The abandoned bridge over the M4 that doesn't go anywhere

When you drive into Swansea on the M4 via junction 44 or 45, you'll drive under a fair number of bridges and flyovers. From underneath, it's hard to actually see what they are - but you might've noticed one which no cars or trains ever cross.

Between the two junctions there's a concrete bridge which, from below, looks slightly worn but otherwise inconspicuous. But one motorway fanatic took it upon himself to clamber through the trees to see what it was all about - and found an abandoned railway running across it.

In one video, covering some of the M4's quirkiest roundabouts and slip roads, Auto Shenanigans host Jon discovers a bridge heading over the M4 that seems to go nowhere. Dense trees and bushes cover the path on either side, and the bridge can be seen from both the M4 and nearby Ynysallan Road.

READ MORE: Council orders operators of Ffos-y-Fran coal mine to stop mining there

A view from above on Google Maps shows railway tracks running over the bridge, which upon further investigation are still there despite not being linked to a modern-day railway. In the video, Jon asks: "What's this railway all about?

"Well, it's a branch line that came off the main line built by GWR. From here, the railway would've headed north towards Clydach and where today we find a housing estate, back in the 1930s you'd have found several sidings that were built to serve a gravel pit."

The bridge appears to have been part of a railway that hasn't existed for years (Richard Swingler)

You can't see the railway tracks from below but a drone shot shows the full view (Richard Swingler)

Railmaponline's map of historic railways shows the outline of a partly-built line that likely would've passed through Clydach on its way from Felin Fran Halt, Llansamlet, to Gwaun-Cae-Gurwen, NPT.

We sent a photographer to take a look at the bridge and he saw the tracks - fully intact but slightly overgrown with weeds and twigs. At one end it's gated off, and from the motorway below it still looks like any ordinary bridge.

One end is gated off (Richard Swingler)

It looks completely inconspicuous from neighbouring Ynysallan road too (Richard Swingler)

The bridge is one of several quirks of the M4 uncovered by Auto Shenanigans' Jon. One roundabout in Cardiff is the only one of its kind in Wales - you can read more about that here.

READ NEXT:

• Man fined for driving to Bristol Airport through Clean Air Zone he knew nothing about

• 'Aggressive' man tasered three times by police kept on going and still fought back after the fourth

• Mum branded 'nuts' after taking 11-week-old baby to a festival

• What people really think of Mumbles Skatepark

• Warning issued over dangerous equipment as footage shows people inches from speeding train