I have serious doubts that Portway Parkway in Bristol will actually be built.
So here goes:
Does the existing infrastructure cater for current demand? From my limited experience of the beach line in the last few years I think the answer has to be only just.
Could the existing infrastructure cope with a substantial increase in traffic to and from an Avonmouth Parkway station? I would suggest that the answer to that is a thumping great big no.
Will the additional traffic generated by an Avonmouth Parkway station increase traffic receipts sufficiently to warrant an improvement to the infrastructure and, if not, where is the money coming from to provide it? This is a question for the bean counters involved in these things and it is also potentially a political issue. Whilst the government is pretty good at making policy announcements, it often aint so good at the detail, and thats why so many government schemes fall flat on their arses (just see whats going to happen with Brexit mark my words
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To play devils advocate for a moment, there is already a park and ride facility from that car park using buses which I have never seen running anywhere near full (but I admit that I have only seen them running in the off peak). Doubling the number of buses would cost a fraction of the cost of improving the rail infrastructure down there, and that could be a far more cost effective option, no matter what the politicians have said about the new station in a policy document/ wish list (see previous paragraph
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However, my view is that if (big IF) the station ever gets built then the rail infrastructure will need to be improved. Whether that is done by a strategic loop of a reasonable length (say Montpelier to Clifton), or redoubling part of the line wholesale, it will have to be done. The scheme will not work without it.
And thats why I suspect that it never will be built or, if it is, it will be part of the larger and currently shelved scheme to reinstate passenger services on the entire Henbury loop.