Bi-mode Lines

[andy33gmail]

You hear of trains that are bi or even tri-mode.

Are there any lines that have both types of electrification - i.e. overhead high voltage AC and third rail low voltage?

 

[pokemonsuper9]

At changeover points, such as City Thameslink - Farringdon, absolutely.
I don't think there are any long lengths where both are present on the same track.

 

[matt]

You hear of trains that are bi or even tri-mode.

Are there any lines that have both types of electrification - i.e. overhead high voltage AC and third rail low voltage?

Yes, some the lines at Euston have both

 

[pokemonsuper9]

Yes, some the lines at Euston have both

Ah yes that's a perfect example.

 

[rmHawk765]

How long did the NLL 3rd rail last during/after the upgrade to OHLE? Might be a candidate if it was kept for a bit afterwards.

 

[TransportHub]

Depending on how you define dual electrics, Kilburn High Road to Harrow & Wealdstone is electrified with both third rail and four rail systems

 

[swt_passenger]

You hear of trains that are bi or even tri-mode.

Are there any lines that have both types of electrification - i.e. overhead high voltage AC and third rail low voltage?

Normally trains that can pickup from overhead and third rail are described as dual-voltage, bi-mode usually implies electric or diesel.

But regarding the track itself though, as has been said long lengths of both are not at all common, because a lot of ancillary stuff such as track circuits, and their associated impedance bonds, are not usually compatible with both systems, even dealing with traction return current and earthing is not the same On AC and DC systems.

 

[rmHawk765]

How long did the NLL 3rd rail last during/after the upgrade to OHLE? Might be a candidate if it was kept for a bit afterwards.

NLL third rail to OHLE electrification

How come the North and West London Line's are OHLE from South Acton and Shepherd's Bush onwards despite the NLL being third rail throughout prior to becoming part of the Overground?

www.railforums.co.uk

Appears that this may have been the case (link points to specific post) but I will research further.

 

[LocoGuy]

I think there is a part of the Tyne and Wear metro? Possibly around St Peter’s/Stadium of light?

 

[MikePJ]

The (now-disused) HS1 spur to Fawkham Junction, which was used to allow Eurostars to change between third rail and 25kV overhead has about 1km with both systems in place. https://kentrail.uk/fawkham_junction_3.htm

== Doublepost prevention - post automatically merged: 9 May 2026 ==

There's also a similar section at Dollands Moor, which was used by Eurostar in the days before HS1.

 

[Bald Rick]

How long did the NLL 3rd rail last during/after the upgrade to OHLE? Might be a candidate if it was kept for a bit afterwards.

Depends which upgrade you mean. But the most recent one in 2010/11 saw the removal of the third rail between Camden and Stratford, coincident with OLE being installed on the passenger lines between Dalston and Camden.

 

[Zomboid]

I think there is a part of the Tyne and Wear metro? Possibly around St Peter’s/Stadium of light?

That's only DC overheads. No mixed electrification in the area (though I believe historically there's been a few different systems used on Tyneside).

 

[Snow1964]

There is a bit through Ashford station where the extra (International) platform is alongside the former loop. Allows high speed trains to switch systems in the station.

At Reading station the Waterloo line platforms are third rail alongside overhead equipped tracks, but I don't think there is any overlap, even on the transfer spur that passes under the fast tracks, and third rail only trains cannot reach platforms served by the spur.

 

[zwk500]

You hear of trains that are bi or even tri-mode.

Are there any lines that have both types of electrification - i.e. overhead high voltage AC and third rail low voltage?

On a technical point of pedanticness, different electrification standards are not (usually) referred to as being different 'modes'.

E.g. class 319s, 377s, 373s, 395s, 700s were or are not known as Bi-modes but are dual-voltage EMUs.

A bi-mode line, if following this distinction, would be either the Valleys lines with their discontinuous electrification requiring battery or diesel mode, or something like the GW line to Bristol where the OLE just gives up in a place where services could not reasonably terminate.

 

[sharpley]

Does Old Dalby count? Has several miles of OHLE and 4th rail track together.

 

[Beebman]

At Reading station the Waterloo line platforms are third rail alongside overhead equipped tracks, but I don't think there is any overlap, even on the transfer spur that passes under the fast tracks, and third rail only trains cannot reach platforms served by the spur.

That's correct, however the concrete sleepers in Platforms 13-15 have holes ready to accept 3rd rail 'pots' but I can't see them ever being used.

There's still a small section of the NLL which is dual electrified, it's between Camden Road Jct and the old Primrose Hill Station. There's also changeover sections on the line up from Willesden Jct Low Level to Kensal Green Jct, at Acton Central and around North Pole Jct on the WLL. There also used to be a dual electrified section on the Down Main (P.6) at Watford Junction to allow dual-voltage trains on the DC lines to access the WCML if required but I don't know if it's still there.

 

[AlterEgo]

Watford Jn platform 6 is 110mph I believe and has third rail and overhead electrification on the south end. Think it's the highest speed third rail track in the country.

 

[pokemonsuper9]

Watford Jn platform 6 is 110mph I believe and has third rail and overhead electrification on the south end. Think it's the highest speed third rail track in the country.

Yep, 110mph (or 50mph wrong way), looks like the 3rd rail only stretches 50m into the 285m long platform - I can't imagine it has seen much use.

 

[QueensCurve]

Yes, some the lines at Euston have both

Platforms 9 and 10 I believe.

Also, are parts of the North London Line dual electrified?

 

[Class15]

Platforms 9 and 10 I believe.

Also, are parts of the North London Line dual electrified?

Just the power changeover sections.

== Doublepost prevention - post automatically merged: 10 May 2026 ==

There's still a small section of the NLL which is dual electrified, it's between Camden Road Jct and the old Primrose Hill Station.

That’s not really correct, the dual section is quite short and certainly does not go up to Camden Road Junction.

 

[Supercoss]

A small dual voltage section on the “ new lines” between Willesden Suburban Junction /Low Level / and Kensal Green Junction
One passenger train uses the route early morning
2N99 05:51 Willesden jcn low level to Stratford departing on DC then changing onto AC

 

[Bald Rick]

Does Old Dalby count? Has several miles of OHLE and 4th rail track together.

Indeed. 4th rail + OLE is much easier to accommodate than 3rd rail +OLE.

 

[andy33gmail]

Just the power changeover sections.

Is that so a dual-voltage train can pull in, raise/drop its pantograph, then move off?

 

[Class15]

Is that so a dual-voltage train can pull in, raise/drop its pantograph, then move off?

Yes, but the North Pole (West London line) one is on-the-move.

 

[Tester]

Yes, but the North Pole (West London line) one is on-the-move.

On the move for Overground trains, but not for Southern trains, unless anything has changed.

 

[Class15]

On the move for Overground trains, but not for Southern trains, unless anything has changed.

Correct. Sorry about that!

 

[Belperpete]

But regarding the track itself though, as has been said long lengths of both are not at all common, because a lot of ancillary stuff such as track circuits, and their associated impedance bonds, are not usually compatible with both systems, even dealing with traction return current and earthing is not the same On AC and DC systems.

It is usual to immunise tracks that are close to an electrified line, even if there isn't a direct connection, as traction return currents have a propensity to get to all sorts of places through earth paths. I would be very surprised if the signalling equipment on all lines between Euston and Watford wasn't dual immune.

 

[Bald Rick]

It is usual to immunise tracks that are close to an electrified line, even if there isn't a direct connection, as traction return currents have a propensity to get to all sorts of places through earth paths. I would be very surprised if the signalling equipment on all lines between Euston and Watford wasn't dual immune.

On the WCML proper, they are mostly Ac immune. The ammount of DC return around is small, not least becasue fo the 4th rail south of Harrow.

 

[J-2739]

Indeed. 4th rail + OLE is much easier to accommodate than 3rd rail +OLE.

Wait, why?

 

[stuu]

Wait, why?

Because the DC return current uses the fourth rail, rather than the running rails in the case of third rail electrification