7.5T Weight Limit To Be Introduced On Deteriorating M48 Severn Bridge

National Highways has announced a new weight restriction for the M48 Severn Bridge, effective from 27 May, after signs deterioration were found during recent inspections of the cables.

Under this limitation, only vehicles weighing up to 7.5t will be permitted on the 1.6km suspension bridge, a decision aimed at ensuring the longevity and safety of the structure.

With these new measures in place, HGVs exceeding the weight limit will be redirected to the Prince of Wales Bridge for journeys between England and Wales. This restriction is expected to divert approximately 3,270 HGVs per day, which constitutes about 10% of the 32,000 vehicles that typically cross the M48 daily.

The bridge, which opened nearly 60 years ago, has seen significant increases in both traffic volume and vehicle weight – HGV sizes have escalated from 22t to as much as 44t, and traffic has surged by 34% since tolls were removed in 2018.

Concerns over the bridge’s capacity to handle these growing demands have prompted ongoing assessments, particularly focused on its main suspension cables, which have suffered from corrosion and fatigue exacerbated by harsh weather conditions. It currently closes when windspeeds exceed 20mph (32km/h).

There are very small spaces between the 5mm wires that form the bridge cable that allow moisture to enter and cause corrosion. The 511mm diameter main cables are routinely opened up and inspected every five years.

In 2022/23, an assessment of the bridge’s main cables was carried out, followed by further laboratory testing, revealing that the main cables are deteriorating and not as strong

In a comprehensive evaluation finished in December 2024, tests revealed that the main cables of the M48 Severn Bridge are deteriorating and no longer possess the strength required for the current loads. Consequently, National Highways recommended the implementation of load restrictions to mitigate further damage to the structure.

This weight limitation is expected to remain in effect for an estimated period of 12 to 18 months, pending further investigations and the development of a medium-term management solution. Plans are underway to utilise Automatic Number Plate Recognition (ANPR) cameras to enforce the new regulations effectively.

Emergency vehicles, scheduled buses, coaches, gritters, and recovery vehicles will still be able to use the M48 Severn Bridge under the new restrictions. However, should unforeseen closures occur on the Prince of Wales Bridge, HGVs over the weight limit will be redirected via an official diversion route using the M5 and M50 motorways.

As National Highways focuses on preserving the structural integrity of the M48 Severn Bridge, the implementation of these weight restrictions highlights the ongoing challenges faced by aging infrastructure in accommodating modern transport demands.

National Highways programme delivery manager Chris Pope said: “Safety is our number one priority, and this weight restriction is about future-proofing the bridge for years to come.

“Whilst the bridge remains safe, it was not 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 putting greater load on the cables.

“As with all our structures, we will continue to monitor the bridge and ensure it remains safe for users.

“We’d like to thank drivers for their support and must stress that only heavy goods vehicles up to 7.5t weight should use the bridge.

“Continued use of the bridge by heavier heavy vehicles could ultimately see it closed to all traffic. We are acting now to prevent this from happening.”

Like what you've read? To receive New Civil Engineer's daily and weekly newsletters click here.