PERFORMANCE OF HIGH SKID RESISTANT TREATMENTS

Transcription

1 PERFORMANCE OF HIGH SKID RESISTANT TREATMENTS Cassandra Simpson, VicRoads and GeoPave, Australia ABSTRACT VicRoads has placed high skid resistance treatments at various locations in an effort to reduce traffic incidents by providing a more effective skid resistant surface for motorists. This project was expected to provide documented evidence of the trends in traffic incidents at treated sites. This paper relates to an investigation into the performance of calcined bauxite treatments on road surfaces with regard to the impact on traffic incident trends at twenty-none treatment sites. The objective of the project was to determine the skid resistance performance of high skid resistance treatments, and determine if a relationship existed with recorded traffic incident performance. The project investigated twenty-nine high skid resistant treatments within Melbourne and Geelong, Australia. The sites included only calcined bauxite treatments. The investigation showed calcined bauxite treatments provide a uniformly high level of skid resistance for at least five years after placement. The skid resistance of the treatments appeared to be independent of the visual condition of the surface. The investigation was inconclusive regarding the effectiveness of calcined bauxite treatments to reduce traffic incidents. It appears better selection of sites with regard to traffic incident numbers and types of incident may be key to achieving benefits from the treatment. INTRODUCTION This paper presents an investigation into the skid resistance performance of calcined bauxite treatments with regard to the impact on traffic incident trends at specific treatment sites. The investigation was initiated by VicRoads increasing use of calcined bauxite treatments at intersections to provide long term high skid resistant surfaces. The investigation was intended to: Investigate the skid resistance performance of high friction surface treatments with regard to age and traffic conditions Investigate and assess traffic incident performance at sites with specialised road surface treatments. The skid resistance performance of calcined bauxite regarding traffic incident performance is reported in this document. The draft specification is not detailed in this document. For the purpose of this project high skid resistance treatments were taken as road surfacing that was expected to provide increased skid resistance beyond conventional asphalt and sprayed seals. The project did not include asphalt with increased polished stone value, although this should be considered as a treatment to provide increased skid resistance. The objectives of the investigation reflected an expectation the high skid resistant road surface treatments would display long term skid resistance properties and achieve significant reductions in traffic incidents. The expectation of reduced traffic incidents arose from current knowledge of skid resistance influence on traffic incidents. ARRB Group Ltd and Authors

2 METHOD Selection and Condition of Sites The project investigated twenty-nine sites within Geelong and Melbourne, Australia. The project sites were selected based on material type, age of treatment, and traffic volume to provide a range of characteristics and the best opportunity of achieving the project aims. All sites were visually assessed for general condition and to confirm the extent of treated area. The treated areas were visually inspected for rutting, cracking, loss of shape, stripping, calcined bauxite delamination, potholes, and the influence of traffic detector loops. Skid Resistance Testing The skid resistance of the sites was measured using Sideways force Co-efficient Routine Investigation Machine (SCRIM) in accordance with VicRoads Test Method RC (excluding the rolling four point average) in an effort to provide continuous measurement of sideways force co-efficient in both left and right wheelpaths. Surface Texture The surface texture of the treated areas was measured using the VicRoads Test Method RC Surface Texture by Sand Patch. The test provides a low cost and repeatable measure of the macro-texture of the sites. The tests were undertaken on representative areas of each site. The surface texture data was collected to determine if a relationship existed with skid resistance. Traffic Incident Data Traffic incident data was recovered from the VicRoads Road Crash Information System (RCIS) and CrashStats programs for each of the investigation sites. Incident data was recovered for five years prior to the placement of the specialised road surface treatments, and all incidents recorded after placement. Traffic Volume Data Traffic volume data was retrieved from the VicRoads Information Services Traffic Statistics and Rural Traffic Statistics databases. The databases provides traffic volume data from specific points on the road network. The information from the nearest specific point was adopted for the investigation sites. The most recent traffic volumes including proportion of commercial vehicles were retrieved from the database. RESULTS Selection and Condition of Sites Twenty-nine sites were selected from Melbourne and Geelong for the project. The sites are listed in Table 1. The sites consisted of 20 approaches to signalised intersections, 4 curves, and 5 approach and centre of signalised intersection sites. ARRB Group Ltd and Authors

3 The intersection approach sites typically extended 50 metres of the approach to the signalised intersections, although the specific start/finish areas were not uniform. The extent of the intersection approach sites displayed the following variations: Provision of calcined bauxite surface to the Stop line Provision of calcined bauxite surface to the far side of the pedestrian marking Provision of calcined bauxite surface adjacent to the concrete medians at the intersections further into the intersection than the pedestrian marking Treatment provided on the left and/or right turn lanes Treatments provided through the entire intersection and on all approaches. The reason for the variety of extent of treated area was unknown. Visual Condition of Treated Areas The inspection of the treated areas included a record of visual condition as detailed in Table 1. The inspections assigned an overall condition (good, fair, poor) to the areas. Figure 1 provides an example of a treated area in poor condition. The treated areas were inspected for uniform appearance, delaminated areas, potholes, stripping, and cracking. Most of the treatments displayed cracking from the underlying pavement reflecting into the surface treatment, and some sites displayed stripping of the calcined bauxite around these cracks. The cracks all appeared to be initiated in the underlying pavement. The calcined bauxite treatments were not observed to crack within the material itself. The condition rating was based on the appearance of the calcined bauxite treatment, excluding defects attributed to the underlying pavement such as loss of shape or cracking. The sites displayed the following distress and response to traffic stresses: Delamination Areas where the surface treatment has been removed from the pavement. Cracking All of the observed cracking appeared to have initiated in the underlying pavement. Some treated areas included cracks with a distinctive darkening of the surface around the crack and this distress is described within this report as stripping around the crack. The stripping around cracks appeared to be concentrated on sites with significant turning stresses. Stripping Many of the treated areas displayed a darkening of the surface that appeared to be caused by stripping of the aggregate. Pavement Condition The sites were inspected for the condition of the calcined bauxite, not the pavement. Skid Resistance Testing Results Twenty-eight sites were tested for skid resistance using SCRIM. All of the results show the calcined bauxite provided a highly skid resistant surface. Figure 2 shows a typical result for the high skid resistance for SCRIM Run for Site 26 (Punt Rd). Table 1 provides a summary of the SCRIM skid resistance results. ARRB Group Ltd and Authors

4 Site Number Table 1: Site Location, Condition and Skid Resistance Results Road Name Intersecting Road Condition Average Result (sfc) Range of Result (sfc) 1 Barkley Rd Mitford Rd Good to Bayswater Rd Canterbury Rd Poor to Bourke Rd Burwood Hwy (Toorak Rd) Poor to Buckley St (Sunshine Rd) Princes Hwy West overpass Poor to Burwood Hwy 6 Dora St Selman and Forest (two intersections) Good to 0.95 Banksia St, (Bell/ State Hwy) Fair to * Eastern Fwy on-ramp Hoddle St (Punt Rd), Poor to Fitzroy St Grey St Fair 0.80 No average** 0.70 to to Greensborough Bypass Metropolitan Ring Rd Good to Kings Way Queens Pde Fair to Kings Way West Gate Fwy onramp Good to Lysterfield Rd Wellington Rd Poor 13 Midland Highway Packington Street Good to Mountain Hwy High St/ Valentine St Fair to Murray Rd Champ St Poor to Nicholson St Bell St Poor to Plenty Rd, southbound Metro Ring Rd overpass Fair to Plenty Rd, northbound Metropolitan Ring Rd Good to Princes Hwy East Bourke Rd Fair to Princes Highway West Bell Parade Fair to Princes Highway West North Shore Rd/ The Boulevard Fair to Princes Highway West Pioneer Rd Fair to Princes Highway West Sparks Rd Fair to Princes Highway West St Georges Rd Fair to Princes Highway West Victoria St Fair to Punt Rd Alexandra Ave Fair to Smith St Alexandra Pde Good to Surfcoast Highway Princes Highway West Fair to Surfcoast Hwy Pioneer Rd Fair to 0.90 * Site was tested at the slower test speed (refer below) **The results was too variable for an average result Site No.12 (Lysterfield Rd) was closed for reconstruction during the project period. The site was not tested for skid resistance. Surface Texture Twenty-six sites were tested for surface texture (macro-texture). The results provided an average of 0.90mm, with a range of 0.58 to 1.91mm. The extremes of the range were not well represented as shown in Figure 3, and most results were within the range of 0.70 to 1.00mm. ARRB Group Ltd and Authors

5 Overall the texture results between the left wheelpath, centre of lane and right wheelpath were similar. A review of all the sites shows the centre of lane provides very similar results compared with the wheelpath results. Traffic Incident Data Traffic incident data for the five years prior to the date of calcined bauxite treatment was procured for the investigation. However, some sites were younger than 5 years old, and therefore five years of data for the crash history after treatment was not available. To compare the sites within the same timeframes, all data for after treatment was increased on a pro-rata basis to estimate the five year period. Table 2 provides a summary of the Traffic Incidents Before and After the calcined bauxite treatment. Table 2: Traffic Incident Data Site No. Road Name Data prior to treatment Data after treatment Percentage Change Total Incidents* Incidents on Treated area** Total Incidents* Incidents on Treated area** Total incidents* Incidents on Treated area** 1 Barkley St % -100% 2 Bayswater Rd % -20% 3 Bourke Rd % -55% 4 Buckley St % -87% 5 Burwood Hwy % -66% 6 Dora St % -100% 7 Eastern Fwy % -100% 8 Fitzroy St % -33% 9 Greensborough Bypass % 122% 11 Kings Way % -23% 12 Lysterfield Rd % -71% 14 Mountain Hwy % 0% 16 Nicholson St % -100% 17 Plenty Rd % 267% 19 Princes Hwy East % 108% 21 Princes Hwy West % 29% 22 Princes Hwy West % -100% 23 Princes Hwy West % -57% 24 Princes Hwy West % 9% 26 Punt Rd % 11% 27 Smith St % 0% 28 Surfcoast Hwy % 140% Total for Listed Sites -10% *** -14% *** -% represents a reduction in the number of incidents +% represents an increase in the number of incidents *Total Incident Change include the incidents on the treated area ** Treated area represents the calcined bauxite part of the site *** Total Percentage Change was calculated using the total number of incidents for the entire set of sites (Not calculated from the average of the listed percentages for each site). ARRB Group Ltd and Authors

6 The VicRoads Road Crash Information System (RCIS) and CrashStats were used to provide traffic incident data for before and after the calcined bauxite treatments were placed. The data was sourced from RCIS and was drawn from the individual Police Report (formally known as Road Crash Statistics: Victorian Crash Details) for each incident within 100m of the sites. (The data from RCIS and CrashStats was cross-checked to remove duplication of incidents.) The data could not be taken from the RCIS summary sheets, as this data does not provide the true location of the incident, or the direction of travel of the vehicles involved. The Police Reports available through RCIS and CrashStats include information regarding weather conditions, time of incident, vehicle movement types, direction of travel of vehicles, diagram of incident, record of injuries and an assessment of signal operation. The data from the Police Reports was filtered to reveal only those incidents that occurred within the calcined bauxite area of the site, and therefore incidents that could have been affected by the improved surface. Over 600 incidents were assessed in this manner to reveal the influence of the calcined bauxite area. The Police Reports are not included with this report as the information is considered confidential. It should be noted the CrashStats data contains a lag of about 6 months for most incidents. Similarly, the RCIS data contains a time lag of two days for fatal incidents, and 2 to 3 months for other injury incidents. The result of this time lag could lead to an under-estimation of incidents within the last 2 to 3 months. To ensure a systematic collection of data and account for the same potential lag of information, the incidents on sites with treatments older than 5 years were only recovered for the 5 year period (not to the present time). The total set of sites provided a 10% reduction of Total Incidents (all incidents at the defined site) over the study period. It is understood traffic incident trends are expected to show increases and decreases in traffic incident data, and the overall reduction is considered reasonable. The data for the Treated Areas showed a 14% reduction for incidents within the study period. Given the 10% Total Incident reduction includes the data for the Treated Areas, the reduction due to the calcined bauxite appears negligible. The seven sites with a significant number of traffic incidents (approaching >10 incidents in 5 years) were reviewed to reveal the impact of the calcined bauxite treatment on the number of traffic incidents. These sites were considered to contain sufficient data to be more reliable and show a better trend as shown in Table 3. Table 3: Traffic Incident Data for specific sites Site No. Road Name Change in Total Incidents Change in Total Incidents (Incidents not located on treated area) Change in Traffic Incidents on Treated Area 3 Bourke Rd -43% -22% -55% 5 Burwood Hwy -5% 45% -66% 8 Fitzroy Site -17% -3% -33% 17 Plenty Rd 158% 126% 267% 21 Princes Hwy West -25% -54% 29% 24 Princes Hwy West 16% 20% 9% 26 Punt Rd 15% 17% 11% TOTAL 17% *** 27% *** 2% *** -% represents a reduction in the number of incidents +% represents an increase in the number of incidents *Total Incident Change include the incidents on the treated area ** Treated area is defined as the calcined bauxite part of the site *** Total Percentage Change was calculated using the total number of incidents for the entire set of sites (Not from average of the listed percentages for each site). ARRB Group Ltd and Authors

7 Traffic Volume Data Limited traffic volume data was available for the sites. VicRoads maintains and collects data for Freeways and Highways, but only some Main Roads. The traffic data is shown in Table 4. The traffic data was not adjusted to account for traffic growth rates. Site No. Table 4: Traffic Volume Data Road Name Intersecting Road Traffic Volume Percentage Commercial Vehicles (%) 5 Burwood Hwy Selman and Forest (two intersections) Greensborough Bypass Metropolitan Ring Rd Midland Highway Packington Street Plenty Rd, southbound Metro Ring Rd overpass Plenty Rd, northbound Metropolitan Ring Rd Princes Hwy East Bourke Rd Princes Highway West Bell Parade in 1992 Not Available 21 Princes Highway West North Shore Rd/ The Boulevard South north in 1993 Not Available 22 Princes Highway West Pioneer Rd in Princes Highway West Sparks Rd 24 Princes Highway West St Georges Rd 25 Princes Highway West Victoria St 17600south, north in 1993 Not Available north, south 1993 Not Available south, north in 1993 Not Available 26 Punt Rd Alexandra Ave DISCUSSION Condition and Extent of Sites Most of the visual inspections recorded the sites in fair condition. The majority of the sites were affected by delamination, potholes, cracking, and stripping over cracked areas of the pavement. The condition of the sites was compared to the age of the treatments, and showed the condition of the sites is not linked to the age of material. The site condition and traffic volumes were compared to determine if a trend existed. The data suggests the condition of the treated surface is not dependent on the traffic volumes. The sites included many variations for the extent of the treated area including left and right turn lanes, providing the calcined bauxite to the stop line or pedestrian lines. The extent of treated area was expected to be based on recorded incidents at the sites, however the data provided some contradictory results. Site 24 (Princes Hwy West) provides a useful insight for the size of the calcined bauxite treatment regarding width of treatment. This site includes calcined bauxite on the three through ARRB Group Ltd and Authors

8 lanes of the southbound carriageway approaching a signalised intersection. The two right turn lanes and left turn lane have not been treated and maintain a conventional road surface. The incident data showed 7 rear end incidents on the southbound approach of the through lanes, and 2 rear end incidents on the southbound right turn lanes. The exclusion of the southbound right turn lane areas from treatment appears inconsistent with the two recorded incidents on this part of the intersection. Site 24 was one of several sites where the calcined bauxite was not provided across the entire width of the approach to the intersection. The traffic movement history for the remainder of the sites that provide the calcined bauxite only on the through lanes, was not further investigated for this report. From the analysis of Site 24 it appears the Police Records for the incidents should be reviewed prior to determining the extent of the proposed calcined bauxite treatment. Skid Resistance All of the sites returned a high level of skid resistance above the Investigatory Level, and therefore the sites are considered to provide adequate skid resistance. The SCRIM results include the remainder of the (untreated) intersections, and the results typically show skid resistance less than the Investigatory Level for the remainder of the intersection. Figure 2 shows a typical result. The consistently high skid resistance results (above Investigatory Level) for every site is surprising given the difference in visual condition of the sites. Although the sites were listed in good fair, and poor condition, the skid resistance of the sites was uniformly high. The results for Sites 8, 21 and 22 included tests for the wheel path, and centre of lane. The results show the skid resistance of the wheel path was equivalent to the skid resistance of the centre of the lanes, and indicated the treatment was not affected by traffic. Variation within Skid Resistance Results SCRIM results show skid resistance above the Investigatory Level for all tested travel lanes at each site. The majority of the SCRIM results showed a uniformly high result, however some results showed more variation than was typical. The result is concerning as the skid resistance performance could not be expected from visual inspection. Site 7 (Eastern Fwy) was expected to return a poor skid resistance result due to the poor visual condition of the site, but the SCRIM results (Run ) showed a high level of friction ranging between 0.65 and 1.00 sfc. The result was taken from the outer lane and the poor condition of the surface is shown in Figure 1. The majority of the sites showed the visual condition of the surface does not indicate the skid resistance of the site, as shown in Site 7. The variable skid resistance result of Site 8 belies the fair condition given by visual inspection. Some SCRIM results showed distinct areas of low skid resistance within the sites (Site 2 Bayswater Rd, Site 6 Dora Rd and Site 15 Murray Rd). The results were attributed to large delaminated areas on the sites, where the underlying asphalt was exposed. The result is important as it demonstrates large areas of removed calcined bauxite can influence the skid resistance of the site, and may pose an increased risk to motorists. It should be stressed all of the sites returned a high level of skid resistance on the calcined bauxite areas. It appears the visual condition of the site is not an indicator of the skid resistance performance of the surface, until the aggregate is significantly stripped, or significant areas of the calcined bauxite are removed. ARRB Group Ltd and Authors

9 Surface Texture The average surface texture of the project sites was 0.90mm, with a range of 0.58mm to 1.91mm. The range of results is considered large, given (mostly) the same sized aggregate was used on the surfaces. To consider the texture results, it is useful to compare the texture of conventional asphalt which is typically between 0.5 to 1.5mm (VicRoads, 2002). The calcined bauxite provides surface texture comparable to asphalt, which is a conventional material for intersections. It appears the calcined bauxite surfaces do not suffer from a reduction in surface texture with time and traffic stresses. There appears to be no relationship between surface texture and skid resistance, or age of treatment. There appears to be no relationship between surface texture and traffic incident trends for this investigation. The Austroads Guidelines for the Management of Road Surface Skid Resistance includes reference to 0.6mm surface texture (sand patch equivalent) for Highways with speed zones >80kph and other main roads subject to stopping and turning with speed zones <80kph. Without further specific study of the influence of surface texture on traffic incidents at calcined bauxite sites, it is recommended 0.6mm is adopted. Traffic Incident Data The data in Table 2 shows the number of (pro-rata) recorded incidents before and after the calcined bauxite surface was placed. The results show three different trends for the percentage change of traffic incidents on the treated area; reduced number of incidents, no change in the number of incidents, and sites with increased numbers of incidents. The three trends are surprising given the high skid resistance achieved at each of the sites. It was assumed that high skid resistance would lead to reduced incidents, but this does not always appear to be the case. A traffic incident study of this nature would normally include control sites untreated sites with the same traffic and incident characteristics to provide a do nothing comparison. The project did not include investigation of such sites. The project also did not include investigation of network changes and intersection improvements over the incident search period. This means improvement works or traffic flow changes have not been taken into account, and these works may account for the total incident changes. The project did not consider the impact of the treatments on the severity of casualty incidents. The data suggests no relationship exists between the traffic incidents and texture or condition of the site. The data shows a reduction of traffic incidents at thirteen sites. These sites show reductions from 100% to 20%. Reduction in Traffic Incidents Site 23 (PHW intersection with Sparks Rd) is a good example of a site which achieved a reduction in total and affected incidents (-67% and -57%) after the surface treatment. The site displayed 21 total incidents for the 5 years prior to the treatment, with 4 incidents assessed as on the treated area. The incident data after the treatment shows only 4 incidents total, and one on the treated area. The result appears to support the use of the surface treatment. However, it should be noted the total reduction in incidents of 67% may account for the reduction on the treated area. ARRB Group Ltd and Authors

10 Reviewing the before data more carefully, 11 of the incidents can be described as incidents in the intersection (traffic movements against signals resulting in collisions with through traffic, or failure to give way when turning right). It appears a signal problem or movement conflict may have occurred at the intersection, and the after results may reflect a change to the signal cycle or reduction in conflict. This site shows the apparent improvement may not be attributed to the surface treatment, and provides a good example of a site that should be investigated further. Site 2 (Bayswater Rd) also displays a total reduction of incidents (-27%) and a reduction of incidents on the treated area (-20%). The incident trend appears to support the placement of the surface treatment. Again, it should be noted the total reduction in incidents of -27% may account for the reduction on the treated area. The reduction in incidents due to the improved skid resistance is not evident at this site. Site 6 (Dora St) reveals some interesting trends in the data. The data records a 78% increase in total incidents, and yet a 100% reduction in incidents on the calcined bauxite surface. The result appears impressive however further investigation shows; The before data on the treated area relies on three rear end incidents - two incidents were merging incidents where the front vehicle has/was stopped and the following vehicle has collided with the first, and the last rear end incident occurred approximately 60 metres before the stop line and in congested conditions The 100% reduction in incidents on the treated area is very sensitive to the small amount of data (3 incidents over 45 months) The recorded rear end incidents on Bell St (untreated area of the intersection) changed from 2 incidents before treatment, to an estimated 5 incidents after the treatment. With a similar number of rear end incidents on the two parts of the site, it is unclear why Dora St was chosen for improvement works. Site 5 (Burwood Hwy) provides better support for the surface treatment. This site displayed a 5% total reduction of incidents, and a 66% reduction of incidents on the treated area. The reduction in incidents on the treated area therefore cannot be accounted for from the trend of the total incidents. No Change in Traffic Incidents The data shows no change in incidents for the treated area of Site 14 (Mountain Hwy) and Site 27 (Smith Site). Both sites recorded a significant total incident history near the intersection before the treatment date. However, analysis of the Police Reports showed the incidents at the Mountain Hwy site were associated with the Rail Crossing and not the High St intersection which was treated. Similarly the Smith St site revealed many incidents on Alexandra Pde (entrance to Eastern Fwy), with no recorded incidents on the treated area of Smith St. The data shows no incidents for the treated areas either before or after the calcined bauxite was placed. The sites showed no benefit from the treatment, and it is difficult to determine why the treatment was placed at these locations. Site 27 showed an increase in total incidents after the treatment, while Site 14 showed a reduction in total incidents. The two trends are contradictory. Increase in Traffic Incidents The data showed an increase in the number of incidents for the treated area at seven sites. The increased number of incidents was not consistent with the percentage change in total incidents at the sites. A detailed investigation of some of the sites was undertaken to assess the reason for the increase in incidents. Site 19 (PHE) includes only four before incidents, and only eight after incidents on the treated areas and should be analysed with caution due to the small amount of data on the treated area. The before treatment data included only rear end incidents. The after treatment data included ARRB Group Ltd and Authors

11 three loss of control incidents on the calcined bauxite surface, one rear end incident, and one incident with no additional information. The loss of control incidents were retained in the data as no additional information was available to assess the cause of the incidents. Table 4.6 shows the detail of the incidents at Site 19. The reasons for treating part of Site 19 are unclear, and it appears the calcined bauxite treatment has not been effective at this location. Site 26 (Punt Rd) provides records of rear-end incidents approaching the intersection for northbound and southbound vehicles. The after incidents on the treated area increased by 11%. The data also shows a north/south rear end split of 2:6 which was reversed after the calcined bauxite treatment to 7:2 (the 7:2 has not been pro-rated). It appears the northbound rear end trend has been exacerbated by the treatment, while the southbound has benefited. It should be noted many of the rear end incidents occurred in congested conditions and at slow speed the skid resistance of the surface may not considered causative in this case. It appears the calcined bauxite treatment has not been effective at this location. FURTHER INVESTIGATION This investigation has raised concerns for the use and targeting of road projects for calcined bauxite (high friction surfaces). Further investigation was recommended for the following: Development of guidelines to increase the efficiency of targeting sites which would benefit from a high friction surface. An analysis of the traffic incident movement data is expected to provide this information. The guidelines should ensure only sites which would provide a reduction in traffic incidents are treated, and result in the best use of VicRoads budget. Comparison of incident trends for calcined bauxite and other high friction surface treatment. The RTA paper (Kinnear, 1984) showed skid resistance equal to or greater than the Investigatory Levels would return the same traffic incident reductions. The use of high friction asphalt may provide a cost-effective alternative to calcined bauxite treatments. UK standards for high friction surfaces. A full investigation into these standards is recommended to determine if the draft VicRoads specification should include some of these material and performance requirements. The investigation may provide a better specification for materials. The traffic incident trends for high PSV asphalt may provide a useful alternative for calcined bauxite treatments. The impact of asphalt skid resistance with traffic incident trends should be investigated, especially with long-term effects and cost/benefits. CONCLUSION Skid Resistance Performance The investigation has shown calcined bauxite treatments provide a uniformly high level of skid resistance for at least five years after placement. The skid resistance of the treatments appears to be independent of the visual condition of the surface. Where calcined bauxite is used, skid resistance was: Independent of the age of treatment Independent of the traffic volumes Independent of surface texture Affected by large areas of defects ARRB Group Ltd and Authors

12 Surface Texture The surface texture of the sites was measured equivalent to a conventional asphalt surface, and the texture does not appear to be influenced by traffic volumes or age of treatment. Traffic Incident Trends The investigation was inconclusive regarding the use of calcined bauxite treatment and reduction in the number of traffic incidents. Considering how widely this type of treatment is used, the investigation raises doubts over the effectiveness of the treatment. The investigation showed eleven of twenty sites for this project showed a reduction of incidents on the treated surface. Of the sites with a significant amount of data, only three of seven sites showed a reduction in the number of incidents. It appears better selection of sites with regard to traffic incident numbers and types of incident, may be key to achieving benefits from the treatment. The data suggests sites with the calcined bauxite placed approaching and in the centre of the intersection, appear to provide a reduction in the number of incidents, compared to placing the material only approaching the intersection. RECOMMENDATIONS The report raised concerns for the effectiveness of a calcined bauxite surface to provide reductions in traffic incidents, and the identification of appropriate sites for calcined bauxite treatments. Many of the sites provided a small amount of data for analysis, and theses sites were very sensitive to the limited data. The outcome of the seven sites with a significant amount of data (greater than 10 incidents prior to the placement of the calcined bauxite), indicates the treatment has not provided the expected benefits, and more knowledge for the traffic incident performance is needed to improve the targeting of proposed sites. It appears the Police Reports were not reviewed as part of the bid process, and the data for each of the project sites should be investigated to improve the process. The following is recommended to improve the process of identifying treatment sites: The Police Reports should be reviewed for each proposed site for a high friction treatment, to assess if a potential reduction in traffic incidents is probable; The traffic incident movement data for existing treated areas, should be investigated for trends of reductions to provide guidance for future sites; The traffic incident data be investigated to provide guidelines for typical extent of calcined bauxite treatment areas (eg. left and right turn lanes). Further guidance for practitioners should be provided for the impact of large defects on the skid resistance of a calcined bauxite surface. The note should provide advice regarding the size of repair and methods of repair, and will assist to maintain consistent and high levels of friction on treated areas. Greater awareness and training of the importance of scoping works at calcined bauxite sites to ensure the new roadworks provide a high friction surface in keeping with the existing surface. DISCLAIMER This paper is presented with the permission of VicRoads. The views in this paper are those of the author and do not necessarily represent the views of VicRoads. ARRB Group Ltd and Authors

13 REFERENCES Austroads (2005), Guidelines for the Management of Road Surface Skid Resistance, Austroads Iskander & Stevens, The Effectiveness of the Application of High Friction Surfacing on Crash Reduction, Beca Infrastructure Ltd, Auckland, New Zealand, International Surface Friction Conference 1 4 May 2005, New Zealand Kinnear, Lainson, Penn (1984), An Evaluation of Four Pavement Treatments in Sydney in Relation to Crash Reduction Skid Resistance and Cost, Dept of Main Roads NSW Roe, Parry and Viner (1998), High and Low Speed Skidding Resistance: the Influence of Texture Depth, TRL Report 367 UK Roe, Webster and West (1991), The Relation Between the Surface Texture of Roads and Accidents, TRRL Report 296 UK Rogers and Gargett (1991), A Skidding Resistance Standard for the National Road Network, Highways and Transportation UK RTA and VicRoads (1995), A Guide for the Measurement and Interpretation of Skid Resistance Using SCRIM VicRoads (2002), Use of Surface Texture in RAS, GeoPave Technical Note 58 AUTHOR BIOGRAPHY Cassandra Simpson has worked in both local and State government and has been involved in all aspects of road construction, including realignment projects, batter stability projects, bridge strengthening and routine maintenance, with more recent work focusing on sprayed seal and asphalt projects. Cassandra Simpson currently works with GeoPave and provides specialist advice on bituminous surfacing, coloured surface treatments, asphalt specifications, skid resistance and specialised high friction treatments. She represents VicRoads on the Austroads Asphalt Research Review Group. ARRB Group Ltd and Authors

14 FIGURES Figure 1: Site 7 - Example of treated area in poor condition. Start of treated area Finish of treated area Figure 2: SCRIM Run Example of typical skid resistance result. ARRB Group Ltd and Authors

15 Surface Texture Results Texture (mm) Site Number Figure 3: Surface Texture Results ARRB Group Ltd and Authors