It is the 21st of June, 2020. And news

agencies across the country are showing

a very concerning picture. Two trains

uncomfortably close. Now, you might

think that this was some kind of

emergency permissive working, where two

trains were allowed in a signaling block

to allow for a detrainment. I mean,

there are loads of people milling

around. But, no. Two trains on this one

track was not anyone's intention. It is,

in fact, an event that was a cigarette

paper away from a catastrophic head-on

collision. Just 23 m away, in fact. So,

what actually happened here? Well, it

would be a deadly mixture of

interoperability between two different

train companies, differing operating

practices, and National Rail trains on

tube train tracks. So, sit back, relax,

and watch our short documentary on the

Chalfont & Latimer balls-up. My name is

Jon, and welcome to Plainly Difficult.

This video wouldn't have been possible

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as always, the links will be in the

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>> National Rail trains on London

Underground metals. So, the near

catastrophic disaster that unfolded in

2020 can trace its roots all the way

back to the early days of London's

railways.

That is to say, the reason for the

non-segregation

of Underground trains and National Rail

trains along a few particular parts of

the capital city's rail network.

There are a few places where this

happens, like the Bakerloo line, which

runs partially on the Watford DC,

District Line trains and Southwestern

trains operating near Wimbledon, and

mainly for our story today, Chiltern

services on Metropolitan Line tracks.

You see, when the Metropolitan Line was

initially envisioned in the 1860s

as the world's first underground

railway, it wasn't thought of something

separate from normal regular trains.

As it extended out of London into the

Buckinghamshire countryside, during the

years of extension the line would share

trains running in and out of Marylebone.

With the route being connected to

Aylesbury

for a while, Met Line trains even ran

and terminated at Aylesbury itself.

Changing over from electric trains to

steam at Rickmansworth.

However, from Amersham in the 1960s, the

line was electrified. This marked

beginning of a separation of services

when Met Line trains operations would

end at the end of the traction current,

thus not needing a changeover from

electric to steam locomotives.

Now, I'm no historian, so pretty much

watch any Jay Foreman Hazard video on

the Met Line for a better and less all

over the place explanation of the

route's history.

But a TLDR is two types of train

services

that run on the line are electric

underground trains to Baker Street and

from the 1960s, diesel trains to

Marylebone. And from Amersham to Harrow

on the hill, both types of trains worked

through the route.

But there is a slight issue here.

British Railways and London Underground

used two different types of signaling

and operation systems.

So, what do you do?

Well, in these cases it all comes down

to who owns what. In our story, the

owner is the Underground and they get to

set the rules of the game. So, let's

have a look at how this is done

in the modern day on the Metropolitan

Line. The National Rail trains that

share the route are operated by Chiltern

Railways and the section of the Met Line

that it shares with underground trains

signaling resembles more national rail

style signaling principles rather than

underground ones.

It's kind of more like how someone would

set it up if it only been explained to

them rather than actually shown.

The signaling here is three and four

aspect unlike the two aspect and

repeater based style used on other

underground lines.

But here there is no AWS or TPWS.

Instead protection is provided with

mechanical tripcock train stop

protection like other underground lines.

GSMR however is provided but only for

Chilton trains. Now at selected

locations signals are given fog

repeaters. They can show white if the

signal it's repeating is showing a clear

aspect or a single yellow if the signal

it's repeating is at danger.

They act as an additional warning to

drivers even when there isn't fog. Now

there are loads of other differences

during this section of track between

national rail and LUL rules and

procedures.

Such as trains can pass a signal at

danger under their own authority as long

as it is an automatic signal. Plus after

passing a signal at danger they must

only proceed at a speed that they can

see to be clear and be able to stop

short of any obstruction. Underground

trains are actually physically limited

in their speed to just under 10 mph. A

train can resume line speed only after

it's proceeded past two stop signals

showing a proceed aspect.

What is important to note with the

tripcock system is it can be susceptible

to being triggered accidentally by

debris along the track.

This is because the system relies on a

mechanical arm that is mounted next to

the first set of wheels on a train.

Things like rubbish, footballs, coats,

umbrellas

and well pretty much the list is endless

of things can trip a train. But

regardless if spurious or not the driver

must stop their train and report the

trip to the signal.

To be tripped, reset and carry on

without informing the signal

is a serious incident.

Which leads us on to the

the event.

So this is Chalfont & Latimer station on

the Metropolitan line. It has three

platforms and three tracks. Platform one

is for trains heading on the northbound

line towards Amersham. Platform two is

for trains southbound heading towards

London and platform three is a bay

platform. This is used for shuttle

services to Chesham on a single line

branch.

Now trains from both platforms one,

two and three with two for shunting

movements only can go onto the single

line branch to Chesham. From platform

one, this brings in a conflicting

movement across the southbound line. So

it is the 21st of June 2020 and a driver

is taking over London bound Marylebone

Chiltern service from Aylesbury.

They are working the second half of

their shift and the train is arriving

for the handover just a couple of

minutes late.

The Chiltern service departed around

21:15 and began its journey towards the

LUL boundary just north of Amersham.

Upon arriving at Amersham, the train

driver undertook their usual station

duties and started their train from

platform three.

The starting signal Juliet Whisky two

was showing double yellows. This meant

that two signals ahead were showing

danger. This was Juliet Tango six.

Now this was because the signal at

Amersham had a late running Met Line

Chesham service on approach to Chalfont

& Latimer.

They had prioritized the underground

service thus set up the conflicting

route from platform one at Chalfont &

Latimer across the junction onto the

Chesham single line.

No bother. This was often done and the

movement was in theory protected by

signal and train stop protection.

The Chilton train departed Amersham and

moved over the tripcock tester below the

required speed of 10 mph. The test was

completed successfully, thus proving

that the train's tripcock was in

operation.

Once clear of the station, the driver

took full power. Shortly after, the

train was at around 55 mph. It

approached the fog repeater associated

with signal Juliet Whisky 5 and then

signal Juliet Whisky 5 itself, showing a

single yellow.

The driver should have slowed down a

while ago. Many companies recommend a

maximum speed of between 30 and 35 mph

when passing a single yellow.

Around 15 seconds later, the driver

noticed the train speed had risen to

around 62 mph. This was over the max

line speed of 60 mph. They then applied

a small amount of brake step one

to drop the speeds down to below the max

line speed.

The train was hurtling towards Juliet

Tango 6 at danger. The train approached

the yellow aspect of the fog repeater

for Juliet Tango 6. This should have

reminded the driver of the danger signal

ahead, but sadly not. At the same time,

the Metropolitan line train due to go to

Chesham was on platform one at Chalfont

& Latimer, undertaking its normal

platform duties.

Signal Juliet Tango 80 was showing a

proceed aspect with a junction indicator

in the fourth position.

You can also call this a feather to the

diverging route. At 21:43, the Chilton

train passed Juliet Tango 6 at danger.

The tripcock was tripped by the train

stop for Juliet Tango 6, and the

emergency brakes were triggered. The

train was traveling close to 60 mph at

this point.

Grinding to a halt, the driver reset the

tripcock, thus releasing the emergency

brakes, and then took power.

Meanwhile, the Met Line train had closed

its doors and began to depart the

station.

The operator saw Juliet Tango 80 change

back to danger and slammed on its

brakes.

The train was still, luckily, in the

platform.

The Chiltern train took power reaching a

speed of around 27 mph.

The driver coasted and made a step one

application of the brakes.

It pushed through the points at the

Chesham single line junction.

The driver released the train's brakes

and then applied the emergency brake

when feeling the train jolt as it passed

over the first set of points on the

crossover that was set towards platform

one at Chalfont & Latimer station.

The train was traveling at 25 mph over

the point work intended for a max line

speed of 15 mph.

The train bounced and rumbled across the

second part of the crossover ending up

facing the train on platform one

grinding to a halt just 23 m from the

front of the Met Line train.

Disaster was averted, but by only the

smallest of amounts.

The Met Line train was immediately

evacuated, but passengers aboard the

Chiltern train would be stuck aboard

for another 87 minutes.

Now, no one was injured or killed as the

collision, thankfully, didn't happen.

But the point work was severely damaged

and delays due to the incident would

cause disruptions for the line.

The avoidance of the disaster was more

of just a case of luck. So, what on

earth happened?

Well, this is where long-term friends of

the channel, the RAIB, would slither

into our video.

The investigation.

So, investigators would first of all

download the Chiltern train's onboard

data recorder

and the information they would find was

not good. This, in addition to witness

evidence and CCTV recordings, showed

that the driver did not stop at Juliet

Tango 6 at danger.

Instead being tripped by the train stop.

Basically, the safety system intervened.

But disaster still could have been

averted here as the driver should have

contacted the LUL signaler and informed

them of the unsolicited brake demand.

They did not. Later on in interviews,

the driver would state that they

believed that they had been tripped on a

piece of debris on the track. Thinking

this, that they did not then need to

seek permission to restart the train

after resetting the tripcock equipment.

This is a massive no-no as you're

basically overriding the key piece of

equipment to protect trains from

crashing into one another. The RAIB

would highlight the reasons behind the

driver's actions. The first being

fatigue. The driver claimed that they

had been experiencing ongoing issues

with getting adequate rest. This would

explain the apparent lack of responding

to the restrictive aspects that they

were driving to. They weren't really in

their head in the cab that evening.

The other main issue was that Chiltern

Railways had a few gaps in its

competence management and training,

especially concerning operating over LUL

infrastructure. Reportedly, even

the assessment paper completed by

Chiltern Railways drivers didn't have

any questions about the actions of what

to do after a tripcock activation.

The RAIB would summarize, "Chiltern

Railways driver management processes did

not effectively manage safety related

risk associated with the driver.

It is probable

that this is a factor underlying the

incident and possible that this was the

consequence of an insufficient number of

driver managers and their high

workload."

The RAIB would also say,

"Assessments undertaken by Chiltern

Railways and LUL did not accurately

assess the risk of a collision arising

from a Chiltern Railways driver

resetting the tripcock and then

proceeding without authority."

However, the deficiencies identified in

Chilton's management of the driver

suggest that even had the risk been more

accurately assessed, it is unlikely that

improvements to this assessment would

have resulted in sufficient mitigation

to prevent the incident at Chalfont and

Latimer.

So that's my video on the Chalfont and

Latimer near disaster. And it's good to

do a non-disaster for a change. So it's

Skelton. It's going to be a one or a

two. This is what I've got for my root

cause analysis card. Do you agree? Let

me know in the comments below.

This is a Plain English Productions. All

videos are under Creative Commons

Attribution-ShareAlike license. Plain

English videos produced by me, John, in

a currently very cold cold corner of

South London, UK.

And always I say thank you very much for

watching. And may some music play us

out, please.

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