The impact of Truck Platooning on the pavement structure of Dutch Motorways

Abstract

The transportation industry is constantly developing innovative solutions in order to increase efficiency, sustainability and safety. Truck platooning is one of those emerging technologies with high potential. In one way or another, truck platooning will also have an impact on our current infrastructure and the way in which the motorways are managed and maintained.Trucks have the greatest effect on the occurrence of road surface wear unlike smaller vehicles (Mallick & El-Korchi, 2017). The pavement structure is designed according to the amount of truck axle load repetitions that occurs in the design life of the motorway.The current traffic flow is normally distributed on the traffic lane, which is called lateral wander and has a positive effect on the service life of the road structure. Driving in a platoon will influence the wandering effect of trucks which will have a negative effect on the pavement structure. Lateral wander results in the distribution of pavement damage allowing more load repetitions on the lane.Different professionals from Rijkswaterstaat and TNO (research institute) were approached and search engines like Scopus, Elsevier, ResearchGate, ScienceDirect and the library of Tu-Delft were used to obtain scientific papers on truck platooning, pavement structures and the current maintenance strategies. It can be concluded that little to no research has been done into the impact of truck platooning on the pavement structure. This means that there is a knowledge gap in the scientifically area and in the practical area. This resulted in the following objective of this research, which is to fill the scientific knowledge gap and to contribute to the current practise. The resulting main research question has been developed, based on this objective.What are the potential impacts of Truck Platooning on the road infrastructure and how could this affect the construction and maintenance of asphalt pavements on motorways?Research approachA mix of qualitative methods and quantitative methods were used to find an answer on the main research question regarding truck platooning and the pavement structure. First, a literature study was conducted in order to collect the necessary data to identify the characteristics of truck platooning and to analyse the failure mechanisms of the pavement structure.The literature study identified three failure mechanisms which are effected by lateral wander. The literature study also resulted in three basic models, which are used to analyse the failure mechanisms. During the desk research, the models were adjusted to fit the needed situation of truck platooning on the Dutch motorways. After this, the impact of truck platooning on the pavement structure is determined.Next interviews were conducted with the purpose to obtain and evaluate data regarding the failure mechanisms of the pavement structure in relation to truck platooning and their impact on the maintenance strategy. As such, the obtained data is incorporated into the study.ResultsThree possible platooning scenarios were identified, based on the interviews. The impact of truck platooning will depend on the way on which the platoon will be configurated.• The trucks can be connected to each other only in the longitudinal direction.• The trucks can be connected in both the longitudinal and transverse directions, with an independent leading truck.• The trucks can be coupled in both the longitudinal and transverse directions while the leading truck drives in the exact same track as the previous truck platoons. This scenario applies when the trucks start to drive autonomous.The impact of truck platooning will depend on the way on which the platoon will be configurated. As a result of the interview with the professionals of Rijkswaterstaat, it was concluded that only the third scenario will have an impact on the pavement structure. Today's vehicles are getting smarter and are equipped with a lot of technology. The European Uni encourages the use of Advanced Driver Assistance Systems (ADAS) and even made a number of core systems mandatory for vehicles (Dijsselbloem, Asselt, & Zouridis, 2019).The third scenario represents the most negative setting of truck platooning. The trucks in this setting are coupled in both the longitudinal and transverse directions while the leading truck uses a form of cruise control letting it drive in the exact same track as the previous truck platoon. This situation arises when the trucks start using technology to drive. The strains on the pavement structure can be two times as large in case of fatigue failure. The structural damage on the pavement will increase as a result of rut development and of fatigue.The second part of the literature review resulted in three failure mechanisms and three models were identified.• The first failure mechanism is permanent deformation; using the Rut development model.• The second failure mechanism is raveling; using the Raveling prediction model.• The third failure mechanism is fatigue failure. The Dutch Design Method includes a model in order to predict the acceptable amount of load repetitions on the pavement structure,The following findings have been made with regard to the impact of truck platooning on the failure mechanisms:Permanent deformationA maximum rut depth of 18 mm is commonly used on Dutch motorways. It is generally assumed that this standard will be achieved within 30 years without platooning. In most cases, maintenance is already planned when the rut reaches a depth of 16 to 17 mm. The model used to predict the rut development indicates that the rut depth increases with the amount of platoons on the motorway. This development could impact the current maintenance strategy if more than 50% of the trucks drive in a platoon. The maintenance strategy of Rijkswaterstaat will have to be adjusted, because the critical failure mechanism shifts from raveling to deformations of the road surface. Permanent deformation will have to be maintained in a different way than raveling. The critical point of permanent deformation could be reached within 10 years, if all the trucks that participate in traffic on the highways start to drive in a platoon.RavelingRaveling is the loss of aggregate material from the top layer. Literature research shows that, in case of young asphalt, raveling depends on the asphalt composition and traffic characteristics. However, it was also concluded that the impact of traffic decreases and that the impact of climate increases on older asphalt. It was therefore determined that the characteristics of truck platooning won’t lead to an increase of raveling, which means that the same maintenance intervals as in the current situation can be maintained.Fatigue failureMotorways are designed with a lifespan of 20 years based on a certain number of load repetitions and with fatigue failure as criterium. After this, improvements will be made which will extend the service life by another 20 years and so on. Based on desk research and interviews, it is assumed that, in the current situation without platooning, the pavement fatigue life of motorways approaches 25 year. The results in this research show that the acceptable amount of load repetitions will be exceeded within 20 years if 50% of the trafficking trucks autonomously drive in a platoon and nothing is done. When 100% of thetrucks drive in a platoon the acceptable amount of load repetitions will be exceeded within 10 year.Main findingsOverall, it can be concluded that the scale of damage done to the pavement structure depends on the percentage of platoons on the motorways. The current maintenance strategy will be negatively affected if 50% of all freight transport uses a form of truck platooning. The current maintenance strategy, without platooning, mainly focuses on restoring the top layer of the pavement structure due to the loss of aggregate material or raveling. With truck platooning, the other failure mechanisms like fatigue cracking and permanent deformation will change the current maintenance strategy of motorways. The principal design of a pavement structure is based on the criterium fatigue failure, because this is the most expensive maintenance intervention. Especially because motorways are designed for a lifetime.RecommendationsThe development of truck platooning needs to be dealt with in a timely manner. Data needs to be collected with regard to the failure mechanisms in order to determine the impact and to develop a strategy. This can be done during the first use of the technology and during the regular maintenance intervals used for the current motorways. Rijkswaterstaat lacks the data required for predicting rut development in the current situation, because this failure mechanism has no priority.The impact of truck platooning on fatigue failure will result in maintenance in the form of structural interventions, if no measures are taken. Maintenance interventions in the deeper layers of the pavement structure are the most expensive ones. Applying Smart Lanes could be a solution for simulating lateral wander and organizing maintenance more efficiently.Performing a Cost Benefit Analysis (CBA) to determine whether the required interventions yield more than the costs that must be incurred for upgrading the infrastructure. This not only gives the government a clear overview of future costs as a result of truck platooning, but also a tool to determine whether truck platooning can be permitted on the roads. A positive result of a CBA analysis can therefore be used to get support from various stakeholders, to promote cooperation with different manufacturers and with the Market.DiscussionThree models were used to determine the impact of truck platooning on the pavement structure. The models were obtained through literature research and desk research.The rut development model is based on a number of measuring points generated during the LINTRACK tests on a full scale pavement structures. This tests contains a couple variables like temperature, speed of the tire and wheel load, which differ from practice. A correction has been made for the difference in the variables. The LINTRACK tests produced nine measuring points ,from which a regression line has been developed. More measuring points could be used to increase the accuracy of the regression line.The model which predicts raveling was developed by the New Zealand Transport Agency. As a result, this model does not fit perfectly on Dutch motorways. The model was developed for porous asphalt, but the wheel loads had to be adjusted. This research was conducted for motorways in the Netherlands with limited data.