Just how fast will our Electric Trains be?

The first visible signs of electrification are starting to appear across the rail network, which is great to see, but there are still a few big unanswered questions. The biggest of these is what sort of trains we will actually get and probably more importantly how these trains will perform. I feel that this is especially important to those like me who are on the western line – in some places it feels almost pedestrian and not something that can be called a rapid transport network (something Admin has commented on in the past). Kiwirail and Auckland Transport will only say that the new trains will be faster due to better acceleration, but just how much faster is unknown as it will depend on the outcome of the tender process.  I suspect that someone in one or both of these organisations will have a rough idea but, as they aren’t saying what that is likely to be, I decided to work it out for myself.

For those that want to know fully how I worked out the timings, I will put how I have done it at the end of the post.

There are four main things I can see that determine how long a train will take – the time spent accelerating, the time spend decelerating, the time spent travelling at the maximum speed for the line, and the time dwelling at the station. I wanted to be conservative and have used the following figures:

• Acceleration: 0.8m/s² – I found a reference that indicated commuter trains generally accelerate between 0.6m/s² and 1.2m/s². Wikipedia states that Wellington’s new ‘Matangi’ trains have an acceleration of 0.84m/s² so while ours are likely to be more powerful due to the need to be able to climb the steep CBD tunnel I have used 0.8m/s² as a base acceleration rate.
• Deceleration: 0.8m/s² – I haven’t been able to find any info on this so for the time being I have set it to the same as the acceleration
• Max line speed: Varies – I have set this individually for each set of stations. Out west I believe the official speed limit is 80kph between Swanson and Baldwin Ave and 70kph between Baldwin Ave and Newmarket, although there are many speed restrictions due to the curves in the area. As such I have set the limit as 80kph from Swanson to Baldwin Ave and 50kph between Baldwin Ave and Britomart.
• Distance between each station: I have measured this with Google maps and while not exactly to the metre I have it fairly close.
• Dwell Time: 30 seconds – I made some notes last year about how long trains spent stopped at stations – smaller stations were around 15-20 seconds, larger stations about 30 seconds. I have used 30 seconds for all stations with the exception of Newmarket which I have made 3 minutes to allow for the end change (this is the same as the current timetable).
• Additional Time: 5 minutes – There are numerous curves, hills and suchlike that might slow a train down or prevent it from traveling at full speed. To be really conservative with my timing I have added an extra 5 minutes to the journey between Swanson and Britomart (spread out between each station by dividing it up and adding it to the dwell time). This added just under 20 seconds to each leg of the journey.

With all of that out of the way what are the results? I have included just a handful of stations to give you an idea of the improvement we can expect, but if you want anything else just let me know in the comments and I can give specific results.

As you can see, even with fairly conservative figures the results are pretty good and deliver some decent time savings. In most cases they would at least rival peak hour traffic times and in some cases even rival off peak car times. Also considering that we should get times better than these it makes the electrification project quite exciting and would actually go some way to making the western line feel more rapid. Moving away from being conservative and changing a few figures – better acceleration at 1m/s²  (which is quite possible given they will need to be powerful enough to climb the CBD tunnel), faster line speeds between Baldwin Ave and Britomart (Kiwirail mentioned at the open day last year they wanted to get line speed up to 80kph) and halfing the additional time – amazingly sees the time savings double.

How I have worked out this out

The first step I did was to work out how long it would take to accelerate from 0 to the max speed. From there I have also worked out how far the train would have traveled in that time, i.e. at 0.8m/s² it will take 27.7 seconds to get to 80kph and the train will travel 309m.  By doing this for the acceleration and deceleration and taking the distances off the distance between stations we can see how much time the train can spend at the maximum line speed. From there it is just a case of adding all the travel times together along with the dwell time (which includes an equal portion of the additional time).

To check my calculations are accurate I have also worked out the times on the line between Upper Hutt and Petone, which has a similar number of stations and spacing as the western line. My timings were fairly close (only a few minutes slower) which shows they are a good indication of what we can expect.

All of this is in Excel. The variables are able to be easily changed to be used for other lines – I will post the results for them in a few days but they are equally impressive.

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