Thread by @GarethDennis

High Speed 2 won't actually be the UK's second modern high speed railway, just as HS1 wasn't its first... This title should go to another line which opened in 1983 (only two years after France's LGV Sud-Est).

Time for a #RailwaysExplained thread on the SELBY DIVERSION 🚆

Back in the mid-1970s, British Rail was making journeys faster with the introduction of its "Inter-City 125" high speed train, and was busy upgrading and realigning the ECML for 200km/h.

They were already running the 2nd fastest timetable in the world with '125s on the GWML.

The only high speed line in the world was Japan's Tōkaidō Shinkansen which had opened in 1964... This railway was designed for 250km/h and didn't get above 210km/h in normal operation.

France were the next furthest forwards, with contracts being let for the 300km/h LGV Sud-Est.

Meanwhile, the 1973 oil crisis had bumped the price of coal which - alongside some domestic politics - had resulted in a desire to expand coal production across the UK.

In 1974, the National Coal Board placed an application to exploit the Barnsley coal seam around Selby.

The subsequent planning enquiry established that the extraction of coal underneath the ECML would result in the need for repeated speed restrictions due to subsidence, completely undoing all of the time benefits gained by the new 125s and associated infrastructure upgrades.

The alternative was to avoid extricating the coal underneath the railway - called "reserving support".

It was determined that this would reduce mine output from 10m to 7m tonnes per year, which the NCB deemed as unacceptable (it would have cost them £500m/year+ in 1975 prices).

At the time, both the NCB and BR were nationalised... The resulting joint approach between departments resulted in a proposal that benefited both parties:

The ECML would be diverted around the Selby coalfield.
#RailwaysExplained

In total, six route options were developed to meet four key objectives:

⏰ express journey times must not increase
⛏️ mineral workings were to be avoided
🌳 to minimise impacts on environment/property/people
🛫 no impact on RAF Church Fenton airfield

Following agreement to build the new line in 1975, things moved extraordinarily quickly...

The final option - connecting new junctions at Temple Hirst and Colton - was selected and design progressed in-house at BR over the next 18 months.

The new Selby Diversion railway marked a number of UK railway firsts:

It was the first UK railway project to use total station theodolites, automatic data collection and computerised survey plotting - there was no commercial GPS in the 1970s!

The Selby Diversion was the first UK railway project to use computer-aided design for the alignment and earthworks design (using MOSS, the first iteration of the design tools still used today).

Read more about MOSS here: communities.bentley.com/products/road_…

At its northern end, the Selby Diversion also included the UK's first 200km/h junction at Colton...

https://twitter.com/GarethDennis/status/977085015036190720

Crucially, it was built for 200km/h and - much like HS2 - had an alignment with passive provision for higher speeds (270km/h in this case).

The modern definition of a high speed railway is that is designed for 250km/h+ thus the Selby Diversion was the UK's first high speed line.

🚨 MANDATORY PERSONAL NEEDS BREAK 🚨

The British Railways (Selby) Bill passed through parliament between 1977 and 1979.

Reading through Hansard, it is clear that this was felt to be unduly rapid by Conservative MPs of the time: api.parliament.uk/historic-hansa…

In any case, contracts were let in August 1979 and preliminary construction works (gas main diversions, power line lifts, creating the rail head and site compound) started a month later...

That's only four years from inception to construction - a remarkable feat by any measure!

The contractor for the main works was A. Monk & Co. (long absorbed by what is now @SkanskaGroup) and they certainly got to it...

They were in a race against time to complete the haul road before the end of 1980 when winter frost would make the ground unworkable.

The geology of the site was tricky - much of the line was sat on the soil equivalent of custard.

Particular care had to be taken during the construction of cuttings, and a geosynthetic sheet was laid underneath the new formation - in some cases straight onto crops!

The biggest challenge was at Temple Hirst Junction...

📏 the highest embankment of the job at 5.5m
⚖️ settlement of 1.4m was expected
📈 the existing earthworks basically had zero factor of safety against failure
🚫 no speed restrictions were allowed on existing ECML

Next up were the bridges - there were 35 major structures on the new line, of which 15 were overbridges (where a thing goes over the railway)…

These were founded on piles that went down to the sandstone underneath the "custard" soil layers.

For a while, two alignments of the Leeds to Selby line crossed the diversion - one using a temporary level crossing and the other on the new intersection bridge.

The new alignment entered service on 22nd November 1981.

One of the main structures on the route was the 26-span River Wharfe viaduct…

Again, the piers were founded on long piles that went through the gravel and clay layers and onto solid sandstone.

The River Aire bridge required extensive piling works around each abutment to account for the soft ground, and the BR diving team put some serious work in checking the condition of the cofferdam, excavations and new concrete poured below water.

Having created a long and elaborate aggregate road, it was time to turn it into a railway… Ballast, sleepers and rails all needed to be transported to site and stored pending track laying.
#RailwaysExplained

First, the bottom ballast was laid to a tolerance of +0/-15mm, matching the crosslevel (i.e. cant alignment) specified in the design perfectly…

…then, rails were pulled off the back of the long-welded rail train and laid along rollers at a spacing of ten feet apart…

..finally, sleepers were laid between the laid rails at the required spacing, and rails were then pulled into place and fastened down.

In order to connect the railway to the rest of the network at high speeds, several junctions with substantial switch and crossing (S&C) layouts were required…

The largest of these was at Colton, which can be seen here during trial assembly at Sandiacre (and then for real).

Running from Colton towards Doncaster, the next connection was at Hambleton North Junction - in fact it was this section that would open to traffic first, when local trains started using the line from the 2nd January 1983 onwards…

Following testing and commissioning of the whole route, the railway began full operation on Monday the 3rd October 1983, a mere eight years after it was first proposed.

Europe's second high speed line had opened, being pipped to the post by France's LGV Sud-Est, which opened just two years earlier on 27th September 1981.

Sadly, Britain had to wait another 24 years before its next high speed line would open, linking the Channel Tunnel to London.

Unlike the mines of the Selby coalfield (which I am happy to say have been consigned to history), the diversion of the East Coast Main Line they necessitated has endured, carrying more than 160 trains a day to destinations across Britain at speeds of up to 125mph.

I hope that was an interesting #RailwaysExplained (with plenty of juicy railway construction photos)...!

Many thanks to Hugh Fenwick who worked on the original project (spot him in a photo above) for sharing this incredible collection via @PWI_York.

As ever, feel free to show your appreciation in the usual way... Also, please do keep asking questions for new #RailwaysExplained threads! ko-fi.com/garethdennis