Fact check: Around a quarter of HS2 will go through tunnels

A widely circulated social media post has claimed that more of the HS2 train line (50%) will be under ground than the Elizabeth line (45%).

Evaluation

Around 23% of HS2 will run through tunnels, compared with 18% of the Elizabeth line. If including cuttings – sections of a route which are sliced into the landscape, so run below the original ground level but are not covered – then 55% of HS2 runs through cuttings or tunnels.

The facts

The first phase of HS2 – which since the cancellation of phase two is the only remaining part of the project – is set to be around 140 miles long (225 km).

This project will have 11 tunnels, of which five are twin-bore – parallel tunnels which allow trains to go in both directions simultaneously – and six will be so-called cut-and-cover tunnels where the tunnel is excavated and then filled over.

The combined length of these tunnels is 32.55 miles (52.4 km). That means that 23.3% of the 140 miles of HS2 goes through tunnels, not the 50% as was claimed.

It is not entirely clear where the 50% claim comes from. One possibility is that the poster was confused by a datapoint on HS2’s website, which states that there are 65 miles (105 km) of tunnels. However, this is counting the total length of the tunnels on both legs of a 280-mile return journey. Sixty five miles of a 140-mile track is indeed close to half (46.4%), however, the more correct way of measuring would be to take 65 miles of the 280-mile track instead (23.2%).

The other possibility is that the poster is counting so-called cuttings as part of the “underground” section of HS2. Cuttings are sections of track which are cut into the landscape. That is to say these parts are excavated to create an artificial valley along the bottom of which the tracks run. This is not under ground, however, is below ground level.

HS2’s first phase will include 44 miles (72 km) of cuttings in total. That means that between cuttings and tunnels there will be 76.55 miles, which is 54.7% of the first phase.

Data for the portion of the Elizabeth line which is under ground is harder to come by. Most sources only talk about the new tunnels which were purpose-built to house the line.

These show that the line is 118 km (73 miles) long and 42 km (26 miles) of new tunnels were built to accommodate the line. However, cross-referencing against a Tube map which shows tunnels the PA news agency concluded that once again the tunnels were being double-counted, while the length of the line was single counted. This means that in fact 17.8% of the Elizabeth line runs through new tunnels.

It is unclear how many miles of old tunnels have been used for the Elizabeth line. The main existing tunnel which was used appears to be the 550-metre (a third of a mile) Connaught tunnel.

It is also difficult to say where the figure of 45% of the Elizabeth line being under ground comes from. The 45% figure matches the proportion of the whole London Underground system which is in tunnels.

Links

Post on X (archived)

HS2 – Project rescoping: Phase Two cancellation (archived)

HS2 – Tunnels (archived)

HS2 – Cuttings and embankments (archived)

London Transport Museum – The Elizabeth line (archived)

The London Society – The Elizabeth line: Europe’s largest construction project (archived)

TfL – Tube map showing tunnels (archived)

Sixense – Crossrail C315 – Connaught Tunnel (archived)

TfL – New map to help people with claustrophobia and anxiety (archived)