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An Evaluation of the Economics of NZ’s Skid Resistance Policy

An Evaluation of the Economics of NZ’s Skid Resistance Policy. David Cook Highways & Network Operations NZTA. Outline. Overview of New Zealand state highway skid resistance policy Some early NZ background Recent changes Outline of the calculation of the B/C of policy (Range 13 to35)

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An Evaluation of the Economics of NZ’s Skid Resistance Policy

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  1. An Evaluation of the Economics of NZ’s Skid Resistance Policy David Cook Highways & Network Operations NZTA

  2. Outline Overview of New Zealand state highway skid resistance policy Some early NZ background Recent changes Outline of the calculation of the B/C of policy (Range 13 to35) Further work proposed on B/C

  3. Overview of NZ Skid Resistance Policy • Safety • Safety & • Safety • Comment traction • Users cannot see skid resistance, generally

  4. Summary N Z state highway skid resistance policy • For more detail see Owen et al (2008) referenced in paper • Investigatory levels of microtexture are set with the objective of equalising the risk of a wet road crash on SH network • Microtexture measured with SCRIM+ technology • SCRIM Coefficient (SC)really a combination of microtexture & contamination

  5. Seasonal Correction Raw data from the SCRIM vehicle is normalised for travel speed & temperature to produce SCRIM Coefficient, SC This data is normalised for within year variations to produce Mean Summer SCRIM Coefficient, MSSC This data is further normalised for between year variations to produce Equilibrium SCRIM Coefficient (ESC) and used to prioritise maintenance decisions.

  6. Investigatory & Threshold Levels • Table 1 defines Investigatory Levels (IL) • Threshold Level (TL) is 0.1SC below IL Hence three levels of Treatment Priority dependant on microtexture relative to IL: • High; Below TL • Medium; Between TL & IL • Low; Above TL

  7. Macrotexture • Target levels of Macrotexture are set with the objective of minimising the progressive loss of skid resistance with increasing speed. • Macrotexture also used as predictor of low SCRIM Coeffficient

  8. Outcome of NZTA T10 Policy B/C ratio between 13 and 35 Benefits are all in crash savings Costs are in; extra resealing, HSDC Survey, consultancy services, purchase & cartage high polishing resistant aggregate

  9. 2010 Version of T10: Changes • Curve Risk Analysis • Range of IL’s, Hardwiring. Guidance on changing IL’s. Review changes. • Moving from PSV to Aggregate Selection • Updating Macrotexture • Full width Watercutting • More guidance, Responsibility, • Mandatory Training & Experience

  10. Outcome of NZTA T10 Policy B/C ratio between 13 and 35 All on 2002 version of T10, but had been updated by practice & a range of memos.

  11. Rural Crash Rates All & Wet

  12. Factors not included in B/C • There was some skid resistance policy prior to 1998 • There are benefits in crash reduction in dry as well as wet • Some local authorities have skid policies All of these would increase the B/C

  13. Factors not considered

  14. Factors not considered • Changes in: • Rainfall • Policing • Advertising for road safety • General safety initiatives

  15. The Future for skid resistance in New Zealand Despite the difficult economic circumstances in NZ: • We will be continuing towards full implementation of the new T10 Specification • Doing further statistical analysis of the effects of the skid resistance policy • Encouraging Local Authorities to implement better skid resistance policies

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