At least 8,500 Wellington commuters were left stranded on Tuesday when train services were cancelled during rush hour. Unusually high temperatures in the region caused a problem with the wires that provide the overhead power supply on the train lines. That led to cancellations on the Johnsonville and Hutt Valley lines, and to delays on the Wairarapa line and Kapiti lines. Henare Clarke is the chief operations officer for KiwiRail. He joins us with details of what went wrong.