Cambridge Approaches

Introduction

The article below has been written by an anonymous Cambridgeshire contributor who has a keen passion for, and knowledge of, railways. The previous article on this subject showed that the general capacity of the existing twin track between Cambridge Station and Milton Junction was sufficient to take the existing traffic, planned growth and EWR trains without the need for 4-tracking.

In discussions and correspondence with EWR Co, it was clear that they have carried out their assessment based on the current timetable. They claim that this showed that 4-tracking of this section of the track would be required. Our previous article suggested that this was unnecessary as the current timetable would change over the next 10 years before EWR became operational.

However, to address EWR Co’s specific concerns, we have looked at the issues that they raise with the timetable and show that, with a minor revision, even on this basis there is no need to 4-track this track.

Summary

EWR Co’s argued need for 4-tracking in the north of Cambridge in a ‘northern approach’ scenario – which underpins their decision to discount that option in the latest consultation – is based on concerns about interfacing with current operations. EWR Co have not published their full analysis, but state that they cannot fit EWR trains at regular 15 minute intervals alongside the existing timetable. While that statement appears to be technically true (in the most tenuous sense), the analysis presents here suggests that without context, it is likely highly misleading – and 4-tracking is certainly not the only solution. The issue is not too many trains, but a few quirky ‘symmetry breaking’ inefficiencies in the current timetable (particularly the fast/slow Liverpool Street trains). The immediate EWR issue can be solved by slipping a single hourly train by a single minute, and even if we are to future-proof to include the reasonable-worst-case scenario (including a variety of other future trains beyond EWR), only very minor tweaks to the existing are needed to make it work. Once Cambridge to Liverpool Street services are expanded to four an hour (expected in a similar timeframe to EWR’s construction), the asymmetry issues will have resolved themselves anyway – so it is illogical to let such quirks control EWR’s design decisions.

1.      Introduction

(I suggest you grab a cuppa and get comfortable before you continue, as this is quite a long and technical post)

I should start by saying that I’m not a campaigner and am not necessarily pushing for any particular outcome. Having seen the significant campaigning efforts of Cambridge Approaches, CBRR and others, however, I thought it would be interesting to delve into the ‘north vs south’ arguments from an objective viewpoint, to try and determine whether or not the proposed northern approach is actually a viable alternative. A few months of late-night analysis later, and yes, I do think there are – potentially – some aspects which may have been overlooked. I am not an industry expert and am of course willing to be stand corrected if I have missed something important, but am keen to open the discussion so that we maximise our chances of building the best railway possible. Although EWR Co have published many pages of technical documents describing the consequences of 4-tracking, they have unfortunately still not provided a robust technical justification for why they think it is necessary – instead simply claiming that they have “looked at it and concluded that it’s the only solution”. This makes it very difficult to peer review their work and assess the validity of their argument, so some guesswork is required in attempting to re-trace their steps. I’ve tried to present everything as clearly and transparently as I can in this document, so people can see the arguments for themselves.

If, as EWR Co claim, the only way to add four hourly EWR trains through Cambridge North is to add a second pair of tracks through the north of Cambridge, then the associated destruction of nearby properties and other infrastructure costs are very significant (as the infamous “appendix F” goes to great lengths to illustrate). These consequences feature front-and-centre in EWR Co’s justification for discounting a northern approach, and I suspect finding a way to avoid 4-tracking is at the core of the northern approach’s viability.

If my analysis has missed some vital other reason why 4-tracking really is the only solution, then the proposed southern approach certainly has its relative merits. However, there is still a possibility that as even more Cambridge-London trains are added, sending EWR trains into Cambridge from the south might mean it isn’t long before the track from Shelford to Harston needs 4-tracking, alongside grade separation of the Shelford junction, both of which would also be highly disruptive.

2.      Mapping the new railway

In the vector diagram below, every line corresponds to a single hourly train in each direction at present (except for the orange freight line, which is just indicative of routes).

The next diagram is a best guess at how EWR Co’s proposed ‘southern approach’ might look. This analysis is based on an assumed 4 trains an hour, which would be in line with the busiest UK inter-city services running today. I’ve included the potential Wisbech line (either running from Cambridge or splitting from existing trains at Ely), added second hourly trains to both Norwich and Ipswich, and extended a second hourly London train from Ely to King’s Lynn. This gives us a reasonable upper bound for the next few decades to the north and east. I’ve not added potential extra trains south of Cambridge, such as the mooted services to Maidstone or Haverhill, or additional London services (at least three of which are included in Network Rail’s 2030/40 scenarios). There is still some uncertainty about how EWR would be timetabled: I’ve taken the ‘best case’ scenario where Norwich keeps its direct Stansted service, but otherwise 3 of 4 EWR trains continue to Norwich (1/h) and Ipswich (2/h). EWR, then, serves Cambridge South and Central stations with every train; Cambridge North only sees a single hourly EWR service.

Next, we have a potential ‘northern approach’. The same extra services are assumed as above, but EWR now arrives via a junction at Milton rather than Harston. There’s an optional station at Northstowe (and space still for one at Harston too), and 4-tracking may only need to go as far as Cambridge South. In this scenario, the ‘base case’ is that EWR trains all serve all three Cambridge stations, terminating at Cambridge South. There are options, such as linking with existing London (if electrified), Stansted and/or a reopened Haverhill line, or reversing at Cambridge in order to continue towards Norwich/Ipswich. It is a requirement that EWR’s design does not preclude the latter as an option, though it is probably not the most beneficial solution. Freight mostly avoids Cambridge via a new chord south of Ely. This would, admittedly, be expensive to construct (as it would include a new bridge over the Cam), but could remove freight from the single-track Newmarket route, reducing the need to dual quite as much of it.

3.      Improving existing layouts

It is clear from the northern approach diagram that the section through the north of Cambridge is quite busy – so at first glance the argument for 4-tracking seems reasonable. But can it be avoided? The first step is to see what can be done, with only modest adjustments, to increase efficiency in that section. South of Cambridge (central) station we will have 4 tracks, a grade-separated Milton junction confers no additional capacity constraints, so the solution hinges on just the three miles of twin tracks between Cambridge’s central and north stations.

Two hourly Liverpool Street trains terminate at Cambridge North (except for 2/day to each of Ely and King’s Lynn). When they head back south, they block the northbound track until they reach the switch point south of the river. However, this can easily be avoided by moving the terminus platform from the west to the centre. Although it should not be necessary, the through-platforms could be doubled up: There’s space for the western one within the existing footprint, while a 5^th on the eastern side will probably take a sliver of land from neighbouring properties. In the very worst-case scenario, if no extra land is available, then there is space further north to stagger northbound and southbound platforms. If, as has been suggested, the two Liverpool Street trains will in future need to continue to Ely, then a terminus here is not required, and either 2 or 4 platforms would suffice.

Cambridge Central is a large and complex station, currently having four terminus and four through-platforms (the latter all serving trains in both directions). The terminus platforms are all on the western side, so reversing trains again obstruct oncoming traffic as they switch tracks. According to Network Rail’s 2019 report, a southern approach would see a new island pair of through-platforms to the east, and 3-tracking to the Coldham’s Lane junction, as shown on the right in the figure below.

There are many possible iterations for upgrading the station in a northern approach scenario. The first obvious step is to swap Ipswich/Newmarket trains onto a new eastern platform. Without the need to weave Newmarket-bound trains across from the eastern side of the Shelford junction as they approach from Oxford, it should be possible to separate them entirely from other services via 3^rd track to the east towards the Coldham’s Lane junction. Ipswich trains currently only dwell at Cambridge for about five minutes, so even with two or more such services an hour, a single platform and single track under Coldham’s Lane bridge should be sufficient, assuming most freight is diverted via a new spur near Ely.

It may make sense to tidy the central portion of the station into a pair of northbound and a pair of southbound platforms. In a similar approach to Cambridge North mentioned above, it might also be possible to allocate a terminus-priority platform in the middle (the current platform 7) which could eliminate at-grade crossings on the section we’re interested in. This platform could be extended to the south, to also provide a central terminus for trains from London. If the latter option is chosen, platforms 5 and 6 might even become redundant: paved over, they’d make the ideal location for a second station entrance, providing a much shorter route from cycle parking to the platform bridge, and additional income from renting out retail space.

It is worth noting that Cambridge central station is more constrained to the south than the north: the Hills Road bridge is just 100 metres beyond the end of platform 1 (and only four tracks wide), and the post office building & car park limits space to the southeast. At present, there is space for the existing platform island to be extended further south – though if the new eastern platform island were connected to the south, this option may become less viable. In a northern approach scenario, there is much better balance in the number of trains heading north vs south in and out of Cambridge, which should reduce the pressure on platform space and time from terminating services.

For completeness, we should mention Cambridge South. In the southern approach proposal, it has four platforms – two pairs serving ~14/h in each direction (plus any future London services). In a northern approach scenario it may serve slightly fewer trains, but some might terminate at the station. It should be possible for a single platform to cope with as little as 3 minutes between trains (see Tottenham Hale’s southbound platform 1, for example), but in the worst-case scenario a 5^th platform may be required here, offering a central terminus and two through-platforms in each direction. Although there would be some opposition to encroachment on Hobson’s Park, the additional land and cost would be very modest (just the width of a single-track path, as the current proposed station design already has the requisite platform island). If few EWR trains terminate here (instead continuing south to a combination of Haverhill, London, Stansted or elsewhere), the chance of needing a 5^th platform is reduced, but 4-tracking may instead need to continue to the Shelford junction – as is the case for a southern approach scenario.

With a little effort, then, it should be possible (if needed) to entirely eliminate at-grade crossings on the busy section we’re interested in, between Cambridge and Cambridge North. We therefore have a simple scenario of twin tracks, around a dozen trains per hour, and no clashes or constraints linking the two directions. Fewer freight trains should need to use this route (with as many as possible moved to EWR and an Ely chord), so trains should follow very similar acceleration profiles on this short, slow section of track. Nonetheless, we will still aim to ensure one oversized hourly slot remains for freight just in case (because getting as much freight off of the road and onto rail is very much to be encouraged).

If we look at the existing timetables, we see that the minimum gap between trains leaving Cambridge to the north is 3 minutes (xx:00 and xx:03 Cross-Country and Great Northern respectively). A 3-minute headway is also what’s stated in EWR’s requirements [Appendix B 5.7.2 of the latest EWR Co consultation docs] – so we can safely assume this is our minimum acceptable gap. Indeed, it only takes about 3 minutes between leaving one station and arriving at the other, so even spaced this close together, we should never have two trains between the two stations at the same time.  

I should note that the Cross-Country train does not currently stop at Cambridge North station – so despite many examples to the contrary, such as Tottenham Hale mentioned above, EWR Co may still conclude in the worst-case scenario that Cambridge North requires expansion to twin platforms in each direction. This is an expense not required with a southern approach, but that’s only because in a southern approach few (if any) EWR trains actually serve Cambridge North.

4.      Symmetry and inefficiency – the spectre of 4-tracking

In an idealised world without external constraints, 3-minute headings should allow for a theoretical maximum of 20 ‘slots’ per hour (up to 15 of which can be used if we are to stick within the 0.75 resilience requirement). With this in mind, EWR Co’s argument that even the 6 current + 4 EWR trains cannot be accommodated without quadrupling the tracks has led to much head-scratching. So, what is going on; how is the real world so far from ideal that we can’t even manage what is – without even considering future signalling upgrades – just ~50% theoretical capacity?

Although EWR Co have still not published their actual analysis (only the consequences thereof), I recently managed to speak to EWR Co’s Paul Sparrow via their live chat events, and obtained slightly more insight into their analysis:

“We have used some operations specialists to conduct the assessment using rail operations modelling systems in order to ascertain where we could get our 4 trains per hour onto the existing twin track WAML using our regular 15 min clockface service pattern. These results demonstrated that the white space, the space between trains, does not exist to allow us to get 4 trains an hour every 15 mins.” (Paul Sparrow, 29^th May 2021)

This snippet of information, although still quite cryptic, is perhaps just enough for us to solve the mystery. The issue, I now suspect, is actually quite simple – and it’s all down to symmetry. Despite computational advances, building railway timetables is still ultimately mathematically driven by repeating patterns: it’s what the Swiss call ‘taktfahrplan’, or clock-face scheduling. Most train lines interact with several others along the length of their routes, and weaving all of these interconnected requirements together without clashes is much easier if everyone is dancing to the same beat. Although modern timetables may look quite random, they are essentially still just perturbations on an underlying regular symmetry.

We can illustrate this with a simplified example. Consider a railway line serving four locations: Appletown and Bananaville each need four trains an hour; Carrotbridge and Donutland need two apiece. Treating C&D as a single set, we can schedule these 12 trains at 5-minute intervals, with a pattern repeating every 15 minutes (left clock-face below). However, what if Carrotbridge decide they need their pair of hourly trains spaced 20 minutes apart? We start with Appletown’s regular trains, but once we’ve added Carrotbridge’s symmetry-breaking requirements, there’s no space left for Bananaville to have a train every 15 minutes. We can squeeze in the pair of Donutland trains, but the remaining slots are unhelpfully distributed – poor Bananaville!

This scenario is conceptually very closely related to the issue we have at hand. Carrotbridge in this case is represented by the Greater Anglia trains to Liverpool Street – and Bananaville is Oxford!

The two hourly trains from Cambridge North to Liverpool Street arrive in London at regular half-hour intervals. However, one of them is slightly ‘fast’ and the other ‘slow’: the difference is a modest ~10 minutes (~1h10 vs ~1h20). In order to make this work, 30 minutes after the slow train has left Cambridge North, the fast train…sits there for another 10 minutes, and then departs. By stopping at fewer stations on route, by the time it reaches London it has caught back up again to the 30-minute periodicity. On the return leg back north, the fast train arrives back 10 minutes earlier than its slow train equivalent would have done, and so it ends up sitting at Cambridge North…for yet another 10 minutes.

The other trains all tend to run at roughly regular half-hourly slots, into which it would normally be quite easy to add an EWR train every 15 minutes, because their symmetries are in sync. The Liverpool Street train’s timings, however, makes this simple task so much more difficult. As we will see, there are a few other minor quirks in the existing timetables too, all of which can be dealt with quite easily.

5.      Building more efficient timetables

Let us consider how this would work in terms of timetables. We’ve removed all at-grade crossings from the section, and Newmarket-bound trains have been moved onto a separate track. This should make our task relatively straightforward, as we have a single stretch of dual track between Cambridge Central and Cambridge North, with one train simply following the one in front. This is the most constrained section, so if it can be shown to work then everything else should fall into place.

We can start with the current timetable, and then see how the new services might look added in the ‘white space’. In this example, a normal weekday between 1pm and 2pm has been used – the differences from hour to hour are quite minor, so a proof-of-principle assessment needn’t replicate the analysis for every hour of every day. Instead of showing you lots of graphs and lists of timetables, I’ll stick with the ‘clock-face’ diagrams from the Appletown example above.

In the clock-face diagrams below, each service is represented by a 3-minute block, during which no other trains may depart. In the current timetable, we can see the two closest trains’ blocks adjacent to one another at xx:00 and xx03 on the northbound chart, and vast swathes of free ‘white space’ in both directions. These really aren’t very busy lines at the moment, with a train on each track between the stations just 30% of the time! But as you can see, the pairs of trains to Liverpool Street and (in the southbound direction) King’s Cross are not nicely symmetrical, with the Norwich train sitting where one might expect the second Liverpool Street train to be.

Now, if we attempt to add four hourly EWR trains to the existing timetable, it might look something like the figure below. At first glance all seems fine, but on closer inspection one of the four EWR trains has been slipped by a single minute from its ideal 15-minute-interval service, in order to avoid overlapping with an existing train’s 3-minute window. Although you might think this a very minor issue – arising from an existing timetable quirk which will long since have changed by the time EWR is built – as far as I can tell (going by Paul Sparrow’s above quote), it is precisely this which has led EWR Co to claim that the only solution is to build two more tracks through the north of Cambridge!

Nonetheless, sticking for now with the nearly symmetrical EWR trains added alongside the existing timetable, what other services might we need to make room for in the next few decades, to ensure our design is future-proof? A second Norwich train is an obvious one: Northbound it can fit exactly 30 minutes away from the existing train; southbound we have to offset it by a couple of minutes from its ideal position (one bit of broken symmetry forcing another one). After this, there is still space for another half-hourly service (e.g. trains to Wisbech) – and we’re still within the 75% resilience threshold stated in EWR’s requirements [Appendix B 5.7.2]. In both directions, there’s an oversized gap left in the hourly timetable for even a very slow freight train to get through, although this should be avoidable in most instances as freight could travel via Soham or Newmarket instead. We could even (not shown) double up the Birmingham service (which some hope could be extended to Leeds in future), by simply moving the northbound freight slot to ~xx.45.

The figure above illustrates how a northern approach – and a bunch of potential other future services – could work, without any changes to the existing timetable, without any signalling upgrades, and within the documented requirements of headways (3 minutes) and resilience (25% unused wiggle-room), without resorting to knocking down any buildings to build more tracks. However, what if we absolutely must have a symmetrically perfect-to-the-minute EWR service? Or, indeed, what if we would just like to tidy up the existing inefficient broken symmetries, and thus optimise the potential capacity through Cambridge’s only traffic-jam-avoiding cross-city travel corridor?

Northbound, the solution is incredibly simple. The fast train from Liverpool Street (which is about to sit at Cambridge North for more than half an hour) can just wait for a single minute at Cambridge station. That’s it.

Southbound, we have slightly more work to do. First, we align the time for which the King’s Cross trains dwell at Cambridge. I suspect the reason for this asymmetry in the current timetable comes from train-splitting, but with platforms at Ely and Waterbeach due to be extended, Network Rail themselves expect that procedure to be phased out in the coming years. Next, we have the fast Liverpool Street train (which leaves 10 minutes later than symmetry would like), and the existing Norwich train (which is then in the way). A neat, symmetry-restoring solution (as shown in the diagram below) is to push the Norwich train back by two minutes, and have the fast Liverpool Street train depart Cambridge North 10 minutes early, and dwell at Cambridge for 10 minutes (where it will be overtaken by the Norwich train, and then continue to Cambridge South roughly alongside the EWR service on the quad tracks). This would only be needed until two more (slow) trains between Cambridge Central and Liverpool Street are added, at which point both Cambridge North to Liverpool Street trains can become fast services.

The Norwich train, in ensuring regular hourly cycles, has a few minutes of wiggle-room to play with, but in a worst-case scenario it might miss its Stansted spot – in which case its lost slot could be taken up by an EWR train instead. A slightly less neat, but probably still workable and arguably less disruptive, solution (not shown) would have the existing Norwich train unaffected, the fast Liverpool Street train leaving just a minute or two earlier than it currently does, and the second Norwich train 32 minutes after (or 28 before) the existing one. These solutions involve very minor tweaks to the existing timetables, none of which should have any further knock-on effects on other services.

The above is, I would argue, a reasonable worst-case scenario for the 2040s, and is still acceptable within EWR Co’s given requirements. However, I suspect reality will be less constrained, as there are a variety of possible options which would each reduce the number of trains travelling through the busy corridor.

I would be slightly surprised if EWR needed four hourly trains, at least for the first decade or two. Even the busiest UK intercity services such as London to Bristol only have that many – as does Cambridge to King’s Cross (if we ignore the two slow trains which offer no utility for intercity passengers). EWR only serves relatively small towns and cities, and long-distance trips across the country which really aren’t that popular (and are mostly already quite doable via London, especially once Crossrail is operational). Half-hourly 8-carriage trains would have the same capacity as the proposed four hourly 4-carriage ones, and as EWR doesn’t really serve busy commuter routes east of Bletchley (where it’s expected that another 2/h will run from Oxford to the Milton Keynes  branch anyway), I suspect few would be very upset by a slightly less frequent service. Other than for a few select local routes (such as Cambridge and Bedford residents hopping on the train to Bletchley’s IKEA), EWR provides (at best) a modest improvement rather than a genuine transport revolution. Let’s just hope the trains have enough luggage space for flat-pack bookcases!

Next, it’s worth noting that Wisbech and King’s Lynn are a similar distance from Ely. The fast King’s Cross train, which currently splits at Cambridge (with only the front section continuing further north) could instead continue as one further north beyond the new Milton junction (where the track is less congested). It could then split in half at Ely (or the new Waterbeach station), with the front continuing to King’s Lynn, and the back departing for Wisbech three minutes later.

We could go further still. There are actually two routes from Norwich to Cambridge, of similar length. The route currently operating heads via Ely, but there’s another route via Diss and Bury St Edmunds. A direct train using the latter would either need to reverse in Stowmarket, or use a yet-to-be-built spur just north thereof. If a second Norwich train took this route, it would provide direct connections between Cambridge and Diss; Norwich and Bury St Edmunds. Moreover, while a large fraction of trips to Cambridge on the Norwich train involve people travelling the whole length of the line (with small numbers using intermediate stations such as Thetford), most Cambridge arrivals on the train from Ipswich come from Newmarket or Bury St Edmunds. Therefore, instead of having two Norwich trains via Thetford and two Ipswich ones via Bury, sending the second Norwich train via Bury may actually better serve passenger demand – as well as easing Ely’s congestion problems.

As a final potential tweak, it’s worth thinking about how to make best use of the station at Stansted Airport. Airports are the one location where direct trains are hugely advantageous, as swapping trains at intermediate stations is much more difficult if you have heavy luggage in tow (or are jetlagged!). However, the long single-track tunnel under the runway severely restricts how many trains can reach the airport. From Cambridge, two hourly trains make the journey – one from Norwich (Greater Anglia, class 755 diesel/electric hybrid trains) and one from Birmingham (Cross-Country, class 170 diesels). Could we use the advent of “Great British Railways” to shuffle rolling stock around, and thus find a way for these two trains to join together (at Ely or Waterbeach) and travel as one to Stansted? GA has a whole bunch of class 755s on local routes, a few of which could perhaps be swapped for CC’s class 170s – and I see no reason why the resulting 755 pair couldn’t couple together. This would then free up a Stansted slot, which (in a northern approach scenario) could enable an hourly direct EWR train from Oxford to Stansted!

If we put all of the above together in an optimistic scenario for the 2040s, we actually find ourselves with just a single extra train each hour compared with the current timetable (and even that is offset by an expected reduction in freight traffic, given a new spur south of Ely). I appreciate that at least some of the suggested optimisations might prove unworkable, but nonetheless it reinforces how many different options there are for ensuring there is absolutely no need to four-track through the north of Cambridge in a northern approach!

6.      Has this solved the problem?

The above examples show that there doesn’t appear to be any fundamental issue with scheduling all the trains we might possibly need in a way which avoids the need for 4-tracking. None of the tweaks suggested should cause any knock-on effects, so could be achieved while keeping all other timetables intact. Passengers boarding at Cambridge North towards Liverpool Street may see their southbound journey time increased by a few minutes – but I suspect that is an acceptable price to pay, given that a northern approach (unlike a southern one) would bring a regular EWR service to Cambridge North.

However, it is worth stressing that by 2030 (when EWR is expected to begin operation), the current franchises will be long gone: The current Greater Anglia franchise ends in 2025, and Great British Railways is about to completely shake up the way franchises work in the UK anyway. As such, so long as the *principle* of operation is sound, it’s not really worth worrying in fine detail what the precise timetables will look like at this stage – because they’ll all have changed by the time the line is built in any case.

It is, of course, worth noting that even in a southern approach scenario, the frequency of trains will increase – and symmetry-breaking carbuncles, which massively reduce line capacity, will need to be phased out regardless. The Liverpool Street asymmetry will probably be eliminated entirely within a few years anyway, as we expect to require a new pair of WAML trains which terminate at Cambridge Central. With four hourly trains in total, the Cambridge North pair will almost certainly both be designated as similarly ‘fast’, At which point the whole asymmetry issue disappears!

When designing new, it is always better to start as cleanly as possible, rather than adding yet more mess on top of existing inefficiencies. As the existing quirks can be easily tidied up – and will probably need to be resolved soon anyway – it would be wholly irrational to base major infrastructure design decisions around them. Nonetheless, given EWR Co’s claimed arguments, I thought it useful to illustrate how I think 4-tracking can be avoided both in principle, and in practice around the current timetable.

I haven’t considered in detail the extra services to London which Network Rail’s forecasts indicate will be needed by 2040. Most of these won’t pass north of Cambridge Central, so will not affect a northern approach. Looking at NR’s worst-case 2043 scenario, the only extra services needed north of Cambridge are one or two more Ely-KX trains (which could be the Wisbech trains, already factored into my model) and extending the two existing Liverpool Street trains beyond Cambridge North to terminate at Ely (which would remove the need for a 5^th platform at Cambridge North, but add no further constraint issues so long as the junction at Milton is grade-separated). On the other hand, they will add further pressure to a southern approach, which even with 4-tracking may find the south Cambridge corridor eventually becomes problematically congested – risking platform capacity issues at Cambridge Central from so many terminating trains, and perhaps a need to rebuild Shelford junction as grade-separated.

7.      Concluding remarks

EWR’s Paul Sparrow has stated that the existing timetable doesn’t “allow us to get 4 [EWR] trains an hour every 15 mins” for a northern approach. The analysis presented here appears to confirm that this is technically a correct statement, but – unless I am very much mistaken – only in the same kind of way that I can say I was Time Magazine’s Person of the Year in 2006: It’s only *just* correct, and likely very misleading for them to have used it to draw the conclusions they have.

EWR Co claim that the only solution to the above, in a ‘northern approach’ scenario, is to 4-track north of Cambridge station. I disagree. The immediate EWR issue can be solved by slipping a single hourly train by a single minute, and even if we are to future-proof to include the reasonable-worst-case scenario (including a variety of other future trains beyond EWR), only very minor tweaks to the existing timetable – which will almost certainly disappear soon anyway – are needed to make it work.

If my analysis turns out to be sound, then I do not understand why EWR Co decided that 4-tracking (with dozens of demolitions, new bridges etc) is considered a lesser evil. I accept that there may be additional complications of which we are not aware, and which render the proposals in this document unworkable – but if that is the case, then they absolutely must be able to explain to the public why this is the case, and cannot continue to simply state “our modelling says it is not possible” without offering a technical justification.

If the timetabling issue can be resolved and 4-tracking rendered unnecessary, the question of a northern vs southern approach becomes much more balanced. I will leave it to others to expound the pros and cons of each option, but advantages such as keeping more freight out of Cambridge, EWR regularly serving Cambridge North (and potentially also London and/or Stansted), the option of a station at Northstowe (offering direct links to Cambourne, Oxford and Addenbrookes), an easier way to get the Haverhill line back up and running (without it adding even more N-v-S imbalance to the numbers of trains running through the Cambridge corridor), and simplifying the process of electrification between Oxford and Cambridge by decoupling from the Eastern section (not due for upgrade until 2040-50)…are all worth thinking about very seriously indeed.