Article date 5 January 2010
Latest revision 19 November 2013
This article considers the idealised concept of a completed Orbital railway all the way around London without undesireable features such as train reversal. On-the-ground reality may prove to be different. This article is, therefore, of historical interest only. Indeed, proposals for a complete London Rail Orbital no longer reflect our thinking.
The material in this article is presented in a condensed form. It is of historical interest only.
The London Rail Orbital is planned as a high-specification Orbital railway around London and is being designed as a high-capacity railway for express services, albeit with only two tracks. Hence scheduling on the London Rail Orbital will be taken into account at every stage of the design process. A high-capacity railway using only two tracks is planned in order to optimise return on investment.
Scheduling rules are designed as tools to assist with maximising return on investment.
The proposed London Rail Orbital is designed as a two-track railway for express services. Most passenger services will stop at major stations only. For this reason local stopping services are subject to constraints designed to maximise availability of the railway for express services.
A metronome is used to govern the slots available for slower services, both local stopping services and slow-moving freight, which we will now describe. A train that provides a circular service around the Orbital departs from Guildford at 10 a.m. in a clockwise direction. This train is known as train A and is an express service stopping only at major stations. Another train providing the same circular service around the Orbital departs from Guildford at 10:30 a.m. also in a clockwise direction. This train is known as train B and is also an express service stopping only at major stations. In due course, train A will arrive back at Guildford, followed by train B 30 minutes later. As these two trains proceed around the Orbital, they provide the metronome for slower services. A slow-moving service anywhere on the Orbital in a clockwise direction must run after train A and before train B. Thus slow-moving services are limited to a single time slot in each hour. Moreover, some express services on the Orbital may run half-hourly, therefore there are likely to be express services immediately following train A or immediately preceding train B. To cater for this, slow-moving services are limited to a time slot of approximately 20 minutes in each hour. A slow-moving service must complete its journey on the Orbital within this time slot of approximately 20 minutes, following train A and preceding train B.
One corollary of this metronome is that local stopping services cannot be expected to run more frequently than hourly (although see Capacity, below).
Since local stopping services are limited to a time slot of approximately 20 minutes, their length of journey on the Orbital is limited.
Some segments of the Orbital are existing railway lines that have existing local stopping services. Before discussing the impact on these services, we need to put railway stations into categories.
The first category is Major railway stations, an example being Guildford. Express services stop at all, or some, major railway stations.
The second category is Minor railway stations, an example being Cuxton on the line from Strood to Paddock Wood. Express services do not stop at minor stations. Only local stopping services stop at minor railway stations and since these are limited to one an hour, where there is only one local stopping service on a segment of the Orbital, there will be only one train per hour that stops at minor stations.
The third category is Isolated railway stations. An example is Betchworth. An isolated station is a minor station that stretches the scheduling rules. Thus, a local stopping service between Guildford and Redhill adheres to the 20-minute rule, except that the service also stops at Betchworth. Isolated stations take account of the realities of existing local stopping services. Effectively, isolated stations limit the capacity of the Orbital to provide the desired capacity for express services. The term isolated here refers to Orbital scheduling and not to population density.
The fourth category is Intermediate railway stations. Trains stop more frequently than one per hour at intermediate stations yet these stations cannot be categorised as major stations. If the Orbital from Camberley to Maidenhead includes Bagshot, then Bagshot is an example of an intermediate station. The station is currently served every 30 minutes and, thus, is not a minor station, whereas neither is it a major station. A further intermediate station is Higham, between Gravesend and Strood. Intermediate stations limit the capacity of the Orbital to provide the desired capacity for express services.
Having listed railway station categories, we can now outline provisional likely changes to existing stopping services.
The local stopping service between Strood and Paddock Wood runs hourly and takes approximately 45 minutes to complete the journey. This service is likely to be split into two services. Provisionally, stations north of Maidstone Barracks are placed in Zone 1 and those south of Maidstone West are placed in Zone 2. A local stopping service serves the stations in Zone 1 at the same time as a different local stopping service serves the stations in Zone 2. Both services would stop at Strood, Maidstone Barracks, Maidstone West and Paddock Wood. Apart from service retiming, there is little impact on those travelling from any minor station between Strood and Paddock Wood to Strood, Maidstone Barracks, Madstone West or Paddock Wood, nor is there any impact on those travelling between two minor stations in Zone 1, nor on those travelling between two minor stations in Zone 2. Anyone travelling from a minor station in one zone to a minor station in the other zone would no longer be able to complete their journey directly without changing trains although in some cases it might be possible to continue past the desired destination station and stay on the train for the return journey. It should be noted that the two local stopping services will not necessarily terminate at Strood or Paddock Wood and may form part of services that continue further afield.
The local stopping service from Tonbridge to Redhill, East Croydon and London would be subject to the 20-minute scheduling rule and thus split into two services:
Tonbridge, Leigh and Penshurst to Redhill, East Croydon and London.
Edenbridge, Godstone and Nutfield to Redhill, East Croydon and London.
At the time of writing, this split is already as presented by the available summary timetables.
If the London Rail Orbital is built by providing a new railway line from North Camp to Camberley (other options being currently outside the scope of this article), the local stopping service from Reading to Redhill would be split into two zones. Provisionally Zone 1 would be the stations between Reading and Guildford that are on the Orbital. These are North Camp, Ash and Wanborough. Zone 2 would be all stations between Guildford and Redhill. A local stopping service would serve stations in zone 1 as a different stopping service serves stations in zone 2. To maintain similarity to existing stopping services, Shalford manages to place itself into two different categories, both as a minor station for zone 2 and as an isolated station for zone 1. Thus, the existing service from Reading that terminates at Shalford would remain (that is, assuming there is good reason to retain it). Farnborough North, or any possible replacement Farnbourough East, have been omitted from this paragraph.
No attempt has been made to consider scheduling in the event of the London Rail Orbital being built by providing a new railway line from Crowthorne to a possible new station Wokingham East.
At peak times, local stopping services from Reading/Guildford to Redhill run more frequently than hourly. This is a case of requiring an exception to the Orbital scheduling rules. Effectively, the capacity of the Orbital to provide the desired capacity for express services is severely limited on this segment of the Orbital during peak periods, unless services are subject to significant change or further railway tracks are provided.
Between Enfield Town and Seven Sisters, there are two existing services. A half-hourly service from Enfield Town to Liverpool Street runs out of phase with a half-hourly service from Cheshunt via Seven Sisters to Liverpool Street. Together, they provide a service every 15 minutes at stations from Edmonton Green southwards, thus effectively preventing any express services. Possibly the two existing services could be retimed to run one after the other southwards from Edmonton Green instead of out of phase. This would provide two slots per hour for express services, with two 20-minute slots for stopping services in each hour.
From Seven Sisters, Orbital services run on to the Gospel Oak to Barking line to Barking although some may run via Liverpool Street.
For scheduling east and west of Watford Junction, please visit St Albans Rail
Scheduling rules apply both clockwise and anti-clockwise. There are two metronome trains C and D that run anti-clockwise from Guildford similarly to trains A and B that run clockwise. Train D runs 30 minutes later than train C. Anti-clockwise local stopping services are limited to approximately 20 minutes hourly running after train C and prior to train D. The timings of trains C and D are determined relative to the timings of trains A and B in such a manner as to provide optimum or at least reasonable turn-round times for local stopping services that terminate service to provide a return service in the opposite direction. This leads us to the following constraint :
The locations at which trains change direction to provide a service in the opposite direction need to be carefully calculated so that services dovetail in with the scheduling metronomes.
This constraint tells us that local stopping services currently running on railway lines that will form segments of the Orbital might usefully be extended as express services to new locations where train reversal takes place. For example, we might envisage a stopping service from Strood to Maidstone West and then non-stop to Paddock Wood continuing perhaps to Gatwick Airport or to Reading. A service non-stop from Strood to Maidstone Barracks that provides the local stopping service from Maidstone West to Paddock Wood might continue to London. We can only hypothesise at this stage.
Scheduling rules apply to the Orbital principal route. They may not apply for Orbital secondary route services particularly between Canning Town and Gravesend. They are unlikely to apply on approach to London mainline stations, notably Liverpool Street.
The 10 a.m. departure time for metronome train A from Guildford is indicative. The actual departure time would be defined in coordination with other UK national scheduled services.
Capacity on the Orbital is designed to be 15 - 20 trains per hour, that is, one train every 3 or 4 minutes. We would hope that this is achievable with four-aspect signalling, even after allowing for dwell times at stations. The purpose of this design criterion is to provide reasonably high availability of train paths. Actual train frequency is likely to be less than this. Moreover, a section of the Orbital running at capacity would imply dedicated platform staff at major stations to ensure trains run to time. The Orbital is likely to run at less than this design capacity.
Local stopping services limit path availability. On a section of the Orbital where a local stopping service exists, we very much hope that express services intended to run prior to a local stopping service will not be held up to the point where they run after the local stopping service, thus being further delayed.
Some services will use the Orbital as a means of connecting from one radial route to another. Path availability for this style of service is not generally easily achieved, moreover such services inevitably introduce dependencies between different radial routes that would otherwise have run independently of eachother. When a service is delayed, attempting to prevent yet further delay can be a challenge. This is the principal reason why we want the Orbital to provide what we might term flexibility : when a service is delayed, we want it to be likely that the Orbital can accommodate the new order of running services, so that a delayed service is not further delayed on its route onto and along whatever segment of the Orbital it uses. This is the reason for requiring reasonably high path availability. This path availability is enabled by a capacity criteria of 15 - 20 trains per hour, irrespective of whether or not such service frequency might be seen as otherwise likely. We are designing the Orbital as a wide-diameter pipe to facilitate its use both when services are running as planned and when they are not. It is intended to be your flexible friend.
There is another factor to take into account. We do not know how long it will take an express train providing a circular service on the Orbital to run around the Orbital and return to its start point. Guildford to Guildford around the Orbital cannot yet be determined. Our description of scheduling assumes that the journey time will be an exact number of hours. This is unlikely to be the case. Once the journey time around the Orbital is known, it is likely that the 1-hour time slot on which all work has been predicated will need to be adjusted. For example, the 1-hour time slot may be replaced by a 40 minute time slot if the journey time around the Orbital can be expressed conveniently as a multiple of 40 minutes. In such a case, the assumption of a local stopping service once per hour, leaving in excess of 30 minutes per hour for express services, might be adjusted to be a local stopping service every 40 minutes, leaving only of the order of 10 minutes, in place of 30 minutes, for express services.
Thus, the time taken to complete a journey around the Orbital will determine both the frequency of stopping services - no less than one per hour - and line capacity.
Our article Hertford to Stansted Airport and Barking (with plan) includes a plan that may be useful as a reference regarding this section.
We have assumed that stopping services are limited to 20 minutes per hour.
Train services from Hertford East to Cheshunt run every 30 minutes. The journey time is 19 minutes. From here, services run via Tottenham Hale (not Seven Sisters) to Liverpool Street.
Train services from Enfield Town to Seven Sisters run every 30 minutes. The journey time is 14 minutes.
Train services from Cheshunt to Seven Sisters run every 30 minutes. The journey time is 20 minutes.
Train services on the Hertford loop i.e. between Hertford North and Gordon Hill run every 20 minutes. Of these, 1 service is from Peterborough and 2 from Letchworth.
If services were all to run once every 30 minutes, then we might schedule express services by modifying the rule of 20 minutes per hour to be 20 minutes per 30 minutes. Express services thereby obtain slightly more than 10 minutes per 30 minutes. We therefore assume here that Guildford to Guildford journey time around the Orbital can be expressed as an exact number of hours.
How reasonable is 10 minutes in every 30 minutes, as availability for express services? For comparison purposes, let us consider the existing line via Tottenham Hale. The service from Hertford East joins this line and takes 34 minutes from Broxbourne to Liverpool Street, running every 30 minutes. A second stopping service is on the line 4 minutes prior to the previous stopping service reaching its destination. In Orbital scheduling terminology, the time available for express services is -4 (minus 4) minutes in every 30. By comparison, if we are able to obtain 10 minutes in every 30 for Orbital services, this is 14 minutes more in every 30 minutes than on the existing line via Tottenham Hale. If a line is designed to permit one train every 3 minutes, then we should comfortably have the capability to run 4 express services after a stopping service : 3 * 4 = 12 : depending on line topology, it is less than likely that an express service would be held up by a stopping service 2 minutes from its destination. Hence we obtain 8 express services per hour, possibly more depending on line topology, certainly more if we include those that may be slightly delayed by a preceding stopping service.
Services would be subject to new synchronisation rules. We will consider Orbital services clockwise from Watford Junction. A service using the Enfield Tunnel requires southbound services on the Hertford loop to be synchronised with services from Enfield Town to Seven Sisters.
Synchronisation of the local stopping service from Cheshunt via Seven Sisters with the service from Enfield Town to Seven Sisters was mentioned earlier. The journey time from Enfield Town to Seven Sisters is 14 minutes. If the service from Cheshunt via Seven Sisters runs 5 minutes earlier or later, then the total time taken for stopping services on this route is 14 + 5 = 19 minutes. These services are synchronised by running one after the other. In all other references, the term synchronisation refers to synchronisation with the Orbital scheduling metronomes.
A service using the link from Hertford North to Hertford East then via Cheshunt to Seven Sisters requires the following. Synchronisation between northbound services on the Hertford loop, the service from Hertford East to Cheshunt, and the service from Cheshunt to Seven Sisters.
It is not possible for some Orbital services to run via Seven Sisters and some via Tottenham Hale at all frequently. The reason is that the service from Hertford East to Liverpool Street via Tottenham Hale takes 35 minutes from Hertford East to Tottenham Hale, which is too long. If this service were re-routed to run via Seven Sisters, journey time from Hertford East to Seven Sisters would also be approximately 35 minutes. Therefore, Orbital services need to run via Seven Sisters or Tottenham Hale, not both. We also note that capacity on the line through Tottenham Hale is limited by other existing services.
We would not wish to run Orbital services both via the Enfield Tunnel and via Hertford East without careful consideration since this requires additional synchronisation. The service from Enfield Town would require synchronisation both with the service via Gordon Hill and with the service via Hertford East, which might not be possible. If the Enfield Tunnel is built, any route via Hertford East is then probably for access to Stansted Airport and East Anglia (as also any possible Eastern Promise - as introduced in our article Hertford to Stansted Airport and Barking (with plan) ).
We also seem to have strengthened the case for a means of running services via Seven Sisters to Stratford Low Level, as discussed in our article Hertford to Stansted Airport and Barking (with plan) .
Stations on the Hertford loop of interest here are, in a northbound direction, Gordon Hill, Crews Hill, Cuffley, Bayford (not to be confused with Bayeux which is in France), Hertford North.
If the Enfield Tunnel were to commence immediately to the north of Gordon Hill, Gordon Hill would be bypassed as regards Orbital services.
It is proposed that the link from Hertford North to Hertford East does not run via the existing platforms at Hertford North. This would seem to be compatible with our article Hertford North to Hertford East (construction) .
Effectively therefore, stations on the Hertford loop of interest here are Crews Hill, Cuffley and Bayford. We read somewhere that Bayford is the least-used station in Hertfordshire.
It might be possible to reduce stopping services on the Hertford loop to every 30 minutes by reducing the service from Letchworth to one per hour, or by maintaining 2 services per hour from Letchworth and no longer runnning a service from Peterborough. However, quite apart from the inconvenience for users, this does not come for free : we are introducing wider constraints on the rail network by synchronising services via the Hertford loop as part of Orbital scheduling rules.
Further details depend on where the Orbital connects onto the Hertford loop, also in which categories Crews Hill, Cuffley and Bayford are placed.
As stated earlier, scheduling rules are designed as tools to assist with maximising return on investment. Well done for reading this far.