Despite looking alike, not all of Metrolink’s trams are created equal.
This is because Metrolink has: Two Different Signalling Systems
When Metrolink was built initially, and the Altrincham and Bury lines were converted from British Rail operations, it used a railway style signalling system, and part of this is a safety system called ATS fitted to the trams. The plan when the system was expanded in the 2000s was to replace the railway style signalling on the Bury and Altrincham lines with a tram/metro signalling (known in Manchester as “TMS”) coupled with “line of sight” driving, which is being used on the new-build lines to Ashton, East Didsbury, Manchester Airport, and the converted railway line to Rochdale via Oldham. This system doesn’t require ATS.
The majority of the network is now on the newer system, but parts of the Bury Line remain unconverted, as is the section between Timperley and Altrincham Station, which is currently controlled from the Network Rail signalbox on Deansgate Lane, by Navigation Road station. These require use of the ATS fitted trams, which can go anywhere on the network.
Not all the trams are fitted with ATS: only half of them are (the ones numbered 3060 and below, if you’re interested). Therefore these are rostered to work on the lines that require them first (Bury-Picc, Bury-Altrincham, Altrincham-Etihad), but also can appear on other lines, as not all the ATS trams available are needed to operate the Altrincham and Bury services.
The other 50% of the fleet doesn’t have ATS and so can’t operate in the areas with the older signalling. This means they only work on the Ashton, Eccles, Rochdale, Didsbury and Airport lines.
Therefore it’s not necessarily possible to just take a tram that started out in Eccles that was going to Ashton, send it round the 2CC and run it onward to Bury, as that’s likely to be a non-ATS tram.
So there are only two places that a non-ATS tram could be sent once diverted via 2CC to Victoria: either to continue up via Oldham to Shaw or all the way to Rochdale, or empty out at Victoria and run empty to Queens Road.
The decision was taken not to fit the whole fleet with ATS because the plan is to phase it out completely. It seemed a sensible and rational decision at the time.
There are works in progress to convert the Bury line to line-of-sight with TMS signalling, but they are yet to be finished. I’m not entirely sure what the longer term plan is with signalling on Timperley-Altrincham.
This adds another level of complexity for the controllers to manage.
The other issue to consider even if it’s possible to divert the displaced trams to other lines is whether there is sufficient power available to handle the extra demand placed by the additional trams.
The overhead power lines are split into sections, so that they can be de-energised for maintenance, be fed from different parts of the power grid to help localise impact of mains supply interruptions, and more importantly manage the power loads imposed by the trams.
Control need to be careful that trams don’t just run willy-nilly into the same power supply section, or it can overload the power supply and cause even worse disruption, so that needs to be taken into consideration in those parts of the network which have constraints.
It is therefore necessary to regulate the service to ensure that this bunching up of the trams doesn’t happen, because not only can it cause issues on the power supplies, but it can cause congestion on both the tram network itself, and road congestion in areas with street running.
However, neither of these feel like good enough reasons why the entire network needed to be brought to a halt for over half an hour during the peak period.
Next time, I’ll write about what I believe could have been done to minimise the impact to services and not stop the entire network in the middle of rush-hour.