The Herald yesterday ran a story on just how quiet the new electric trains are. In a polar opposite there was a lot of noise on twitter about how the article was initially presented but after getting past that it provided some really useful information on just how good these trains are. Here’s the useful bit:
Informal noise sampling by the Herald measured the highest level inside electric multiple unit (EMU) number 129 at 72.9 decibels, compared with 83.6dB reached inside a locomotive-hauled train and 92dB in a diesel multiple unit between Puhinui and Homai stations on Auckland’s southern railway line.
With just the air-con switched on before the electric motors kicked in, the top level was 69dB.
A rule of thumb is that every increase of 10 decibels represents a doubling of noise, meaning a jet aircraft taking off at 100dB is roughly eight times as loud as a passenger car clocking 70dB at 105km/h.
Differences were even more pronounced outside the various trains, where the electric was at least four times quieter than diesels accelerating out of stations.
It reached a top count of 77dB when pulling out of its Wiri depot, compared with a high of 99.6dB for the DMU and 101.6dB for a loco-hauled train thundering away from Puhinui Station.
But being far quieter than the trains they will be replacing in a line-by-line rollout to mid-2015 presents a serious new challenge for the electrics, as they will be harder for pedestrians to hear coming.
That means rail operator Transdev is asking its drivers to take extra care to sound warning alarms when approaching level-crossings.
The differences in noise levels are substantial and it’s something I’ve noticed on the few times I’ve been lucky enough to have a trip on one of the EMUs. It’s quite telling also as I still remember a conversation with a one of the senior engineers involved in the project over a year ago. He told me that while they knew these trains would be quieter, they weren’t sure just how they would compare to a carriage in an SA set (the loco hauled ones) which are noisy if you’re in a carriage near the locomotive but can be quite as you move away from it. I’ve graphed the results the Herald recorded.
The vast improvement in the exterior noise is impressive and something that is bound to be a welcome relief for those that live, work or play alongside a rail line. In fact if the figures are right then the new trains are quieter on the outside than the existing trains are on the inside. I think it will hugely improve the viability of increased densities along the rail corridor. You can get a sense for how quiet they are from this video
Another good example is this video from TVNZ during the testing.
What caused attention on twitter though was the attention on the noise of the air-conditioning. Basically the trains are so quite that when first turned on the air-con is slightly audible. To me it’s actually a good sign as it shows the rest of the train is of such a high quality that the only issue able to be picked up was air-con noise. What’s more it appears that the engineers are working hard to improve it further.
Acoustic engineers have been trying to soften the air-conditioning noise on Auckland’s new electric trains with a week to go before they are rolled out for commuter use.
A constant air-conditioning hum overlaid the gentle whirring of electric motors and clickety-clack of rail tracks as the Herald joined trainee drivers on a test run of one of five trains being readied to carry passengers between Onehunga and Britomart next week.
Auckland Transport, which is importing 57 three-car trains from Spain for about $540 million in a cost-sharing purchase and maintenance deal with the Government, insists their air-con units already meet noise and efficiency specification limits for both heating and cooling.
That follows considerable design work and the installation of noise-reducing material, said a spokesman for the council body.
But he acknowledged engineers were still fine-tuning the systems to maximise passenger comfort.
He suggested it would be unfair to represent the air-conditioning noise of an empty train heading out of its depot into humid outside conditions as typical of what passengers should expect from next Monday.
“The air-con would have been working very fast until the train reached normal temperature.”
He also believed it would have been more noticeable in an empty carriage with little background noise.
I like the fact that the engineers are working to improve the customer experience further where they can. I just hope that AT manage to start paying this much attention to the customer experience across all of their operations because if they do then there will be a bright future ahead.
Only 5 days to go till these trains start carrying fare paying passengers for the first time