He said drivers were frustrated at being overridden by a new automatic European control system to restrict them to 10km/h when arriving at Britomart through its tunnel, or 15km/h when approaching Onehunga and Te Papapa stations from up to 200 metres away. That compared with a 25km/h limit for the old diesel trains at Onehunga and Britomart.
The top permitted speed for the three-car electric units on open tracks is 110km/h - about 20km/h slower than Mayor Len Brown says they are capable of.
Rail and Maritime Transport Union organiser Stuart Johnstone confirmed the delays and said drivers were becoming frustrated with the electric overrides on what were otherwise "very good trains".
Although the new control system was "a good safety device to have", he believed it needed recalibrating.
Transdev blamed delays of up to 25 minutes last Monday, the first day of work for the electric trains, on passengers' unfamiliarity with a new door-opening system and drivers taking extra care with new equipment.
A spokeswoman acknowledged the control system was "configured pretty conservatively at the moment, which is a good thing, but it will be modified as we get them [the trains] into service".
Auckland Transport, which contracts Transdev, expects the trains to cut 10 minutes off 50-minute trips from Papakura to Britomart in 2015.
It hopes all 57 of the new trains being delivered from Spain will be running on all lines by the middle of next year, although a new timeline published last week suggests it may not be until late 2015 that western services go electric.
Chief operations officer Greg Edmonds said it was "entirely correct" for the train control system to be configured conservatively to start with.
Speeds compared
Electric trains
Top permitted speed on open tracks - 110km/h.
Top test speed - 122.6km/h.
Theoretical top speed - about 130km/h.
Diesel trains
Top speed - about 80km/h.
