How much traffic through Stratford on such a through service are we expecting? Passengers from Thames Valley to Birmingham already have other options.
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The orange alternative. A disadvantage with this for any through service is the 2 miles in, reverse and out of the town station from Parkway. If trains didn't go through to Birmingham at least interchange could be made available at Parkway.
It's a long section with no surviving stations, and around there looks like the best place for one. However one station alone on a short loop usually means a long dwell time if a timetabled passing manouevre is to take place. A stopping service might work anyway with platforms on the mainline, perhaps closely following or preceeding a freight with similar average speed.