My Idea for Great Northern post 2021

[Bald Rick]

King's Lynn doesn't need 8xxs. Don't forget that Hitchin flyover is 50mph (or is it 80 - I think 50), so there would be no point in doing so, without potentially using the non-grade separated junction which causes more problems than it solves.

The flyover is indeed 50.

In the early days IETs (as they then were) were intended to be used on King’s Lynn services, indeed gauge clearance was planned up to Lynn. However when it was realised what a pain they’d be for power, and dwell time at Cambridge, for essentially no benefit (and lots of cost), the plan was changed before they were ordered.

 

[D365]

In the early days IETs (as they then were) were intended to be used on King’s Lynn services, indeed gauge clearance was planned up to Lynn. However when it was realised what a pain they’d be for power, and dwell time at Cambridge, for essentially no benefit (and lots of cost), the plan was changed before they were ordered.

I remember that very well, I believe the five car IETs (now Class 801/1) were involved. Thanks for the details, I had always wondered why that plan had been dropped so quietly.

 

[4-SUB 4732]

The flyover is indeed 50.

In the early days IETs (as they then were) were intended to be used on King’s Lynn services, indeed gauge clearance was planned up to Lynn. However when it was realised what a pain they’d be for power, and dwell time at Cambridge, for essentially no benefit (and lots of cost), the plan was changed before they were ordered.

And, of course, the door layout is not conducive to peak calls at Letchworth and Royston either; nor for places like Waterbeach and the masses of cycles we used to get on Cambridge stuff.

To use a 377/379 (insert other 100mph commuter-based unit) over an 80x, the effective loss of speed is as follows:
Northbound - Oakleigh Park to Woolmer Green, 15mph loss, 15 miles, one minute. Woolmer Green to Hitchin, 25mph loss, 8 or so miles (braking neglected for the junctions), about 1 minute. Hardly a major gain when you have loads of other 100mph units running about too.

Southbound - Hitchin to Welwyn North Tunnel, 25mph loss, 8 miles, one minute. Welwyn North Tunnel to Welwyn North station, 5mph loss, 1 mile, no loss (realistically). Welwyn North station to Potters Bar, 15mph loss, 10 miles. Less than one minute loss.

It's better to just operate a timetable planned for 100mph between Wood Green and Hitchin, with Intercity units having a small engineering allowance plugged in.

 

[MarkyT]

At Hitchin, if a DF turns right at Cambridge Jn is has to slow to 40mph for the flat junction turnouts. If it switches left to DS for the DRF it initially has to slow to 70mph before the 50mph is encountered on the flyover itself. I'd say overall the timing to pass Letchworth would be about the same either way. Checking a couple of examples on RTT the difference in working times between a non-stop LNER express and a Cambridge fast from dep. at Kings Cross to pass Hitchin is 1.5 minutes, much of that no doubt due to the slow down for the junction at Hitchin.

 

[thealm]

I see that it would not make much time but if there was investment in that area allowing for 125 running from KGX to Hitchin then that would be reasonable. Don't forget from 2021 services will be sped up out of King's Cross and having 100mph stock on a line with now 8tph 125 paths will mean that Kings Lynn services will have to have special arrangements out of Kings Cross.

 

[4-SUB 4732]

I see that it would not make much time but if there was investment in that area allowing for 125 running from KGX to Hitchin then that would be reasonable. Don't forget from 2021 services will be sped up out of King's Cross and having 100mph stock on a line with now 8tph 125 paths will mean that Kings Lynn services will have to have special arrangements out of Kings Cross.

It won't mean special arrangements at all.

It will just be a case of instead of a working timetable running time from Kings Cross to Woolmer Green (Knebworth) of, say, 17 minutes it will extend to 18 minutes and everything will be treated as a 100mph unit until Woolmer Green. You therefore can get more capacity if you assume you create just a bit of extra space for something over the Flyover.

 

[Ianno87]

At Hitchin, if a DF turns right at Cambridge Jn is has to slow to 40mph for the flat junction turnouts. If it switches left to DS for the DRF it initially has to slow to 70mph before the 50mph is encountered on the flyover itself. I'd say overall the timing to pass Letchworth would be about the same either way. Checking a couple of examples on RTT the difference in working times between a non-stop LNER express and a Cambridge fast from dep. at Kings Cross to pass Hitchin is 1.5 minutes, much of that no doubt due to the slow down for the junction at Hitchin.
View attachment 79207

I think the flat route is fractionally quicker. Signallers still use it when there's a decent Up gap to get across.

Some drivers really know how to get the most out of the 70 turnout, braking through the platforms at Hitchin. Can make as much as 30 seconds difference compared to a driver who coasts on approach.

 

[Ianno87]

I see that it would not make much time but if there was investment in that area allowing for 125 running from KGX to Hitchin then that would be reasonable. Don't forget from 2021 services will be sped up out of King's Cross and having 100mph stock on a line with now 8tph 125 paths will mean that Kings Lynn services will have to have special arrangements out of Kings Cross.

I suspect tunnels are a big factor on line speed south of Welwyn. It's noticeable that the 100mph on the Up starts immediately before the Hadley Wood tunnels (the Up uses the original tumnel bores)

 

[Bald Rick]

At Hitchin, if a DF turns right at Cambridge Jn is has to slow to 40mph for the flat junction turnouts. If it switches left to DS for the DRF it initially has to slow to 70mph before the 50mph is encountered on the flyover itself. I'd say overall the timing to pass Letchworth would be about the same either way. Checking a couple of examples on RTT the difference in working times between a non-stop LNER express and a Cambridge fast from dep. at Kings Cross to pass Hitchin is 1.5 minutes, much of that no doubt due to the slow down for the junction at Hitchin.
View attachment 79207

Yep it’s quicker across on the flat, not least because it’s a kilometre further via the flyover, all at 50 or 55mph. Although the Azumas are still timed on the old stock running times.

I see that it would not make much time but if there was investment in that area allowing for 125 running from KGX to Hitchin then that would be reasonable. Don't forget from 2021 services will be sped up out of King's Cross and having 100mph stock on a line with now 8tph 125 paths will mean that Kings Lynn services will have to have special arrangements out of Kings Cross.

Why would Kings Lynn services need ‘special arrangements’? I’m not sure what you mean.

Also, there is no prospect of upgrading for higher speeds south of Woolmer Green.

And, anyway, I still don’t understand what you think the benefit of higher speeds for the Cambridge / Lynn fast services would be. They might travel at a higher speed, but the extended dwells mean longer journeys, particularly in peak times. And there would be no capacity benefit. Indeed, the opposite, as you would get fewer people on the trains.

I suspect tunnels are a big factor on line speed south of Welwyn. It's noticeable that the 100mph on the Up starts immediately before the Hadley Wood tunnels (the Up uses the original tumnel bores)

Indeed they are. As is signal spacing, curvature, and the large number of fast line platforms. Fun fact about the Welwyn tunnels: they have different speeds up and down for good reason. The aerodynamic maximum closing speed in the tunnels is 220mph and would ordinarily be 110mph both ways. But, as northbound is uphill, it is set higher at 115 to enable the HSTs (as was) a better run onto the 125, whereas on the up downhill, it’s much easier to get back up from 105 to 115.

 

[Peter Kelford]

I think the flat route is fractionally quicker. Signallers still use it when there's a decent Up gap to get across.

Some drivers really know how to get the most out of the 70 turnout, braking through the platforms at Hitchin. Can make as much as 30 seconds difference compared to a driver who coasts on approach.

I would have thought that by now (5 years after opening) that drivers would have figured out that the flyover is on an uphill gradient and they could coast in. More importantly, does no-one train them?

 

[Ianno87]

I would have thought that by now (5 years after opening) that drivers would have figured out that the flyover is on an uphill gradient and they could coast in. More importantly, does no-one train them?

No, the 70mph drops to 50mph almost immediately after the Down Slow turnout (I think pretty much as the flyover structure starts), so you need to have braked down to 50 *before* the upward flyover gradient starts.

 

[4-SUB 4732]

No, the 70mph drops to 50mph almost immediately after the Down Slow turnout (I think pretty much as the flyover structure starts), so you need to have braked down to 50 *before* the upward flyover gradient starts.

Correct. The 50 is about 200m on the viaduct so you’re having to proactively brake coming off the Slows.

 

[Railwaysceptic]

. . . . as Thameslink pretty much call at stations between Welwyn GC and Finsbury Park . . . .

Thameslink trains run non-stop between Finsbury Park and Stevenage.