W.D.M. Limited North View, Staple Hill, Bristol BS16 4NX Telephone: Web: 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: Web:

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% 2004 Skid Standard HD/2804

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. Reasons for the Increase in Potentially Deficient Sites

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

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 WDM Commission

Approach to Junctions

Bends of strategic Routes

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! Results

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. Implementing the Skid resistance 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 Requirements 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 Review of the Skid Policy

Findings from Crash Analysis Crash TypePrior to % Change Wet injury Crash rate/yr 100Mvehkm % Wet injury Crash density/yr Per lane km % Wet KSI Crash rate/yr % Wet KSI Crash Density/yr % KSI = Killed or Seriously Injured

The average crash reduction since implementing the policy is: 33 wet crashes per year Of these 8.25 crashes per year were KSI’s Crash Reduction

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 km and the cost was £707,488 Only part of each scheme was skid deficient Verifying the Benefits

Crashes – Before and after

Injury and Damage Crashes All Schemes Damage Only Crashes per Year Injury Crashes per Year BeforeAfterReductionBeforeAfterReduction Wet Only Dry Only 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.

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

First Year rate of Return (Average Values Used) All Schemes Cost Wet Collisions Only Value of Collision Reduction FYRR £707,488£665,68794% FYRR – A way of determining whether a scheme is economically justified Benefits of a scheme /Costs of the scheme – in the first year

First Year rate of Return (Value of Severity Used) All Schemes Cost Wet Collisions Only Value of Collision Reduction FYRR £707,488 £1,634,559231%

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: On Input

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: Overall outcomes

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 Conclusions: Before and After Study

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

Thank you