Humber Bridge: open all hours
Maintaining the Grade 1 listed structure involves working round high wind speeds and 24/7 traffic flow.
In January, the Humber Bridge Board (HBB) brought its first private prosecution against an “urban explorer”, Ryan Taylor, who had scaled the 155.5 m tall Barton Tower on the structure’s south bank without permission. The climber was part of a group that had clambered over a barrier and used the bridge’s suspension wires as handrails to walk up the cables to the tower summit.
The group took videos and selfies from the top, posting them on YouTube. They had no harnesses or any other safety equipment.
As a future deterrent against urban explorers, HBB has reinforced the anti-climb, wire-mesh guards on the approach cables (see photograph below). Taylor was fined £400 but the tower climb could have had more serious implications for road users.
The Humber Bridge
In 1927, civil engineer Sir Ralph Freeman, acting for the City and Corporation of Hull, proposed a multi-span road bridge 6.4 km west of Hull connecting Hessle on the north side and Barton-upon-Humber on the south but the financial crisis in the late 1920s halted the plans.
In 1955, Freeman Fox & Partners proposed a suspension bridge with a 1.4 km central span, which was approved (bit.ly/2DQceEj). The Humber Bridge Act 1959, which allowed construction to begin, also created the Humber Bridge Board (HBB).
However, it was only in 1971 when the government lent the board 75% of the costs that the project went ahead. Work began with the substructure in March 1973 and the bridge opened to traffic on 24 June 1981.
The Humber Bridge is the first major suspension bridge to use hollow reinforced concrete towers, each standing 155.5 m high, to carry the spans.
The main steel cables are 700 mm in diameter and weigh 5,500 tonnes each. Each cable consists of 37 strands, each comprising 404 lengths of 5 mm high-tensile galvanised steel wire. The cable on the shorter northern span has 800 additional wires in four extra strands. Each main cable can withstand a maximum pull of 19,400 tonnes.
The road deck structure is 28.5 m wide and 4.5 m deep and is suspended from the main cables by 242 inclined steel hangers. The road deck carries a dual two-lane carriageway and two combined footpath/cycle tracks.
When it opened, it was the world’s longest single-span suspension bridge and remains the longest that can be crossed on foot or by cycle.
Since the tolls were reduced in 2012, car crossings have risen by 31% while truck and lorry usage has gone up by 34%. The government wrote off part of the debt for the 75% loan and the outstanding balance stands at £148m, which will be paid off in 2034.
“If one of them had slipped and injured themselves on top of the cable, we would have had to deploy a full-scale, at-height rescue to recover them,” says HBB head of infrastructure Andrew Arundel. “This would have involved lane closures for safety and significant disruption to the public.”
The tolls collected to cover the annual maintenance bill for the UK’s longest single-span suspension bridge [see box right] support the bridge’s operation and ensure the traffic using the A15 dual carriageway between East Yorkshire and North Lincolnshire continues to flow all day every day. Every week, 120,000 motorists make the 2.2 km crossing.
Maintenance requires careful planning. As Arundel explains, closing traffic lanes at peak hours to undertake routine and essential works is out of the question.
“We have made a commitment to minimise disruption to the road user and maintain commuter traffic at all times if possible,” he says.
For some essential and planned maintenance [see box below], the HBB will sanction small closures and, if necessary, undertake work in the early hours of the morning when there is little traffic on the 24-hour carriageway.
“Night-time work is used for more extensive works on the carriageway network that would affect the road user [in the day],” he says.
“If we can do operations during the day, in between peak hours [6am to 9am and 3.30pm to 7pm], we’ll do that, but you’ve only got a short working window.”
The arrival of chief executive Kevin Moore in February 2017 prompted a review of the HBB’s OSH policies. Arundel was asked to assess the board’s management systems and he recommended bringing in independent OSH consultant Raymond Bone, chair of IOSH’s Humber branch, to provide “a hand and fresh pair of eyes”.
Bone developed an induction programme, which applies both to the board’s 75 site staff and to temporary workers and contractors. Arundel says everyone passed the induction within the first two months of its introduction. HBB has plans to roll out an annual refresher programme from April.
HBB’s reliance on contractors makes management of third parties critical. For example, every six months, engineers service the lifts in the main office building and check the service lifts in the bridge towers.
Arundel says a key part of HBB’s responsibilities as a dutyholder is to ensure contractors report on arrival so HBB can monitor their movements as work progresses.
HBB employs an Industrial Rope Access Trade Association level 3 supervisor on the site, who reviews and checks risk assessments for maintenance involving work at height and ensures contractors are competent for bridge work.
Minor cable maintenance is carried out by HBB’s own work-at-height team and external contractors are used for major maintenance or structural work. The inspection of the main suspension cables is a case in point.
“The contractor has to carry out a mix of high and low level inspections of the main cable,” says Arundel.
“This involves erecting scaffolding adjacent to traffic lanes (low level) and the fabrication and installation of a crawling cradle to do the high-level intrusive investigations.”
Each spring and autumn HBB’s work-at-height team walks the length of the suspension cable to check it for corrosion and other defects. HBB has a wind threshold of around 40 kph, above which the team cannot walk the cables. The board requires a dynamic risk assessment of the weather to check it is safe to proceed.
In 2009, HBB carried out its first intrusive inspection of the main cables to determine the condition of the wires that make up each cable. Although the cable was in good condition, there was evidence of water ingress. The internal main cable inspection revealed widespread corrosion, although the number of broken wires was very low (bit.ly/2nuhm9U).
In December 2010, HBB turned on a new a cable dehumidification system, which involves injecting dry air in and then expelling it via exhausts. The board measures the relative humidity (RH) of the expelled air so it can monitor the RH of the air in the cable and ensure it remains at a level that reduces the risk of further corrosion.
The board also installed an acoustic monitoring system with microphones placed along the main cable.
“The purpose of the microphones is to listen for any potential breaks of the 15,000 5 mm diameter steel wires that make up the main cable,” says Arundel.
We never close
Humber Bridge Board (HBB) head of infrastructure Andrew Arundel says the HBB is carrying out work to replace the side-span expansion joints that connect the anchorages to the side spans. Work started in December 2017 and completion is planned for April.
“As the joint is continous across the carriageway and because of its construction, we cannot carry out the works with a lane one and then lane two closure and maintain the safety zone to comply with chapter eight in the Department for Transport’s Traffic Signs Manual [which governs road works safety] ,” he says.
“We’ve designed the scheme to be carried out overnight and this involves closing a full carriageway with traffic maintained under contraflow on the other carriageway. This incorporates a temporary ramp system, which enables traffic to maintain normal flow. Otherwise, we’d have to go into contraflow 24/7 during the daytime, which would cause major disruption.”
The dehumidification and acoustic monitoring are inspected at least every six months, he adds.
In addition to the cable dehumidification, HBB has similar systems in the anchorages and inside the steel road deck.
Initial access to the anchorages involves descending a fixed ladder from the footway before entering the main anchorage void and then descending and ascending using ladders to get at the mechanical and electrical plant. HBB has to provide a safe means of access and egress.
“We have rescue plans and the appropriate equipment, and we have joint training exercises with Humberside Fire and Rescue,” says Arundel.
The Barton anchorage is the larger of the two and is 82 m in length and 40 m wide. Though work inside is limited, plant must be maintained and inspected.
“Because of the sheer size of the anchorage, you can imagine that to do an inspection of the concrete walls it would require some type of temporary access, so if you are introducing mobile scaffolding that’s another hazard,” he says.
“There are lots of scenarios where somebody could be injured and so the important point is making sure they aren’t and that we’ve got the right equipment.”
The board is having a transmitter antenna installed on the towers to improve radio coverage across its 14 hectare estate. As part of the new induction programme, staff were encouraged to report any safety issues to management, and the operations teams highlighted blackspots where signals dropped.
HBB’s estate, which covers both sides of the bridge, includes three large car parks and land on the north bank of the Humber that adjoins a country park owned by East Riding of Yorkshire Council. Staff carry out a range of activities, some of which involve working on their own for small periods, such as litter picking, grass- and tree-cutting and minor landscaping.
“The upgraded radios now come with a man-down and lone worker facility as well as global positioning,” says Arundel.
“This means we can set up a radio to automatically alarm at regular intervals so the person has to check in with the office. The radio will also send out a call if the person does not respond.”
Once the new system is installed, HBB will have fuller coverage across the bridge site.
“We want to test the coverage of the new radio system within the bridge itself to aid communication and reduce reliance on the existing phone system,” he says. “This may mean installing additional radio boosters in the anchorage or road deck.”
Since November 2015, HBB has operated the first hybrid toll collection system with automatic payments, which allows motorists with HumberTAG to drive across without stopping at the six staffed toll booths on the north bank. More than half the bridge users take advantage of the system.
Although the new toll system has brought many benefits, including more reliable journey times, it has also seen some irresponsible and potentially dangerous driving from a small number of motorists.
Arundel says there have been instances of motorists approaching the toll area in the 50 kph free-flow lane used by HumberTAG users and then changing their minds about crossing.
“A few motorists have chosen to drive in the open lane and then reversed back against oncoming traffic,” he explains. “Then, we’ve had motorists who will drive up to the toll booth and decided they don’t want to cross. [In extreme cases], they have done a U-turn and driven against oncoming traffic.”
HBB carried out a review and has refreshed the signage on both approaches to the open lanes.
“We have put up additional signs at the entrance to the bridge, which clearly say, ‘No reversing and no U-turns’ and repeated these along the open lanes,” he adds.
The board is also running an “awareness” campaign to reinforce the message.
On the buffers
The dual carriageway section across the bridge is restricted to an 80 kph limit but there is no hard shoulder so, if vehicles break down or there is an accident, traffic is restricted to a single lane.
Since April last year, the board has deployed an impact protection vehicle (IPV) to provide improved protection to the HBB response team and the emergency services as they deal with incidents on the bridge or during road deck maintenance.
The introduction of the IPV was a result of OSH consultant Bone’s overhaul of safety and health. The IOSH member reviewed current practices and incident management response and recommended the use of an IPV.
Arundel adds that the decision was taken to provide an IPV and driver for 24/7 use. An external traffic management company supplied these initially, basing the IPV on site for immediate response.
At the same time, the board embarked on a comprehensive training programme for its staff to use the vehicle.
HBB also purchased two of its own IPVs, which its staff will drive and operate once fully trained. The decision to deploy two vehicles means there is at least one IPV available at all times should HBB need to respond to two incidents at the same time.
“If there is a breakdown, we’ll deploy the IPV and a support vehicle,” he says.
“Our staff will go out and assess the situation. If it’s a broken-down vehicle, we’ll determine whether recovery is imminent or whether we have to make other provisions to recover it.”
Staff have attended the National Highways Sector Scheme 12A/B for static temporary traffic management on high speed dual carriageways, which was delivered in-house.
However, during training the HBB became aware of a new, more relevant, sector scheme specifically designed for incident management on the highway, which comes into force on 1 April, and has trained its staff to this new standard.
The exposed position of the bridge leaves it to the mercy of powerful crosswinds. The structure is designed to withstand speeds of around 169 kph on the deck and 241 kph at the tops of the towers but not all vehicles crossing the bridge are so stable.
Overturns in high winds are rare but the HBB is trying to reduce the number of incidents further. Bulky but light abnormal loads, such as portable buildings, are particularly vulnerable to crosswinds.
To mitigate the risk, HBB promotes a “high wind” policy, which includes different levels of warning signs on both sides of the Humber and the surrounding motorway network.
For instance, any load heavier than 50 tonnes must be escorted if there is a cross wind stronger than 54 kph and it is moving in the windward carriageway. When the wind exceeds 76 kph, HBB closes the bridge to abnormal loads.
HBB is launching an education campaign this month that focuses on high-sided vehicles and is working with the police, the Road Haulage Association and local authorities to publicise the restrictions on using the bridge.
As some drivers may not appreciate that their vehicle is classed as high-sided, HBB will be planning ahead for extreme weather conditions and will work with the police to direct relevant vehicles away from the bridge.
As a vital link between East Yorkshire and North Lincolnshire, traffic is increasing, not only during the week but also at weekends. Whatever restrictions are introduced, the board recognises that keeping the bridge open to traffic is a priority.
“It is important that we maintain the flow because any backlog here has an impact on the adjacent infrastructure, particularly on the East Yorkshire side and the roundabout on the approach to the bridge, and this could knock on to the Highways England network,” says Arundel.
Nick Warburton is deputy editor of IOSH Magazine