The driver's sunglasses may have reduced her visibility when a tram hit and killed a man in Sheffield.
That is one of the findings of an investigation into the death of an 81-year-old who was struck at the Woodbourn Road tram stop, in Attercliffe, on December 22 last year.
The Rail Accident Investigation Branch (RAIB) today published its report on the tragedy, which includes recommendations to reduce the likelihood of future accidents.
The pedestrian had just got off an inbound tram, shortly after 10am, when he was hit at a crossing by an outbound tram headed for Meadowhall which was not stopping at the platform.
The tram driver had been looking in her mirrors until shortly before the collision, the investigation found, and consequently saw the man too late to prevent the accident.
She was also wearing sunglasses, which may have reduced her visibility of the pedestrian, who was in a shaded area at the time.
And, having been driving for three hours by that point without a break, her ability to concentrate may have been reduced.
The pedestrian was seemingly unaware the tram was approaching the crossing, and the vehicle did not give an audible warning it was passing through non-stop.
The RAIB found Stagecoach Supertram had failed to assess the risk when introducing request stops in around 1999. It also identified 'inconsistencies' with training and assessments for new drivers when it comes to passing platforms without stopping.
The operator has since introduced audible warnings for non-stopping trams, added an extra warning sign for pedestrians and taken steps to reduce drivers being distracted looking in mirrors, the report states.
It has also updated its risk assessment and implementing other measures to reduce the risk of trams hitting pedestrians.
The watchdog makes two recommendations in its report.
One is for Stagecoach Supertram to continue working to review its training material.
The other is for UK tram operators to work together to monitor the development and application of new pedestrian detection technology, which could alert drivers to potential risks.
It also identifies three 'learning points' from the tragedy, highlighting the risks of non-stopping trams passing foot crossings, the potential hazards of drivers wearing sunglasses and the need for tram drivers only to use their mirrors where 'essential' when passing through stops.
The driver had more than 20 years of experience, having qualified in 1994, and was travelling at 13mph at the time of the collision, which is within the guidelines for that location.
But there are no records she had received additional training when request stops were introduced on the service some five years after she qualified.
A spokesperson for Stagecoach Supertram said: "Our first thoughts remain with the loved ones of the pedestrian who died in the accident. Safety will always be our absolute priority and we have worked closely with the authorities to understand the full circumstances involved.
"Since the incident, we have implemented a number of changes to strengthen our safety regime, as acknowledged in the RAIB report. We are also committed to working with the wider industry to enhance safety at Supertram and other tram networks."