For some time now the question of whether or not HS2 should serve Heathrow and if so how has been somewhat of a thorn in the side of the debate on the exact details of the project.
On the one hand, serving Heathrow brings with it the potential to transfer considerable volumes of currently domestic air travel to rail. This would involve mainly people connecting to and from intercontinental flights. On the other hand, running via Heathrow would add to the journey time to and from London with a consequent negative effect on the attraction of HS2 services for purely domestic journey options.
Solutions that have been floated over the past few years have involved huge nearby interchanges with connections, diverting the line a few miles and permutations of both that include triangular junctions to allow some trains to literally bypass the question altogether. There are also suggestions that involve connections with HS1 to the airport.
None of this so far seems very elegant and each of the proposed solutions seems to bring with it a new set of problems. So let us stop and think about a number of factors for a moment:
To stand any chance of picking up connecting intercontinental passengers, HS2 must serve Heathrow directly the time taken for a connecting transfer to be made would mean that for these passengers a domestic flight connection would still be an attractive proposition.
To maximise the attraction of HS2 for purely domestic travel ( that is travel which starts or finishes in or goes via London itself ) services need to take the shortest route in or out of London with the fewest stops.
A connection with HS1 is essential in order to maximise network benefits a quick connection between services on the two lines as well as the ability to run at least some through services is very important.
There was already a suggestion, before it was shelved, that the proposed direct link between HS1 and HS2 should be twin track instead of the originally planned single track link; this is good and it deals with the third point, as does the proposal for a single large interchange at Euston and Kings Cross / St Pancras. The question of the airport does, however, remain largely please excuse the pun in the air.
Looking at this logically, the suggestions of a large triangular junction do seem to be the most sensible as this would allow services to and from London and through direct services between HS2 and HS1 to make their way without being delayed by going via Heathrow or a nearby interchange by using the north side of the triangle which would be similar to the complex south of Lille in France.
Through services between Heathrow and HS1 would use the eastern side of the triangle. Such services would most logically consist mainly of an expansion with additional services of the current Southeastern High Speed domestic services to the airport. In addition some international services could potentially be run as connections between Heathrow and the near continent.
The west side of the triangle would allow for HS2 services starting and terminating at Heathrow itself; this would effectively turn Heathrow into a second southern terminus for HS2 and would allow the airport services to be operated distinctly from the central London services and provides the vital direct link at the heart of the airport that is needed to make the airport option viable.
With an HS2 station directly under Heathrow the potential would then exist to do something very exciting as an add on project an extension of HS2 to Gatwick. The distance between the two airports is not huge 43 miles by road and 24 miles as the crow flies. A high speed rail link could therefore be expected to be approximately 30 miles, similar to the distance between Ebbsfleet and Ashford which implies that if this section was engineered for 140mph then a 15 minute transit time between the two would be a reasonable expectation.
This relatively short distance means that there is little point in engineering for higher speeds as it is reasonable to expect that all services would call at both airports. As a result, the line need not be quite as arrow straight as HS2 which means it would be easier to find a route for it through what is an area with a relatively dense population an approximate route running along the course of the M25 to roughly half way between junctions 9 and 10 then passing in a long tunnel ( on the face of it this would be yet another NIMBY tunnel but it does also allow the most direct route to be taken so in this case it would be required anyway! ) from north of Effingham Common and running underneath Mickleham and Box Hill; this would emerge roughly half way between Dorking and Reigate leaving the line a fairly straight run direct to Gatwick through a largely open area.
The tricky bit, really, is going to be the section between the northern portal of this Box Hill tunnel and Heathrow as this is the area of extremely dense population and there are also numerous important parks and heritage sites that need to be avoided. For this sector, the line would probably need to literally hug the M25!
To extend the line like this would effectively turn Heathrow and Gatwick into a single airport over two sites. You would not be running all the HS2 services through the Gatwick rather you would have a high frequency shuttle service using an additional build of class 395s between the airports running every 10 minutes or so with perhaps two HS2 through services every hour running below Heathrow to Gatwick. Most of the HS2 services would not run below Heathrow.
This carries other benefits as well if half of these Heathrow Gatwick class 395 shuttles were then extended to central London ( the Euston / St Pancras interchange ) using the eastern side of the previously described triangle, you would have a 20 minute interval service between London and Gatwick via Heathrow taking roughly 35 minutes end to end; this could allow the present Gatwick Express to be removed from the northern part of the Brighton Line which would considerably ease the pathing on that route and allow a re-cast of that lines services without losing any direct services to or through Gatwick from anywhere else.
The suggested HS2 Gatwick station would be separate from the present railway infrastructure, but it may be worth considering a link to the present tracks south of the airport in order to allow some of these class 395 workings to run through, at conventional speeds, below Gatwick to Brighton in order to allow easier connections to Heathrow and HS2 from the south coast. There is little point in building a high speed alignment below Gatwick the distances are not great so the speed would be far less beneficial than the connections gained. There would also be serious cost implications plus we are again in an area of quite dense population meaning routing such a line would be very difficult.
So, we should perhaps not be asking whether or not HS2 should serve Heathrow directly but instead whether or not we can use HS2 to create a true interface between domestic rail and intercontinental air travel without the need for additional runways or short stubs of high speed line or diverting high speed services out of London itself. This article suggests we can and at the same time ease pressure on the Brighton line and improve connectivity for a large chunk of the south coast.
In a sense, then, the answer is that HS2 should not run to Heathrow. It should run to Gatwick via Heathrow,
