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The South West is in line for a new high-speed rail link to London in a move welcomed with cautious optimism by passenger watchdogs.

Network Rail is considering turning the Penzance to Paddington mainline into a 186mph super route, slashing journey times to the capital.

The line is one of five key rail routes under consideration following a 40 per cent increase in passengers using trains over a decade.

If the proposals go ahead, it is hoped to have new tracks laid by 2025. Most would be similar to those built in France to carry the high-speed TGV network.

Stuart Walker, regional spokesman for transport users group Travelwatch South West, said the scheme could have huge benefits to Devon and Cornwall ^ if it comes off.

At the moment, the main rail route through Devon and Cornwall is restricted to a speed of around 60mph, with a 110mph section between Reading and Paddington. More than an hour could be shaved off the five-and-a-half- hour journey time to London if the route is chosen for expansion.

See http://www.thisisplymouth.co.uk/news/TGV-style-train-link-transform-West/article-195365-detail/article.html

Have they put some speed restrictions in place and not told us? 

Indeed, Padd-Reading reaches 125mph, Reading-Taunton is between 90 and 110 most of the way, Taunton - Exeter is 100mph, Exeter - Powderham is 100mph, Powederham - Dawlish Warren is 80mph, Dawlish Warren- Teignmouth is between 60 and 75mph, Teignmouth - Hackney is between 80 and 90mph, Hackney - Newton Abbot is 60mph:
Torbay Branch: Newton Abbot - Aller is 45mph, Aller - The Willows is 60mph, The Willows to Torre is 40mph, Torre to Paignton is 30mph.
Plymouth: Newton Abbot - Totnes is between 50 and 60mph - not sure about further west.

But do HSTs actually manage to reach this speed?

Cotswold trains must be time-tabled for 90 mph running max as far as Oxford, as when the service is subbed to a Thames Turbo it can manage to run on time!

I suppose this is less of a problem after Reading.

Why is the speed so long after Newton Abbot, on both branches? Only 30 mph in Torbay... it's not that bendy is it?

Torre station is. It might be slightly faster after TQY, can't say ive ever bothered to check though. Lots of the track is 40years old or something.

West of Newton Abbot to Plymouth/Cornwall track curvature and gradients severely limit line speeds.Newton Abbot to Aller junction is 60mph,Aller to Totnes is 55mph,Totnes to Hemerdon is 60mph,Hemerdon Bank is 80mph falling to 60/70mph to Plymouth.Plymouth to Penzance is generally 60/65 apart from the odd 70mph,which explains why Exeter to Paddington(172 miles)can be done in as little as 2 hours while Exeter to Penzance(134 miles) takes 3 hours.
  As you say little more than a branch line.Lets hope the government is seriously looking to speeding up journey times to the far west as they will look pretty feeble as the 21st century unwinds.