An event for councillors and stakeholders was held last week in the Town Hall. A similar public event is scheduled to be held next week. I would recommend people living near the bridge or using it regularly go if they possibly can.
I am a member of Peterborough Cycling Forum (PCF) (one of the council’s stakeholders), which has put the council’s event on facebook. Quite a few PCF members turned up and three or four councillors also popped in while I was there.
Which bridge? Rhubarb Bridge is the popular (but strictly incorrect) name of a cycle and pedestrian up and over bridge at the junction of the A15 (Lincoln Road – Bourges Boulevard) with the A47. The name is taken from a bridge which has long since gone. It went over a railway and had rhubarb growing on its embankment. The council calls it J18.
The council had claimed that the bridge needed to be demolished because it was no longer viable to continue to repair and maintain it: it had reached the end of its life. My overriding concern was to establish whether or not this was fair: I’d not spotted problems with the structure, so I was sceptical. The council’s structural engineer attended.
The bridge is a complex structure with four ways up onto a wider part of the bridge, which dips down a little into a tunnel under the A47. So it is both a bridge over Bourges Boulevard but also a tunnel under the A47. The council thinks of it as six bridges, two, the wider bits extending out from the tunnel, and the four, each of the four “legs” down.
At the event we were shown photographs of the bridge showing its condition. These will be published online on Wednesday 9th along with all the other planning documents we saw. These were a map, a description of the problems presented by the bridge and how the council proposes to deal with them, and the photographs. There is also a movement model, showing how traffic will be held at crossings and how it will flow once there are four lanes leading into some of the stop points. Extra lanes will be added to the A47 slip road from the east, and to the junction with the Lincoln Road coming from the north, so four lanes of traffic will queue at each of these two sets of traffic lights.
So this is what we now know (things we don’t know are in bold)
The bridge was constructed in 1975.
At PCF’s last meeting we were told that there is nothing structurally wrong with the tunnel under the A47. This is very important, because it means it could be incorporated into a new design. We were told that once the bridge structures are demolished, the tunnel will be closed off and filled with foam. You can see pictures of the tunnel under the A47 here. You can see that the tunnel is neglected decoratively, so it is good to know that at least it is structurally sound.
The bridge structure requires repair and maintenance costing £60,000 a year to keep it safe for use.
I asked why since so many of the city’s bridges have been capable of repair, this particular one isn’t. The answer I was given is that the structure is more delicate than most of Peterborough’s repaired and mostly road over road bridges, meaning that any internal problems will be closer to the surface and integrity is less likely in the absence of sheer size and bulk. Relatively speaking, it is an elegant structure.
The bridge is made of a number of elements formed of reinforced concrete with tensioned steel at their heart. Some of these support the weight of a span and some of them are the spans.
If for example you need to repair or even replace a stanchion (a supporting pillar), you might not be able to lift the span resting on it without first repairing the span itself. This is complicated and the council argues more expensive than can be justified.
I’m not going to comment on the state of the bridge, except to say that I am no longer confident that it is structurally sound. My impression is that there were some basic concrete mixing failures when it was originally constructed. It is a huge shame, because it is a nice bridge. The pictures are worrying, although they don’t give a complete picture of the state of the whole bridge and you’d need to be a bridge expert to quantify the risk.
The problem areas have been repaired and wrapped in Kevlar, so those pictured here will not be visible. I asked what would happen if you unwrapped the Kevlar and was told the concrete might very well come off too.
However we have not seen itemised maintenance and repair expenditure on the bridge to date or estimated future costs for this.
The council argues that if it was to proceed and maintain this bridge at high cost, a route through for cyclists and pedestrians would have to be provided while works were underway.
The route through at ground level is essentially what the council’s proposal is and what is proposed could stay there while work was undertaken on the bridge, whether the bridge was repaired, or the bridge was replaced.
The proposal includes a route which goes all the way round the central island which holds up the A47. This means that during future bridge works, people could be diverted away from whichever section was being worked on by simply being sent the other way round the centre.
This central ring is partly shared use & 3wide which means cyclists don’t have to dismount and a smaller part, on the eastern side which is much narrower, which will require dismounting (designing in conflict, in other words).
If the bridge could be repaired, it could be kept much as it is. The existing bridge is marked, though faintly, on the plan.
If the bridge was replaced with a new bridge, then it would have to meet current standards and specifically its ramps would have to be a lot shallower and therefore longer than they now are. So a ramp which meets the ground now, might have to go an awful lot further in a new design and there might be a road junction just where it is almost at ground level…..
Skanska has prepared a number of options for a replacement bridge, but these were not presented at the event.
The council’s £30M replacement figure has been arrived at by an accounting formula. It is not based on the Skanska designs, which may not have been costed.
What we don’t know is:
The significance and heritage value of this structure. It has been described as a very early “Dutch roundabout”. Peterborough doesn’t sing the praises of the development corporation which put much of its road infrastructure on the map. The mini roundabout was born in Peterborough. We demolished that. At grade separation of cyclists and pedestrians was pioneered here and this bridge is part of that revolution in road design. Now we are changing the original plan and working to lower speeds on the very roads whose high speeds were once seen as their selling points. This roundabout is where old meets new. One thing is certain: cyclists (and I am guessing pedestrians also) don’t want to be at ground level at this particular point in the city! Is Peterborough going to let the Dutch get all the glory for cycling infrastructure or will it assert the value and interest of having once tried to get things right for cyclists?
Why the council has not planned in a replacement bridge and applied for funding for it, possibly as part of its sustainable travel spend. I’d missed it, but apparently this bridge was on the list of things which needed tackling two – or maybe more – years ago.
How long the bridge could stay in place as is (i.e. what leeway there is to postpone demolition).