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

David CookHighways & Network OperationsNZTA

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Outline

o Overview of New Zealand state highway skid resistance policy

o Some early NZ background

o Recent changes

o Outline of the calculation of the B/C of policy (Range 13 to35)

o Further work proposed on B/C

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Overview of NZ Skid Resistance Policy

• Safety

• Safety &

• Safety• Comment traction

• Users cannot see skid resistance, generally

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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

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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.

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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

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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

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Outcome of NZTA T10 Policy

B/C ratio between 13 and 35

Benefits are all in crash savingsCosts are in; extra resealing, HSDC

Survey, consultancy services, purchase & cartage high polishing resistant aggregate

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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

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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.

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Rural Crash Rates All & Wet

Figure 4: Rural crash rates, “all” and “wet” (1998-2008).

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1.0

1.2

1.4

1.6

1.8

2.0

2.21988

1990

1992

1994

1996

1998

2000

2002

2004

2006

2008

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year

state highway indexed traffic growthHeavy All

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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

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Factors not considered

0

200

400

600

800

1,000

1,200

1,400

1,600

1998 2000 2002 2004 2006 2008

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(mm

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year (January-December)

rainfall (1998-2008)

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Factors not considered

• Changes in:

• Rainfall

• Policing

• Advertising for road safety

• General safety initiatives

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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