I think you speak great wisdom. Following the longest ever closure of the route through Dawlish it seemed for a brief moment that anything and everything was on the table, regardless of cost, and it's not surprising that aspirations have been stretched to breaking point. Personally I remain fully committed to a high speed cutoff in stages to Newton Abbot and then further to Plymouth, but I recognise the time is not right now and, if in the meantime, we can get a second route to Plymouth through Okehampton quickly and relatively cheaply that is a very good result both for the areas it passes through, and for the general resilience of the network and the region. Whilst rail freight plays a very small part in the traffic mix today, the security of a second route could help greatly in it's future prospects, and although passengers can be much more easily transshipped to buses past such a rare extended emergency closure with surprising little impact on overall journey times, the inconvenience could be avoided for a large proportion with such an alternative route available.
I think outline planning and safeguarding for future cut-off routes should commence soon however even if construction may not occur for another 20 years. Much expenditure and political strife could be avoided if new housing in particular is not built over or too close to potential routes.
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Not really. The Okehampton route would stand on its own as a new transport artery during normal operations, serving settlements en route. Assuming, as seems reasonable, services were linked through Exeter Central to destinations on the LSWR line perhaps as far as Waterloo, that could also provide new direct links from Plymouth that could be attractive, including to Exeter's growing airport via the new Cranbrook station, especially important since Plymouth lost it's own airport.
Further improvements to the GWR route would not be jeopardised in the longer term by the existence of the Okehampton line if those changes were justified for longer distance growth or to accomodate the traffic mix constraints of the the existing double track route (stopping /non-stopping service mix see previous posts ad infinitum).
I would also like to think that the two routes could remain in the hands of different operators so that a degree of price competition can exist to help incentivise use of the slightly slower route via Okehampton (with the likely stopping pattern), keep the GW operator honest and help to grow the overall market.