ONE OF THE biggest questions facing metro operators considering the conversion to automation is how to ensure safety at station platforms and/or detect obstructions on the track. The UITP metros conference in Nürnberg included a round table on the use of platform screen doors.
Opening the debate, Holger Albert from Hamburger Hochbahn suggested that doors were 'self-evident for greenfield projects', but the cost and complexity of retrofitting stations meant that the argument for conversion was much less clear-cut. Experience in cities such as Lyon and Vancouver had shown that intruder detection could be equally satisfactory. Nürnberg had opted to go down this route and equip its stations with high-frequency intruder detection.
Singapore adopted screen doors at underground stations to reduce the cost of air-conditioning, but the open-air stations are not equipped. Both lines use manually-supervised ATO. The fully-automated North East Line runs entirely underground with doors at all stations, but the three automated peoplemover networks do not have screens on their elevated station platforms. Philip Hartheiser from the Land Transport Authority commented that local residents were 'extremely disciplined' and there was good public awareness that safety was a user responsibility.
København Metro Operations Director Per Als agreed that screen doors were 'the Rolls Royce solution' and very expensive; his network had also limited the use of screens to underground stations where they could be justified by the air-conditioning savings.
However, Jean-Michel Erbin from Keolis noted that design criteria have changed since Lyon Line D was equipped 15 years ago, and 'what was good enough then may not be now'. The 16 stations had been designed for conventional operation, and when the decision to automate was made it was simpler to overlay an 'infra-red carpet' than install doors. But the concessionaire has experienced a much higher incidence of trespass in Lyon than in Lille and Rennes, where the 45 stations have screen doors as an integral part of the VAL design.
With the cost of installation a significant factor in the final choice, Alcatel's Firth Whitwam pointed out that specification of the appropriate safety integrity level was critical. He explained that moving from SIL2 to SIL4 could add around US$50000 per station to the cost of fitting screen doors. This posed a conundrum to suppliers bidding against a general specification, and Whitwam suggested that there would be significant benefits if the metro sector could agree on a world standard.
Legal framework
The round table also considered whether legal requirements had a major influence on the decision to fit doors. Erbin said that the current requirement in France is for 'safety equivalence', requiring proof that automated metros are 'as good as' conventional systems. RATP's Serge Lagrange confirmed that the operator has been undertaking a detailed risk analysis for its automation programme (p89).
Hong Kong MTR Corp's Managing Director, Operations &Business Development, Phil Gaffney said safety regimes were less-developed in some countries. In the absence of specific legal requirements, MTR was basing its safety case on international best practice. Hartheiser agreed that in the absence of legislation, LTA had to approve safety regimes for all modes in Singapore, allowing a realistic comparison between road and rail. This was based on economic factors including ALARP principles (As Low As Reasonably Practical) and the Value of Preventing a Fatality.
RATP's Alain Caire picked up on the problem posed by different safety standards for road competition, noting that 'safety is a big selling point' for rail operators. VAG Technical Director Rainer Müller asked 'in an ideal world, should we screen off the pavements too?' Per Als emphasised the competition aspect, warning that 'when we deal in the real world, don't compare with perfection. Don't get into the position of gold-plating your systems; make them affordable.'
Retrofitting
Hong Kong MTR is leading the way in retrofitting screen doors to an existing network, having decided five years ago to install full-height screens at all its underground stations. With the programme nearing completion, Gaffney said the experience had been 'entirely positive'. He emphasised that the decision was primarily taken for environmental reasons and to reduce the energy cost of air-conditioning; the company did not accept the suggestion that screen doors would materially improve passenger safety. Surface stations do not have screens, but the fully-automated line to the Disneyland complex at Penny's Bay, which opens this year, will have half-height barriers and gates at its two stations (p80).
According to Serge Lagrange, RATP found the full-height doors on the automated Line 14 difficult to justify in cost terms, but he believed that the frequent service and improved perception of personal safety had a pay-off as the line attracted more passengers. However, trespassing on the track is a big problem in Paris, and RATP is looking at the value of half-height barriers and gates 1500 to 1750mm high; pilot screens are to be installed on Line 13 this year.
Lagrange said there were many problems in retrofitting screen doors to lines built between 1900 and 1935. Barriers would reduce the usable width of platforms that in some cases are already less than modern standards. There is also the issue of protecting the gaps between screen and train at sharply-curved platforms, and Lagrange warned that 'we can't afford to create additional hazards, such as people becoming trapped.' As part of its process, RATP has commissioned a study into how people behave when using the metro.
- CAPTION: Platform screen doors are fitted to all stations on Singapore's North East Line. Westinghouse Brakes is supplying 288 sets of doors for the 24 platforms on the first two phases of the Circle Line now under construction and will supply 432 more sets for 36 platforms on phases 3, 4 and 5 by 2010
- CAPTION: Semaly opted for intruder detection rather than doors when converting the part-built Line D in Lyon for automatic operation in 1991
- Photo:Semaly/Rodarie
