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Skid resistance is related to the friction generated between car tyres and the road surface. It enables drivers to shorten their stopping distances and to follow their desired trajectories along a road. It depends as much on the road surface characteristics, as on the car tyres and the operating conditions. For the road surface, texture remains the main parameter governing its contribution to skid resistance. This texture is composed of a multitude of irregularity scales, but two of them (Macrotexture and Microtexture) are mainly considered to contribute to skid resistance.\ud \ud The work proposed within this paper aims to proceed to a study to identify the exact role of Macrotexture and Microtexture on a road surface, by investigating the effect of different smoothing levels upon these scales using the ‘Dynamic Friction Model’ (DFM), a computational skid resistance model recently developed. The smoothing procedure of the road surface is conducted as following:\ud •The original profile of the road surface is decomposed via an Empirical Mode Decomposition method (part of the Huang Hilbert Transform (HHT)) to a multitude of constituent fundamental profiles of different scales termed “Intrinsic Mode Functions” (IMF). \ud •The first IMF is subtracted from the original profile to give derive to a smoother profile.\ud •The second IMF is subtracted from that smoothed profile to derive a further second even smoother profile.\ud \ud Accordingly, the derived two new profiles displays the texture within different Macrotexture and Microtexture. The DFM is then applied to these new profiles to highlight the role of the respective two roughness scales. The results from these simulations show that for two wet road surfaces with the same Macrotexture, the higher the Microtexture can be maintained, the better the skid resistance will be at all speeds, even at a speed limit at which the skid resistance will start to drop. Furthermore, for two wet road surfaces with same Microtexture, the higher the Macrotexture can be maintained, the later hydroplaning will occur.

8th Symposium on Pavement Surface Characteristics: SURF 2018 - Vehicle to Road Connectivity, BRISBANE, AUSTRALIE, 02-/05/2018 - 04/05/2018; Fine particles originated from road and tires debris or traffic and industry emissions can be at the origin of some safety-related issues such as accidents at the first rain after a long dry period or seasonal variations of skid resistance. This paper presents a laboratory study reproducing under controlled conditions the process of particles' buildup and washing by runoff water. Surfaces composed of rough and worn aggregates are studied. The test protocol is described. Friction is measured by means of the British Pendulum. On a surface initially covered with particles, dry and wet tests are performed. Results show that on a contaminated surface, the friction coefficient drops significantly, compared to a clean state, and then increases. Mechanisms related respectively to dry and wet lubrications are presented. In parallel, mass of particles are monitored. It was found that friction and mass of particles evolves similarly but in opposite directions. Discussions are made in terms of the effect of particles' size and surface's microtexture.

8th Symposium on Pavement Surface Characteristics: SURF 2018 - Vehicle to Road Connectivity, BRISBANE, AUSTRALIE, 02-/05/2018 - 04/05/2018; The presence of water on runway significantly affects aircraft safety on ground and runway friction. Under such conditions, pilots have to be informed of runway surface conditions to assess required landing distances. This assessment is based on runway surface characteristics (design, construction and maintenance), water depth and water-covered surface (operational conditions). However, estimation of water depth and water-covered surface may be tricky due to the lack of tools and methods, and to the rapid changing conditions during rainfall. This paper presents a method and its related tool, called OPHELIA for runway condition monitoring. A road model has been adapted to model water flows on a runway from its geometrical and surface characteristics, and to predict water depth during rainy events. An experimentation held on one of the two runways of Lyon airport is performed to validate OPHELIA tool and the water depth estimation. It is concluded that the model provides good results of the water depth estimation, compared to those measured by Vaisala sensor and it allows in the meanwhile the detection of water accumulation area on the runway.

8th Symposium on Pavement Surface Characteristics: SURF 2018 - Vehicle to Road Connectivity, BRISBANE, AUSTRALIE, 02-/05/2018 - 04/05/2018; Water on runways may significantly reduce aircraft braking performances. That's why pilots have to be informed about runway surface conditions, so they can calculate their required landing distance. Friction measuring devices are generally used to characterize runway surface conditions. These devices provide results that may not be representative of aircraft braking performances due to scale-effect (mass, speed, pressure...). A research work has therefore been launched by STAC and IFSTTAR in the framework of a PhD thesis to relate aircraft braking performances to ground friction measurements. A Brush-based model has been adapted to take into account the effect of water and applied to both one friction measuring device and aircrafts. This paper focuses on the validation of this model applied to the friction measuring device. Friction-slip curves have been measured by STAC laboratory on the IFSTTAR friction test tracks using the French reference runway friction device (IMAG, Instrument de Mesure Automatique de Glissance). The IMAG has been equipped with two tires (PIARC smooth tire and a grooved aircraft tire). A pool has been designed to maintain constant water depths ranging from 4 to 46 mm. Three increasing speeds have been tested until tires aquaplaning. A total of 35 friction-slip curves have been experimentally obtained and compared with predicted friction coefficients. Results show that the model is adapted to the IMAG configuration and measurements. The combined effect of water depth, vehicle speed and tire grooves is correctly described by the model, with an error in the range of +/- 0,06 friction unit. In this PhD thesis, a new approach is implemented to correlate IMAG friction measurements and aircraft braking performances on a physical basis. This physical basis makes this approach adaptable to any friction device, thus open the way to a physical harmonization of friction measurements.

SETAC Europe 28th Annual Meeting, ROME, ITALIE, 13-/05/2018 - 17/05/2018; Addressing the sustainability of transport infrastructures requires exploring the environmental, social, and economic impacts of technological options while balancing the often conflicting priorities of different stakeholders, at an early design phase of the infrastructure delivery process. That is a typical multi-criteria decision-making (MCDM) problem, in which the decision-makers need to measure the sustainability through a set of meaningful, representative and quantifiable criteria, balance the relative importance of those criteria and determine the sustainability sequence of multiple alternative technologies for fostering transportation sustainability. This paper describes a tool and a methodology developed in the framework of Super&ITN project.

Colloque avec actes et comité de lecture. Internationale.; International audience; Accidents increase during the first rain after a long dry period. This trend is due to the accumulation of fine particles originated from different sources such as atmosphere, road and tires debris, fuel emissions, etc. These particles accumulate on the road surface during a long dry period and induce a friction loss between the tire and the road surface. In the road field, the tire/road skid resistance on dry conditions is considered satisfactory (considering the road surface as clean) and the loss of skid resistance is attributed to the sole action of water. Thus, there is an unexplored field concerning the particles' effect, alone in dry period and mixed with water in wet period, on the skid resistance. In this paper, we investigate the action of the particles during a dry period using two approaches developed in tribology: the third body approach, particularly the mass analysis inspired from Fillot et al. [1], to understand the particles flows at the tire/road interface; and the dry lubrication theories developed for powders (as molybdenum disulfide MoS2 ) [2] [3] to understand and model the friction. Experiments are conducted in laboratory to understand and model this phenomenon. Particles are collected, by drying and sieving, from sediments sampled from a catchment area which collects runoff water. Analyses are performed to determine the particles' chemical composition and size distribution. Experimental protocol allows simulating the particles' build up process on the road surface. The specimen surface, representative of a road surface, includes a microtexture scale, representing the asperities of the aggregates, and a macrotexture scale, representing the space between the aggregates. Friction measurements are realized by means of the so-called Skid Resistance Tester Pendulum, widely used in the road field, which simulates the friction between a rubber pad sliding at 3 m/s on the specimen surface. On a surface initially covered with particles, successive friction runs are performed, without resupplying particles between two consecutive runs. Specimen's weight is recorded before and after each friction run. Results show that friction drops significantly, compared to a clean state, when the surface is covered by particles. Successive runs induce an increase of friction coefficient until reaching a stable value which is below that of a clean surface. Three particles' flows are calculated: particles ejected from the contact area between the friction slider and the test surface; particles trapped by the surface microtexture; particles stored by the surface macrotexture. Close relationship was found between the friction coefficient and the flow of particles trapped by the microtexture. Similarities are found, in terms of lubrication mechanisms, between the behavior of studied particles and powder [3]. Discussions allow understanding the relationship between particles' characteristics and Stribeck curves' parameters such as viscosity, lubricant film thickness and pressure. A first attempt of modeling allows to calculate the friction coefficient from the fraction of surface covered by particles. This study has allowed to see the contribution of tribology to the understanding of complex phenomena in the road field such as skid resistance on contaminated road surfaces. Perspectives, especially in terms of study of water and particles mixing, are presented. [1] Fillot, N., Iordanoff, I., and Berthier, Y. Wear modeling and the third body concept. Wear, 262, 949-957, 2007. [2] Higgs, C.F., Wornyoh, E.Y.A. An in situ mechanism for self-replenishing powder transfer films: Experiments and modeling. Wear, 2008, 264, 131-138. [3] Heshmat, H. Wear reduction systems for coal-fueled diesel engines ? Experimental results and hydrodynamic model of powder lubrication. Wear, 1993, 162-164, 518-528.

AOP 2017 - 3rd International Conference on Applications in Optics and Photonics, Faro, Portugal, 08-/05/2017 - 12/05/2017; Microtopographic and rugometric characterization of surfaces is routinely and effectively performed non-invasively by a number of different optical methods. Rough surfaces are also inspected using optical profilometers and microtopographer. The characterization of road asphalt pavement surfaces produced in different ways and compositions is fundamental for economical and safety reasons. Having complex structures, including topographically with different ranges of form error and roughness, the inspection of asphalt pavement surfaces is difficult to perform non-invasively. In this communication we will report on the optical non-contact rugometric characterization of the surface of different types of road pavements performed at the Microtopography Laboratory of the Physics Department of the University of Minho.

Maintenance of paved roads is carried out to preserve and improve the pavement and reduce the deterioration process. An adapted treatment will make the pavement last for a certain time interval before next treatment is necessary. Pavement managers deal with complex decisions when identifying lengths of their networks in need of maintenance and selection of the appropriate maintenance treatments. Decades of road network monitoring and follow up projects have generated a huge volume of empirical data on pavement condition. To complement this information, several decades of research and development has accumulated a substantial volume of knowledge, models and tools that can use the information to assist in maintenance decisions. Even so, these support tools are not yet implemented to their full potential, and most tools do not address user expectations and new environmental impacts such as fuel consumption and emissions. This paper will demonstrate a tool to assist road authorities in optimising the maintenance of their road networks.

Last century has seen the emergence of many active safety systems, which have highly participated in reducing the number of car crashes. Nevertheless, those systems can be improved. In particular, information about the wetness of pavement surface could be of high importance to evaluate real tire/road friction. This paper deals with a new way to estimate local water depths under the tires as the car is running. A direct measurement of the amount of water droplets thrown from rotating tires of the vehicle is used. Tests are performed on test tracks with a real passenger car equipped to estimate spray and splash of water created by the front right tire of the car. Different water depths are obtained by flooding test tracks then measuring while they are drying. An indicator linked to the amount of water droplets is defined and studied under different conditions. Effects of travelling speed, road texture or tire tread pattern are assessed. The relationship between the indicator and actual water depth is verified by using non-contact optical water depth sensors as a reference. This new method of measurement via water droplets is a major breakthrough in automotive engineering since low-cost sensors can be used to estimate the water depth.

Most of past research on the skid resistance/road wetness relationship deal with thick water depths (> 1mm). Questions remain as to the variation of skid resistance with thin water films and the transition between the dry state and the so-called “damp” or “humid” state at which the skid resistance drop can be as high as 30-40%. This paper deals with a theoretical and experimental assessment of the friction/water depth relationship. The main objective is to estimate local water depths trapped between the tire and the road asperities and to define a so-called “critical” water depth which can be used for driver assistance systems. Tests are performed in laboratory and on test tracks. It was found that the friction-water depth curves have an inverse-S shape and present an initial constant-friction part before decreasing to a minimum value. A “critical” water depth, defined as the water depth above which the friction coefficient collapses significantly, is determined from observed friction-water depth curves. Influence of test speed and road surface texture on critical water depth is discussed.

Megatexture corresponds to surface irregularities with wavelengths of a pavement profile lying between 50 mm and 500 mm and vertical amplitude ranging from 0,1 to 50 mm. Wavelengths of megatexture are the same order of size as tire/road interface. Megatexture is measured by a profilometer called RUGO (mlpc device) composed of a non-contact sensor, which measure the distance between its datum-line and the pavement surface examined. Then, the profile curve is analyzed by digital filtering technique in order to determine the magnitude of its spectral components at different wavelength. Thus, the texture spectrum of the profile is calculated with a texture level, given in dB, for each one-third-octave band and each path of measurement. This study investigates elements that may affect megatexture measurements like the type of captor, the speed or the operator. Experiments were realized in order to evaluate the reproducibility and the repeatability of the megatexture measurements following the international standard ISO 5725. In the first part, the device used and the information relative to the megatexture measurements and indicators are described. In the second part, the statistical analysis results are exposed and the value of repeatability r and reproducibility R are given for each one-third-octave band.

Ce papier présente quelques résultats d’une étude qui a pour objet la modélisation de l’évolution des caractéristiques de surface de différents revêtements routiers. Dans un premier temps, une base de données est constituée à partir de mesures réalisées sur le réseau routier national français au cours des deux dernières décennies. Cette base contient des informations relatives à la technique routière, au trafic, à l’âge et aux caractéristiques de surface (Coefficient de Frottement Transversal mesuré par le SCRIM et Profondeur Moyenne de Profil). Dans un deuxième temps, des lois d’évolutions sont proposées. Elles sont basées sur des méthodes de régression non-linéaire en première approche. Cette analyse statistique permet de déterminer les variables explicatives de l’évolution des caractéristiques de surface comme l’âge ou le trafic. Dans un troisième temps, les lois d’évolution obtenues dans le cadre de cette étude sont analysées et comparées à d’autres lois proposées dans des études antérieures. Enfin, les accidents s’étant produits sur quelques itinéraires sont corrélés aux niveaux d’adhérence relevés. Une des difficultés vient du fait que les mesures d’adhérence (CFT et PMP) sont ponctuelles (tous les ans, deux ans ou trois ans) et ne correspondent pas toujours au moment où se sont produits les accidents. Les lois d’évolution sont donc utilisées pour évaluer le niveau de coefficient de frottement et de macrotexture au moment de l’accident et corréler ainsi les données entre elles. Des valeurs seuils affinées au-delà desquelles le risque devient très important sont ainsi proposées par les auteurs.