Well on another forum, some are saying that the older VT's are experiencing reliability issues. Which being 14 years old now wouldn't be surprising, despite less miles on the clock.
But I was thinking about why it might actually be logical why operators don't want them and why even London Bus don't use tri-axles (beyond the above mentioned trial).
Someone above mentioned you would need 3 regular double deckers to replace 2 tri-axles, which is true. But I've been thinking that might actually be preferable to operators!
Think about it, the tri-axles are much more expensive to buy then regular double deckers, they would be the most expensive bus in your fleet, yet they are also your least used bus, you only use them on-peak, because off-peak their capacity isn't needed and they guzzle fuel.
So from an operators perspective, they are a bit of a waste, expensive to buy, expensive to maintain, expensive to fuel, but not used much!
I haven't seen prices on new tri-axles (there are very few, which is telling), but I suspect you could actually buy 3 SG buses for the price of 2 modern tri-axles. So there is no real money saving there, and 3 SG's would offer greater flexibility.
Yes, you would have the cost of an extra driver, but that would be offset by lower fuel and maintenance costs of a SG or similar.
But also 3 SG's would also have more capacity then 2 VT's (255 people for 3 SG's, versus 238 for 2 VT's conservatively speaking) so extra passengers would go towards paying for an extra driver. And you have the advantage of greater frequency on the route.
Of course I get why drivers like the VT's why it seems better that it can take more people. But sometimes if you step back and look at it from an operators perspective, you might see reasons why higher capacity vehicle isn't the better option.
Look at BE and Aircoach, BE use double decker coaches on some routes, then look at Aircoach, all single decker coaches, when they are busy, they just send a second single decker, so obviously it isn't a straight forward decision.