Edinburgh Trams have today been issued with urgent safety advice following an investigation into a fatal collision in September last year.
The Rail Accident Investigation Branch has found that the warning horns on the tram fleet are no louder than the tram bell, and does not provide a sound pressure level in line with current industry guidance.
At about 12:10 hrs on 11th September 2018, Correa Palacio, 53, was using a footpath crossing located between Balgreen and Saughton tram stops, he was struck and fatally injured by an outbound tram travelling from Edinburgh city centre towards Edinburgh Airport.
The tram driver had observed the pedestrian approaching the crossing and, in response, applied the service brake to reduce the tram’s speed as well as sounding repeated warnings using the tram’s bell. The pedestrian did not respond to these audible warnings and continued onto the crossing.
Although the driver then operated the emergency brake (which automatically activated the warning horn) before arriving at the crossing, the tram was too close to be able to stop before reaching it.
Since this accident, the RAIB has conducted acoustic measurements of both the bells and the warning horns fitted to the tram involved in this accident and on one other Edinburgh tram.
Tests were conducted from a distance of 7 metres in a flat, open area as per a specification referred to in the tramway guidance.
Results showed that the sound pressure levels from nine tests of the warning horns were approximately 86 dB(A) and 85 dB(A) on the two trams tested and falls short of 93 dB(A) or greater as recommended.
The RAIB said that a reduction of 10 dB is approximately equivalent to a halving in loudness as perceived by the human ear, and concluded that both the bell and the warning horn are not sufficiently discernible above the level of background to indicate the approach of a tram at line speed.
The warning horn produces a lower sound pressure level than the bell and can therefore be regarded as quieter.
At the time that the trams were procured and commissioned there were no specified numeric requirements for the sound pressure levels for tram audible warning devices.
However, guidance existed at the time of procurement, and continues to exist, which states that there should be two levels of audible warnings; the lesser level for on-street use, and the greater for off-street sections and emergencies.
It is common practice on tramways in the UK that the former is provided by a bell, and the latter by a warning horn.
A spokeswoman for Edinburgh Trams said: “When Edinburgh Trams commenced passenger service in May 2014 we were satisfied that suitable and sufficient testing of the audible warning horn had been undertaken.
“We want to provide a safe tramway for our customers and take cognisance of the notice issued today by the RAIB. Further testing is already underway with modifications to the warning horn being implemented across the fleet.
“We continue to work with the RAIB and do not wish to predetermine the outcomes of their final report which is expected in the spring.”