Thank you, Mike, for the helpful pointers! I believe both route uses the same number of trains — the route via West Hampstead involves a Jubilee and a Metropolitan line train, though you raised a very good point on train mileage.

I have done further research and put together a case that I’ve posted on the TfL help & contact page. I’ve included the text below if anyone else is interested — hopefully, that’s most of the hard work done from TfL’s perspective!

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“I am writing to request adding an alternative route to the “Avoiding Zone 1” fare based on a recent journey of mine. The particular journey in question is between New Malden and Harrow-on-the-hill. However, this should apply to journeys starting/ending in every SWR station south of Wimbledon and ending/starting in every Metropolitan line station north of Harrow-on-the-Hill (both inclusive).

The current alternative route allows “Avoiding Zone 1 via Clapham Junction, Willesden Junction and West Hampstead (or Brondesbury/Kilburn).” This request concerns adding Kenton/Northwick Park as a valid alternative routing point alongside West Hampstead and Brondesbury/Kilburn. In other words, I would like to see the route New Malden – Clapham Junction – Willesden Junction – Kenton/Northwick Park – Harrow-on-the-Hill to qualify for the alternative fare (Adult peak £4.40 / off-peak £3.30) rather than the default fare (Adult peak £8.00 / off-peak £5.70).

I believe adding this alternative route has multiple benefits to TfL and Londoners:

1. It follows the spirit of zonal pricing.

Both routes via Kenton/Northwork Park and via West Hampstead avoid Zone 1 entirely, and thus making both routes qualify for a Zone 2-5 mixed-TfL/NR fare will ensure the pricing is consistent (and thus reduce customer confusion and subsequent customer service contacts).

2. It frees up capacity by reducing unnecessary train mileage.

The route via Kenton/Northwick Park passes through 15 stations, as opposed to 20 via West Hampstead. It also incurs a train mileage of ~28.7km, 6km less than that via West Hampstead. In addition, the TfL Journey Planner often suggests doubling back at Finchley Road to take advantage of the Metropolitan line not calling at any stations until Wembley Park. This adds even more train mileage.

By enabling customers to change at Kenton/Northwick Park (already a valid OSI), TfL can cut out the 17%+ mileage that is unnecessary to start with. This has the benefit of increasing capacity and reducing one’s environmental impact on travel.

3. It is no slower than existing “Avoid Zone 1” routes and is often the quickest alternative route that avoids Zone 1.

Both routes via Kenton/Northwick Park and West Hampstead generally take a similar time. The TfL Journey Planner gives a range of 1h20m-1h36m for the former and a range of 1h21m-1h32m across a weekday (see attached spreadsheet). Indeed, once a customer reaches Willesden Junction (where the routes diverge), the Journey Planner estimates it takes 36-37m to go via Kenton/Northwick Park (including initial transfer time) and 36-40m to go via West Hampstead (removing initial transfer time as they should already be on the train).

In addition, the route via Kenton/Northwick Park is often the fastest throughout the day. Of the 74 journeys suggested by the TfL Journey Planner that go via Clapham Junction and Willesden Junction on 20 Nov (Monday), 33 have the fastest routing via Kenton/Northwick Park (as opposed to 18 via West Hampstead LO/LU; see attached spreadsheet). The results are the same for other weekdays. I do note the Journey Planner suggests the fastest route via West Hampstead LU/LO for most journeys in the other direction.

4. It avoids penalising those who know the Kenton/Northwick Park OSI exists and those encouraged to walk between these two stations.

Kenton/Northwick Park has been a valid OSI for years, and its existence is being increasingly advertised on maps and signages under the TfL Walking Action Plan post-pandemic. By also including this OSI under the said journey (and hence not overcharging those who decided to walk), TfL can avoid being seen as putting up artificial barriers against, or worse, being hypocritical on their major initiatives.

5. It lowers safety risks due to perverse incentive-induced crowding.

Leaving the fare as is creates a perverse incentive: The default fare between New Malden and Kenton is the “Avoid Zone 1” fare (Adult peak £3.60 / off-peak £3.00), whereas that between Northwick Park and Harrow-on-the-Hill is the standard Zones 4-5 fare (Adult peak £2.10 / off-peak £1.90). This means there is a substantial incentive to intentionally break their OSI at Kenton, as the sum of the two segment’s fares is less than the default fare for New Malden – Harrow-on-the-Hill.

Given there are only three gates at Kenton, incentivising people to do a hokey-cokey around the gateline (a common way to break the OSI) to save money may create some crowding & safety issues. The current pricing may also incentivise people to get on a bus (Adult fare £1.75) along the very busy Kenton Road corridor, leading to the same issues. Adding Kenton/Northwick Park as an alternative routing point addresses these issues, which has a far higher cost than any “lost revenue”.

I understand that adding an alternative route is a lengthy process, which, in this case, may involve getting an agreement with other Train Operating Companies. I will be very grateful if you can update me with any progress. I am, of course, more than happy to provide any additional information required to reach a decision.”