Yes - in fact changing at Watford Junction is shown for around a third of the suggested itineraries (without entering any via points). However only the London Northwestern Railway service that avoids Watford High Street is suggested. As it happens, that train connects well at WFJ with a quick WFJ-EUS service in the BSH-EUS direction.
Yes, although here I think it would be advisable to buy your ticket in conjunction with an itinerary showing the validity of the route via Watford Junction. Websites such as the
old MixingDeck TPE interface offer such a capability.
You can take whichever route you like when travelling on PAYG, subject to the provisos that you must:
- Tap in and out
- Remain within the Oyster PAYG area
- Tap any pink reader you pass when changing trains
- Have sufficient credit for the cost of your journey (or alternatively have Auto Top-up enabled)
- Remain within the maximum journey time, as appropriate the number of zones travelled through, and the time of day and day of the week
If you comply with all the conditions outlined above for Oyster PAYG, then you can similarly travel via any route you like. If you don't comply with all of the conditions for PAYG then you can only travel within the zones/stations of your season ticket.
According to RailMiles, the distance between Bushey and Watford Junction is 1mi 35ch or 1mi 54ch on the Overground, if this is relevant.
This is potentially relevant, inasmuch as you can travel by any route no more than 3 miles longer than the shortest route. On that basis travelling via Watford High Street wouldn't be permitted.
However that relies on the Routeing Guide in Detail, which suggests that mileages should be calculated by reference to the National Rail Timetable. That timetable isn't currently being published but it has the issue if rounding mileages to the nearest quarter mile, and of sometimes being inaccurate in terms of distances.
So it's possible that it would say the mileage via Watford Junction is more than 3 miles longer than the shortest route, even though in reality it isn't.
Far easier to simply rely on an itinerary given by a booking engine when buying your ticket - or to use Oyster in PAYG mode.
To save £652.
There are services from Bushey to Euston I'd use normally, but sometimes it's quicker via Watford Junction.
If travelling from Bushey I would have no hesitation in travelling via Watford Junction in accordance with an itinerary (or on Oyster/contactless PAYG).
If you intend to travel from Watford Junction, I would carefully consider whether the difficulties you are likely to regularly encounter at the barriers are worth the saving...