quieter,
developing reliable methodology for designing tread brake blocks
that would result in smoother wheel rolling surfaces.