High-speed con­nec­tions.

In the first of a two-part look at HS2, GARETH DEN­NIS ex­am­ines why any re­duc­tion in fares or im­prove­ment in ur­ban con­nec­tiv­ity is im­pos­si­ble with­out a step-change in net­work ca­pac­ity

Rail (UK) - - Contents - Gareth Den­nis Con­tribut­ing Writer rail@bauer­me­dia.co.uk

DE­SPITE hav­ing largely com­pleted its jour­ney through Par­lia­ment, and with con­struc­tion hav­ing started in earnest at Eus­ton sta­tion, the UK’s new high-speed rail line con­tin­ues to stir up de­bate.

Why is HS2 be­ing pri­ori­tised over other cor­ri­dors, such as those in the North or South West? Does it fol­low the best route? Is it even nec­es­sary?

The UK rail net­work is one of the most densely traf­ficked in Europe, even be­fore freight is con­sid­ered. On key routes, ex­ist­ing lines are al­ready reach­ing ca­pac­ity - the re­cent timetable om­nisham­bles is proof of how in­ter­con­nected the en­tire sys­tem is. And with rail’s modal share hav­ing dou­bled since the 1990s, it is lit­tle won­der that it is now creak­ing un­der the strain.

Sig­nif­i­cant jumps in pas­sen­ger num­bers would re­sult in a dra­matic drop in re­li­a­bil­ity and a dis­pro­por­tion­ate hike in oper­at­ing costs. To fa­cil­i­tate even a mod­est modal shift in favour of the train, we need a step-change in the rail­way’s ca­pac­ity to move peo­ple and things around na­tion­ally.

In terms of the ca­pac­ity co­nun­drum, there is of­ten talk about the pos­si­bil­ity of up­grad­ing ex­ist­ing lines with new sig­nalling, im­proved line­speeds or even ex­tra tracks.

While these may be use­ful in­ter­ven­tions in iso­la­tion, none can pro­vide a sig­nif­i­cant re­gional or na­tional im­prove­ment in ca­pac­ity. Ma­jor up­grades to the ex­ist­ing in­fra­struc­ture are ex­cru­ci­at­ingly com­plex. To say that it is dif­fi­cult to ac­cu­rately es­ti­mate costs and timescales would be an un­der­state­ment.

The high­est-ca­pac­ity lines are the ones that op­er­ate the rolling stock with the clos­est per­for­mance pa­ram­e­ters (ac­cel­er­a­tion, de­cel­er­a­tion and top speed). If the dif­fer­ence be­tween top speeds is min­imised, then the trains can get nice and close to one another and you can run more of them per hour. The prob­lem is… the Bri­tish rail net­work rep­re­sents the op­po­site of this sce­nario.

Slow freight and stop­ping trains in­ter­min­gle with re­gional medium-speed ser­vices. And try­ing to ne­go­ti­ate its way through all of this traf­fic is the most ef­fec­tive ca­pac­ity-killer of all - the longdis­tance, high-speed ser­vice (LDHSS).

High speeds and lim­ited stops mean these trains re­quire a large in­ter­val or ‘head­way’ (the dis­tance be­tween trains), with other ser­vices be­ing pushed out of the way. Route ca­pac­ity suf­fers.

The so­lu­tion is to ex­tri­cate these fast trains from the rest of the rail­way - in other words, the seg­re­ga­tion of LDHSS. Which brings us to the hub/rich club model.

Con­sider the ma­jor ar­eas of pop­u­la­tion and eco­nomic out­put as a se­ries of ur­ban ‘hubs’. These are the clus­ters of cities that are con­nected by less than an hour’s travel and which have a pop­u­la­tion greater than one mil­lion peo­ple.

When think­ing of a rail net­work, we can con­sider con­nec­tiv­ity on two lev­els: in­tra-hub (travel within hubs) and in­ter-hub (travel be­tween hubs). Com­bin­ing these two lev­els of con­nec­tiv­ity gives us a map that starts look­ing like the cur­rent GB rail­way net­work...

It’s easy to see that there is a con­flict be­tween the in­tra-hub and in­ter-hub ser­vices through the Mid­lands and the North. At the same time, the north-south cor­ri­dor

gets busier as you get closer to Lon­don, with the south­ern-most sec­tion car­ry­ing all north-south in­ter-hub traf­fic from the Mid­lands, the North and Scot­land.

In con­trast, the in­ter-hub routes from Lon­don to the South Coast and from Lon­don to Bris­tol and South Wales don’t carry traf­fic from other hubs. They also don’t have to carry in­tra-hub and in­ter­hub traf­fic at the same time. These cor­ri­dors are there­fore less crit­i­cal to over­all ca­pac­ity.

HS2’s route aims to solve both the in­tra-hub and in­ter-hub ca­pac­ity con­straints be­tween the North, the Mid­lands and Lon­don, by pro­vid­ing a new line car­ry­ing high-speed pas­sen­ger trains on the north-south rail cor­ri­dor.

By segregating LDHSS onto their own lines, ca­pac­ity is cre­ated for more in­tra-hub ser­vices (as well as freight and lo­cal trains). Ex­ist­ing ur­ban and re­gional net­works then feed pas­sen­gers onto HS2.

In net­work sci­ence this rep­re­sents a ‘hub/rich club’ model, where high flow rates ex­ist be­tween hubs that are them­selves fed by lots of in­ter-con­nect­ing path­ways.

HS2 Phase 1 cov­ers the south­ern­most cor­ri­dor that car­ries all in­ter-hub traf­fic from north of Lon­don. This sec­tion will have the great­est ca­pac­ity, com­pris­ing what is ef­fec­tively a straight line from Lon­don to Birmingham. HS2 Phase 2 pro­vides two ‘legs’ to sep­a­rate in­tra-hub/in­ter-hub ser­vices across the North and in­ter-hub traf­fic from Scot­land. But why must it be high speed? The rea­son for con­struct­ing this new line to high-speed spec­i­fi­ca­tions is sim­ple: to in­cen­tivise the di­ver­sion of longdis­tance, high-speed ser­vices from the three ma­jor north-south main lines (the West Coast Main Line, the Mid­land Main Line and the East Coast Main Line) onto the new seg­re­gated line, jour­ney times from the north­ern­most des­ti­na­tions must be at least as good as the cur­rent ser­vice. Es­sen­tially, HS2 there­fore gives us six lines for the price of two.

High speed rail isn’t re­ally about high speed at all

Oddly enough, high-speed pas­sen­ger ser­vices only form a small part of what the UK’s new high-speed rail line will de­liver - in com­bi­na­tion with up­grades to in­tra-hub con­nec­tiv­ity, it is the freed ca­pac­ity on the rest of the net­work that will have the great­est ben­e­fit for pas­sen­ger and freight trans­port.

Yet the story doesn’t seem to be get­ting through. As en­gi­neers, it is not just our duty to cre­ate new in­fra­struc­ture, it is also our duty to com­mu­ni­cate its pur­pose. Help­ing the Bri­tish pub­lic to get be­hind HS2 must be a pri­or­ity for our in­dus­try if we are to truly make this mega-project a suc­cess. ■ Gareth Den­nis is an en­gi­neer and writer, spe­cial­is­ing in rail­way sys­tems. As well as roles in engi­neer­ing con­sul­tancy, he leads the lo­cal sec­tion of his pro­fes­sional in­sti­tu­tion and is a lec­turer in track sys­tems at the Na­tional Col­lege for High Speed Rail. Fol­low him on Twit­ter: @gareth­den­nis

“High-speed pas­sen­ger ser­vices only form a small part of what the UK’s new high-speed rail line will de­liver - in com­bi­na­tion with up­grades to in­tra-hub con­nec­tiv­ity, it is the freed ca­pac­ity on the rest of the net­work that will have the great­est ben­e­fit for pas­sen­ger and freight trans­port.”


Freight­liner 66605 passes a Vir­gin West Coast Class 390 Pen­dolino bound for Eus­ton on Fe­bru­ary 24. The West Coast Main Line is the busiest mixed-use rail­way in Europe, with lit­tle scope to in­crease cur­rent ca­pac­ity.

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