M48 Severn Bridge weight restriction

We'll introduce a 7.5t weight restriction for heavy goods vehicles (HGVs) on the M48 Severn Bridge from 27 May 2025 for an estimated 12 to 18 months

Exemptions

Even if they're over 7.5T, the M48 Severn Bridge will remain open to:

all emergency vehicles, gritters and recovery vehicles
scheduled bus services and coaches

What will happen

Diversion route across the Severn Estuary for HGVs over 7.5t

All HGVs over 7.5t will need to use the M4 Prince of Wales Bridge to cross the Severn Estuary.

This is a diversion of 14 miles.

What will happen when the Prince of Wales bridge needs to close?

Planned overnight closures

For planned overnight closures of M4 Prince of Wales bridge, we'll:

put additional control measures in place
allow HGVs over 7.5t to use the M48 Severn Bridge.

We'll divert all traffic off the M48 to roundabouts at Junctions 1 and 2. We'll use traffic management similar to preparation for high winds.

Traffic will then continue onto the M48 bridge from the entry slip roads, where access can be controlled by traffic signals.

We'll monitor traffic to make sure there aren't too many HGVs over 7.5t on the bridge at any time.

This arrangement can only work overnight, when the traffic volumes are much lower. 7.5t weight restriction signs won't be displayed when this diversion route is in use.

Unplanned closures

If there is an unplanned closure of the Prince of Wales bridge, HGVs over 7.5t will need to follow the official diversion route via the M5 and the M50.

This is a diversion route of approximately 100 miles.

How long will the weight restriction last?

We'll need to keep the weight restriction in place for an estimated 12 to 18 months:

depending on further investigations
while we develop and install a medium-term solution to help us manage the number of vehicles over 7.5t using the bridge over the longer term.

The medium-term solution aims to lift the 7.5T restriction by combining technology and traffic management tools (like signs, barriers or signals).

Together these will:

control access to the bridge
ensure vehicle loads remain within safe limits at all times

What enforcement will stop HGVs over 7.5t using the bridge?

We'll work with the local police to enforce the weight restriction.

We're exploring the use of Automatic Number Plate Recognition (APNR) cameras to help do so.

Will this reduce the number of wind closures on the M48 bridge?

At this time, we're introducing mitigation to protect the bridge long term.

We will reassess wind speeds and levels in the future to see what is safe and practical.

Impact

What will the impact of the restrictions be on local economies?

Traffic modelling suggests most HGVs over 7.5t using the M48 Severn Bridge have a destination within 50 kilometres of the bridge.

This means the weight restriction will have a localised impact.

We're working with the haulage sector and regional stakeholders to help them adapt their operations.

Will you provide compensation for businesses and drivers affected by the weight restriction?

We're not obliged or required to pay compensation for disruption, costs, or inconvenience, caused by roadworks.

This is because the work we do (maintaining and improving the highways for all to use) is considered a statutory duty on behalf of the Secretary of State for Transport.

This is covered under section 278 of the Highways Act 1980.

Will the Parkrun need to stop using the bridge?

The Severn Bridge Parkrun can continue.

Timing

If there's an issue with the bridge, why is the weight restriction only coming into force from 27 May?

We need time to engage with stakeholders including the local haulage industry who'll be affected by the restriction.

We're satisfied that the bridge is safe and confident there's no risk allowing HGVs to use it while we engage with stakeholders.

Why not wait until the Prince of Wales work is complete before introducing the weight limit?

If heavier vehicles continue using the bridge, it could ultimately close to all traffic.

We're acting now to stop this happening.

Background

Is the bridge safe?

While we carry out further investigations, we are :

satisfied the bridge is safe for traffic to use
confident that that there has been no risk to safety by allowing HGVs to use the bridge

Safety is our number one priority. As with all our major structures, we'll continue to monitor the bridge.

There are multiple structural health monitoring systems active on the bridge. They're all currently indicating the bridge is operational and safe to use.

However, continued use of the bridge by heavier vehicles could ultimately see it closed to all traffic.

We're acting now to stop this happening. We're looking at long-term measures to ensure the bridge stays open to traffic for many years to come.

What's caused this issue?

Corrosion

The M48 Severn Bridge is almost 60 years old. It's exposed to hostile marine and weather conditions all year round. This has contributed to the corrosion of the cables.

Increased traffic levels and weight

The bridge wasn't designed and built for today’s levels or weight of traffic. Vehicles have got heavier and traffic levels have increased significantly over the last 60 years.

Since tolls were removed on the bridge in 2018, there's been a 34% increase in traffic.

Taken together, these changes have substantially increased the load challenges on the bridge.

How long have you known there's a problem?

Over the last 20 years we have:

regularly assessed the bridge’s main cables
taken steps to mitigate ongoing deterioration

To keep the bridge open and minimise disruption to road users, we've employed measures including:

installing an Acoustic Monitoring System
lane restrictions so vehicles over 7.5t are not allowed in the offside lanes on both sides
installing a cable drying system - which has helped control the rate of visual corrosion to the main cable

We performed our latest assessment and laboratory testing in 2022-23 and finalised our findings 2024.

The results show that

corrosion has become worse
the main cable on the bridge has deteriorated and weakened

After the 2023 assessment, you said corrosion levels were as expected and mitigation was working well. Why and how has this changed?

At the time of the 2022/2023 assessment, visual levels of corrosion were the same as previous inspections. This indicated that the cable drying system we had installed had continued to prevent further visual corrosion.

As part of the main cable inspection, we removed a large number of highly corroded wires for laboratory testing.

Test results showed a significant percentage of these wires had a lower strength than previously expected. This had led to a reduction in cable capacity.

Your recently published Delivery Plan Update says there are latent defects with the bridge cables so why are you only acting now?

We found corrosion of the suspension cables during the first intrusive inspection in 2006.

This inspection was commissioned after the National Cooperative Highway Research Program (NCHRP) in the USA issued “Guidelines for inspection and strength evaluation of suspension bridge parallel-wire cables” in 2004.

This document was published after some older major American suspension bridges were showing signs of deterioration in their main cables.

Since 2006, we've continued a programme of work to manage the operation of the bridge with the corrosion defects.

The inspection programme is a significant element of this work. It has resulted in the current strength assessment.

How often do you survey the bridge?

The main cable has an internal inspection approximately every five years.

We conduct external inspection of the entire length of the cable every two years.

We conduct structural health monitoring, such as acoustic monitoring, constantly. We review this monitoring on a monthly basis.

Will you repair the cables?

We've started to look at the feasibility of adding more cables on the bridge to provide more strength. This will take a number of years to finish.

What will be the cost of repairs?

We estimate repairing the cables could cost between £300m and £600m.

We'll confirm final costs when design work is complete.

Who will fund the repairs?

We have to agree funding of large schemes with DfT

Will there be long-term funding to maintain the bridge until repairs take place?

We have funding for current plans, including:

installing weight restriction
routine and reactive maintenance
the next major cable inspection in 2027.

Have you ever strengthened the cables or had the option to do so?

The Department of Transport first strengthened the bridge, not including the main cable, in the 1980s. This was in response to increasing traffic volumes.

No strengthening of the main cable has ever been carried out.

Why isn’t the restriction 18t or 22t?

The vast majority of the loading for the bridge comes from the weight of the bridge.

This means structure is very sensitive to traffic loading.

We've examined the effect of different traffic restrictions and a 7.5t HGV restriction is deemed necessary.

What other options have we considered?

We've looked at various lane closure options, but these wouldn't reduce the weight of traffic enough.

Lane closures would also have a significant impact on traffic congestion on the wider road network, especially during peak times.

The new M49 junction would help mitigate the impact of this weight restriction. When will it open?

South Gloucestershire Council will soon start building the local link road from Severnside Industrial Estate to the new junction.

Construction will take approximately a year to complete. The junction will open shortly afterwards.

Facts and figures

the M48 Severn Bridge opened to traffic in 1966
annual Average Daily Traffic (AADT) for the bridge was 31,936 vehicles in 2024
3,720 HGVs over 7.5t use the M48 Severn Bridge every day. They account for approximately 10% of the traffic over the bridge.