What acceleration should HS2 / Cl. 895 aim for?

[Crithylum]

There has been alot of chatter about the top speed of HS2, but what about the acceleration?

My proposal is for a maximum acceleration of 1m/s^2, and a power/weight ratio of 50w/kg. Here is my reasoning:

• The Elizabeth Line has an acceleration of 1m/s^2, which feels somewhat strong (compared to DMUs for example), but in no way overbearing, unlike the Victoria Line.
• The power I have proposed is far in excess of anything currently on the UK rail network, however, it would enable the maximum acceleration to be achieved up to 50 m/s, half of the top speed. With the advances in modern EVs, motors in excess of 10,000 w/kg are in use, meaning that a 40 tonne carriage would only need 200kg of motors. Especially as they won't need to carry around batteries, motors of this power are certainly technically viable.

For deceleration, I would assume that the aim would be for regenerative braking (in normal service), so using the same motors should provide similar acceleration and deceleration.

I have made a spreadsheet to calculate the time savings/costs of different performance, and found that my proposal loses 54s from a standing start, compared to instantly reaching 360km/h. Bear in mind that this is doubled when also considering slowing down. This is compared to 150s (x2) for the Javelin, if they had a higher top speed.

 

[HSTEd]

I don't see any reason not to go for the highest achievable acceleration.

I believe customer tolerance for standees falls rapidly above about 1.1-1.2m/s assuming jerk can be kept negligible - which should be achievable with modern motor drives.

After all the AGV motor bogie is rated ~1.5MW continuous, and that was from 2008.

 

[osmarks]

The existing specification calls for much lower acceleration for whatever reason: 0.5m/s² normal brake performance and 535 seconds to 360km/h. https://www.hs2.org.uk/about-us/documents/hs2-rolling-stock-train-technical-specification/

 

[Bletchleyite]

The existing specification calls for much lower acceleration for whatever reason: 0.5m/s² normal brake performance and 535 seconds to 360km/h. https://www.hs2.org.uk/about-us/documents/hs2-rolling-stock-train-technical-specification/

Nearly ten minutes to full speed sounds really quite slow!

 

[The Planner]

I expect the acceleration aspects are causing some headaches for people dealing with the power issues on the classic network. I can imagine significant acceleration rates will cause real spikes in power draw.

 

[SynthD]

If I understand the spreadsheet correctly, there is a minute loss in journey time because the acceleration rate is halved from 1. The braking rate can remain high and have less impact, assuming the power supply is set up to take the load back from the train.

Is there a customer experience issue in the same service having different acceleration rates in its journey? On a HS2 train to Scotland it could be 200mi/h and 1m/s/s south of Handsacre, 110-125 and 0.5 south of Lancaster and adjust accordingly further north as the power supply is limited. Classic trains may be retimetabled/regulated to not leave classic stations at the same time as a HS train.

 

[NCT]

I suspect the acceleration rates would have been determined based on what the likes of Velaro and ETR1000 were offering or were likely to offer, so to not trigger any requirements that couldn't be met by off-the-shelf kit.

 

[JamesT]

I note the OP is talking about maximum rates, whereas the HS2 spec is for minimum rates. How does the performance of the platform the 895 is based on compare to those?

 

[NCT]

If Wikipedia is accurate, the acceleration rate of the ETR 1000 is 0.7m/s/s. Can't quickly find anything on Velaro.

The specification of 0.5 does feel conservative, and I wonder if this was due to not wanting to rule out the TGV platform.