Improving Passenger Safety at Platforms. T.A.W. Geyer, C.P. Chapman, and M.I. Morris, Four Elements Limited, 8 Cavendish Square, London, UK; and P.R. Chislett, London Underground Limited, London, UK
BACKGROUND
A number of passenger accidents at the platform/train interface,
some resulting in fatal injuries, has led London Underground Limited
(LUL) to consider what additional measures might be adopted to
improve passenger safety in this area still further. In fact
the London underground system is very safe at the platform/train
interface -- over two billion passenger boardings and alightings
take place each year without incident. Nonetheless, whenever
a passenger accident does occur, there is justifiable public concern
as to whether LUL has taken, and is continuing to take, all reasonable
steps to avoid passengers being exposed to undue risk; and LUL
itself recognises the need for continuous monitoring and improvement
where practicable.
For these reasons, LUL, in conjunction with Her Majesty's Railway
Inspectorate commissioned Four Elements Limited to consider various
measures intended to improve passenger safety at platforms, to
evaluate their benefit using the technique of quantitative risk
assessment (QRA), and on this basis to recommend for further consideration
those measures which seem cost effective. This paper describes
the approach and findings of the study.
HOW SAFE IS SAFE ENOUGH?
The regulation of safety in the United Kingdom is based upon the
principle that risks must be reduced to a level which is "As
Low As Reasonably Practicable" (the so called ALARP principle).
The meaning of "reasonably practicable" is well established
in English case law:
"Reasonably practicable" is a narrower term than "physically possible" and seems to me to imply that a computation must be made by the owner in which the quantum of risk is placed on one scale and the sacrifice involved in the measures necessary for averting the risk (whether in money, time or trouble) is placed in the other, and that, if it be shown that there is a gross disproportion between them -- the risk being insignificant in relation to the sacrifice -- the defendants discharge the onus on them. "(Judge Asquith, Edwards v. National Coal Board, All England Law Reports Vol. 1, p. 747 (1949)).
Thus the ALARP principle allows cost to be taken into account
in determining how far to go in the pursuit of safety, so that
if a risk reduction measure involves "grossly disproportionate"
cost, it is not "reasonably practicable". This principle
was adopted in the Health and Safety at Work Act (1974), and is
the basis of the approach adopted by the Health and Safety Executive
in their regulation of the major hazard industries, such as the
offshore oil and gas industry. It has also been adopted by BNM
in its application of the Railways (Safety Case) Regulations (1994).
It is against this background that LUL, as a major railway operator,
aims to provide a safe, efficient and quality service to its many
millions of customers. As such it requires effective decision
making support to assist in the management of safety and the prioritisation
of capital expenditure, ultimately to discharge its legal obligation
to ensure that risks are managed and controlled to levels which
are as low as reasonably practicable.
LUL believes that the techniques of risk assessment can help managers
make better decisions on safety issues by providing a more systematic
basis for appraising safety options. The study presented in this
paper is therefore a key part of the decision making process within
LUL, whose aim is to achieve an optimum level of safety for passengers
at platforms, by identifying and prioritising opportunities for
investment in measures which can effectively improve safety, whilst
avoiding expenditure on measures whose cost is grossly disproportionate
to their benefit.
ASSESSING THE EFFECTIVENESS OF MEASURES TO IMPROVE SAFETY
In order to demonstrate reasonable practicability, or gross disproportion,
it is becoming increasingly the norm in the railway industry,
as well as in the major hazard industries, for the extent of the
benefit of a safety measure to be evaluated using the technique
of quantitative risk assessment. In essence this involves firstly
identifying a comprehensive set of possible accident scenarios,
and then for each scenario deriving quantitative estimates of
both how often it may occur (eg, once in ten years) and how severe
the consequences may be (eg, one person suffers fatal injuries).
The effectiveness of the safety measure is then assessed by considering
the extent to which it can be expected to reduce either the frequency
or the severity of each accident scenario. Finally, the results
of this calculation are incorporated into a cost benefit analysis
to determine the balance of practicability.
In this case the relevant accident scenarios and the current level
of risk at the platform/train interface have been established
from the record of passenger accidents for the last few years.
The accident categories considered in the study are person under
train, person on track, caught in doors, and fall between train
and platform (or between cars).
The next stage involved assessment of each safety measure, to
determine its effectiveness in reducing the risk. Consideration
has to be given to each category of accident separately, as some
safety measures are effective only against certain types of accident.
In addition, both the frequency and the severity components of
the risk must be addressed. This is important because the various
measures address these components differently.
For example, a measure such as the use of closed circuit television
(CCTV) is of benefit because, once the driver becomes aware that
a passenger has fallen between the train and the platform, he
will not start the train, and so the injuries suffered by the
passenger will be much less severe. However, the measure is not
expected to influence the frequency of incidents -- passengers
are still just as likely to fall between the train and the platform.
Alternatively, the benefit of a measure such as platform edge
doors is that it would reduce the frequency of accidents, rather
dm the severity of their consequences.
The risk reduction assessment process was essentially a judgemental
exercise, based on the experience and expertise of LUL operations
personnel familiar with day to day operations, and facilitated
by a risk assessment consultant with considerable experience of
the issues involved. In particular, a meeting was held where
estimates of the risk reduction achievable by each measure were
agreed. In some cases human factors specialists with experience
in railway procedures provided additional input where the improvement
envisaged relies on assumptions about staff and passenger actions.
As regards the cost estimates, LUL provided general background
data on the number of stations, trains, platforms, etc., and prepared
a preliminary specification of each of the potential risk reduction
measures.
In assessing the net cost to LUL, it is necessary to take into
account the capital cost (eg, for hardware and its installation),
any change in on-going operating costs, for example, in maintenance
costs and/or staff costs, and any operational benefits (revenue
from increased usage due to passenger benefits). In terms of
passenger benefits, there is the societal benefit associated with
the reduction in accidents, the reduction in the costs associated
with delays (as a result of reducing the frequency of accidents),
but also any potential disbenefit associated with disruption caused
by passenger mis-use of the safety measures (eg, mis-use of emergency
stop plungers).
A standard cost benefit calculation was then performed for each
option. LULs prefer-red measure for distinguishing the merits
of each of the candidate risk reduction measures is the benefit
to cost ratio, calculated as the sum of passenger benefits divided
by the net cost to LUL.
Although there is always a margin of uncertainty associated with
the results of a quantitative analysis, experience has shown that
the envelope of uncertainty is often swamped by the much larger
variation in the effectiveness of safety measures themselves.
Thus the benefit to cost ratio is generally a useful discriminator
between upgrade options because some options are usually found
to be clearly worthwhile, and others clearly ineffective, even
allowing for uncertainty in the risk and cost estimates. In fact
in this study, for two of the measures the overall benefit was
found to be negative.
THE SAFETY MEASURES CONSIDERED
Guards on trains. A guard is positioned at the rear of
each train and has access to an emergency brake device with which
to stop the train in an emergency. His primary role is to observe
the doors closing and the departure of the first passenger carriages
from the platform. Trains are also fitted with standard passenger
emergency alarm equipment.
Platform attendants and emergency stop plungers. A platform
attendant with access to an emergency stop plunger device is positioned
in a prominent position on each platform with maximum available
visibility of the length of the train and platform. Operation
of an emergency stop plunger will illuminate red signal lights
at the trackside ahead of train to warn the driver to stop immediately
whilst entering or leaving a platform. On Automatic Train Operation
(ATO) lines, the Victoria Line for example, the device will interrupt
track circuit signalling to bring the train to a halt automatically.
Emergency stop plungers on platforms. A series of platform
wall mounted alarm devices are positioned at predetermined intervals
along the platform for use by passengers and staff.
Emergency stop plungers on trains. An alternative to installing
emergency stop plungers on the platform wall would be to install
them on the outside of the train. This would be a simpler device
and quicker acting as it could directly apply the train brakes,
and would not have to illuminate red signals or interrupt ATO
codes.
Train borne passenger emergency alarm automatic braking system.
Fitting all trains with a (Central/Jubilee line type) modified
passenger emergency alarm system which, if operated whilst leaving
the platform area, will automatically apply the emergency brakes
and bring the train to a halt. Beyond the platform area, the
system will function as normal, alerting the driver to stop at
the next station.
Reducing gaps between platform edge and doors. Platform
gaps modified to comply with a maximum gap criteria (150 mm both
vertical and horizontal).
Inter car barriers. A simple, robust and flexible barrier
(either a gate/screen type or a simple rope) is installed between
all cars to prevent passengers from falling between cars or, in
the case of the visually impaired, mistaking the gap for a door
aperture.
CCTV monitors in cabs. A Central Line type CCTV facility
is provided in all operational cabs to enable the driver to observe
the approach and departure of a train from the platform.
Platform edge doors. Doors are provided which run the
full length of the platform and cannot be readily climbed
by passengers. The doors can only open if a train has properly
berthed and must be proved to be closed before a train departs.
A door may need to be opened manually from the train side if
normal power falls.
Platform surveillance using CCTV. Sufficient station staff
available to monitor all departing trains from a central point
in the station. This measure would necessitate enhanced communication
systems to ensure that the station staff monitoring the CCTV have
a means of immediate contact with the driver in the event of an
incident, or some means of automatically stopping a train for
example, access to an emergency stop plunger.
Improved door engineering/control mechanisms. Reducing
the doors closed tolerance to the latest standard - 6 mm. All
rolling stock would be fitted with door closing alarms, and all
door system tolerances improved. Door edge rubbers would be stiffened
to the maximum practical extent.
FINDINGS AND RECOMMENDATIONS
Each of the measures described above has been assessed, and the
findings and recommendations are described below.
It should be noted that some of the measures recommended for further
consideration address the same accident scenarios. The overlap
between different measures therefore needs to be taken into account
if more than one measure is taken forward for implementation.