HS2’s Transformation: Building more than just a High-Speed railway …

Just outside Aylesbury in Buckinghamshire, one of HS2’s large construction sites is almost as busy building roads as it is building a railway.

Even though the High-Speed railway passes through the countryside, there’s still a lot of existing infrastructure in the way to be moved, and as part of the agreement to build HS2, it was decided that simply moving things wasn’t enough. A major upgrade is being delivered at the same time.

When the HS2 builders have moved on to their next project, they won’t just leave behind a high-speed railway, there will also be an upgraded rail line linking Aylesbury with Princes Risborough, an improved A418 road, and a bridge to nowhere, which one day will be part of the planned Aylesbury Ring Road (SEALR ^[1]).

Area overlay on Google maps

That doesn’t come without pain though, and at the moment, the railway ^[2] between Aylesbury and Princes Risborough is closed for 10 weeks ^[3] to allow the upgrade to be delivered.

The Aylesbury–Princes Risborough line is a 160 year old single track railway that is today shared between an hourly passenger service, calling at two intermediate villages, and freight services carrying London’s waste to a landfill site near Calvert.

It also happens to be right in the way of the HS2 railway ^[4], so a nearly 2km length of the older line has been rebuilt to allow for a large railway bridge to be installed that’ll sit over the HS2 line. In order to build that called for some of the largest concrete piles used in HS2’s phase 1 to support a bridge in an area of poor soil quality, even as they built a brand new railway right next to the older line, which was still in use while people worked close to it.

Although the new bridge is in the countryside, the realignment starts close to the edge of Aylesbury town, and that added some unexpected challenges, with a local school that couldn’t have construction carried out when the pupils were in school, and noise restrictions on the work that could be carried out in the evenings and weekends.

Major electric mains also needed diverting, and several sewers that crossed the line needed work. Oh, and Bucks Council wanted a new road bridge for a road that doesn’t exist yet.

So what would otherwise likely be a modest job to slice a new bridge into a railway line has turned into a year of preparatory work and a 10-week closure of the railway.

Over the past six months or so, the contractors, EKFB and CRSA have been building a new embankment to the west of the old railway, and then, where the new bridge is sitting, several huge concrete piles were drilled into the ground. At 2.5 metres in diameter and some 58 metres deep, they’re probably the largest on HS2’s main railway line. They have to be that deep because of a combination of local ground conditions, but also because they straddle either side of the high-speed railway and need to buttress that as well as the normal railway bridge they will be supporting.

A single-span corten steel bridge was delivered to sit on top of the embankment, but there’s no space for the HS2 trains to pass underneath it! That’s because it’s much easier to position a large span railway onto solid ground, then dig the hole out underneath than it is to slide a bridge over a large gap in the embankment.

Now that the existing railway is closed, they’ve been digging out the soil underneath the bridge to create the 8-metre deep space that will eventually allow HS2 trains to race through. The underdigging started just under two weeks ago and should be completed in just over a week’s time, exposing the tops of the four huge piles in the process.

One of the issues adding a bit of complexity is a long white conduit on the far side of the new railway alignment carrying Network Rail communications cables, so they have to be very careful not to damage that when swinging their diggers around.

Elsewhere along the 2km length of the new railway, they’re laying new tracks, a tamping machine was on site to pack the ballast, and they’re connecting the new to the old railway at either end.

Once they’ve finished, the old railway tracks will be removed, and some of the tracks and sleepers will be donated to the nearby heritage railway ^[5].

Some new water culverts that have been dug through the embankment have also been fitted with ledges for amphibians to be able to pass through, and the base of the culverts was given a textured finish to help soil washed through to settle and start to create a plantlife environment.

Future-proofing the Aylesbury to Princes Risborough line has also been thought of. At the moment, the railway is speed restricted to 40mph, but the new alignment has been designed to allow trains to use it up to 90mph, if or when the speed restrictions elsewhere are removed. The new bridge is also double the width it needed to be, to allow for a double track to be added later. The rest of the line is single-track, so the double track here would allow trains to pass each other — potentially doubling the number of trains that can use the line.

People often say they object to HS2 because they won’t use it, but here at least, HS2 is delivering the option to double the service on a small shuttle branch service in the countryside.

But more than that.

They’re also building two new road bridges, which are required as part of the approval to build the HS2 railway.

One sitting right next to the current construction site is future-proofing for a road that doesn’t exist but will eventually. There’s a large ring road project to run around Aylesbury and link up future housing developments over the next few decades, and that ring road will pass over the HS2 railway at this location.

A new road bridge to straddle HS2 railway just past the old railway (to be removed)

It’s therefore sensible to build the road bridge today, even if it’s not needed for many years. There’s also an underpass built into the new railway embankment to allow the ring road to pass underneath it if it’s ever needed.

Building the roads today adds costs to the HS2 railway but saves a huge amount of road building money in the future.

Further north, the A418 also runs across the HS2 route. While they could have closed the road for a few months to slide in a bridge, they’re required to build a new road and bridge next to the old one instead.

What should be a fairly routine railway job has become so much larger to reduce disruption to motorists and provide more roads for motorists in the future.

But the long-term benefits will last for centuries.

When it’s completed, the new railway bridge also opens up a route for HS2, which eventually will be carrying trains, but in the meantime, it enables a north-south route for the construction company so they can move between Great Missenden and west Aylesbury without having to use local roads.

In the meantime, as we headed home, the tamping machine was working its way along the top of the new railway embankment while diggers kept working beneath, and later next month, the new railway would open to passengers.

If you want to try it out, the line is due to open on Monday 30th October 2023.