Case Study: Improved Line Marking and Rumble Strips - State Highway 1, Waikato New Zealand
Between 2000 and 2004, a 200km section of State Highway 1 experienced 402 crashes, including 54 fatal crashes and 84 serious injury crashes.
A detailed analysis found that a high proportion of the crashes were loss of control and head on, and of these, two thirds occurred when it was raining and/or at night. Fatigue and inattention of both local and non-local drivers were identified as significant factors in the crashes.
A 3-E’s Approach
A 3-E’s (Education, Engineering & Enforcement) approach was undertaken to address the problem. The overall study was titled South Waikato And Taupo Towards 2010 Targets (SWATT 2010). Education and enforcement efforts were applied to the entire 200km section of road. However, 37km of that section was also subject to engineering efforts. This involved upgrading signs and delineation and installing audio tactile pavement markings (or rumble strips). The focus of this case study is on the 37km stretch.
The focus was to keep drivers alert, on the road, and within their lane. Enhanced line delineation and audio-tactile devices were obvious mitigation measures. However, this presented a number of challenges, including
- New Zealand’s Manual of Traffic Signs and Markings (MOTSAM) allows for the installation of wide and profiled markings however edgelines could only be widened to 200mm.
- MOTSAM requires a clear tracking width of 3.5m between profiled markings.
- Installing wide double yellow profile centrelines would require relocating the wider profile edgelines a further 250mm outwards. This has cost implications of removing the existing edgeline and safety implications of reduced shoulder width and vehicle tracking closer to an often unforgiving roadside.
- Anecdotal evidence that traditional thermoplastic profiled markings were not proving to be durable under frequent over-tracking particularly by heavy vehicles and/or on the inside of curves.
- The high initial and maintenance costs.
To address the challenges, a system was devised by a group comprising of New Zealand Transport Agency staff led by Colin Brodie (national safety engineer), consultants, Damar Industries and NZ Road Markers Federation staff. The system involved
- Marking dual 150mm double yellow profiled centreline markings with a 100mm gap. This provides a 400mm wide painted barrier between opposing lanes.
- Widening the existing 100mm edgeline to 150mm.
- Installing 150mm wide ribs immediately outside of the painted edgeline. When looking along the edgeline from a driver’s viewpoint, the line appears to be 300mm wide. The resultant clear trafficable width between edgelines is 3.25m and a slightly substandard 3.4m between profiled markings. The layout is illustrated in the ‘Related Images’ box to the right. The Related Images box also contains photos of the finished treatments.
An comparison of the number of crashes on the 37km section of road before the treatment (April 2004 to November 2005) and after the treatment (April 2006 to November 2007) was undertaken. This showed that fatal and serious injury crashes dropped by 67%.
The evaluation also involved comparison of the crash reduction on the 37km section of road with the remainder of the 200km section of road, which had been subject to enforcement and education efforts, but not engineering efforts. This section of road experienced a reduction in fatal and serious injury crashes of 38% in the same period.
The evaluation also determined the reduction in crash costs as a result of the treatments. The 37km section of road experienced a 72% decrease in crash costs, while the remainder of the 200km section experienced a 29% decrease.
The 3-E’s road safety initiatives along State Highway 1 was successful in reducing the number of injury crashes and the cost of road trauma.
The most successful element was the audio tactile pavement markings (rumble strips), which reduced crashes substantially more than the un-treated sections.
Efforts are now underway to lay rumble strips along other sections of State Highway 1 throughout New Zealand. It is estimated that treating approximately 20% of the national highway (2000km) will result in the prevention of 13 fatal crashes and up to 200 injury crashes each year, with a benefit to cost ratio of more than 6:1.
This case study was provided by the New Zealand Transport Agency.