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Andy Stevenson Anuradha Premathelaka John Donbavand. Targeted Approach to the Management of Skidding Resistance. W.D.M. Limited North View, Staple Hill, Bristol BS16 4NX Telephone: 0117 956 7223 Web: 2004 Skid Standard HD/2804.

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andy stevenson anuradha premathelaka john donbavand
Andy Stevenson

Anuradha Premathelaka

John Donbavand

Targeted Approach to the Management of Skidding Resistance

W.D.M. Limited

North View, Staple Hill, Bristol BS16 4NX

Telephone: 0117 956 7223 Web:

2004 skid standard hd 2804
2004 Skid Standard HD/2804
  • In 2004 a new National Skid Standard was issued in the UK.
  • Although the HD Standard was specifically for the trunk roads, most Local Road Authorities followed the standard rather than develop their own.
  • Cornwall implemented the new standard but found that the amount below the IL increased from about 16% to 40%
reasons for the increase in potentially deficient sites
Reasons for the Increase in Potentially Deficient Sites
  • The bend definition changed to include all radii up to 500m to be classified as bends (Previous 250m)
  • Therefore sites with radii between 250m and 500m which were previously a non event site with an IL of 0.4 or 0.35 now required an IL of 0.45 or greater.
relatively high proportion of bends
Relatively High Proportion of Bends

The effect of changing the bend criteria had a significant impact on Cornwall because of the proportion of bends in the area

wdm commission
WDM Commission
  • Cornwall Council commissioned WDM to review their Skid Policy - To determine if the IL’s in the National Standard for trunk roads are indeed appropriate for the Cornish local roads
  • Using the results of the study a policy was developed and a few changes to the HD Standard were recommended But with regard to bends it was found that:
    • Including sites with radii up to 500m as bends was justified and
    • The IL should be increased from 0.45 to 0.50!
implementing the skid resistance policy
Implementing the Skid resistance Policy
  • Cornwall Council after much debate accepted the results and realised they needed to get on top of the skidding problem.
  • In the Cornwall Local Transport Plan 2006 to 2011 it was stated that priority would be given to safety schemes
  • Skid deficient sites have been targeted as part of this strategy.
requirements of the skid policy
Requirements of the Skid policy
  • A significant proportion of the surfacing budget was allocated to treating skid sites
    • 66% of all schemes carried out between 2006 and 2008 were skid related
  • Therefore – Paramount to ascertain that the skid policy was producing positive results in terms of crash savings
review of the skid policy
Review of the Skid Policy
  • An analysis of the crash data was undertaken for a 3 year period
    • 01 Jan 07 to 31 Dec 09
  • These data were compared with crash data from the earlier study prior to 2007.
findings from crash analysis
Findings from Crash Analysis

KSI = Killed or Seriously Injured

crash reduction
Crash Reduction
  • The average crash reduction since implementing the policy is:

33 wet crashes per year

Of these

8.25 crashes per year were KSI’s

verifying the benefits
Verifying the Benefits
  • Nine sites that were treated within the 3 year study period were selected at random for before and after studies.
  • The total length of these schemes was 15.843 km and the cost was £707,488
  • Only part of each scheme was skid deficient
injury and damage crashes
Injury and Damage Crashes

The wet crashes have reduced from 19.7 per year to 7 per year, a 65% reduction.

The number of dry crashes have not changed – Indicating that the skid policy is likely to be responsible for the reduction of wet crashes.

first year rate of return
First Year Rate of Return
  • FYRR was used to evaluate the schemes
  • Two ways to calculate the benefits were used:
    • Firstly an average cost for an injury and damage only crash was used, £75,610 and £1,970 respectively
    • Secondly where the value of a crashes saved is based on severity. Fatal £1,876,830; Serious £215,170; slight £22,230 and damage only £1,970
first year rate of return average values used
First Year rate of Return (Average Values Used)

FYRR – A way of determining whether a scheme is economically justified

Benefits of a scheme /Costs of the scheme – in the first year

conclusions on input
Conclusions: On Input
  • A revised skid policy was implemented in Cornwall in 2006/07
  • Cornwall has used a targeted approach in selecting sites for treatment
  • 66% of all Schemes undertaken are based to some extent on improving the skid resistance
conclusions overall outcomes
Conclusions: Overall outcomes
  • The wet crash rate has dropped
  • The total proportion of wet crashes per km has dropped by 16%
  • The proportion of KSI per km has dropped by 24%
conclusions before and after study
Conclusions: Before and After Study
  • From a before and after study on 9 sites it was found that:
    • There was a 65% reduction in wet crashes
    • Virtually no change in dry crashes
    • The FYRR for the 9 sites was 94% when using average value of crashes saved and 231% when using severity to value the crashes
overall conclusion
The Implementation of the Skid Resistance Policy has successfully achieved its objective of reducing the number and severity of wet skidding crashes on the Local Roads in Cornwall Overall Conclusion