Why were most multiple units 4 cars or less ?

[dch82]

Was it because of platform length or because it was more economical to run short trains?

 

[30907]

Flexibility of operation would be another factor. For example, being able to divide a train en route to serve different destinations, or to strengthen peak formations vs offpeak (both have been in and out of favour over the decades).
Remember that short local trains were the norm outside urban areas, and these were early candidates for diesel units at least.

 

[edwin_m]

Probably a slightly different answer for busy commuter routes and more rural ones.

For the commuter routes passenger numbers were very "peaky" so they needed to run maximum length trains at those times. Platform length might have limited that maximum length but it wouldn't explain why they ran several shorter units coupled together instead of one long one. That's probably because originally they tended to uncouple the units to run shorter trains at less busy times of day. As the network itself has got busier, it has become more and more difficult to do that and find somewhere to park the surplus units and paths to get them there and back. So nowadays most commuter routes run at maximum length all day and units have tended to get longer accordingly.

For more rural routes, units initially replaced the shorter loco-hauled trains on branch and stopping services, so it was natural to specify a unit of similar length. Here too unit lengths have increased, but not so much, as the quieter routes were closed and the remaining ones got busier. When the longer intercity trains started to be replaced by units, this naturally led to longer units too. Where intercity services use coupled units these days, many of them would have just attached and detached coaches on route when they were loco-hauled.

 

[Bevan Price]

DfT.
1. For example, Trans Pennine wanted some trains longer than 3 coach 185s, and more than were actually built. DfT cut back the proposed number ordered and blocked anything longer than 3 coaches. The depots such as Ardwick were then built to service 3 coach 185s, making it impractical for any future attempts to extend the number of coaches per unit.

2. When the 2nd generation dmus (Sprinters, Pacers) were built, it is understood that spending was authorised often on the basis of 2 new coaches to replace 3 old coaches. Sometimes the effect was even worse - Loco + 5 or 6 coach formation on Trans Pennine routes were replaced by 2 or 3 coach 158s...totally.insuffient to cater for passenger number growth created by more frequent services.

 

[Taunton]

A train out of service for a straightforward defect, say one broken window which is out of stock, means, if it is a 2-car unit, you are 2 cars down. If it is a Thaneslink unit you are 12 cars down. Likewise if you want to reinforce a unit for extra demand, if 2-cars you can add another 2-car. For anything more than about 6 cars, you can't - you would need to run another train. So it doesn't happen.

 

[yorksrob]

Don't forget, the original Brighton main line stock (PAN/PUL) were six carriage units, as were the Hastings thumpers from the 1950's. These didn't have inter-unit gangways, so there would have been a reduced need for onboard staff

 

[Bletchleyite]

Was it because of platform length or because it was more economical to run short trains?

4 car (in 20m coach land) is a pretty sweet spot for London commuter EMUs. It's long enough to be a useful length on its own at quiet times, and gives three options for length on most routes, 8 for average loadings and 12 for particularly busy trains.

In 23/24m coach land, that's 3 car. Which is also convenient for EMUs in that you can have traction motors under the end coaches and the transformer under the middle one.

 

[Sun Chariot]

Was it because of platform length or because it was more economical to run short trains?

If you mean the DMUs and EMUs introduced in the 1950s & early 1960s, then it was against a backdrop of replacing the steam hauled services like-for-like on secondary or on minor lines; or attempts to revive passenger usage of such lines.

Secondary and - in particular - minor / more remote services, trains were often infrequent, with pre-Nationalisation stock in varying conditions of "unkemptness". Trains were - based on photos and literature I've seen, over the decades - typically 1 coach to 4 coaches.

30907 mentioned in post #2, operational flexibility was also a factor; and the ability to hook up two / three small units, was more favourable than having one longer fixed rake unit.

There were exceptions, but longer consists were more likely diesel loco hauled rakes.

 

[Bletchleyite]

"Sprinterisation" was about replacing long, infrequent loco hauled regional trains with short (generally 2-car but some doubling up) more frequent ones operated with second generation DMUs. Like with Voyagers where the same thing was done, this was a victim of its own success except on very rural lines, and so overcrowding ensued.

 

[Sun Chariot]

"Sprinterisation" was about replacing long, infrequent loco hauled regional trains with short (generally 2-car but some doubling up) more frequent ones operated with second generation DMUs.

We shall not use profanity!

In the mid 1980s, when awaiting intended photos of a train service, my brother and I used a call-sign to denote "stand down, not worth a photo" - we'd shout:
"Oh it's a bl..dy Sprinter" or "It's a bl..dy Pacer"

 

[D Williams]

You also need to bear in mind that on rural routes the number of passengers could easily be accommodated in one coach. There was also the knowledge that most of these lines were to close even before Beeching got going.

 

[Rescars]

Don't forget, the original Brighton main line stock (PAN/PUL) were six carriage units, as were the Hastings thumpers from the 1950's. These didn't have inter-unit gangways, so there would have been a reduced need for onboard staff

A rather different proposition from most were the Pullman multiple units. The Brighton Belle units had 5 cars and the Blue Pullmans 6 or 8. No inter-unit gangway on any of these either, nor any expectation of trains being formed of more than one unit for that matter.

 

[yorksrob]

"Sprinterisation" was about replacing long, infrequent loco hauled regional trains with short (generally 2-car but some doubling up) more frequent ones operated with second generation DMUs. Like with Voyagers where the same thing was done, this was a victim of its own success except on very rural lines, and so overcrowding ensued.

I often think that the Regional railway for the most part, didn't "get" the full benefit of the multiple unit railway as the Southern region did - i.e. the ability to lengthen and shorten trains as required. Too often the two carriage standard became a mill stone.

 

[norbitonflyer]

A rather different proposition from most were the Pullman multiple units. The Brighton Belle units had 5 cars and the Blue Pullmans 6 or 8. No inter-unit gangway on any of these either, nor any expectation of trains being formed of more than one unit for that matter.

The Belle did run as two units on some services, but the staff to passenger ratio was quite high anyway on those trains!

The six-car Blue Pullmans were also later disfigured with jumper cables so they could run as a 12-car train

 

[The exile]

I often think that the Regional railway for the most part, didn't "get" the full benefit of the multiple unit railway as the Southern region did - i.e. the ability to lengthen and shorten trains as required. Too often the two carriage standard became a mill stone.

In general it wasn’t resourced enough to do so.

 

[yorksrob]

In general it wasn’t resourced enough to do so.

Indeed.

 

[Strathclyder]

When it comes to the Strathclyde/former SPT network, the part of the network I'm most familar with, flexibilty, operational requirements, platform/carriage lengths and passenger demand varying dramatically throughout the day all factor into why it's been predominantly a 2/3-car MU fleet - the 380s & 385s are the only permanent exceptions as far as EMUs go - since the introduction of the 303s, which directly replaced steam haulage on the North Clyde routes; DMUs (mostly 101s I think) had been running on the Cathcart Circle for a few years prior to electrification.

As far as EMUs are concerned, a mix of 3 & 6 car trains are the norm throughout the day on most of the network and has been for as long as I can personally remember, though single 3 car units can get pretty cosy during the peaks (speaking from extensive experience of a single 318 or 320 turning up on a evening peak Airdrie - Balloch service). Whether or not this norm will change when the 318s/320s come up for replacement remains to be seen.

There are/were exceptions to the 3/6-car rule, like 9-car trains on the Cathcart Circle on match days at Hampden (made up of three 303s/311s) and the 305s/322s (the former never worked a regularly scheduled passenger train in Strathclyde as far as I know, the latter had a token presence on Glasgow - Carstairs - Edinburgh - North Berwick services plus a one-off appearence on the Ayrshire Coast Line in 2010). There's also the 7-car trains that run on the Ayrshire Coast (mainly to Ayr, 7 coaches are about as much as can fit into Ayr's bay platforms both from a physical and signalling standpoint).

 

[Dr_Paul]

Suburban services to Waterloo services in the 1960s and 1970s were nearly always 4 SUBs, in pairs during the rush hours, and singles off-peak. There would be quite a bit of coupling and uncoupling at Waterloo at transition times. It's very rare to see a single 455 running into Waterloo these days, and I have a feeling that the Waterloo suburban services were pretty much eight-car rakes (two 4 SUBs and later on two 4 EPBs) all day by the time the 455s were introduced.

When I started commuting to Waterloo in 1972, there would be various combinations on longer-distance services, mostly eight or 12-car rakes, at first kept fairly segregated, so there would be a 4 CIG, 4 BIG, 4 CIG formation, two or three 4 CIGs, two or three 4 VEPs, a pair of 4 TCs and a 4 REP. I think, although I'm not sure, there would be an occasional 4 VEP with a 2 HAP. Later, there would be all sorts of combinations, 4 CIGs coupled to 4 VEPs, etc, etc, with only the Bournemouth 4 TC, 4 TC, 4 REP formation being constant. Later on a few 4 CEPs appeared, but I can't recall if they were coupled to anything else. Then came the five-car 442 sets, usually running in pairs.

 

[Peter Mugridge]

I have a feeling that the Waterloo suburban services were pretty much eight-car rakes (two 4 SUBs and later on two 4 EPBs) all day by the time the 455s were introduced.

I'm not sure they were; a lot of my early photos of 455s show them as single units - except in the peaks - even as late as the early 1990s, so ten years after introduction, and I have a number of pictures of single EPBs / SUBs from the time immediately prior to the 455s appearing.

 

[Shaw S Hunter]

"Sprinterisation" was about replacing long, infrequent loco hauled regional trains with short (generally 2-car but some doubling up) more frequent ones operated with second generation DMUs. Like with Voyagers where the same thing was done, this was a victim of its own success except on very rural lines, and so overcrowding ensued.

What you're describing is the effect; the policy on replacement of first generation dmus was Treasury driven and basically said 3 old cars should be replaced by 2 new ones. This was justified on the grounds that BR as a whole lost money and Other Provincial Services, which relied very much on dmus, lost more than any other part of the railway. Since dmus longer than 3-cars were nearly all on metro suburban routes it was inevitable that the new regional fleet would be dominated by 2-car units.

It was extremely unfortunate that this thinking prevailed at the point at which BR had just about stopped the decline in passenger numbers meaning it was ready to start expanding timetables on key inter-urban routes. Given the higher profile of these services it was no surprise that the new Sprinters were put on them regardless of whether they were really suitable. No wonder that overcrowding soon became commonplace, the overall passenger fleet simply wasn't big enough.

 

[contrex]

Suburban services to Waterloo services in the 1960s and 1970s were nearly always 4 SUBs, in pairs during the rush hours, and singles off-peak. There would be quite a bit of coupling and uncoupling at Waterloo at transition times.

My main experience with SUBs was (in the 1960s) on the Central Division, and if they started the day as 8-car formations, they tended to stay together all day. I believe this was due to the inter-unit traction current jumpers, which could only be dis- or re-connected by depot staff. EPBs (after the first few, and these were soon removed) lacked power jumpers.

 

[yorksrob]

It was extremely unfortunate that this thinking prevailed at the point at which BR had just about stopped the decline in passenger numbers meaning it was ready to start expanding timetables on key inter-urban routes. Given the higher profile of these services it was no surprise that the new Sprinters were put on them regardless of whether they were really suitable. No wonder that overcrowding soon became commonplace, the overall passenger fleet simply wasn't big enough.

That was the policy at the time, but it was also about 30-40 years ago.

It wouldn't have been such an issue if more had been done in the subsequent 30 years or so to match capacity with increasing patronage.

 

[Western 52]

I think another factor when considering longer DMU formations is the cost balance between longer units and the equivalent loco hauled train. It's been said somewhere that this is about 6 coaches, so longer trains may be cheaper per coach as a loco hauled than as a DMU.

 

[Rescars]

A further consideration regarding multiple units on the Southern was the reduced amount of passenger accommodation available in the demus because the power plant took up almost half a car's length. This meant that each 3-car unit had only 2.5 cars length of usable space.

 

[Big Jumby 74]

Was it because of platform length or because it was more economical to run short trains?

Suburban services to Waterloo services in the 1960s and 1970s were nearly always 4 SUBs, in pairs during the rush hours, and singles off-peak. There would be quite a bit of coupling and uncoupling at Waterloo at transition times. It's very rare to see a single 455 running into Waterloo these days, and I have a feeling that the Waterloo suburban services were pretty much eight-car rakes (two 4 SUBs and later on two 4 EPBs) all day by the time the 455s were introduced.

As with many such scenarios, the changes made were done so on a 'need to do so' basis. If one goes back to the initial LSWR electrification on the Southern (SW) as an example in 1912/13, the electric units that formed the basis of most services were the 3 SUB units, which may well have been formed as such, as they essentially were replacing 3 carriage loco hauled suburban sets, either singly or in pairs.
It is well known that the electrification and service upgrade that followed created extra demand, and hence the 3 SUB's were augmented with an all steel trailer to become 4 car units and hence the 4 car regime that most remember well.
The main restricting factor in regard to further lengthening of suburban trains (at Waterloo) as demand has increased over the years, has been Waterloo station and its physical footprint. To understand this aspect I would strongly recommend the printed works of the 'South Western Circle' which give a very detailed account of the transformation of Waterloo station through the years.

The last train formation upgrade that took place, ie that of 2017, involved a not insignificant amount of work, platform length increases being a major part, not only at Waterloo, but at various other locations, all of which had to be achieved within the railway boundary limits. Compulsory purchase and demolition of adjoining properties to make way for viaduct widening and longer platforms (as happened in late 19th/early 20th century) is no longer an option.

As for Dr_Paul's comments about splitting/joining: you are correct this was common place off peak until the mid 1980's as I recall, but with the impending privatisation on the horizon, a number of planning themes were worked through to improve timetable resilience, one of which was to do away with off peak splits and joins (on the suburban side at Waterloo particularly, but not exclusively), which would both improve performance on a daily basis, and especially during disruption, but also free up paths between Waterloo and Clapham/Wimbledon, ergo, same result, improve overall timetable resilience by having fewer train movements in that corridor. That was the aim.

 

[norbitonflyer]

. It's very rare to see a single 455 running into Waterloo these days,

Sadly increasingly common, as they are running out of hours and their replacements are now more than five years late

== Doublepost prevention - post automatically merged: 6 Apr 2025 ==

. Later on a few 4 CEPs appeared, but I can't recall if they were coupled to anything else.

usually with a CIG or VEP. There were also a few BEPs, which usually ran with something else, whether the buffet was in use or not.

== Doublepost prevention - post automatically merged: 6 Apr 2025 ==

A further consideration regarding multiple units on the Southern was the reduced amount of passenger accommodation available in the demus because the power plant took up almost half a car's length. This meant that each 3-car unit had only 2.5 cars length of usable space.

The Hampshire units (later class 204/205) were initially built as 2-car units, giving even less space. A few remained in that condition to work the Alton-Winchester route (now the Watercress Line) as the better power/weight ration suited the steep gradients, and were only later augmented to three car using redundant driving trailers from the "Tadpoles" (originally from 2EPB units)

== Doublepost prevention - post automatically merged: 6 Apr 2025 ==

the electric units that formed the basis of most services were the 3 SUB units, which may well have been formed as such, as they essentially were replacing 3 carriage loco hauled suburban sets, either singly or in pairs.
It is well known that the electrification and service upgrade that followed created extra demand, and hence the 3 SUB's were augmented with an all steel trailer to become 4 car units and hence the 4 car regime that most remember well.

For most of the inter war period the LSWR and SR also had 2-car cabless trailer units which were marshalled between a pair of 3SUBs to make an eight car train. This involved a lot of shunting if one of the 3SUBs was to be used solo for part of the day.

During WW2 the 3SUBs were converted to 4-car - some using new Bulleid-style cars, others using cars from disbanded trailer units. And, being the Southern, there were inevitably some units cobbled together from the surviving cars of two or more accident- or war-damaged units.

 

[Big Jumby 74]

There were also a few BEPs, which usually ran with something else, whether the buffet was in use or not.

Slightly OT I appreciate, but to fill in some detail. The SW had seven BEP's on the books in those times, 7301-07 (2301-2307 as they became), five of which were used for traffic purposes on the Pompey Direct, the other two maintenance spares. As a consequence of engineering work requiring diversions via Chertsey, and therefore an additional diagram/circuit of stock required (on Bournemouth line services at the London end) on one weekend in Jan 86, I made use of one such BEP/CIG formation, otherwise spare in Clapham Yard, to fill in on the day concerned, with the thinking that all Bournemouth semi (92) trains would still have a buffet car, and my colleagues in the Buffet Car Dept. might be able to staff same. Being an additional 'body' was required in that regard, on paid overtime on the day, if they did or not cover said 'sandwich' diagram on the day I have no idea to this day?

There may well have been previous add-hoc occasion(s) when BEP's worked to Bournemouth, but to my knowledge this was the first planned move during the period concerned.
Here's the unit concerned (2306) in Bournemouth Central Middle Siding No 2 on the day concerned, having worked Down with (AFAIR) the 0845(?) from Waterloo.

 

[Peter Mugridge]

The SW had seven BEP's on the books in those times, 7301-07 (2301-2307 as they became).

Not quite; the previous numbers were:

2301 - formerly 7019
2302 - formerly 7194
2303 - formerly 7208
2304 - formerly 7175
2305 - formerly 7016
2306 - formerly 7021
2307 - formerly 7018

The numbers in the 73xx series were CIGs which later became 17xx and 18xx on refurbishment; the 230x were numbered and outshopped as such upon refurbishment. The front ends were a different style; the CIGs had the rounder front style - the 230x BEPs, formerly 70xx, had the flat front style. The later series of buffet units, BIGs, did have the rounder front style.

The first picture below shows CIG 7301 alongside a later build BIG at Victoria in 1985; the second shows 2301 at Waterloo in 1996. The difference in front end style is quite obvious.

 

[Sun Chariot]

I hadn't realised the SW had seven 4BEPs on its books.
I had always associated the 411 4CEP and the 412 buffet brethren, with rhe SE
Similarly, I always associated the 421 4CIG and 422 4BIG with Brighton, Pompey Direct and the SW Main.

 

[Big Jumby 74]

Not quite; the previous numbers were:

Quite so. Not sure what I was thinking there. Put it down to a senior moment!

I always associated the 421 4CIG and 422 4BIG with Brighton, Pompey Direct and the SW Main

The BEPs replaced the BIG's on the Pompey Fasts (81's) AFAIR, but it was a long time ago now, and can't remember the detail of why/when exactly.