It's late afternoon and I'm walking towards the Avonmouth bridge on the M5 near Bristol, on my way to collect a vehicle from an industrial estate in Avonmouth itself.
This is one of the few motorway bridges in the country that has a footpath included at the side of it, and after dropping a vehicle in the auctions in Bristol, and catching a bus out to the motorway junction, I am now about to walk across it for the first time. It has recently stopped raining and a full rainbow dominates the sky to the north.
Despite getting off the bus less than a mile from the bridge, and having a map that shows public footpaths, the way proves surprisingly hard to locate. I eventually zig-zag there via a bridge over the motorway, a tunnel back under it, a footpath so overgrown I have to abandon it, another so flooded I have to paddle along the edge of it, and another running through a field so picturesque and bucolic it is difficult to believe that I'm in close proximity to both a motorway and a city.
I finally reach the start of the ascent onto the bridge, and in a secluded spot where the path is lined by both a wooden fence and an overgrown hedge there are tributes of flowers and cards, all now looking weatherbeaten, attached to the fence. I pause to read some of the messages - expressions of grief for a lost husband and friend, but nothing to say what happened.
I walk up onto the bridge itself, the traffic roaring to my left, and to my right a steep drop down to the brown river Avon sliding slowly between equally brown banks, wrinkled by the flow of countless small rivulets.
I have driven over this bridge hundreds of times, and have admired the view only in quick sideways glances. It feels suddenly liberating to be able to study it in as much detail and for as long as I like.
The crossing is perhaps half a mile long, and I pause in the middle to crouch down and take some pictures through the railings with my phone. But doing so makes me aware that the bridge is actually shaking as the lorries rumble past, which does not improve my lurking sense of vertigo. I decide that one photo is all I need.
At one point along the wide path, on the white line separating the pedestrian half from the cycleway, there is a single piece of neatly stencilled graffiti - a black rifle with no accompanying words of explanation from its creator.
In the centre of Bristol, and some other parts of the city, there is a long and stubborn tradition of producing slightly surreal, slightly menacing graffiti that never has the name of a group or individual attached to it. I wonder if someone came all the way out here just to do that single piece.
I reach the far side and have a choice of descending more of less straight down via several sets of steps or continuing down a ramp which will bring me to the ground a few hundred yards further along. I crouch down again to study my map, and another piece of graffiti on the floor catches my eye - 'Gemma' and a txtspeak smile written in black marker pen on the top step.
The motorway and its transient traffic which dominate this place both in sight and sound seem to make such small details seem more significant - reminders that not everyone is just passing through. I wonder who she was and why she was hanging around here.
I work out that the steps are my best bet and then climb down from a bridge that has been in my mind for years as only a passing blur, but which now seems full of life and stories.