Case Study - Site Investigations 
 
Introduction 
Oxfordshire County Council updated their policy for skidding resistance on the highway network and adopted a requirement for conducting site investigations to prioritise the likely risk to road users. This policy was based upon the current best practice principles as defined in the Highways Agency’s Design Manual for Roads & Bridges, Volume 7; HD28/04 and supplemented by Oxfordshire’s own policies. Wilson Pym May provided a new methodology for targeting sites ensuring all treatments were suitable.  
 
This case study highlights the innovative use of geographical information to promote informed decision making through a customised user interface. 
 
Problem 
The existing strategy for dealing with sites exhibiting a less than adequate skid resistance was to plan them for surface dressing as part of a safety treatment programme. Cursory driven inspections were undertaken to confirm the suitability for treatment. 
 
This approach meant that condition data was being used as intervention criteria rather than investigation criteria and consequently unsuitable or unnecessary treatments were sometimes applied. 
 
Solution 
Oxfordshire tasked Wilson Pym May with providing a methodology for targeting sites and prioritising suitable remedies to bring about an overall high and consistent standard of skidding resistance in the longer term. 
Wilson Pym May analysed the skid resistance data within a Geographic Information System (GIS) to determine sites that required investigation in line with the published OCC policy. Bespoke data collection forms were developed to enable a reliable site record to be produced using mobile GIS data capture devices.  
Timely pavement investigations were carried out and comprised the following main elements: 
 
A check of the Site Category events present; 
Determination of the existing surface type; 
Factors contributing to the observed skid resistance readings 
Assessment of the nature of potential accident risk; and 
Identification of defects affecting treatment selection 
 
A further aim of the survey was to determine the surface integrity of the existing pavement and to recommend cost effective treatment that would enhance the engineering performance of the pavement in response to the observed data. 
 
 
 
Outcomes 
The findings from the investigations were presented in a report ordered by route, detailing the priority sites for treatment and those that may be incorporated within a programme of future works. Additional condition information from Scanner and Deflectograph were also considered to inform proposed treatment selection and extent. 
 
Specifically, the client is now able to 
 
Verify the current actual surface condition of the existing pavement compared to the measured values presented from the skidding resistance survey. 
 
Identify the presence of additional defects where these may contribute towards the reasons for failure at the site, or where these might affect the selection of the most appropriate and cost effective treatment. 
 
Ensure that site investigations were carried out consistently for all sites and in line with current best practice. 
 
Objectively limit the liability through risk management. 
 
Recommend the most appropriate treatment based on site observations, using minimum whole life cost as a key driver for any recommendation
 
Make better informed decisions regarding the maintenance of the network, and to more efficiently target its own resources and manpower towards resolving skidding resistance issues.