M4 Junctions 3 to 12 Smart Motorway Topographic Mapping

Mouchel Awards IBI Group a large topographic mapping survey on the M4 between Junctions 3 to 12 for a Smart Motorway scheme

As a part of the 2010 Spending Review, The Highways Agency proposed to improve 28Km of the M4 between junction 3 to the west of London Heathrow to junction 12 at Reading by making it a “smart motorway”. Smart motorways help relieve congestion by using technology to vary speed limits. They also allow the hard shoulder to be used as a running lane at peak times to create additional capacity.

In 2013, the scheme was approved and the designer, Mouchel was appointed, the initial task was to produce scheme options to overcome specific challenges as the existing motorway did not have a continuous hardshoulder with structural envelopes, sufficient for the application of dynamic hardshoulder running. Given these issues, acquiring accurate topographic information for the scheme was critical, however, the use of traditional site based methods would have taken five months to gather and caused disruption given the requirement for traffic management not withstanding the associated costs.

To resolve these issues Mouchel engaged IBI Group to develop a topographic mapping specification for the required features and a mythology to ensure that the spatial tolerances were met.

IBI Group’s approach was to collect MMS data over two nights to minimise potential occlusion from passing traffic, to ensure a very dense point cloud was attained, maximising the potential for extraction of distant features. In addition, five ground control sites were established on overbridges throughout the scheme to ensure that the 30mm RMS absolute and 10mm RMS relative accuracies could be achieved and maintained throughout.

The LiDAR point cloud was then used to extract the topographic features within seven weeks from initial collection. The extent of final deliverables included;

  • 3D topographical survey 1:200 scale drawings
  • 3D MX (MOSS) Genio Model
  • Permanent control witness diagrams
  • Survey report

The use of MMS to deliver the above datasets resulted in a net saving of 80% over traditional means excluding traffic management cost and in a fraction of the time.

Mouchel plan to use MMS topographic mapping techniques for all future smart motorway schemes and other projects where the technology is deemed appropriate.