Uncommon Road Safety Hazards

Uncommon Road Safety Hazards

Available online at www.sciencedirect.com ScienceDirect Procedia Engineering 177 (2017) 375 – 380 XXI International Polish–Slovak Conference "Machin...

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Available online at www.sciencedirect.com

ScienceDirect Procedia Engineering 177 (2017) 375 – 380

XXI International Polish–Slovak Conference "Machine Modeling and Simulations 2016"

Uncommon road safety hazards Marian Dudziaka, Andrzej Lewandowskib, Michał Śledzińskic* The President Stanisław Wojciechowski State University of Applied Sciences in Kalisz, Kalisz, 62-800 Poland b Institute of Forensic Research, Cracow, Poland, ul. Westerplatte 9, 31-033 Kraków, Poland c Chair of Basics of Machine Design, Poznan University of Technology, Poznan, 60-965, Poland

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Abstract This paper describes certain uncommon road safety hazards resulting from road surface contamination, driving on split-mu surfaces or explosive decompression of car tire. One of the analyzed cases involves a road accident due to inadequate emergency reaction of a motorist after running in road surface covered with spilled grain. A methodology of experimental research allowing to analyse and explain road traffic incidents has been developed. The research results indicate an importance of improving the driving skills, as well as the motorists’ capability to make right decisions on the road. © 2017 Published by Elsevier Ltd. Ltd. This is an open access article under the CC BY-NC-ND license 2017The TheAuthors. Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of MMS 2016. Peer-review under responsibility of the organizing committee of MMS 2016 Keywords: unusual road safety hazards; driver’s perception; road traffic safety;

1. Introduction The causes of road accidents are a subject of statistical analyses and are used to determine the required preventive measures. Besides speeding the most common (so-called typical) causes of road accidents include collisions with other road users (cars, two-wheelers, pedestrians), running into stationary obstructions (parked vehicles, roadside trees, utility posts, safety barriers), running over surface defects (potholes, bumps, ruts). Another group of causes is related to technical problems concerning the vehicle (defects of mechanical systems, lamps and tire problems) and road surface condition. In the case of common driving hazards the motorist usually has sufficient knowledge and skills which, subject to being alert and cautious when driving allows him or her to avoid most potential traffic collisions and accidents [1]. In real-life road environment besides common safety hazards and situations which could be reasonably expected by the driver (such as a pedestrian on a pedestrian crossing) there are also unusual and unexpected situations which can surprise a driver. Such situations are often a cause of a road accident. They are associated with unusual and *

Corresponding author. Tel.: +48 61 224 45 13; fax: +48 61 665 20 74. E-mail address: [email protected]

1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of MMS 2016

doi:10.1016/j.proeng.2017.02.214

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unexpected conditions encountered on the road, both in terms of the character of obstruction and/or the place of its occurrence. These include for instance unprotected and unmarked potholes, unmarked obstacles within the right-ofway (e.g., unlit vehicles, unprotected accident sites); house animals and wildlife suddenly entering the road; big stones lying on the carriageway, goods which fell on the road during transport, oversize farming equipment travelling on public roads (such as combine harvesters) and sudden change of the road surface quality. These situations are so unusual and so haphazard that a rule they surprise a driver whose perception is not sufficient. Any obstacle, when noticed too late, can be a serious safety hazard. This paper deals with uncommon safety hazards related to a sudden change of the type and quality of pavement, especially when the coefficient of friction differs between the two wheel paths (the situation know as split friction or split-mu surface*) and breakdown of a vehicle on the road. The ability to make correct decisions in such unusual (extreme) situations depends, to a large extent, on the driver's knowledge and motor functions and, in particular, on the driver's hazard perception ability. 2. Uncommon road safety hazards 2.1. Soiled road surface Motorists can encounter areas soiled with various substances, such as mud/ dirt carry-out, fallen goods or sand, fuel or oil spillage and sudden change of the surface type and condition (patch of ice, puddle, etc.). When faced with an uncommon safety hazard the drivers' reaction is in most case natural, i.e. he or she initiates hard braking or an evasive manoeuvre with the purpose to avoid the obstacle. Without anti-skid braking system (ABS) or one of the stability enhancement systems (such as ESP) vehicles often become unstable and break away [2]. Making right decisions when faced with unexpected and extraordinary safety hazard requires knowledge and skills which in most cases exceed the average driver's capabilities. Reference can be made to the road accident in which a car ran over a layer of spilled grain [3,4]. It was determined that the driver of the vehicle moving on the surface covered with grain lost control of the car as a result of the undertaken evasive manoeuvres. The vehicle crossed into the opposing traffic lane where it crashed into an oncoming car. The analysis of the causes of the above-described accident involved, among other things, investigating what sensory and motor functions were at the drivers disposal at that time. He needed to identify the encountered unusual (non-typical) hazard situation to decide whether to brake hard or gently or do nothing i.e. continue driving without any extra manoeuvres. For this purpose an experiment was performed on runways of a disused military airfield. Two strips of grain, each ca. 0.5m wide spaced by a distance corresponding to the wheel track were placed on the test section. The grain layers were ca 0.02 m thick. The test section was 70 m long. The experiment was carried out jointly by the research teams of the Forensic Investigation Institute in Kraków and of the Poznań University of Technology. The research method and the actual experiment are reported elsewhere [4, 5]. The total number of seventeen braking tests were carried out on a wet asphalt pavement contaminated with grain for different initial speed values in the range of 80120 km/h. The outcomes demonstrate that contamination of the road surface with grain has a significant adverse effect on the braking performance. This could be well expected, yet still the motorists are often not fully aware of the consequences of running into spilled grain. On the test surface a drastic drop of the braking distance was noted – by ca. 60% as compared to a wet reference surface without grain. In a test using a car equipped with ABS system hard braking on the section contaminated with grain did not result in any sign of a loss of stability or problems with keeping the car straight. Over the course of the experiment a few test runs were also made at speeds of up to 120 km/h without braking. The purpose of these tests was to check if spilled grain can cause any adverse effects leading to loss of stability. Directional control was maintained during all the test runs. This demonstrates that without braking or evasive manoeuvres undertaken by the driver the accident would not have happened. Hence an obvious conclusion that the driver must have ignored the hazard related to the contaminated road surface and went on driving as if nothing happened. The rear wheel drive of the vehicle (without *

Vehicle riding on a surface with different friction coefficients for the right and left wheel paths [6, 7].

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traction control system) caused skidding and loss of directional stability. This led to a head-on crash with an oncoming vehicle. The results of the investigation turned out to be different and contrary from the previous knowledge on good driving practice in such non-typical conditions A vehicle running at a constant speed over a section covered with spilled grain did not lose directional stability owing to the sufficient grip of the wheels. Were it not for the driver's emergency reaction, the vehicle would have continued without breaking away since the grip on the surface contaminated with grain is similar to the grip on compacted snow [1]. Moreover, the tests confirmed that vehicles equipped with ABS are able to maintain directional stability during hard braking on such surfaces. 2.2. Split-mu braking It happens that a vehicle travels off the side of the road onto the shoulder or runs in a surface with varying friction coefficient and starts hard braking as a result. If a vehicle is fitted with ABS and the driver has sufficient skills to effectively perform emergency braking than in most cases the situation can be brought under control. Without such as system or in the event of its failure the vehicle will behave in a different manner. Without ABS assistance the vehicle suddenly loses its directional stability and changes its path in an uncontrolled manner. Unless specifically trained, most drivers are not aware of such braking behaviour on split-mu surfaces [6-10]. Without such knowledge and skills required in such situations the drivers react naturally making emergency manoeuvres which, when inappropriate to the situation, can have serious consequences and pose a safety hazard for other road users. a

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Fig. 1. Vehicle stability on split-μ surface during braking on wet asphalt covered with grain: (a) without ABS, (b) with ABS.

Special field tests were developed to check the behaviour of vehicles with and without ABS during hard braking on split-mu surfaces [4]. In the test two side wheels travelled on the surface contaminated with grain with the other two on a clean surface. The behaviour of the vehicle was recorded over the course of the test. Figure 1 presents pictures from the test runs. Fig. 1a illustrates loss of directional stability during hard braking on a split-mu surface. The graphs in Fig. 2 and Fig. 3 represent the vehicle behaviour during the field tests. Figure 2 shows the speed and braking deceleration curves for the test vehicle with ABS off. This test run featured high variability of the recorded parameters. The front wheels locked up after ca. 5 metres after putting on the brake. On the other hand, variation of speed and braking deceleration were much smaller in the test run with ABS on. Besides the speed and braking deceleration curves Fig. 3 presents also the curves representing the linear speed of the front wheels with varying relative slip.

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Fig. 3. Change of motion parameters of a test car travelling on a split-mu surface – asphalt partly contaminated with grain.

2.3. Explosive decompression of tire Explosive decompression is typical of heavy truck tires. This kind of tire failure can be attributed to errors during operation, resulting in weakening of the structural components of the tire and an increase of the tire temperature. Similar damage can result in tyre blow-out due to decompression. Another potential cause of tire blow-out is sidewall damage which can lead to sudden release of air and loss of stability of the vehicle. Explosive decompression is always preceded by the primary damage located in the sidewall, in the shoulder or in the tread. The effect of the tire failure on the vehicle stability depends on the place of the initial damage. The most common failure modes are:

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 explosive decompression through the tire tread tearing apart the rubber, the steel carcass cords and the bead. The sudden release of air generates a vertical force acting on the vehicle in the direction from the surface up. The resulting rapid loss of air pressure in the tire reduces the tire radius and results in side pulling of the vehicle. Braking will intensify the side pull.  explosive decompression through the tire shoulder makes the vehicle change the direction under the effect of a new side force and the force of inertia.

Fig. 4. Failure due to explosive decompression through the tire sidewall.

 explosive decompression through the tire shoulder (Fig. 4) poses the biggest safety hazard. The whole process is too short for the driver to react to pulling and during rapid deflating the vehicle is pulled aside losing stability and steerability. The forces acting on the tire push it away from the rim and can even strip it completely from the wheel. The side forces generated by the blowout cause the vehicle to swerve and potentially even overturn. Vehicle breakdowns on the road (such as tire blowout, brake failure) which occur suddenly without any warning signs put the driver in a situation in which he/she may not be able to take the right action to properly handle the situation. 3. Summary Unusual driving conditions than can be suddenly encountered on the carriageway (such as, for instance, spilled grain, mud or patch of ice, fallen cargo) pose a serious traffic safety hazard. Learned responses of reflex nature can prevent the tragic consequences of such hazards. Drivers often tend to uncritically rely on the on-board electronic control, assistance, as well as the active and passive safety systems in which contemporary cars are equipped. However, in extraordinary situations it is perceptual and motor functions that become a critical factor enabling the driver to take appropriate action which can save his/ her health or even life. Knowing the actual behaviour of a car on non-typical surfaces it is possible to provide the driver with guidelines and instructions of how to react to sudden hazards on the roads, such as a sudden change in the surface parameters. The essence of analysis is identification and assessment of the situation on the road on a case-by-case basis. Understanding the physics of road incidents resulting from unusual safety hazards requires developing dedicated research and test methods.

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