Why do we need to know about 4-tracking?
EWR Co’s decision to prioritise a southern approach into Cambridge primarily hinges on their assertion that a northern approach will require to be 4-tracked from the Milton junction with the existing West Anglia Main Line (WAML) into Cambridge. They also say that the existing Shepreth Branch Line between Hauxton Junction and Shepreth Junction (SBR) does not need to be 4-tracked but accept that this assessment needs further testing in later design stages.
It is vital that these matters are properly assessed now. To implement 4-tracking on either of these sections of existing lines would be extremely expensive. Major existing bridges would need to be modified or rebuilt and other infrastructure modified. If it is not resolved now, detailed design work would proceed based on a potentially faulty premise with the risk of locking the project into a solution that will lose valuable benefits of the alternative route.
To test EWR Co’s assessment, we have carried out our own evaluation of both their claims. We start by looking at the likely number of trains on the sections of the lines in question. We estimate the total number of trains likely to use the line including current traffic and probable growth for both passengers and freight. We discuss the likelihood of each of the scenarios occurring in practice and compare these rail traffic estimates with the capacity of the lines.
We found that EWR Co’s conclusion about the 4-tracking of the northern approach section NA2 is incorrect and that, for our estimate of the reasonable worst-case scenario, it does not need additional tracks. In fact, even with just traditional signalling there is likely to be sufficient capacity. With digital signalling, which is already specified by EWR Co, we expect there to be over-capacity.
Likewise, the southern approach section of the SBR line can probably take the reasonable worst-case passenger rail traffic estimate (which are based on Network Rail’s figures up to 2044). However, interfacing with the Thameslink services will impose severe restrictions on possible growth in traffic in excess of the figures shown due to anticipated expansion after 2044 as a result of the Ox-Cam Arc plans. The SBR line would not be able to accommodate EWR’s 6 trains per hour that are specified in the Project Wide Output Specification. The freight services estimated by Network Rail may not be able to be fully catered for because of limitations on the Newmarket line.
If EWR Co are wrong in their assertion that the SBR line does not need to be 4-tracked, the construction work that would be required exceeds the theoretical (but unrealistic) case for 4-tracking part of the northern approach.
The reasonable worst-case rail traffic scenarios for the northern and southern approaches to Cambridge are shown in Table 1. For the northern approach, we have considered the likely rail traffic on the critical section between Milton junction and Coldham’s Lane. All Newmarket trains would use platform 8 at Cambridge station enabling those services to avoid crossing movements between Cambridge Station and Coldham’s Lane. There is sufficient space in that length to increase the number of tracks should this be required.
The assumptions and data sources used in compiling Table 1 are discussed below.
- We have not assumed any long-term change in the pre-pandemic forecasts for growth and and ‘existing’ services due to impact of COVID, even though this is likely to reduce the amount of rail traffic in the short and perhaps the medium term.
- For consistency and independence, we have used Network Rail’s 2019 Cambridgeshire Corridor Study [Ref. 1] for assessing passenger and freight growth forecasts on the existing network for the two approaches. This will allow a fair operational comparison to be made between the approaches. We have resisted the temptation to consider in this assessment the beneficial effects (for a northern route) of an alternative future route via Newmarket for Norwich trains which has been suggested for many years, or the possibility of March trains splitting/joining other services at Ely. Combined, these could potentially reduce demand on the northern approach by 3tph. Nor have we considered the impact of a potential new Thameslink service between Cambridge and Maidstone East which may increase demand on the southern approach. Lastly, we consider that, if the Ox-Cam Arc proceeds as planned, there would be demand for even more Kings Cross services than mentioned in the Cambridgeshire Corridor Study with a timescale to 2044 only.
- Future demand for freight on EWR is taken from a scenario suggested by Network Rail in the EWR Co’s Technical Report 3.10.7.
- For a northern approach, EWR freight would be diverted northwards onto the WAML from Milton via a new grade-separated junction and then onto the main Felixstowe to Nuneaton freight line via a new chord just south of Ely. Any residual freight needing to pass through Cambridge would be planned out of peak hours.
Basic ‘open-track’ Assessment
In addition to the basic number of trains per hour that could use an open railway line, the capacity is affected by a number of other factors, including timetabling, any crossing movements between tracks, whether the section of track is between junctions or between stations and the mixture of freight and passenger services. We start by looking at the open-line capacity and then go on to consider these other issues.
(i) Traditional signalling
Traditional signalling systems would allow for about 15 trains per hour with no other compounding factors. This is based on international standards (International Union of Railways or UIC which is the international rail transport industry organisation); a headway (the time between trains) of 3 minutes, as convention and a minimum required by EWR Co (Technical Report Appendix B 5.7.2); and a resilience ‘safety factor’ of 0.75 (UIC Code 406 for mixed traffic lines). The reasonable worst-case scenarios for both the northern and southern approaches as shown in Table 1 appears to be within the capacity of the existing twin track based on open track conditions and traditional signalling.
(ii) Digital Signalling
However, digital signalling will be used by EWR [Ref. 2] One of the benefits of digital signalling is the additional capacity that it provides. UIC have shown that on main railway lines, the capacity increase of ETCS level 2 (with ‘block’ lengths of 400m) over ETCS level 1 could be about 37% [Ref. 3]. This is supported by a statement by Network Rail quoting capacity increases ‘of up to 40%’ [Ref. 4]. These figures should be used with care, but they demonstrate that there would be a real and significant increase in capacity. Even using a capacity increase of half of these amounts, the number of trains per hour able to be accommodated could be increased to 18 by digital signalling without the need for 4-tracking,again without any complicating location-specific issues.
Importantly, digital signalling will also allow bi-directional running on tracks. This can provide significant flexibility, especially at stations, for reversing trains.
Other Factors in Capacity Assessment
There are several factors that could reduce actual capacity on a line, including whether clock-face timetabling is used (which is it on EWR) and the number of crossing of main lines radiating from London. Below we only consider those issues that are different between approaches.
(a) The Thameslink Effect and Slow Trains
Capacity reduction can arise when other train services use the section of track and the times of those services are not possible to change. This occurs for the southern approach where Thameslink services use the track. This leads to tight and sensitive interfaces with those services. The result is that the existing 6 passenger services are almost immutable because they form part of the complex Thameslink network and the East Coast Main Line traffic. The complexity of Thameslink can clearly be seen in the map below, especially all the strands of services coming together in central London where it is planned to have 24tph crossing the Thames (which, incidentally, would not be possible without the capacity-enhancing benefits of digital signalling). EWR Co are very likely to be faced with predetermined ‘paths’ (planned slots for trains) at the Cambridge end of the route that do not mesh with their required paths elsewhere. This poses a serious risk to the effective capacity of this line, the outcome of which can only be resolved when timetabling of services is attempted. This is not the case for the northern approach.
If that were not sufficiently restrictive to the timetable, this line also has a slow service calling at all stations without a ‘loop’ or overtaking section for faster trains before they reach the East Coast Main Line near Hitchin. This means that timetabling for fast trains needs to allow for these slow trains, which will lead to greater gaps between trains. There are minimal such restrictions for a northern approach.
(b) Crossing Movements and Junctions
Crossing movements required across other tracks and junctions can also reduce the capacity of a line. In the case where junctions are flat (‘at-grade’), one train joining another line could have to wait if another train were using the section of track the first one wanted to use. ‘Grade-separated junctions’ involving ramps and bridges over lines significantly reduce this delay. The southern approach into Cambridge has two junctions (Hauxton and Shepreth Branch junctions) compared to just one for the northern approach.
The northern approach allows trains that are temporarily blocked by other trains to wait for a short time at Cambridge North station. This would allow following trains to also wait at Cambridge North (obviously on another platform) and so minimise any concertina-type delay. On the southern approach, conversely, delayed trains would have to wait in line between junctions, magnifying the impact of such a delay.
Operationally, slower freight and more speedy passenger services do not mix well. Freight on a northern approach (via a new northbound chord at Milton onto the WAML and then onto the Felixstowe to Nuneaton line via another new chord south of Ely), means that freight would have no impact on EWR operations in the busy section between Milton junction and Coldham’s Lane junction. Conversely, freight and passenger traffic on a southern approach intermingle, potentially resulting in less overall capacity. If the line were eventually used for even slower moving, heavy-haul freight, such as building materials, this would only exacerbate the situation.
For a southern approach, the Cambridgeshire Corridor Study estimates that the Newmarket line, even with the anticipated dualling between Coldhams Lane junction and Teversham, could accommodate 1tph for freight during off-peak hours. Network Rail estimate the freight demand could be 1.3tph during an 18-hour window (i.e. including peak and peak hours), assuming the scenario suggested by Network Rail in the Technical Report 3.10.7. This implies that there could be insufficient capacity on a southern approach for the anticipated freight.
Another operational disadvantage of a southern approach is that because freight needs to pass through Cambridge and Cambridge South stations, the problem of platform provision in both locations would be exacerbated.
What Do EWR Co. Say?
EWR Co have stated (Appendix F, 2.2.4) that the results of their analysis of a northern approach showed that there would be several conflicting movements between EWR and other services including:
- Trains towards Ely and eastbound EWR services conflicting where EWR services join the WAML; and
- Conflicts on various platforms at Cambridge station.
We find the first point hard to understand as there could be a grade-separated junction at Milton specifically to overcome this issue. We find their conclusion that the only remaining option is ‘to add two extra tracks to the WAML, making it a four-track railway between the new Milton junction and Cambridge station’ (Appendix F 2.2.10) curious when they could much less onerously provide a grade-separated junction at Milton than the 4-tracking option. Confusingly, they then state in Appendix F 2.2.12 that ‘a grade-separated junction is required where the EWR route joins the WAML…’.
The second point would be overcome by the construction of two more platforms at Cambridge station which EWR Co already confirm would have to be done (App F section 2.2.10). Interestingly, they fail to mention that the southern approach also needs two new platforms at Cambridge station (Technical Report 11.1.5 ). Indeed, as we will see later, there is more pressure on Cambridge station platforms from a southern approach because a freight service will need to pass through. CamBedRailRoad documents provide a solution without the need for additional platforms at Cambridge.
EWR Co state (Technical Report 11.4.1): ‘…it is most likely that the SBR can remain as a twin track railway as there is sufficient existing capacity to be able to add the EWR services required to achieve the Project Objectives and leave spare capacity for an increase in services in the future.’ (Our underlining). So they have not confirmed this vital point before choosing a southerly route.
They go on to state: ‘The working assumption for the operational timetable will be assessed further in the next design phase to confirm that it is correct. The focus will be on timetable and performance modelling of the SBR to ensure that both the EWR and GTR services can run as required with suitable resilience to allow for delay, disruption, and updates to service patterns.’
They appear to acknowledge from the last statement that there could be a problem of interfacing with existing services but without being explicit about it. The Sponsor’s Requirements (App A, 5.3 and 5.4) oblige them, as far as practical, ‘to be resilient to any periods of poor performance on the wider network’ and to ‘isolate the wider network from any periods of poor performance on the Railway [EWR]’.
We consider that such a fundamental point as this should be resolved at this stage or, if it really cannot be resolved now, to base decisions on a risk-based approach (i.e. they should analyse the chances of success and the costs of each scenario) in making the choice between a northern or southern approach.
EWR Co mention that two more platforms are required at Cambridge station for a southern approach. This it is not necessarily just a case of removing some sidings to add an extra pair of platforms at the east of Cambridge station: the Royal Mail building really isn’t that far away, and may need to be removed or reduced to allow space for the extra switching tracks, particularly if another pair of side-by-side platforms are needed. Additionally, there is a very short distance between the platforms at Cambridge station and Hill’s Road bridge, in which space all the different platform tracks need to condense down to just four tracks. Indeed, that itself could become quite a bottleneck for a southern approach, as each of the various trains from London and Oxford terminating at Cambridge need to reverse & switch on their way back out.
Other Issues With Approaches
Although the above sections attempt to show whether the two approaches need to be 4-tracked, there are other arguments that need to be considered in the choice of route from a railway operations and cost viewpoint.
EWR Co state (Consultation Document page 52) that trains using a northern approach would need to terminate at Cambridge South station. Similarly, a southern approach would need to terminate at Cambridge North station since this area is also an important employment hub.
If EWR Co persist in their conviction that a northern approach would need to be 4-tracked south of Milton, a southern approach would also need to be 4-tracked to Cambridge North as it would carry at least the same amount of rail traffic. This means that, according to EWR Co’s logic, 4-tracking on this section would be needed whichever approach were adopted.
We fully understand some of the severe practical difficulties in providing this. But this underscores our assertion that the northern approach, by providing relatively easy access to all three stations in Cambridge, serves Cambridge’s employment needs better than does a southern approach.
2. Risk and Impact on Infrastructure
We have already referred to the risk of EWR Co being wrong in their future assessment of whether the Shepreth Branch line would need 4-tracking between Hauxton and Shepreth Branch junctions. If they were wrong, the structures that would require to be constructed or modified specifically for 4-tracking are:
- M11 crossing
- River Cam crossing
- Widened cutting E between Cam and A1301
The first two items are major construction works in their own right.
This list is in addition to those that are required even if 4-tracking is not required, including:
- Hauxton grade-separated junction,
- Harston level crossing changes,
- A1368 bridge rebuild,
- Hauxton Road level crossing changes,
- A1301 (rebuilt bridge likely if grade-separated junction at Shepreth Branch junction)
- Shepreth Branch grade-separated junction.
Clearly none of these 9 structures would require to be constructed if a northern approach were adopted.
Compare this to the two structures (the level crossing near Milton and the A14 crossing) that EWR Co state would be required if 4-tracking were required for a northern approach (which we, as detailed above, strongly refute). The other structures requiring modification (Fen Road, river Cam crossing, Newmarket Road and Mill Road) would need to be carried out anyway as a southern approach needs to terminate in Cambridge North station (see point 1 above). But all these works are less than those required for a southern approach.
This discrepancy in construction works between the approaches demonstrates EWR Co’s apparently sanguine approach to risk-based decision making.
3. Reversing Move at Cambridge
EWR Co have made much of the fact that a reversing move (i.e. the driver changing ends of the train) would be needed in Cambridge for onward eastbound traffic.
Two points are worth highlighting here. Firstly, it is not much of a penalty at all. A train approaching Cambridge from a southern approach would need to stop in the station for approximately 3 minutes before proceeding. For a train from a northern approach, the maximum time for the driver to change ends is about 5 minutes – a difference of some 2 minutes!
The second point is that onward eastbound passenger services are excluded from EWR Co’s remit. Although they need take such provision into account (the Sponsor’s Requirements 1.6 state that ‘Consideration should be given to the provision of or integration with services beyond the Oxford Cambridge sections…’), using this weak argument against a northern approach highlights their lack of strong arguments. It is especially rich when, in response to our queries about the problems that a southern approach would cause with freight east of Cambridge, EWR Co claim that it is not within their scope.
- The northern approach would not need to be 4-tracked between Milton junction and Cambridge station for the predicted maximum amount of rail traffic including future expansion of services to Wisbech and Norwich. As a result of digital signalling, it could also cater for EWR Co’s aspiration of 6tph. EWR Co have appeared to ignore a grade-separated junction at Milton in their analysis of 4-tracking of this section.
- It is not certain whether the southern approach between Hauxton and Shepreth Branch junctions (SBR line) can take any growth in passenger rail traffic beyond EWR’s 4tph until further timetabling work has been carried out by EWR Co. This is because of the severe constraints imposed by Thameslink and other services using the line. It would certainly not be able to provide capacity for the 6tph EWR services stated in the PWOS. This lack of flexibility to provide for growth is contrary to the Sponsor’s Requirements.
- If EWR Co’s future assessment of the SBR line shows that they do require to 4-track it, the construction works required is likely to exceed the theoretical additional works required for 4-tracking the northern approach (as stated in conclusion 1, they are not actually required).
- EWR Co have not been transparent about the adverse impact of freight using a southern approach on railway operations.
 Network Rail Cambridgeshire Corridor Study 2019.
 Programme-Wide Output Specification (Technical Report Appendix B 5.20.2) is ‘at least’ European Train Control System (ETCS) Level 2. The current signalling system in the general Cambridge area on existing track (i.e. in addition to the EWR track) is being upgraded to provide a platform ready for digital technologies and is planned to be complete by 2025, five years before the currently planned EWR completion date.
 ‘Influence of ETCS on line capacity – generic study’, UIC, Fig 24
 By Mvpo666 – Own work, CC BY-SA 4.0,
 CBRR Northern Approach Into Cambridge.