Nexus staff have been carrying out temperature monitoring work on Metro's 77km of tracks during the heatwave, which has hit the UK this week.
He said: "We have an annual hot weather plan and a series of controls and measures that we put in place to mitigate against issues.
"It has been particularly hot this week and that has been continuous over a number of days, so we have specialist teams out monitoring the tracks, the overhead lines, the signalling systems and other associated infrastructure.
"We have seen rail temperatures at 37 degrees centigrade, and it has peaked at 42 degrees already this week.
"We have to monitor the track because steel expands considerably during a heatwave and we have to ensure that it doesn't expand too much under normal service trains, so it's a case of monitoring and measuring temperatures continuously."
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