I'm so glad this hidden monorail broke down.

0:00 Do you want to see a hidden, suspended monorail?

0:03 My road trip brought me to Gloucestershire, and to the River Severn.

0:06 The Severn Estuary has one of the highest tidal ranges in the world,

0:10 15 metres between high and low tide,

0:13 staggering amounts of water flowing in and out every day.

0:16 Crossing it are two bridges: the Severn Bridge,

0:19 from the 1960s, and the Second Severn Crossing,

0:23 completed in 1996 and now officially called the Prince of Wales Bridge.

0:27 That’s the bridge that, these days,

0:29 takes most of the traffic crossing the water between England and Wales.

0:33 And it is a masterpiece, five kilometres long, the outer parts, the approaches,

0:38 are held up on concrete piers 100 metres apart,

0:41 anchored to the rock under the estuary.

0:43 But the inner part of the bridge needs to be wide

0:46 enough and tall enough that large ships can still pass under it,

0:49 so, that is a metal cable-stayed bridge a kilometre long.

0:53 Cable-stayed means, unlike a suspension bridge,

0:56 the bridge deck is held up by the cables

0:58 that are physically connected to the pylons, the two big towers.

1:03 But I wasn’t there to see the bridge itself, at least not at first.

1:06 After a lot of negotiation between my producers and National Highways,

1:10 I was there to see the suspended monorail that’s tucked away underneath it.

1:17 Full disclosure: National Highways did ask

1:19 to check this video before it went out.

1:21 But they’ve had no editorial control beyond my offer to blur stuff if needed.

1:25 I met the folks from National Highways at the maintenance depot

1:28 at what’s called the Avon Abutment on the English side of the bridge.

1:32 It’s a lovely day for it.

1:33 It’s beautiful, yeah, you’ve picked a very good day.

1:36 That is Dan, he’s been part of the team

1:38 working on the bridge since its construction.

1:40 Holding the camera is Liam, who’s from the National Highways media team.

1:44 And who had no idea quite what he was getting himself into that day.

1:48 Because the plan was: take the monorail out to the English pylon.

1:52 and then go up to the top of the bridge.

1:53 That’s not exactly what happened.

1:56 The first thing we saw was the maintenance gantry.

1:58 Currently being decommissioned and replaced.

2:00 That’s how they get people to inspect the outside of the bridge.

2:04 It could rotate around for transport and be moved along

2:06 the bridge on the two blue rails that you can see.

2:09 We were just talking about that old gantry when...

2:11 We’re looking at replacing this...

2:13 (engine starts) So, that’s the RAT...

2:16 That’s the RAT?

2:17 ...starting up.

2:18 We’re about to go out onto the rail in the centre, Tom, that’s the RAT rail.

2:22 -Yeah?

2:23 And RAT stands for Rapid Access Train.

2:25 -Yeah.

2:26 It’s a monorail that the RAT hangs off.

2:29 See the rail just there, and the square holes in the bridge?

2:32 That’s what we’ll be travelling on and through.

2:35 -Okay, so we’ll make our way up?

2:36 -Yeah, lead the way.

2:37 Just to be clear to the audience,

2:39 there has been a long safety briefing before I’ve been allowed up here.

2:42 And every single piece of equipment in the hand is being safely tethered on.

2:49 You have a little railway station up here.

2:51 -It is.

2:52 The RAT is a very rare thing: a suspended monorail.

2:56 It’s on the underside of the road deck, the surface of the bridge.

2:59 And almost none of the tens of thousands of people who travel over

3:03 the Prince of Wales Bridge each day have any idea that it exists.

3:07 Alright.

3:09 Yeah.

3:11 Hit my head again.

3:12 (laughs) There’s no room for your legs.

3:14 I was sitting on a chair but the seat of the chair was just on the floor.

3:18 And of course, what I have to remember is: this is the bottom of the train.

3:22 There’s...there’s very little headroom and there’s very little legroom.

3:25 (clanking, clicking) -Okay, Steve, thank you.

3:28 -Where are you going, Dan?

3:29 Oh, M2, mate, please.

3:30 That was the view that Steve the driver gets.

3:33 It’s quite limited, but given that it’s a monorail,

3:35 that’s probably not a massive problem.

3:37 That big box is the generator for the RAT, and it’s the first of four carriages.

3:41 We were sitting in the second,

3:43 our other driver was sat in the third, for safety.

3:45 And the fourth was a metal cage

3:47 for any equipment that we’d need to bring across.

3:49 We started at the Station Four pier, N48.

3:52 This is very tight clearances here.

3:55 That is maybe two inches?

3:57 -Yeah, yeah.

3:58 And just down there is the tidal mudflats of the Severn.

4:02 We are out over water now.

4:04 Such a tight clearance.

4:05 -It is.

4:06 So, if it’s, for whatever reason,

4:09 really howling winds, unfortunately, we can’t run the RAT.

4:12 Now it is quite protected here, so, the winds have to be really bad.

4:16 So, we have another driver in the back there?

4:18 We do, you’ve always got one driver in each cabin

4:22 and the driver is always facing the direction of travel.

4:26 Presumably in case of emergency?

4:28 There’s...I mean, I know this ’cos I had the long safety briefing,

4:31 but there are so many levels of safety here.

4:35 -Yeah, there has to be, yeah.

4:36 -So, two drivers.

4:37 -Two drivers at all times.

4:39 -Yeah.

4:39 Big thing is, if this was to break down,

4:42 for whatever reason, if we lost power with the diesel generator...

4:45 -Yep.

4:46 -...we’ve got a battery, an auxiliary drive that kicks in.

4:50 I’ve worked on this structure since I was 18 years of age.

4:53 And I’m 50.

4:54 I’m 50!

4:55 So, yeah, I’ve worked here...

4:57 my whole working life has been spent on this structure.

5:00 I worked in construction.

5:02 However, all through construction, which was 1992 to 1996,

5:07 the furthest I ever got out over the water

5:10 was the stitch beams back on the Avon Abutment.

5:12 Oh, right!

5:13 So, it wasn’t until I come onto the maintenance that I

5:16 was lucky enough to see the structure from all sides.

5:20 We passed through another station, which made me realise:

5:23 when you get off at a station, where are you going?

5:26 And who’s going there?

5:27 Because surely there’s nowhere to walk to underneath the bridge?

5:30 Like obvious question, what’s the RAT used for?

5:33 I haven’t even established that yet.

5:35 Not a silly question, it is logistics.

5:38 Getting labour, plant, materiel out onto the bridge.

5:42 You could walk out.

5:44 If you ever come back, Tom, I’ll take you for a walk through the bridge.

5:48 But presumably that’s up on the road deck?

5:50 -No.

5:50 -No?

5:51 -These viaducts are hollow.

5:53 -Oh!

5:54 Inside is a walkway, and you can walk.

5:57 It’s five kilometres.

5:59 But you can go inside the bridge at the Avon abutment

6:02 and you can walk all the way out to the Gwent abutment.

6:05 Let me just show you that shot looking up at the bridge one more time,

6:08 ’cos it’s important: there’s no place to walk along the underside of the bridge.

6:13 You’re either taking the RAT, or that big gantry,

6:16 or you’re walking on the inside of the bridge,

6:18 in the hollow parts, the viaducts, one on the north side, one on the south.

6:23 I really wanted a closer look at that, and I realised,

6:25 as we trundled along in the RAT that I was missing half the story here.

6:29 There are hidden viaducts, and we were speeding right past them.

6:32 And there were expansion joints.

6:34 The metal cable-stayed bridge, out in the centre of the river,

6:37 that’ll expand and contract day-to-day,

6:39 as the sun warms it and the night cools it.

6:41 But the big concrete approaches, where we were then, they have many,

6:45 many times the thermal mass: so, they’ll expand and contract with the seasons.

6:50 And over kilometres of concrete bridge,

6:52 that means there have to be gaps that it can expand into.

6:55 We are going over a movement joint.

6:57 You know you said to me about the expansion joint?

6:58 I was going to say, we’ve slowed down a lot here.

7:00 So, this is one of the ten movement

7:03 joints that allow the bridge to expand and contract.

7:06 That’s such a big gap.

7:08 -Yeah.

7:08 -Wow.

7:09 That’s...

7:13 massive.

7:14 I wanted a better shot of that.

7:16 So, we’re coming up to another station, it looks like?

7:17 Yeah, another RAT station.

7:19 So, the RAT could stop, and people could get out onto the station

7:23 and go into either the north or the south viaducts,

7:26 according to where they’re walking.

7:28 Oh yeah, we’ve got a station on both sides here.

7:30 There’s a road up there.

7:31 -Yeah.

7:31 Why not use the road?

7:33 Because presumably there’s an access between the road

7:35 deck and the internals of the bridge.

7:37 Why bother to put a suspended monorail in?

7:39 We have got a maintenance strip, and we do use it for access.

7:44 The team quite often walk in and out on the maintenance strip.

7:47 By maintenance strip, Dan means just the side of the road,

7:50 with high-speed motorway traffic going past inches away.

7:54 With the best planning in the world, it’s out of our control.

7:57 Items do come off vehicles.

8:00 -Oh.

8:00 Yeah.

8:01 So, we try and not use the maintenance strip.

8:06 It’s not a public right of way, like the Severn Bridge.

8:09 -Right.

8:09 -It’s not a public right of way.

8:11 (engine stops, beeping) -Turn it off and on again?

8:14 -I think so.

8:14 (laughs) So, as I said,

8:17 this RAT has just undergone 18 months of totally being stripped down.

8:22 -I’m riding a brand new refurbished RAT.

8:24 -You are.

8:25 (beeping) There we go.

8:25 As I said to you, I’m really excited.

8:27 It’s the first time in 18 months that I’ve been on it.

8:29 The RAT actually had a bit of a troubled history:

8:31 shortly after the bridge opened, engineers found cracks in the monorail,

8:35 and it was decommissioned for a few years before

8:37 everything was repaired and resurrected in the early 2000s,

8:39 because it is very useful.

8:42 Long-time viewers of this channel will know

8:44 that I have quite a history with monorails.

8:47 I actually think they’re terrible in almost all circumstances,

8:50 particularly for public transit,

8:52 but in this case: it seems like it’s a good option.

8:54 But alas, that day, luck was not with the newly refurbished RAT.

8:59 And the next few moments seemed terrible at the time,

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10:30 As I was saying: the RAT was...

10:32 not having a good day.

10:35 (rumbling, beeping) (engine stops) This might be a good time,

10:40 and I realise it’s not gonna happen, that we...

10:42 we were talking about rescue procedures.

10:44 So, there would be a backup electric generator.

10:48 That’s your auxiliary drive, yeah,

10:49 that these guys can basically turn the diesel generator off.

10:54 You might even witness it in a moment.

10:55 -Oh, okay.

10:56 And move using the...it’s a battery, but we call it the auxiliary drive.

11:00 It’s very slow, however, very powerful.

11:03 Right.

11:04 Oh, just huge amounts of torque?

11:06 -Yeah.

11:07 So, all you would do is get to the nearest

11:11 RAT station and then obviously you can get people off.

11:13 You might have to walk in or out.

11:15 (beeping) So, was that beep an acknowledgement

11:17 from the other driver there that all’s good?

11:19 -Just the radio.

11:20 -Just the radio, okay.

11:21 There is another way of getting people out using RA1,

11:25 which is a minibus and a backup vehicle.

11:27 -Yep.

11:27 -We don’t like doing it.

11:29 -No.

11:29 Because you’ve got people in...

11:30 next to live traffic.

11:31 Yeah, 100%.

11:33 (to radio) Neptune Kilo, Kilo Neptune India.

11:39 (bleeping) So, auxiliary drive...

11:41 -(radio) Go ahead, Steve.

11:42 (bleeping) Yeah, you take over.

11:44 You take us back to the last station.

11:47 So, what they’re doing now, you don’t really appreciate here,

11:50 but the bridge is on an angle.

11:53 Yep.

11:53 So, the reason we’re gonna go back that way,

11:55 and that’s why there’s two drivers, we’re gonna use gravity to help us go back.

11:59 Right.

12:00 Breakdowns happen.

12:01 Ideally not when someone’s got two cameras on you and your monorail,

12:04 but they can deal with this.

12:06 Plan A...

12:07 well, actually Plan B, I guess, we were already on Plan B,

12:11 that was to use the generator again, but go in the other direction.

12:14 Back in the day when this first came out and had one cabin,

12:18 honestly, I’m not making this up,

12:20 there was a little wheel under the seat and a pole and you

12:25 had to put it in a slot on the generator and turn this wheel.

12:28 -Right.

12:28 -It worked.

12:29 -To crank it?

12:29 -To turn it, just to get back to...

12:31 but it took forever.

12:33 It took forever and you’d have to take it in turns as the people in there.

12:36 We got rid of that.

12:37 The generator still kept causing trouble, and while the drivers kept trying,

12:41 it was clear we were going to Plan C: the battery backup.

12:44 Which did work, which is great, we very slowly moved on, but I will admit

12:49 to a slight disappointment that we didn’t end up using Plan D.

12:53 We’ve got permanent roped access on the bridge.

12:55 A lot of our inspectors, not all of them,

12:57 but a lot of them are roped access trained.

12:59 This is folks who can abseil?

13:01 This is folks that can abseil, industrial abseil, and folks that, if need be...

13:05 (bleeping) ...and in 30 years we’ve only ever done it once,

13:11 can climb out...to the RAT, actually get to us, and...

13:18 So, they’d send a rescue boat out and we’d have to abseil down?

13:21 We would.

13:22 (engine stops, beeping) Generator’s off, that’s the auxiliary drive.

13:28 Oh, so we’re actually on the auxiliary now.

13:30 Yeah.

13:33 Well, sorry to have a technical problem when we’re filming.

13:34 -I know!

13:35 -(laughs) The electrical team will have to walk out from the station.

13:39 So, we’ve got a decision now.

13:42 I think we are probably better off,

13:45 rather than waiting for the electrical team to come out,

13:48 and it could take an hour to diagnose.

13:50 I think we should go into the structure...

13:52 -Yeah.

13:53 -...which wasn’t planned but is very interesting, and walk to the cable-stay.

13:56 Absolutely, yeah.

13:58 100%.

13:58 Like, thank you.

13:59 -Yeah.

14:00 That’s a whole section I didn’t expect to get in this video, so, thank you.

14:04 This was meant to be a little video about a monorail...

14:07 and all of a sudden, that’s become a lot more.

14:08 Thank you.

14:09 My thanks in particular to Liam behind the camera,

14:11 who again is from the media team, and kept smiling despite,

14:15 I assume, being somewhat frustrated that filming wasn’t going to plan,

14:19 and that the RAT wasn’t behaving.

14:20 What you won’t be privy to is all the cussing back there.

14:24 Now the electrical department’s got to walk all

14:25 the way through the viaduct carrying their kit.

14:27 -Oh, they have!

14:27 Which pier are we on?

14:29 We started at N48.

14:30 No, luckily, we’re about halfway out.

14:34 -Okay.

14:34 -So, we have got a walk inside.

14:36 Yeah.

14:38 I keep hitting my head on this.

14:41 So, what do they say in the media world?

14:44 Never work, was it, with children and animals?

14:46 Children and animals, yep.

14:47 So, technically, well, this is a RAT, rapid access train, so there you are.

14:51 Okay, thank you, Steve.

14:52 -Thank you very much!

14:53 -Sorry about that.

14:54 -No problem.

14:55 It’s not your fault!

14:57 -Thank you for getting us back.

14:58 -Right?

14:58 I’ll tell you what wasn’t on the schedule.

15:01 Stopping at this pier and seeing that view.

15:04 Good heavens!

15:06 Blimey.

15:07 Alright.

15:08 Let me get my GoPro back out of there and I guess we’re going for a walk.

15:11 -We’re going for a walk.

15:13 -Right.

15:15 (gasps) I’m glad someone’s made a padded surface here, that’s nice.

15:21 (laughs) Oh, wow.

15:25 So, welcome to Avon Viaduct North!

15:27 The structure’s five kilometres long,

15:30 and we’ve got 48 piers plus the abutments, so, 50.

15:34 So, now we walk that way.

15:37 -We walk that way, yep.

15:39 -For quite a while.

15:40 And what you’ve got to remember to do is...

15:44 -Oh!

15:44 -Turn the lights out as you go.

15:46 -Alright.

15:46 -Let’s go.

15:47 Let’s go.

15:48 Let’s walk inside a bridge.

15:50 We’re still out on the concrete section there.

15:52 The cables you can see are internal post-tensioning: during construction,

15:56 those cables were passed through ducts

15:58 in each hundred-metre section of the bridge,

16:00 stretched, and then while they were stretched,

16:02 anchored into the structure at both ends.

16:05 Because they want to return to their original length,

16:07 that pull puts the entire concrete structure under permanent compression.

16:11 And concrete is strong in compression, but weak in tension, so,

16:15 it’s like having someone permanently squeezing

16:17 to hold everything together and keep it strong.

16:20 -What you’re about to get to now...

16:22 -That sounds like an expansion joint.

16:23 It’s one of the movement joints, yeah.

16:25 So, that huge gap that we saw earlier that I pointed out from the RAT,

16:29 we’re about to cross this?

16:30 -Yeah.

16:31 -Wow!

16:32 Okay, down is the River Severn.

16:37 Forward...

16:39 thanks to Liam who’s holding the camera there...

16:42 and backwards is the bridge.

16:45 (loud trundling) And that is the expansion joint.

16:50 A hell of a lot more close up than I thought I’d ever get to see it.

16:53 Yep.

16:56 Okay, well, I’m gonna keep going.

16:59 I didn’t expect to see that close up.

17:01 Thank you very much.

17:02 This is really good actually, because normally, you know,

17:06 you go out on the RAT or you get RA1 out,

17:08 and everyone wants to see the cable-stayed bridge but this, this is the truth.

17:13 This is what our guys have to walk, day in day out, most of the time.

17:17 Right!

17:18 Oh yeah, everyone wants to see the pretty bits,

17:20 but the repetitive concrete structure here, with...

17:27 no clue of where we are or how deep we are.

17:30 Do you know what?

17:30 I’ve worked here, like I say, my whole life.

17:33 If you were to bring me in one of these viaducts, spin me round,

17:39 the only real way I’d know if I was heading to England or to Wales,

17:43 the cable-stayed bridge, is the markings on the wall.

17:48 So, this tells me, remember I said everything numbered from Wales to England?

17:52 -We started at N48.

17:54 -Yeah.

17:54 So, this just lets me know I’m in the North Viaduct.

18:00 I am closer to Pier 35 than I am to Pier 36.

18:06 35, 36 and 05 is...?

18:09 And 05, I’m the fifth segment from Pier 36.

18:15 Oh, so when you say segment, that’s...’cos this is 04 over here.

18:19 -Yeah.

18:20 -So, this is the connection between the segments just here.

18:22 -Yeah.

18:22 If you look from a drone shot on the outside,

18:24 you can see the lines where each segment ends.

18:27 The same ones that we’re seeing from the inside as we walk over them.

18:31 So, these were precast either on the English side or the Welsh side.

18:35 Primarily most of it was done on the English side, although not all of it.

18:39 And yeah, this...

18:40 -That’s the joint.

18:42 This just there.

18:42 -This would be, yeah.

18:43 This would be brought out,

18:45 dropped into place, literally glued, and through here,

18:50 something called a Macalloy bar that, obviously,

18:52 you can’t see now, but it’s a steel bar,

18:56 like 50mm diameter, and it would be bolted, four segments,

19:00 and that would support it until X amount

19:03 of segments were in, and the post-tensioning can go through.

19:07 So, it’s just build it out, build it out,

19:09 get to the next pier, build it out, build it out, build it out.

19:12 -Yeah.

19:12 And I haven’t yet figured out a pattern, if that makes sense.

19:16 Every single time we go to a new section,

19:20 I’m surprised by the gradient, or what it’s doing.

19:22 When you get to 29, it’s the transition.

19:25 We leave the concrete.

19:27 And then we go on the cable-stayed bridge.

19:29 -Yep.

19:30 -Which is a kilometre of steelwork, then.

19:34 It’s getting dark up ahead.

19:36 That’s just a deep black hole.

19:38 You forget, you’re down here with the lights on.

19:41 -Yeah.

19:42 -And it feels normal.

19:43 -Yeah.

19:44 This should be pitch black.

19:46 We are completely encased.

19:48 So...

19:50 -Alright.

19:51 Onwards.

19:52 -Okay.

19:52 You can just see, if you’ll pardon the pun...

19:54 -I can just see!

19:54 You can just see light at the end of the tunnel.

19:56 There’s light at the end of the tunnel there.

19:58 Okay, so this is the transition...

20:00 -Oh, yeah, okay.

20:01 -...from concrete to steel.

20:03 So again, watch your head.

20:04 -Mind my head.

20:05 Yep.

20:06 -As Liam...Liam rightly pointed out.

20:08 -Every time!

20:09 Yeah.

20:10 I personally don’t think anyone over 5′7″

20:14 should be employed to work on this structure.

20:16 It’s too much of a safety risk.

20:18 -(laughs) We reached the end of the concrete part of the crossing.

20:21 Now, it was out over the channel in the middle, onto the cable-stayed bridge.

20:26 There was another movement joint to let the two parts expand and contract,

20:29 and it was incredibly loud there...

20:31 -Above your head there...

20:32 -Yep.

20:33 ...the reason it’s so loud, that is called a bridging plate.

20:37 -Right.

20:38 -It is solid steel, about 100mm deep, wrapped in rubber,

20:45 and some car tyres are on top of that plate.

20:50 -Right.

20:50 -The live traffic is running over that.

20:52 Ten centimetres of rubber-wrapped steel between us and the car tyres.

20:57 No more concrete structure:

20:58 we headed out on the metal catwalks under the cable-stayed bridge.

21:02 So, we are literally just above the Severn Estuary here.

21:06 We are, indeed, yeah.

21:07 I hope the camera is getting the scale of this.

21:13 So, the RAT would pass through the big ol’ hole next to where we were.

21:17 -The walkway, yeah.

21:18 -And just head out under there.

21:21 So, I casually walked out on the catwalk,

21:24 with just the metal grating and about 50

21:26 metres of air between me and the Severn Estuary.

21:29 The tide had mostly gone out by this point,

21:31 so, it was just mud and rocks down there.

21:33 We had a couple of hundred metres of catwalks to get across.

21:36 I know for a huge number of people this is their job.

21:39 This is not remarkable.

21:41 This is just where they have to come out day after

21:44 day after day in wind and cold and sleet and snow.

21:52 But for an average civilian...

21:54 (laughs) ...thank you so much to everyone.

21:58 Three points of contact.

22:00 There’s a very weird effect here where, if I look down,

22:04 if I show you the view down here...

22:07 my brain refuses to accept how far away that is.

22:10 I keep thinking that it’s an optical illusion.

22:13 We are so high up and that is so massive that it’s

22:17 not the size of structure that the brain’s designed to deal with.

22:23 Alright.

22:23 This is M2 pylon?

22:26 This is M2 pylon, yeah.

22:28 Woo!

22:29 Wow.

22:30 So, the RAT would...

22:31 well, we’re under the RAT rail.

22:32 -We are.

22:33 -If the RAT was running right now, we would not be allowed to be here.

22:36 -No, these chains would be across.

22:37 And when the RAT parks here, this is where you embark, straight down the steps.

22:42 The last things to do, then: get to the bottom and the top of the pylon.

22:46 -Right, so shall we head down?

22:48 -Yeah.

22:49 Bag coming down.

22:51 It’s quite heavy, watch out.

22:53 You’ve got it.

22:54 We set down most of our bags in the welfare,

22:56 the little rest area in the middle of the pylon.

22:58 And if you need a cup of tea, you can make a cup of tea.

23:00 The next bit was gonna involve some very cramped spaces, so,

23:03 I switched to my 360 camera, and we headed to the elevator.

23:06 Oh, that is a long way down.

23:08 So, we’re going down first?

23:10 We’re gonna start at the bottom, at caisson level, and work our way up.

23:14 So, these are quite rickety lifts.

23:17 They’re called rack-and-pinion lifts.

23:19 And they are the lifts from construction.

23:23 -Right.

23:23 -As the pylon went up, they were put in.

23:26 So, they’re very basic.

23:28 You’ll be pleased to know on this occasion, Liam,

23:31 if these break down, it’s purely gravity-fed to the next lift.

23:35 -(laughter) And there is ladders, landings, from top to bottom.

23:40 Right.

23:40 It is spectacular, the view at the pylon top,

23:43 but this view, from an engineering perspective, for me, is The View.

23:49 This is what I actually get excited when I show people,

23:52 ’cos no one really wants to see this as much as the top.

23:59 Okay.

24:00 Oh, wow.

24:02 So, just get your bearings a moment.

24:05 We are on...

24:07 this pylon is the English one.

24:10 That one is the Welsh, that’s M1.

24:12 Oh, so, the border is just here?

24:14 Yeah.

24:14 Above our heads there is the walkway that we walked in on.

24:17 (laughs) You can also see the other gantry there,

24:20 hanging underneath the road deck.

24:21 Dan’s right: from an engineering perspective, this was the most impressive view,

24:26 ’cos you can see all the details of the bridge.

24:28 So, how high up will we be?

24:30 Above the seabed, about 150 metres, 155 metres.

24:34 I never let my colleagues forget on the Severn

24:37 Bridge that we’re a couple of metres higher.

24:40 -(laughs) It’s very minimal but...

24:42 -But it counts.

24:43 -It counts.

24:44 Alright, if you just wait there a minute, guys, I will get us...

24:49 I will get us some light on the subject.

24:53 I can’t see a thing, I’m glad you know where you’re going.

24:56 (clanking, creaking) -We’re all good?

25:01 -Yeah, all good.

25:01 If you come on up.

25:03 -Alright.

25:03 Okay, if you want to, you can use that there.

25:07 -Yep.

25:08 -This will move only slightly.

25:10 It won’t come down, okay?

25:11 -Okay.

25:13 -That’s it.

25:13 Keep coming up.

25:14 -Yep.

25:15 (motorbike roaring) (gasps) Okay, so get your bearings.

25:23 Oh, wow!

25:26 England.

25:27 Severn Bridge.

25:29 Wales.

25:30 Sometimes it’s really difficult to keep my profanity PG-rated...

25:35 -Yeah.

25:35 -...when I’m somewhere like this.

25:38 Yeah.

25:39 I can honestly say it never gets boring.

25:41 The wind!

25:41 There’s wind on this side.

25:43 -Yeah.

25:43 -And the whole structure...

25:45 -Moves.

25:45 -...is just moving a little bit.

25:46 It’s got to bend, because if it doesn’t it’ll break.

25:48 And the cables come in, well, we can see them over that side, can’t we?

25:51 Yeah, well, you can...

25:53 you can see them there.

25:55 -Oh.

25:55 That’s the first time I’ve had a moment where I’m afraid of heights up here.

26:01 Thank you so, so much, sir.

26:03 -Pleasure.

26:03 -Absolute pleasure.

26:04 And Liam, thank you.

26:05 I know you didn’t expect half of this today, let alone holding the camera.

26:08 I’m just glad we had a media guy here, ’cos I would have been,

26:12 “Oh, I’m not sure about this.” -This was not the plan.

26:15 -No.

26:15 Thank you to both of you.

26:17 That is incredible.

26:18 Well, thank you for persevering with it.

26:20 Many wouldn’t have.

26:22 How do we get back?

26:24 (laughs) -That’s a good point.

26:25 -(laughs) Let’s see what I can do.

26:27 (radio bleeps) Neptune Alpha, Neptune Alpha, National Highways, over.

26:33 In the end, we did take RA1, the minibus.

26:35 But you’ll notice there’s another van behind it,

26:38 tucked away into the tiny maintenance strip

26:40 to the left of lane one: and that’s because,

26:42 if someone loses control on the motorway,

26:45 they’re probably going to hit the crumple zone

26:47 at the back of that van first, before they hit us.

26:50 It is risky to be that close to the traffic.

26:53 And I feel like that point wouldn’t have been made nearly as well,

26:56 and this whole video wouldn’t have been nearly as good,

26:59 if the RAT had just taken us out and back.

27:03 Next time, or right now on Nebula, I’m joined by astrophysicist, Dr Becky,

27:08 for something far more down to earth, as two nerds pile up some rocks.