The Mersey Gateway Project is a 9 km long scheme that will carry traffic over the River Mersey between Widnes and Runcorn in the borough of Halton, in Cheshire, United Kingdom.
A new cable-stayed crossing is part of a 9 km long project designed to reroute traffic over the River Mersey in the borough of Halton in Cheshire, United Kingdom.
July 16, 2013—For the second time in 36 years, work is under way to relieve traffic congestion on the Silver Jubilee Bridge, in the borough of Halton in Cheshire, United Kingdom. A previous effort to accommodate the large volume of traffic that travels the crossing involved adding lanes to the existing structure, but this time a wholly new bridge and adjoining road network are being constructed to divert traffic away from the through-arch bridge.
The Silver Jubilee Bridge opened over the River Mersey to connect the towns of Widnes and Runcorn in 1961. Known at that time as the Runcorn Bridge, the crossing carried one ample traffic lane in each direction and quickly became a popular route over the river, boosting economic activity and development in the area. In fact the bridge became so well traveled that by 1977 it was necessary to divide the existing traffic lanes to create four lanes—two in each direction. Also at that time, a cantilevered walkway was added to the upstream side of the bridge, which was renamed in honor of Queen Elizabeth II’s Silver Jubilee that year. While the increased number of travel lanes initially eased congestion, it wasn’t long before traffic backups were a norm once again. Originally designed to carry approximately 10,000 vehicles a day, the bridge currently carries approximately 85,000 vehicles daily.
As early as 1978 consideration was given to constructing a new bridge to take some of the traffic off of the Silver Jubilee Bridge, but it wasn’t until 1998, when Halton became a unitary authority, that the project was given serious attention. As a result of subsequent traffic modeling, local authorities determined that roughly 80 percent of the traffic that uses the Silver Jubilee Bridge is just passing through the area and therefore could be easily transitioned onto a new, more accommodating structure nearby. To that end, a £2-billion effort known as the Mersey Gateway Project is advancing upstream from the existing bridge to improve traffic flow and encourage new development through the area. “The project objective is moving the traffic off of the existing crossing as much as possible and by doing so providing a much more reliable crossing point over the Mersey,” says Ian Draycott, the highways authority liaison engineer for the Mersey Gateway Project.
The 1 km long cable-stayed bridge over the upper estuary of the
River Mersey will have three towers, the middle tower being shorter
than the outer two.
The Mersey Gateway Project includes more than just a new river crossing. It is a 9 km long scheme that will route traffic from the existing Speke Road north of the river in Widnes, onto the new 1 km long crossing over the River Mersey, around Runcorn Town Center, and onto the existing Central Expressway in Runcorn. “We’re talking about nine kilometers in total length, so starting from about two kilometers north of the river crossing in Widnes and then extending probably six kilometers south of the bridge to join in with the motorway network in this area,” Draycott explains. “We’re talking approach viaducts that curve over the salt marches on each side of the river and then a kilometer-long raised cable-stayed crossing over the water itself.” The principal technical advisers on the project on behalf of the Halton Borough Council are the United Kingdom division of CH2M HILL, an engineering firm headquartered in Englewood, Colorado, and the United Kingdom branch of Ramboll, an engineering firm headquartered in Copenhagen, Denmark.
The new bridge will carry six lanes—three in each direction—across the upper estuary of the River Mersey, approximately 1.5 km upstream from the point where the Silver Jubilee Bridge crosses a bend in the river known as Runcorn Gap, between the river’s upper and middle estuaries. While protecting the entire river is a priority, particular consideration was given to how the new bridge would impact the middle estuary, a habitat that is frequented by migratory birds. As a result, the number of piers permitted to land in the river was limited to three, leading to the selection of a cable-stayed bridge for the crossing. “Once you’ve established that you’re going to put only three supports on a kilometer-long crossing, then the optimal design tends toward a cable-stayed crossing,” Draycott says. “And then by going with a cable-stayed bridge, you’ve automatically got something that has an iconic, emblematic sort of design that will provide a symbol for the regeneration that goes with the project scheme.”
As a result of the environmental concern the bridge will have only
three piers in the water.
One of the unusual features of the bridge is the fact that one of its three towers will be shorter than the other two. “That’s driven by these three positions in the estuary that were determined to be acceptable from an environmental point of view,” Draycott says. “Once we got these three positions in place, it followed that the middle tower needed to be shorter than the other two.” All of the towers will be within a 150 m height restriction, which was established so as not to interfere with aircraft flying in and out of nearby Liverpool John Lennon Airport. The two outer towers will be approximately 125 m tall and the middle tower will be roughly 90 m in height. A single array of steel cables will extend from each tower and connect to the middle of the posstensioned concrete bridge deck.
The towers will be founded on spread footings on bedrock 20 to 30 m below the riverbed. While the foundations will be fairly straightforward, an extensive £2.3-million cleanup effort was conducted in advance of the bridge’s construction to remove soil contaminates left behind by past industrial uses at the site. “One of the challenges we’ve had locally is chemical pollution because the chemical industry in the UK started in Widnes,” Draycott says. “So as part of our advanced works, we’ve already successfully dealt with dense non aqueous phase liquids that were polluting the ground on the north shore.” That effort resulted in the recovery of 16 tons of chlorinated hydrocarbons from the ground.
Windshields on the bridge’s outer parapets will protect travelers
from gusts coming off of the nearby Irish Sea.
Another consideration for the project is the height of the bridge. The superstructure has to provide enough clearance to accommodate vessels traveling down the historic Manchester Ship Canal, an inland waterway that extends for more than 60 km along the south bank of the River Mersey. To that end, the bridge will be 28.6 m off of the canal, the same clearance afforded by the Silver Jubilee Bridge. While the height of the bridge does not make wind loads a governing design factor, the bridge’s proximity to the Irish Sea means wind is a concern. As a result, windshields will be installed outside of the bridge’s parapets to ensure the crossing can remain open to traffic during times of high wind.
In addition to being a wholly new structure, the bridge will bring a new technology to the area: open road tolling. Using that system rather than installing traditional toll booths will save the project approximately £20 million, Draycott says. The Silver Jubilee Bridge will also become a tolled structure following the completion of the project. The Halton Borough Council will put the toll money toward payment to the preferred bidder on the design, build, finance, and operate contract—Merseylink, a consortium comprising equity members Macquarie Capital Group, Bilfinger Project Investments Europe, Vialia Sociedad Gestora de Concesiones de Infraestructuras SL, and FCC Construcción SA. Merseylink will not only finance and construct the project but also operate the project for 26 1/2 years following its completion.
Construction of the project is expected to take three years and completion is anticipated in 2017. At that time, the Silver Jubilee Bridge will be reconfigured to be similar to its original design—one traffic lane in each direction—and a majority of the traffic will be diverted to the new bridge, ending the decades long struggle to adequately accommodate traffic over the River Mersey in Halton once and for all.