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• Managing Our Roads

Bridge Structures Frequently Asked Questions

Q1 Which bridges is the Highways Agency responsible for?

With a few exceptions, the Highways Agency is responsible for all bridges on the trunk road network in England.  The trunk road network consists of almost all motorways and a number of major 'A' roads and provides the main inter-urban and inter-regional routes for through traffic. 

The Highways Agency is also responsible for most other structures associated with those roads, such as drainage culverts, sign gantries, lighting columns and retaining walls.  The exceptions are bridges carrying railway lines over trunk roads and certain privately-owned structures, which are maintained by the owners by arrangement with us. 

Bridges and other structures on trunk roads in Wales are maintained by the Transport Directorate of the Welsh Assembly, and those in Scotland by Transport Scotland.

Q2 Why do so many bridges need repairing?

Most of the bridges on the trunk road and motorway network were constructed in the 1960s and 1970s, and some bridges on the 'A' road network are very much older.  Most were built in reinforced or pre-stressed concrete and have steel embedded within them. 

A combination of natural weathering and the effect of de-icing road salts can over time cause the steel to corrode which often leads to concrete being shed from the surface of the structure, exposing the steel (known as spalling).

This requires repairs to be carried out before the structural performance of the bridge begins to deteriorate and to maintain the aesthetic appearance of the bridge.  Modern methods and materials have improved the durability of bridges and whilst no structure can be classed as maintenance free, modern bridges should require less future work than the older ones do.

Q3 Why do bridges need strengthening?

Over the years, traffic flows and the maximum permitted weight of heavy goods vehicles have both increased, and required standards of safety have improved.

A combination of these factors and occasionally the deterioration of elements of a bridge creates the need for strengthening or protection.  One of the main programmes has involved the protection of bridge supports to ensure they can withstand the impact of the heavier goods vehicles now using the roads.

Q4 What about before bridges are strengthened, are they safe to use?

All bridges on the trunk road network are maintained to a high standard and are safe to use.  The strengthening and protection that is taking place is to safeguard against the unlikely event of a vehicle colliding with a part of the bridge or driving onto an area not originally designed to take the weight of traffic.

Q5 How does the Highways Agency ensure that bridges remain safe to use?

All bridges are inspected regularly, at least once every two years by an experienced bridge inspector.  In addition, routine maintenance is carried out annually to clean and service vital components.  The Highways Agency has a programme of re-assessing the strength of bridges to ensure that they remain capable of carrying the weight of current and increased traffic.

Q6 How long are bridges intended to last?

Bridges are generally designed to last 120 years.  This does not mean that at the end of this period they will fall down, but that all the main components should not require major repair or replacement during that life span.  However, regular maintenance is needed during the life of a bridge and some of the minor elements such as bearings and joints may wear out and need replacement.

Q7 Why do you reduce the speed limit when you are working on bridge supports off the carriageway?

We introduce speed limits to reduce the risk of an accident occurring at the works in the interests of the safety of road-users and the workforce.  Sometimes, we have to reduce the width of the traffic lanes, and reducing the speed limit makes it safer for traffic to negotiate these narrow lanes.

Q8 Is it really necessary to close lanes for bridge works?

We have to maintain an adequate safety zone between the workforce and the traffic.  Depending on the width of the bridge, protection can be provided with a temporary barrier.  Sometimes we have to close one of the lanes to make space for the barrier.

Occasionally if the bridge is very narrow the only way of safely working on certain areas, particularly in the middle of the carriageway, is to close to the carriageway completely.

Q9 Why are there so many different types of bridges on the road network?

The ages of the bridges on the trunk road network span a period of at least 100 years, some of them having been built many decades before the trunk road network was designated.

Methods of design and materials have changed and improved dramatically over that period and modern designs tend to be more efficient in both labour and materials.  The most efficient type of structure at each location will also vary, depending on the loads to be carried and the obstacle to be crossed.

Q10 Why do hard shoulders sometimes not continue under bridges?

When motorways are widened, there is not always room to maintain the hard shoulder under the bridge without demolishing the existing bridge and building a new one.  Providing the safety of road users is not compromised it is much cheaper to stop-off the hard shoulder either side of the bridge.

Q11 Why do you resurface bridges when often the tarmac surfacing doesn't look worn out?

To protect them from the damaging effects of water, bridge decks include a waterproofing layer beneath the surfacing material.  This waterproofing layer can deteriorate independently of the surfacing, allowing water and road salts to enter the structure.

To repair or replace the waterproofing layer we first have to remove the surfacing.  Bridges also include expansion joints to allow for thermal movement  of the materials without cracking or buckling.  These joints have a limited life span and periodically need replacing.

This often requires us to cut out and replace an area of the surfacing.  To minimise costs and inconvenience, we usually replace joints and waterproofing at the same time, and this requires complete resurfacing of the bridge deck.

Q12 Why do you paint bridges, which often don't appear rusty?

There is an increasing number of steel structures on the trunk road network.  The condition of the paint and other protective coatings on these structures is monitored as part of our regular inspection programmes, and any deterioration of the coatings is categorised by severity.

The most cost effective time to repaint a bridge is when the top coat has worn out but the steel has not started to rust.  Little preparation is then needed to clean down and overcoat the paintwork to extend the life of the protective system.  This means less time is taken, costs are lower and there is less traffic disruption.

Q13 Could you not work through the night to avoid closing lanes during the daytime?

Where possible, work on trunk roads which is likely to cause traffic disruption is carried out overnight, or, where the scope of the works requires the traffic management cones and signs to be left in place for longer periods, 24 hours a day.

By doing this we minimise the periods during the daytime when lanes are closed.   However, there are some aspects of bridge works which are temperature- or moisture-sensitive, making them unsuitable for night work, and there are other tasks which for safety reasons cannot be carried out at night.  Some tasks are too noisy to be carried out at night in urban locations because of the effect on neighbouring dwellings.

Q14 Why are lanes often closed when there is no sign of anyone working?

We understand that this can be frustrating, but there are many situations when work is underway but not immediately obvious.  These include periods when works may be going on underneath the bridge, requiring the 'live' traffic loading to be removed from an area of the bridge deck above, or when materials such as concrete and bituminous surfacings are drying out ('curing').

There are also occasions when we have to suspend works at short notice due to bad weather but the works are in a condition which prevents the lanes being re-opened.