Wednesday, 19 November 2014

Ride Quality - still very bouncy...

I took a ride out and back to St Ives today - 3 years after it opened in Aug 2011.

It is clear that a greater proportion of beam joints are getting out of alignment, and subsidence (and heave) are becoming more noticeable. Whether upstairs on a full 'B' service, or in the front seat of an 'A' service, the ride is poor - certainly in relation to the 'smooth' service expectations.

The sideways movement was unexpectedly bad on the 'A' service, which was quite empty. But the front seat may experience the worst of sideways jolting, and it may be better in the middle. The bus driver confirmed my suspicion that a fuller bus is more stable. Any experiences you'd like to share?

If this is what it's like after 3 years, it's clear something must be done to make the service in 2021 palatable. Let's just hope the proposed repairs will achieve their desired effect - and do so for at least anther 10 years, if not the 40-year 'design-life' of the system. As I've said before, what happens at 40 years, I just don't know. Presumably another set of rolling repairs to completely replace the track and/or supports?


  1. Up and down movement is clearly caused by track subsidence / heave.

    Side to side movement felt on the buses can be caused by four things:
    - swaying caused by subsidence on just one side.
    - sideways drift of the tracks.
    - wear on the side of the track where the guidewheels run.
    - worn guidewheels, allowing the buses to oscillate from side to side.

    When the track was new, so were the guidewheels. I wonder how often guidewheels are adjusted or renewed?

    I suspect the jostling is caused by worn guidewheels.

  2. The up down bounce on the B buses seemed to affect the new buses. Is this due to stiffer suspensions? I do find it unfortable and prone to motion sickness while reading as a result.

    1. Morse, I too think it's to do with suspension stiffness - and the natural oscillation frequently it produces. If this is near 2Hz (the frequency the beams go past at) the bus starts to bob up and down (it's a rotary motion). This is I believe due to beam sag between supports (measured to be a ubiquitous 7mm) rather than subsidence/misalignment.

  3. Stephen, I think the bounce and sideways jerkiness is worse at the back of the bus. Returning from Cambridge this afternoon on an A, I was reflecting how badly the guided buses compare with the smooth glide of the new Edinburgh trams (and indeed of trams everywhere).

  4. This interesting document compares construction of the Cambridge and Manchester guided busway tracks. They are claiming a tolerance of +/- 1mm at Manchester. They are casting with the track 10mm too narrrow then grinding it to the required width.