Mobile Mapping - adopt, adapt and analyse
Mobile Mapping - adopt, adapt and analyse
Mobile mapping is just one of the technologies adopted by National Highways to maximise the benefits of new technology for its data-driven concrete roads programme. This programme, for the improved inspection and maintenance of concrete roads, has been developed with two key aims in mind, firstly to produce immediately useful results and secondly, to be part of a larger end to end digital strategy.
Addressing the challenges
Undertaking highway surveys is an activity that brings its own unique set of challenges:
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For health and safety purposes, roads historically had to be closed whilst surveyors walked the network looking for defects. This took time to plan, required traffic management and disrupted the network, severely inconveniencing road users. In a recent calculation undertaken by Michael Ambrose (Technical Lead on National Highways concrete roads programme) when the A14 near Haughley, Cambs, was shut unexpectedly, a diversion added around 45 minutes to the journey costing road users in excess of £300k in fuel during the 8-hour closure as well as increasing carbon emissions.
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Defects were recorded by chainage using only pen and paper and therefore lacked an accurate position and visual detail.
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There was an information lag between the information being collected, transcribed, report preparation and this report being shared with different stakeholders.
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Collected data was effectively siloed with no single source that could be referenced by the different stakeholders. Because of this, once surveyed, the works management of the repair was disjointed.
National Highways was aware that Building Information Models (BIM) had been successfully implemented into other industries and was therefore keen to assess what technology was available to create a single, as-built 3D model of the highway whilst minimising disruption to the network.
The case for mobile mapping
National Highways commissioned consultants Mott MacDonald to manage two trials in the East of England which would include the use of mobile mapping. Following an evaluation of the systems available, National Highways contracted KOREC Professional Services to survey the two selected routes using the Trimble MX9 system. Trial 1 was a 1km stretch of the A12 in Chelmsford (concrete), Trial 2 was a 1km stretch of the A12 in Mountnessing (concrete overlaid with asphalt).
The two sites were surveyed to the National Highways specification using the MX9 Mobile Mapping system. Ground control was established every 200m using checkerboards of at least 30-50cm in size to achieve the highest absolute accuracy (although GCP’s are not required for pavement condition assessments). Data was captured by driving both carriage ways in all running lanes at normal traffic speeds of between 50 and 60mph.The surveys were executed during daytime hours to simultaneously capture high quality imagery and LiDAR point cloud and during the hours of reduced traffic flow to minimise occlusions, any data gaps and to ensure sufficient point cloud density. Adverse weather conditions such as dense snow or fog were also avoided as were any times when there were puddles on the highways.
Deliverables
The collected data was processed by the KOREC Professional Services team and the point clouds matched to a relative accuracy of better than 10mm. The point cloud was then colourised using the captured georeferenced imagery and exported for use in the KOREC portal.
Specified deliverables included:
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RGB coloured and classified Laser point cloud (LAS 1.4 format)
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360° imagery (in georeferenced Jpeg format)
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Down facing imagery
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Down facing orthorectified and mosaiced imagery
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Defect survey (delivered as shape file and containing UKPMS DVI* user specified information)
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Toporaphic mapping
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Full survey report
Post-trial findings
National Highways were able to draw several conclusions from the two trials and these findings further backed up their belief that this type of survey would provide them with access to a complete dataset for defect extraction along with full information of a pavement condition. Furthermore, the surveys could all be completed with accuracy, speed and efficiency reducing carbon emissions, contributing to the safety of surveyors and vastly reducing disruption to road users.
National Highways also appreciated that a single survey could have many different applications including pavement condition, geometry of roads and bridges, recording of signs and road assets and vegetation encroachment. Importantly, this method would bring repeatability which would enable managers to use the portal to access a full history of defects, points etc and interrogate collected data, for example, ‘How long is our end-of-life concreted lasting?’ and ‘How are new materials holding up?’
The Trimble MX9
“One drive through with the Trimble MX9 Mobile Mapping system equals 4 or 5 walked surveys which significantly reduces the carbon footprint because there is less travel to and from the site.”
(Michael Ambrose (Technical Lead on the National Highways Concrete Roads Programme)
A mobile mapping system comprises high-density laser scanning, a spherical high-res camera for panoramic and multi-angle imagery, and a high-precision (Global Navigation Satellite System) GNSS and IMU (inertial measurement unit) component for (satellite) positioning. The synchronisation of these sensors allows all recorded points and images to be properly aligned in post-processing.
The Trimble MX9 is one of the most advanced systems in the world combining state-of-the-art, hardware with intuitive field software and a reliable, efficient office software workflow. The MX9 is mounted on the top of a vehicle and rapidly captures dense point clouds and images—both panoramic and multi-angle. Rich corridor data can be collected at highway speeds, significantly improving data collection on busy highways and avoiding costly lane closures.
