Traditionally, highway infrastructure redevelopments, civil engineering projects, utility diversions and even single excavations are designed around the information contained in utility company record drawings.  This is still seen by some as an essential practise, but, just how accurate are record drawings that are sourced from the various utility companies?  This is a difficult question to answer as the accuracy of these records can vary dramatically from company to company and even from area to area within the same service company.

Technics Group were commissioned by a major organisation, who were concerned with this situation, to evaluate the benefits of an accurate Utility Mapping Survey over the information supplied by Statutory Undertakers.

Using the most comprehensive and reliable utility tracing methodology possible, an entire central London site was thoroughly investigated using Radio Location and Ground Penetrating Radar, a 3D model of all detected services was then produced.  The client then conducted a significant number of excavations around the site to verify the accuracy of the survey results.

Following this all the record drawings from all the utility companies that had any plant in the area were accurately digitised, using the OS background maps as the common feature.  Within a CAD environment, the utility record drawing information was laid over the survey results and cross sections generated at 10m intervals around the site.  Each section was then analysed and the horizontal distance measured between the record position and the traced position for each service.

The resulting statistics surprised everyone involved and certainly proved the case for using accurate and reliable utility information, to base important design and excavation decisions on.  The headline statistics included:

• Average plan distance error was 1.6m across all utilities measured, with largest recorded error being 7.17m.
• An additional 186 buried linear features were detected that were not described on any utility record drawings.
• 61 utility services were detected within 200mm of the surface of the ground within the area.

Admittedly this is only a tiny snapshot of the national situation; however, would you be happy for your designs to be based on this level of accuracy?  Indeed, would you be happy knowing that your personnel are excavating in areas that these plans show to be risk free? Our client for this project now instructs Utility Mapping at the earliest opportunity for each new project.

Below are some examples of individual utility record drawing positions (Blue) versus traced positions (Red):

Barclays Cycle Superhighways are new cycle lanes into central London from outer London. They will provide cyclists with safer, faster and more direct journeys into the city.  The first two are already in operation and two more are planned to be in operation this summer with a further 8 superhighways to be introduced by 2015.

Technics Group has been working with Jacobs Consultancy who are currently designing Routes 2 and 12 superhighways for TFL.  A number of sites were identified along the intended routes where the designs could be in conflict with existing utilities.  With it being essential that disruption to the public is minimised and that delivery of the routes are not delayed through unexpected encounters, Technics Group were commissioned to thoroughly investigate these areas.  The information generated through these surveys is now being used to base essential alterations to footpaths and kerblines to accommodate various proposals along each route.

Utility surveys were undertaken to “level 6” survey methodology, this includes radio location and comprehensive coverage with Ground Penetrating Radar (GPR). 13 sites were surveyed along Route 12 in north London and the results appended to a topographical survey in a digital CAD format to allow Jacobs Consultancy designers to work directly with the survey output.  Below is an example of one of these sites:

See our Utility Mapping web page

For more information on the cycle route please visit http://www.tfl.gov.uk/roadusers/cycling/11607.aspx