1) relationship between crash frequency and pavement surface

1)     INTRODUCTION:-Improving road safety through proper pavementengineering and maintenance should be one of the major objectives of engineer.When pavements are evaluated in terms of safety, a number of factors related topavement performance are raised, such as roughness, rutting, cracking, mobility& speed (Cenek et.

al. 2014). Each year there are huge annual reports ontraffic accident in Pakistan. Accordingto Pakistan Bureau of Statistics, in the last 10 years data on trafficaccidents present a terrible picture, as average 15 people died every day intraffic accidents across the country (Traffic accident report, 2016 P.P 16). Therefore discussion ofsuch road safety issues as road safety modeling and pavement safetymeasurements and criteria is necessary. The main pavement engineeringrelationships associated with road safety should be identified, and the variousaspects of road safety related to pavement performance indicators should bediscussed.  2)     PROBLEM STATEMENT:- With the passage of time, vehicles movement, and environmentalconditions road pavement deteriorate.

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  Ifthis deterioration is not properly addressed, the amount of surface distresswill increase and be harmful to traffic. In this sense, pavement surface characteristics are a significant issuebecause of its influence in preserving roadway safety. Maintaining thesecharacteristics during pavement construction or rehabilitation may lessen oreven prevent crashes and incidents related to loss of vehicle control, slipping,and excessive skidding. Many road crash investigations and statistical analysis havesuggested that there is a relationship between crash frequency and pavementsurface characteristics (Noyce et. al.2007). Additionally, a recent paper has suggested that little has beendone to incorporate pavement management and maintenance into roadway safetyevaluations (Tighe et. al.

2000).  Thus,research is needed to confirm the relationship between crash frequency andpavement surface characteristics, and to develop strategies to incorporatethese findings in roadway safety evaluations.  3)     OBJECTIVES:- Following are the main objectives of thisresearch:- ·        To evaluate the correlation between traffic oriented parameters,roadway safety and pavement performance indicators.  ·        To identify / estimate threshold values of pavement performanceindicators, after which there is a need of improvement. 4)     LITERATURE REVIEW:- Various studies have been done using pavementperformance indicators i.

e roughness, rutting, cracking, macro texture and skidresistance to find its relationship with traffic safety. All of the studies showthat there is a strong relationship between pavement performance indicators andtraffic safety. Salimi et. al. (2015) evaluatedthe effect of friction behavior of tire with road surface in different roadconditions in winter i.

e bare dry, dry with ice path and three levels of snowsurface which can be directly related to road safety. This study was done bydriving trucks at target speed of 30, 50 & 60 km/h on different roadconditions. No considerable correlation between vehicle speed andthe friction measurements for bare dry, ice- and snow-covered conditions wasfound. But bare dry asphalt surface had the highest Halliday Friction Number(HFN), presence of ice reduced the dry surface friction by 55%. For light,moderate and heavy snow on the dry surface reduced the HFN further than ice, by69, 75, and 81%. Analysis of the effect of number of truck passes over ice at  -3.5 and -5 °C showed that ice can become moreslippery after each pass of traf?c but for light snow, even at low temperatures(<-10 °C), passes of traf?c will melt the snow through frictional heat andresult in higher friction values. A similar study wasdone by Najafi et.

al. (2015). He investigated the effect of friction onroadway safety on urban roads. Friction was measured using ribbed tire,locked-wheel skid trailer and their regression analysis was done by usingANOVA. Friction was measured for both wet and dry road condition. Friction is asignificant factor that affects the ratio of both wet and dry road condition,vehicle accidents on urban roads.

Seasonal variation and temperature changescan also affect the friction measurements. Relationship between friction andaccidents is not linear, so some logarithmic transformation was used indeveloping the regression equations. Relationship developed in this researchcan be used by designers to define the acceptable level of friction fordifferent roads. Wang et.

al (2006) examinedthe effect of speed on road safety. Study illustrate that high speed limits onsignalized intersections could result in rear end crashes. As the speed limitincreases, drivers attempt to travel into the dilemma zone, as they may not beable to implement the intersection crossing or implement the stopping actionsafely at the start of yellow. However, at lower speed limits the drivers caneasily take braking action or change lanes to avoid the impact or striking ofthe leading vehicle. Chan et.

al. (2009)studied the effect of surface roughness using International Roughness Index(IRI), rut depth and Present Serviceability Index (PSI) on crash frequency forasphalt pavements. He used divided highway in urban environment with a speedlimit of 88 km/h and the total length of highway used in analysis wasabout 117 km. It was found that rut depth has no significant effect oncrash rate except for the accidents at night and in rainy weather conditions. Onthe other hand roughness has a direct relation with the crash rate as crashrate increases with increase in roughness. Different models were developedbetween roughness, rut depth and PSI with crash rate. This study suggests thatrut depth model should not be used for predicting accidents, however roughnessand PSI models perform well in predicting crash rate.

 Chan et. al.’sfinding are consistent with the finding of H.R. Al-Masaeid (2003). He estimatedthe effect of pavement condition including International Roughness Index (IRI),Present Serviceability Index (PSI) and rut depth and pavement geometry on ruralroad accidents. For this study 32 road segments were selected from 12 primaryrural roads, which shows that by increasing IRI level or by decreasing PSI,single vehicle accident rate will decrease but it would increase multiplevehicle accident rate. This study also shows that by increasing roughness, no.

of vertical curves and no of intersection, it would increase multiple vehicleaccident rate.Saplioglu et. al.(2012) investigated the effect of skid resistance on road accidents at theintersection of the road. Four, four leg intersections were selected which havethe same properties. In this study skid resistance was measured in terms oftexture depth. This study shows that when texture depth decreases, skidresistance also decreases resulting in high chances of the accidents.

When theaverage texture depth was 0.75mm probability of accident occurrence was 15%,when texture depth became 0.5mm then the probability of accident was 85%. Furthermore Hussein et.al. (2016) evaluated the effect of surface condition including rutting, skidresistance and roughness on traffic safety at signalized intersections.

Theystudied the crash rate at signalized intersection before and after improvementswere made for road surface conditions. Analysis period of 3,4 & 5 yearswere selected based upon the data available before and after improving thesurface condition. This study shows that before and after the treatment therewas a difference in crash type and most of the accidents occurred at the speedof 60 – 80 km/h. It was seen in this study that after the treatment, accidentsdue to roughness were considerably low. However with increased rutting areduction in accidents was observed. Cairney et. al.

(2008) investigated the relationship between road surface characteristic (includingmacro texture, rutting & roughness) and crashes for rural roads. Roadsselected in this study was two-way undivided and the speed limits was 100 km/h.This study shows that with the decrease in macro texture (below 1.8mm) trafficaccidents increases. They could not find a reliable relation between ruttingand crash rate and they found that with the increase in roughness crash ratealso increases but only when traffic volume is high. A similar study, butincluding only rutting and crash rate was done by Cenek et. al.

(2014). Thisstudy was done for New-Zeeland state highway network, which results in thatcrash rate slightly decreases as rut depth increases over the normal range ofrut depth particularly for dry crashes because driver normally reduce speed inthat area in order to keep vehicle in control. This study shows that even withthe rut depth more than 10mm there was no indication of an increase in crashrate but there was increase in crash rate when there was water on the roadsurface.  Noyce et. al. (2007)studied the relationship between asphalt mix design, skid friction and roadwaysafety.

Additionally this research studied relationship between macro textureand friction for high speed roads. This research show that for a wet pavement,with the decrease in skid friction, crash rate increases. Relationship between MeanTexture Depth (MTD) and friction comes inversely proportion which was againsttheir prediction. According to this research dense graded asphalt mixes haslowest mean texture depth value resulting in high friction value. This researchsuggested that minimum of 35 FN value should be maintained for safe trafficoperation. 5)     RESEARCH METHADOLOGY:-  Tasks are developed for determining therelationship and their analysis between different pavement performanceindicators and road safety as shown in Fig 1.

·        Task 1 :- Literature review will be conducted to find out any informationavailable regarding impacts of pavement performance indicators on trafficoriented parameters and roadway safety. ·        Taks 2 :- Selection of the test sites for research. Test siteshould be selected on the basis of pavement performance indicators, where theseindicators vary from each other and can affect road safety.

 ·        Task 3 :- Field data collection should be done for selected sitesbased on the procedure mentioned below in data collection methods. ·        Task 4:- Data regarding selected roadway safety & trafficoriented parameters will be collected using techniques and surveys, mentioned below. ·        Task 5 :- Based on the data collected, relationships betweenpavement performance indicators under study with traffic oriented parametersand with the crash data will be developed, for roadway’s safety measurement.


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