Tram Operations Ltd (TOL) in partnership with London Trams won the 2020 Global Light Rail Awards ‘Project of the Year under €50m’ in November 2020, for its approach to reducing risk associated with speeding at high-risk locations on the network using existing technology to address the challenge in a new way. Physical Prevention of Over Speed (PPOS) is an on-tram automatic braking system using radio frequency identification (RFID) beacons – the first time these have been used on a light rail network in Europe.
PPOS Track Beacons.
How does it work?
TOL identified the 13 highest risk tight curve locations on its network, assessing factors such as gradient, visibility, and proximity to tram stops. At each location, it created a ‘PPOS zone’ on approach to the curve. It installed a series of beacons to act as a step-down speed zone, providing maximum protection for the driver and passengers.
The trams are fitted with beacon readers and an on-tram controller. As the tram passes though the speed zones, the beacons transmit the permitted speed and other data to the beacon readers which inform the on-tram controller. If the tram exceeds the permitted speed in one of the protected zones, the on-tram controller stops the tram before it reaches the high-risk area, tells the Tram Operations Control Room (TOCR) which tram is affected and where it is. The driver then travels to the first available safe location and lets the passengers off. The driver won’t then carry out any safety-critical duties until the circumstances of the incident are investigated.
What challenges did TOL face and how were they overcome?
Success relied on staff understanding and embracing the new approach. TOL worked with ASLEF the Union to agree a blended approach to training which combined briefing packs, classroom sessions and time in the TramPro simulator.
A key challenge was training all drivers in four weeks rather than the 33-35 weeks it would normally take to deliver a programme of this size. An intensive programme addressed this, including working on rest days and reducing revenue checks on trams for a period of time, to free staff to participate. In total, 97% of drivers were trained over four weeks.
As this technology had not been used on the tram system before, maintenance teams at London Trams also attended specialist training so that they could repair faults and carry out routine maintenance effectively.
Another key challenge was to understand and address the impact of the new system on driver performance – specifically usability, impact on workload and human error. TOL undertook a human factors assessment using the TramPro simulator to identify any risks.
It also worked with London Trams to determine the impact of the new system on the TOCR and implemented ergonomic changes to integrate the new system safely and effectively.
What impact has the new approach had?
Between February and July 2020, there was an 88% decrease in the number of trigger events: the number of occasions the PPOS system was activated. This was partly as drivers became more familiar with the PPOS system, but also resulted from behaviour changes among TOL drivers. The new system and associated training meant they had to reassess their driving and modify their braking techniques. As one driver said:
“With the training and guidance that has been given, we understand that this provides a safer ride for both our passengers and us drivers. The PPOS system has made the tramway safer.”