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Sebastian Anthony - May 9, 2016 12:56 pm UTC

I'll let you in on a secret: I love big things. Big holes, big houses, big bridges, big cars. I suspect it has something to do with being very large myself. After spending most of my formative years living in old, low-ceilinged British houses, and developing a hunchback, I now find expansive spaces rather comforting. Which is why I recently paid a visit to the new Elizabeth line (née Crossrail) tunnels near Bond Street, London.

It's funny. If you've ever been on the London Underground, I doubt you'd ever describe it with words like "spacious" or "airy." More like "claustrophobic" and "ooh, look at that big rat!"

As the elevator juddered its way down the giant access hole at the new Bond Street station on London's Hanover Square, though, the only word that came to mind was "whoa." The Elizabeth line ticket halls, walkways, and train tunnels are really quite big.

Enlarge / A big ol' Crossrail tunnel boring machine (TBM).The London Crossrail project, which will eventually connect Reading and Heathrow in the west to Shenfield and Abbey Wood in the east, is Europe's largest construction project, and one of the largest in the world. The centrepiece of the project is 13 miles of new twin-bore deep-tube tunnels that run through central London, at depths of up to 40 metres, from Royal Oak near Paddington in the west to Victoria Dock near Canary Wharf in the east.

Eight tunnel boring machines (TBMs), each about 100 metres long and weighing roughly 1,000 tonnes, worked around the clock for three years, with excavation completed at the end of 2015. Because the TBMs are so large and unwieldy, two of them—named Phyllis and Ada—were left buried in the ground near the new Farringdon tunnels. (I like to think that they were pointed at the centre of the Earth with a brick on the pedal... and they'll get there eventually.)

As you can see from the photos at the top of the story, the Crossrail train tunnels are a lot larger than those on any of the other Underground lines. The TBMs dug out raw tunnels that were about seven metres in diameter, but after numerous layers of reinforcement, and over-engineering and concrete cladding, the final internal diameter of the tunnels is 6.2m (20ft 4in)—the Victoria line, by comparison, has a diameter of just 3.81m (12ft 6in).

Another thing to note is the length of the platforms. At 250 metres (820ft), the Elizabeth line platforms are more than twice the length of current Underground platforms, which range between 122 metres (400ft) and 107m (350ft). The first trains will be 200 metres (660ft) long, but they can be extended to 240m (790ft) in the future if passenger demand increases. Because the platforms are so long, and the capacity of the trains so great, most Elizabeth line stations will have two large ticket halls that are spaced far apart. The two ticket halls for the Bond Street station, for example, are on Davies Street and Hanover Square—about 500 metres (1,640ft) away from each other.

I didn't learn much about the external construction of the Elizabeth line, but a Crossrail site manager did tell me one interesting anecdote. Slip forming (continuously poured concrete) is being used to build some of the taller ticket hall structures. The process is noisy, though, which means that in residential areas it can only be done during work hours. To speed up the process, Crossrail temporarily relocated some people who live near the ticket hall building sites to hotels, so that construction could be carried out around the clock.

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