1964+2017 Firth of Forth Road Bridges

1964: (Historic Bridges; TheForthBridges; Satellite)

2017: (TheForthBridges; Satellite)

The cantilevered railroad bridge is so famous that I, and others, have ignored the two non-trivial road bridges that cross the forth.

The suspension bridge was the longest in the world outside of the United States when it was completed. [HistoricBridges]

This would be the last trip by a street view car before the bridge was closed to general traffic.

Street View, May 2017

Olena Bykova, Jun 2018

 Václav Pavlík, Aug 2021

Jacques Dezeure, May 2019

Bruce Duncan, Dec 2020

 

Edinburgh HD posted, cropped
The Forth Bridges along the Firth of Forth from Norweigan Flight DY1355 bound for Oslo.
Over at Experience Norway I share my photography from Northern Norway so far. I'm not long back from my 3rd trip to Tromso. Check it out from something a bit different 🙂

"Pressure to replace the original Forth road bridge began in the 1990s as traffic growth put it under heavy pressure, with up to 70,000 vehicles using it every day. In 2004, inspections discovered corrosion of its main cables, which reduced their strength by up to 10%. Work began on entirely replacing it with a new bridge, four lanes wide in each direction, but in time engineers discovered the cables could be saved with dehumidifiers. The Scottish government then decided to keep the existing bridge as a dedicated bus-only and cyclist crossing. Transport Scotland says increased public transport will absorb future traffic growth." [TheGuardian] The old bridge is also used by emergency vehicles. [A TV show]

Image courtesy of Transport Scotland via Ramboll
It is the UK’s tallest bridge and the world’s longest three-tower, cable-stayed bridge.

 

Jacobs
"23,000 miles of cabling, almost enough to wrap around the circumference of the Earth, connects the bridge deck to the towers."
The bridge is 684' tall and 1.7 miles long. (The suspension towers of the old road bridge are 150m (492') [HistoricBridges])

Jacobs

The wind shield destroys the view from the Google car.

Street View, Sep 2021

But a bad view is a small price to pay to allow the bridge to remain open during windy conditions, which are often on the Firth of Forth. The suspension bridge was frequently closed to HGVs (Heavy Goods Vehicle) because of wind. When a driver ignored the warning, his truck was not only blown over, it was blown over the barrier and into the opposite lanes!

BBC-wind

This was the post that motivated researching the road bridges.

Bridges Now and Then posted
Scotland's Forth Road Bridge under construction, 1962. (Robert Blomfield).

 

Bridges Now and Then posted
Forth Road Bridge construction, Scotland, c. 1963. (The Forth Bridges)

Gill Freestone, Mar 2016

Eight photos from AmericanBridge. The project, which included relocating the road, cost $1.3b. (The original estimate in 2009 was $3b [Jacobs])

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They may have solved the old weather problem of wind, but cable=stayed bridges introduce a new weather problem: falling ice.

NewCivilEngineer
"The bridge closed three times in 12 months due to the risk of falling ice." Falling ice was flagged as a potential issue during the design phase, but Transport Scotland decided it would figure out how to deal with it by learning from similar bridges elsewhere in the world. The problem is, "a completely successful prevention or removal methodology has not been identified, currently most operators close the bridge and wait for the ice to fall." Potential options identified for further study include "cable sheath surface modifications to retain and control the accreted ice, mechanical vibration systems - targeted vibration systems, dynamic actuation - ultrasonic de-icing systems and robotics." Heating the cables is considered too expensive and hard to maintain. 

Using Forth Road Bridge as a diversion route and robotics are the front runners. [TheTimes, but I hit a paywall]

PeterDow
But an engineer advocates heating the cables by passing electricity through the outer strands of the support cables. The paper is too technical for me to dig through, but I would hope those in charge of operating the bridge would dig through it.

EdinburghNews
In the meantime, they are developing two emergency diversion procedures to move the traffic back to the suspension bridge. A low-capacity, but quick to implement, diversion and a higher capacity diversion that takes a few hours to implement.

The first incident was after the bridge had been opened for 2.5 years. So the operators were comfortable that it was a rare problem. But three closures in less than a year has changed the severity of the problem. [BBC-ice]