Is it a guided bus system, that will use buses with guide-wheels, but where there are just some (a few?) sections of proper guided busway, where the rest of the running is either on segregated normal roads or on mixed use normal roads?
sounds a reasonable summary to me Colly.
But I think there may be an issue underlying your question; as Metrobus has been knocking around so long as a scheme, that its operating identity as an 'enhanced bus' service is pretty blurred.
There is a general agreement that the standard 'stopping bus' model; though it satisfies well a large number of users, is seriously deficient as a potential alternative mode to private car use over peak periods. Some model of 'enhanced bus' would seem to be needed.
So far, in this country, it seems two very different 'enhanced bus' models of service have emerged.
- the first - as per the Cambrigeshire Busway, Luton Busway, Leigh-Salford-Manchester Busway and Gosport-Farnham Busway - is based around higher specification standard buses, mostly seated accommodation, with a peak period speed in service substantially faster than a stopping bus, running at high frequency (4 services per hour or better), with limited stops, over longer distances (normal journeys greater than 5km). These have a lot in common with commercial services such as York-Leeds Cityzap, and Ripon-Harrogate-Leeds route 36; even though these have no access to busway reservation. Riding them is nothing like riding a tram.
- the second - as per the Birmingham Sprint services and the Belfast BRT services - are based on high capacity articulated buses, with a high proportion of accommodation standing, a limited top speed, multiuple access doors and pre-ticketing to encourage high proportion of short distance journeys (2km-5km). They are often marketed as 'the bus that thinks its a tram'; with the subliminal message that, if you eat your crusts and finish your greens, they might turn into trams some day,
My impression is that the Metrobus routes conform better to the first model, but that the specification of the kit has more in common with the second. The first model does, it seems, often incorporate sections of guided buswheel running; but need not do so. None of the current proposals in the second model seem to use guide-wheel track. Maybe that aspect is a red herring?