UKCW Birmingham: 1-3 October 2024 | NEC
UKCW London: 6-8 May 2025 | ExCeL


M4 Smart Motorway

SDS Limited Stand: N140
M4 Smart Motorway
UK's first installation of BBA-certified Weholite pre-fabricated chambers.


Much of the M4 currently suffers from heavy congestion, often in excess of 130,000 vehicles per day. Improvement of the M4 to a smart motorway will help to relieve this congestion by permanently converting the hard shoulder to a running lane and using technology to monitor traffic flow. At 32 miles, this is the longest smart motorway project in England to date.

The redeveloped motorway will provide much needed additional road user capacity, ensure faster and safer journey times, and also facilitate economic growth within the region. SDS was asked to ensure any surface runoff, that is contaminated by pollutant spills from the carriageways, is prevented from entering the natural surroundings.


SDS introduced within the existing structure of filter drains, an environmentally safe surface water storage and drainage solution. The scheme design includes replacement of the existing drainage system where required and additional storage within the drainage system to maintain current discharge rates to outfalls. The existing central reservation drainage system will be replaced with surface water channels or linear drains, and some sections of the verge drainage will also be replaced with new linear drains.

Since the scheme involves minimal additional impermeable areas, and discharges will essentially be limited to current rates, the adopted mitigation measures will ensure that any impacts on the water environment, in terms of surface – and ground – water quality, drainage and flood risk, will be negligible.

Image kindly supplied by Balfour Beatty


The product’s versatile nature and ability to be delivered from its South Wales factory in a timely manner, in unique sections of pipework, ensured that this project could be delivered on time.

The client also recognised the benefits of the Weholite product’s light weight, proven durability, resistance to abrasion and toleration of ground movements.


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