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North Dartmoor Rail Route
The former LSWR route from Exeter to Plymouth via Okehampton and Tavistock is just under 58 miles, as compared to 52 miles via the Coastal route and current main line.
In the Steam era and also during British Railway up until closure in 1968 speed restrictions were in place at various points on the railway. Fastest journey times of 90 minutes giving an average of 40mph over the entire route. This need not be the case if the line was rebuilt.
The line can broadly be divided into four portions:-
With modern technology speeds can be increased above those of 50 years ago.
Additionally services take around 2 minutes from a standing start to reach Cowley Bridge Junction, and at the other end around 5 minutes to reach St Budeaux Junction from Plymouth. Potential speeds have been calculated on the basis of current curvature. A lower speed than theoretical maximum is suggested to leave a suitable safety margin. The formula at the bottom has been used to calculate maximum speeds. Beneath that is a list of curvature radii, maximum speeds and those suggested.
Section 1 offers the best higher speed improvements though the remainder of the line also gives faster speeds. Even Section 4 which is very curvy.
In section 1 the average speed that could be achieved over the 19 miles is 95-100mph. Speeds of 110mph can be achieved for around 6 miles Through Bow and North Tawton. Speeds lower than 100mph would have to be in place as follows:-
a) Just after Crediton 600 metre radius curve- 60mph
b) Coleford Junction 400 metre radius curve- 55mph. However this speed can be increased if curve eased (400m curve eases to 1200m after less than 200m length). Perhaps even up to speeds of 90mph with minimal additional engineering especially at the junction where pointwork needs to be suitable for line speed.
c) Speed through Sampford Courtenay needs to be 90mph due to curvature through platform.
In Section 2 the average speed over the 5.5 miles could be 65mph. At present there is only a single track tunnel under the A30. This could be widened. However a reasonable alternative strategy could be to leave this portion of line single and continue on over Bridge 613 (Meldon Viaduct). A distance of 1.5miles. This could be beneficial as it would spread weight over both sections of this Viaduct. It was built as 2 single structures intertwined. The load could be spread across the decking section much as is the case with Largin Viaduct on the Cornish main line between Liskeard and Bodmin Parkway. Again speeds would need adjusting in one location:-
d) Speed through Okehampton Station would need to be 55mph to account for curve through platform and also 400m radius curve just after at Milepost 198.
In section 3 the average speed could be 75mph. Again areas where speed would need reduction are given.
e) Just after Milepost 202 there is a short 600m radius curve limiting speed to 70mph. There may be possibilities to re-engineer this short section.
f) A short 400m radius curve on the approach to the former Lydford station would limit speed here to 55mph. This could be relatively easily eased. When open Lydford actually had land enough for sidings and also the former Great Western branch to Launceston. Old railway land could be used to ease this curve raising speed to 70-75mph fairly easily.
g) Bridestowe station 70 mph through station.
Section 4 is more challenging. However in BR days speed was limited to 40mph. This can be much improved with speeds of 55-60mph average. This section has been analysed even more closely as below. Some curves may be able to be re-engineered. Here though there are limiting factors through some of the stations. These are listed below
h) Speeds of 55mph at the following locations due to 400m radius curves. Milepost 209.5, Milepost 210.5Milepost 214.25.
i) Brentor station. 55mph through platforms due to 480m curve.
j) Bere Alston. 50mph due to station on 400m radius curve.
k) Bere Ferrers 55mph due to station on 500m radius curve.
Using the above information (which is conservatively based) and could still be improved on with minor modifications on selected curves. Assumption is made that junctions at Cowley Bridge and St Budeaux Junction are improved to optimise times. The latter Junction is currently 15mph for crossover speed. Potential times for non-stop travel are listed below:-
Exeter St Davids to Cowley Bridge Junction. 2 minutes
Section 1 12 minutes
Section 2 5.5 minutes
Section 3 7.5 minutes
Section 4 21 minutes
St Budeaux Junction to Plymouth 5 minutes
Total 53 minutes
These times could be improved on further. This is NOT the 90 minutes that Network Rail have quoted from the 1965 timetable. Additionally reversal times with all but HST’s can be 5 minutes at each end making total times of 58 and 63 minutes from Plymouth or Penzance respectively. Presently trains take 58 minutes from Plymouth!
HST turn around times need not be the 10-12 minutes quoted. A driver Manager for Crosscountry (Name can be supplied) which also use HST’s has said the time ‘in the book’ for reversal is 7 minutes. If a relieving driver takes over a total of 9 minutes. This would make HST times 60 mins and 67 mins respectively. Still not a bad time for a diversionary route compared to diversion to London via Yeovil adding 60 minutes!
Finally there would be potential for a service from Plymouth to London Waterloo requiring NO reversal and adding competition for fares to Plymouth
Vmax = Maximum speed in km/h
R = Radius of curve in m
E = Cant in mm
D = Cant deficiency in mm
Vmax = Square root of (Radius x (Cant + Deficiency) / 11.82)
There are some rules that have to be adhered to; Max allowable cant in plain line is 150mm (110mm through a platform) and Max allowable deficiency in plain line is 110mm.
Radius (in metres) Max Speed(mph) Suggested Speed(mph)
400 58.6 55
460 62.8 60
480 64.2 60
500 65.5 60
580 70.5 65
600 71.8 65
700 77.5 70
800 82.9 75
1000 92.6 85
1200 101.5 90
1400 109.6 100
1600 117.2 110
1700 120.8 110
1800 124.3 110
2000 131.0 120
All these curves exist on this route. These figures are for curves not through stations. These speeds have been adjusted for stations such as Bere Alston and Bere Ferrers.
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