From Slaithwaite to the site of the former Diggle station is 8 miles by road.
Slaithwaite is not Marsden however.
From the ODM Slaithwaite's traffic slants far more heavily towards Yorkshire, and is only five/six minutes from Huddersfield, whilst the current service takes 36+ minutes to reach Manchester.
People probably wouldn't cycle that, but then again the double back option will crush today's railway.
It’s still going to be very slow if it has stops at typical Metrolink distances between Piccadilly and Stalybridge, unless you are proposing a new concept of semi-fast Metrolink services.
Well that would be down to the conversion, however previous Metrolink conversions have been relatively light on new stations. They wouldn't really be semi-fast in the railway sense since there would be no stops skipped.
Ofcourse it is entirely possibel that a detailed business case would want to put in additional stops, but I don't think it is reasonable to assume that additional stops are inherent to such a conversion. I don't think the Altrincham line had any at all after all.
And what do you propose for that?
As a starting point, half hourly. If it turns out that the post electrification timings will need two tracks for reliable running using a fast accelerating EMU, whatever higher frequency can easily be obtained on that infrastructure.
Given electrification would already be in place, I think operating as either one or two independent lines is likely to be the cheapest option.
The idea of taking a local service into Huddersfield and then a high speed one back towards Manchester is incapable of being assessed without some idea of the local service provided, the interchange arrangements and the high speed service provided. Happy to comment on it if you can give a realistic scenario of what those would be and how they fit together.
Call it ten trains per hour from Manchester to Leeds on the fast line.
As a rough cut example:
4 trainns per hour Liverpool-North East
2/3 trains per hour Birmingham/XC-North East
3/4 trains per hour London-Manchester-Leeds (will match or beat the ECML example if a fast transpennine line is built)
Maximum wait time of six minutes, average weight time of three.
11 minutes from Marsden to Huddersfield, 5 minutes physical connection time, 3 minutes average wait time, 12 minutes Huddersfield-Manchester.
31 minutes end to end average, 34 minutes worst case, at whatever the tph of the Marsden-Huddersfield segment.
Slaithwaite would be 6 minutes Marsden Huddersfield, so 25 minutes end to end average, 28 minutes worst case.
If you didn’t want me to comment on what a daft idea it was, why suggest it in the first place?
Fair enough.