Ghim Ping Ong

Prediction of Wet-Pavement Skid Resistance and Hydroplaning Potential

The current means of predicting the skid resistance of a wet pavement and the speed at which hydroplaning would occur are based on empirical models or relationships derived from experimental studies. These models and relationships are applicable only for the conditions specified, and extrapolations beyond the applicability range of parameters (e.g., vehicle speed, tire load, tire inflation pressure, water film thickness, and type of tire and pavement surface) are not advisable. Such restrictions could be overcome by developing an analytical model based on theoretical considerations. An analytical model also would provide a more in-depth understanding of the relative influence of different parameters. A three-dimensional finite element model is presented to predict wet-pavement skid resistance and hydroplaning speeds (i.e., wheel speed at which hydroplaning occurs) under different magnitudes of passenger-car wheel load, tire inflation pressure, water film thickness, and vehicle speed. The analysis shows that hydroplaning speed increases (i.e., hydroplaning risk decreases) with wheel load and tire inflation pressure but decreases with the depth of water film thickness. The skid resistance measured in terms of skid number decreases as the sliding-wheel speed or the water film thickness increases but increases with the magnitude of the wheel load and is affected marginally by the tire inflation pressure. Within the normal passenger-car operation range of each of the parameters, the hydroplaning speed is affected most by tire inflation pressure followed by water film thickness and is least influenced by the wheel load; the skid resistance is most influenced by sliding-wheel speed followed by water film thickness and wheel load and is least affected by the tire inflation pressure.

Effectiveness of Tire-Tread Patterns in Reducing the Risk of Hydroplaning

Grooving of tire tread is necessary to provide sufficient skid resistance for wet-weather driving and to reduce the risk of hydroplaning. Many different groove patterns of tire tread are found in the market. However, their relative effectiveness in reducing hydroplaning risk is generally not known to motorists and highway engineers. The effects of changes in the groove depth of a tire treads groove pattern also deserve further investigation. This paper presents an analytical study that aims to characterize quantitatively the influence of different tire-tread patterns and groove depths on the hydroplaning behavior of passenger cars. The analysis is performed by means of a computer simulation model with a three-dimensional finite element approach. The following six forms of tire-tread groove patterns are considered: (a) longitudinal groove pattern, (b) transverse groove pattern, (c) V-groove pattern with 20° V-cut, (d) V-groove pattern with 40° V-cut, (e) combined groove pattern consisting of longitudinal grooves and edge horizontal grooves, and (f) combined groove pattern consisting of longitudinal grooves and 20° V-cut grooves. The analysis shows that a parameter computed as the groove volume per tread area of the tire is a useful performance indicator to assess the effectiveness of various tire-tread groove patterns in reducing vehicle hydroplaning risk. The significance of V-shape grooves is discussed. For vehicular operations involving both forward and lateral movements, the analysis indicates that a combined pattern would provide a good compromise in lowering hydroplaning risk sufficiently in different modes of vehicle movements.

Analytical Modeling of Effects of Rib Tires on Hydroplaning

Hydroplaning is known to be a major cause of wet-weather road accidents. The risk of hydroplaning in wet-weather driving is a function of the depth of surface water, pavement texture properties, and tire characteristics. With the aim to improve and ensure wet-weather driving safety, extensive experimental studies have been conducted by researchers to understand how tire characteristics (in particular, tire tread depth), would affect vehicle hydroplaning risk. Rib tires have been commonly used for such experiments. Relationships derived experimentally by past researchers are available to estimate the effect of rib-tire tread depth on hydroplaning risk. However, such statistical relationships have limitations in their application range and transferability. They also do not provide detailed insights into the mechanism of hydroplaning. These limitations can be overcome through development of a theoretically derived analytical model. This paper presents an analytical simulation study that is based on the theory of hydrodynamics. The method of modeling using finite element techniques is described. Measured data from past experimental studies are used to validate the simulation model. The simulation model is applied to analyze the effect of tire tread depth on hydroplaning for different surface water depths. The effect of tire inflation pressure on the hydroplaning risk of rib tires is also examined. In addition, the effect of different rib tire designs in relation to the number of grooves is studied. This study demonstrates that the proposed model can be a useful analytical tool for evaluating the hydroplaning risk of wet-weather driving.

Modeling and Analysis of Truck Hydroplaning on Highways

The widely adopted NASA hydroplaning equation has been able to predict closely the hydroplaning speed of passenger cars on a wet pavement. However, field observations and experimental studies have found that the equation cannot explain the hydroplaning behaviors of trucks. According to the NASA equation, trucks hydroplane only at a speed much higher than the normal range of travel speeds on highways. However, this conclusion is not supported by real-world experience and field tests. In addition, field observations and experimental studies have found that lightly loaded trucks are more prone to hydroplaning than heavily loaded ones. This phenomenon cannot be explained by the NASA equation, which states that, regardless of the magnitude of wheel load, hydroplaning speed is the same if tire inflation pressure remains unchanged. To the authors’ knowledge, no studies have demonstrated theoretically or analytically why trucks behave differently from passenger cars in their hydroplaning behaviors. Using the technique of three-dimensional finite element modeling, this paper analyzes the problem of truck hydroplaning with an analytical simulation model based on hydrodynamics theory. The formulation of the model is described, and the computed results are validated against past experimental studies. The effects of tire inflation pressure, footprint aspect ratio, and truck wheel load on truck hydroplaning speed are also examined to help explain the different hydroplaning behaviors of trucks and passenger cars.

Effectiveness of Transverse and Longitudinal Pavement Grooving in Wet-Skidding Control

The use of grooving in the pavement surface is a common approach to improve wet weather skid resistance and reduce hydroplaning risk. Field measurements have found transverse grooves effective in significantly improving skid resistance and reducing the occurrence of hydroplaning. Nevertheless, despite the reported effectiveness of longitudinal grooving in wet weather accident reduction, most experimental studies do not record any significant increase in the measured skid resistance of longitudinally grooved pavements. An analytical study is presented to evaluate the relative effectiveness of the two types of grooving in terms of their ability to reduce hydroplaning potential and their respective skid resistance available at the onset of hydroplaning. The groove dimensions examined cover widths from 2 to 10 mm, depths from 1 to 10 mm, and center-to-center spacing from 5 to 25 mm. It is found that in terms of the ability to raise hydroplaning speeds (i.e., to lower hydroplaning risk) and skid resistance values, transverse grooving consistently produces much better results than longitudinal grooving. The simulation results confirm that, for longitudinal grooving with dimensions within the practical ranges, only marginal improvements occur in both hydroplaning speed and skid resistance in the longitudinal directions. However, an analysis by the simulation model indicates that, unlike a smooth plane surface that has the same skid resistance properties in all directions, longitudinally grooved pavements have significantly higher skid resistance as the skidding direction deviates from the true longitudinal direction. The quantitative simulation analysis suggests that this relationship has the effect of enhancing traction to keep skidding vehicles within the roadway and to cut down on wet-pavement accidents, a result that has been widely observed in field applications of longitudinal grooving.

Development of a Structural Index as an Integral Part of the Overall Pavement Quality in the INDOT PMS

Transportation agencies spend billions of dollars annually on pavement maintenance and rehabilitation to meet public, legislative, and agency expectations. Knowledge of the structural condition of a highway pavement is crucial for pavement management at both the network level and the project level, particularly when the system monitoring, evaluation, and decision-making are to be made in a context of multiple criteria that include structural condition. A key aspect of the performance criteria for multiple criteria decision making is that the criteria must be amenable to scaling so that it can be duly incorporated in the overall utility function. The main objectives of this research study are: 1) To develop a pavement structural strength index (SSI), scaled logistically from zero to a 100, based on the falling weight deflectometer (FWD) deflection measurements; 2) To formulate SSI in such a manner to be used as an index or employ the value of “100 – SSI” as a deduct value from pavement distresses surface index; and 3) To develop models by which the SSI could be estimated given functional class, age, and drainage condition wherever deflection measurements are not available. Extensive literature review of existing information related to pavement structural capacity assessment was conducted. Necessary data was collected from the Indiana Department of Transportation (INDOT) pavement management databases and deflection measurements available at INDOT Research and Development for both project and network levels. Information from INDIPAVE (a database that includes data on weather conditions, highway classification, traffic, and other information at over 10,000 one-mile pavement sections in the State of Indiana) were also employed. Weather information was also collected from the Indiana State Climate Office. The data includes information on 12,250 road sections from 1999 to 2007. Data was classified by pavement surface type (whether it is asphalt or concrete) and system classification (whether it is an interstate, a non-interstate but part of the national highway system (NHS), or a non interstate and not a part of the national highway system (non-NHS).

Methodology to Evaluate Quality of Pavement Surface Distress Data Collected by Automated Techniques

Highway agencies commonly use automated pavement data collection techniques to collect pavement surface distress data at the network level. Although an immense amount of data is collected at the network level, agencies realize that there is a lack of understanding of the quality of the data collected. Traditionally, either the overall pavement condition rating or individual distress ratings are used to evaluate the quality of the condition data. However, each measure has its own pros and cons, rendering the use of a single measure inadequate. This paper presents a set of performance measures that highway agencies can use to quantify the quality of the pavement condition data collected and processed. The set of measures consists of (a) the pavement condition rating and hypothesis testing for differences, (b) the percentage cumulative difference in the pavement condition rating over its entire range, and (c) kappa statistics for individual distresses. This set of performance measures can be used to assess the effectiveness of an automated method for the collection of pavement condition data and the effect of sampling on the pavement condition ratings obtained by automated techniques. The effectiveness of an automated technique is assessed by comparison with the findings of benchmark manual visual surveys. The performance measures offer a complete assessment of the effect of sampling on the overall pavement condition rating, its variation over the entire range, and the identification of individual surface distresses.

Runway Geometric Design Incorporating Hydroplaning Consideration

An important aspect of airport runway geometric design is ensuring prompt removal of water from the runway to reduce skidding and hydroplaning risks of aircraft operating under wet-weather conditions. However, current airport geometric design methods do not explicitly consider hydroplaning risk, and the adequacy of runway geometric design and the associated drainage system against hydroplaning has not been evaluated. In recognition of the need for a design procedure to ensure safe aircraft operations, a framework for runway geometric design that incorporates hydroplaning consideration was proposed. Runway cross-slope is the main runway geometric element affected by the hydroplaning consideration. The proposed framework involves adding an independent module for hydroplaning risk calculation to determine whether a trial runway geometric design meets the safety requirement against hydroplaning for the selected design rainfall and aircraft traffic. For a trial runway geometric design, taking into account the probabilistic distributions of aircraft characteristics, landing speed, and aircraft wander, the level of hydroplaning risk can be computed by comparing the landing speed at each point on the width of the runway with the corresponding estimated hydroplaning speed. The hydroplaning speed at each point of interest is estimated by using an analytical computer simulation model. A numerical example is presented to illustrate the application of the proposed procedure.

Relative Effectiveness of Grooves in Tire and Pavement for Reducing Vehicle Hydroplaning Risk

Grooving of pavement surface and tire tread has been accepted as good practice to enhance road travel safety against wet weather skidding and hydroplaning. Many guidelines on this practice have been derived from findings of experimental studies and field experience. However, theoretical studies to provide insights into the factors and mechanisms involved are lacking. A theoretically derived analytical simulation model was used to study the relative effectiveness of pavement grooving and tire grooving in reducing vehicle hydroplaning risk. Three basic grooving configurations were considered: ungrooved, longitudinally grooved, and transversely grooved. There are nine different combinations of grooving configurations. To form a common basis for comparison, constant values of groove width, groove spacing, and water-film thickness were considered in the computation of hydroplaning speeds for different groove depths. Transverse grooves performed better than longitudinal grooves in raising hydroplaning speed (i.e., reducing hydroplaning risk), and pavement grooving was a more effective measure than tire tread grooving in reducing hydroplaning risk. Further detailed examinations of the results were conducted to study the practical implications of the findings. For longitudinal grooving, which is commonly adopted in highways, pavement and tire grooving are of equal importance in their contributions toward reducing hydroplaning risk. In the case of runways where transverse grooving is the standard practice, pavement grooving is the dominating component in guarding against hydroplaning.