One of the lines which has recently been spouted by proponents of HS2 is that the only reason the costs of the project have spiralled, is because of all the tunnels they have generously added to try and shut up us pesky objectors.
We’ve known this not to be the case ever since the 2011 consultation event in Wendover, when engineers admitted that the deep cutting between two tunnels was ‘unsustainable’ and the only real option was to join the tunnels together, and of course everyone who saw the impact of the original surface route for Hangar Lane in Ealing and the Chiltern Line in Ruislip surely knew it would only be a matter of time before HS2 Ltd realised what they were proposing was insane.
But just exactly how much of the new tunneling has been added for reasons of environmental mitigation, and how much has needed to compensate for engineering mistakes in the original designs? John Marriott investigates:
The debate in the House of Lords this week featured several comments arguing that the cost of Phase One was high because of all the extra tunnelling that had been added to try and placate objectors and to reduce the environmental impact. How much extra tunnelling has been added and why?
The initial scheme published in 2010 had just over 20km of tunnels. Just over half of this was in the Chilterns AONB for the main 9.6km Amersham tunnel and a 1km tunnel near Little Missenden. The tunnels connecting Euston to Old Oak Common accounted for 7.4km. There was also a 1.4km tunnel under Long Itchington wood which sits on top of a hill. I think it could be argued that these were absolutely the minimum amounts of tunnelling for the proposed route through the Chilterns.
Before consultation in 2011 some minor changes were made which increased the tunnelling by 2km. This was mainly because short “green tunnels” were added at South Heath and Chipping Warden. In both cases these replaced deep cuttings necessitated by the undulating topography.
In 2012, following Consultation, the length of tunnelling increased by 13km to just over 35km. The largest change was the addition of a 4.4km tunnel near Ruislip as an alternative to trying to accommodate the HS2 tracks alongside the existing Chiltern / Underground tracks. A driver for this change was almost certainly the difficulty and cost of achieving a surface route. The fact that the surface route was limited to 250kph whereas a tunnel offered speeds up to 320kph may also have been influential given HS2’s lust for speed. Significant technical problems in the Chilterns led to the decision to join the Amersham and Little Missenden tunnels into one which increased the length of tunnelling there by 2.5km. The Wendover tunnel was extended by 800m to reduce impact on the town. The green tunnel at Chipping Warden was extended by 1.5km to eliminate some more of the deep cuttings and a new 2.1km green tunnel was added at Greatworth to eliminate deep cuttings and reduce impact on the village. The tunnel at Long Itchington was extended and joined to a new green tunnel, adding 1km.
A further 11km of tunnelling was added in 2013 following a Design Refinement Review. The largest change was the decision to replace the Ruislip tunnel with a 13.5km Northolt tunnel, extending all the way from Ruislip to Old Oak Common. This change was said to cost no more than the very problematic surface option. The other change was the addition of a new 2.9km tunnel at Bromford on the Birmingham spur. This was to avoid many problems that had become apparent with the original proposal to follow an existing railway and canal which run alongside and under the M6.
During the Hybrid Bill’s examination in the House of Commons the promoter agreed to extend the Chiltern tunnel by 2.4km, on a very steep gradient, as an alternative to longer options. Part of this replaced the green tunnel at South Heath. The total length of tunnels currently stands at around 49km. (28% of the total route to Birmingham).
The total length of tunnels has increased from 20km to nearly 49km. Only around 3.3km of the 29km increase may have environmental reasons as the main reason for the change. Many of the major changes have occurred in response to technical or cost problems that have been identified since the scheme was proposed and several are described as cost neutral. More diligence during the design process would have identified far better and much cheaper options.
Changes to tunnels since HS2 was published in 2010 and reason for change (3.3km added mainly for environmental reasons)
BT = Bored Tunnel GT = Green Tunnel
Some tunnels require porous portal structures which may not have been allowed for in lengths shown
|Year||Tunnel description / changes||Tunnel Length km||Reason.|
(The reason is taken from statements in HS2 documents where available. Costs are rarely provided.)
|2010||Euston BT||7.4||7.4||7.4||Original scheme in dense urban area||Tech|
|2010||West of Old Oak Common BT||0.3||0.3||7.7||Original scheme in dense urban area||Tech|
|2010||Amersham BT||9.6||9.6||17.3||Original scheme in AONB||Tech|
|2010||Little Missenden BT, single bore||1.1||1.1||18.4||Original scheme in AONB||Tech|
|2010||Wendover GT||0.3||0.3||18.7||Suggested option for original scheme in AONB||Env|
|2010||Long Itchington BT, single bore 400kph||1.4||1.4||20.1||Original scheme (route goes under hill and wood)||Tech|
|2011||Little Missenden BT extended, single bore||1.1||1.3||0.2||20.3||Extended to go under existing railway||Tech|
|2011||South Heath GT added||0.9||0.9||21.2||Minimise deep cutting||Tech|
|2011||Chipping Warden GT added||1.0||1.0||22.2||Minimise deep cuttings in hilly region||Tech|
|2011||Long Itchington BT shortened, twin bore||1.4||1.0||-0.4||21.8||Unknown, may be error|
|2011||Burton Green GT added||0.3||0.3||22.1||Reduce cutting depth and minimise impact on village||Both|
|2012||West of Old Oak Common BT extended||0.3||0.8||0.5||22.6||Unknown||Tech|
|2012||Ruislip BT added||4.4||4.4||27.0||Avoid problems with surface route||Tech|
|2012||Little Missenden BT joined to Amersham BT||10.7||13.1||2.4||29.4||Avoid problems with deep cutting and aquifer||Tech|
|2012||South Heath GT extended||0.9||1.1||0.2||29.6||Needed to mitigate change to alignment||Tech|
|2012||Wendover GT extended||0.3||1.3||1.0||30.6||Minimise impact on town in AONB||Env|
|2012||Greatworth GT added||2.1||2.1||32.7||Minimise deep cuttings, reduce impact||Tech|
|2012||Chipping Warden GT extended||1.0||2.5||1.5||34.2||Further reduce deep cuttings||Tech|
|2012||Long Itchington extended and GT added||1.0||1.9||0.9||35.1||Minimise various impacts, cost neutral||Both|
|2012||Burton Green BT extended||0.3||0.5||0.2||35.3||Further minimise impact on houses & village||Env|
|2013||Northolt BT replaces Ruislip BT (to OOC)||4.9||13.2||8.3||43.6||Severe problems with surface route, cost neutral||Tech|
|2013||Bromford BT||2.9||2.9||46.5||Severe problems with surface route||Tech|
|2016||Chiltern BT extended, replaces Sth Heath GT||14.2||16.0||1.8||48.3||Avoid Mantles wood and minimise impact in AONB||Env|
|2016||Lichfield, Underpass under A38 and canal||0.4||0.4||48.7||Avoid large impact of going over A38||Both|
Note. Statements and figures in HS2 documents are often misleading, inconsistent or wrong.
Feb 2010 Initial scheme, Arup Route Engineering Study
Feb 2011 Prior to Consultation, Arup Route Engineering Report and contemporary plans
Jan 2012 Post consultation, Decisions and Next Steps and contemporary plans
Nov 2013 Prior to Hybrid Bill, Design Refinement and contemporary plans
Jan 2016 Following House of Commons Hybrid Bill Committee changes and contemporary plans