If a small platform is to be added, I reckon it should be by Treloggan crossing between Quintrell Downs and Newquay. Newquay is hilly, sprawling and growing very fast (a bit like Falmouth) and a halt inland enabling travel into the town centre/beaches from the outskirts, and towards St Austell without having to get into the town centre first would fit in with the metro concept.
I think a trick was missed in putting a loop on Goss Moor instead of relaying the 2m of track from St Dennis Junction to Parkandillack. That would have effectively created a huge loop between Par & St Dennis junction. That said, it's great to see the "poor relation" of Cornish branches finally being invested in.
Although the missing section is only 2 miles long would the existing track from Parkandillack to Burngullow then need to be altered/upgraded to be suitable for passenger traffic? That would inevitably add significant extra costs, plus there would be need for at least one level crossing on the missing section, all of which would probably tip the cost to benefit ratio too far the wrong way
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You're right. I know the County Council and then Cornwall Council looked long and hard at the Parkandillack line more than once and it was just too expensive to convert to a passenger line, on top of the extra cost of the connection to the existing line. I don't know the detail.