1 Introduction

There are several initiatives, research activities and studies on truck platooning across the globe, driven by the European Union, various governments and the industry. Truck platooning is the linking of two or more trucks in convoys, using automated driving support systems. These vehicles automatically maintain a close distance between each other when they are connected for certain parts of a route. The truck at the head of the platoon acts as the leader, with the vehicles behind reacting and adapting to changes in its movement, e.g. accelerating or braking. Drivers of the trailing vehicles remain in control of their vehicle, so they can leave the platoon and drive independently. [1] Truck platooning has great potential to make road transport safer, cleaner and more efficient in the future [1]. Therefore, truck manufacturers are striving to develop and deploy truck platooning systems. First trials have been carried out by several projects and initiatives. However, further research on truck platooning technology is necessary before truck platoons are permitted to operate widely on public roads. Experience with recent truck platooning technologies under real traffic conditions is a prerequisite to, e.g., be able to assess how other road users react to truck platoons and what the ideal number of vehicles in a platoon is. With each trial under real traffic conditions, new challenges and opportunities can be derived together with relevant stakeholders. This includes not only OEMs, Tier 1 suppliers, software and service providers but also road operators, logistics companies, insurance companies and policy makers.

With the (further) development of driver assistance systems, connectivity, sensor technology and the digitalisation of the traffic system, truck platooning has gained in importance. While truck platooning was initially seen primarily to reduce fuel consumption, the discussion soon shifted to how truck platooning can contribute to a sustainable transport system. Major research projects and trials were conducted in the USA, Europe, Asia and Australia to evaluate the benefits and feasibility of truck platooning. In California, the PATH programme has been conducting trials for years. The European project Promote Chauffeur I was one of the first demonstrations of truck platooning with two trucks using tow-bar technology. In the continuation of the project in Promote Chauffeur II, the feasibility of a fully operable truck platoon with three trucks was demonstrated under real conditions [2]. The German KONVOI project investigated the advantages and operational issues of truck platoons used in mixed traffic scenarios on the motorway [3]. The European SARTRE project demonstrated a platoon consisting of both passenger cars and trucks on the motorway, using a manually operated truck trailed by automated passenger cars [4]. This is only a fraction of trials with such and related topics around the world.

2 Opportunities and Challenges of Truck Platooning

2.1 Interoperability

In Europe, given the predominance of small fleets with only few trucks of a single brand, interoperability between multi-fleet and multi-brand trucks plays a key role. The project Sweden 4 Platooning, e.g., demonstrated the feasibility of truck platoons with vehicles from different manufacturers in DB Schenker’s operations. This was achieved by harmonising the systems of the manufacturers Scania and Volvo. The research project COMPANION (cf. [5]) investigated possibilities for the application of the truck platooning concept for commercial freight transport. For this purpose, a coordination system was developed within the project, which enables the dynamic formation and dissolution of truck platoons. This means that vehicles participating in a platoon do not have to have the same origin and/or final destination but can also run together on parts of their route. Furthermore, it was investigated how truck drivers can be informed when a potential truck platoon can be formed or dissolved. The project CONCORDA (cf. [6]) also focuses on the interoperability and networking between different systems. A core objective of the project is to improve the interoperability of technologies, services and their implementation in the European Union. The European project ENSEMBLE (cf. [7]) investigates the impact of multi-brand platooning on infrastructure, drivers, traffic safety and traffic flow. The project plans to test multi-brand platooning on test tracks and on public roads across national borders in 2021.

2.2 Road Safety and Traffic Efficiency

According to the European Truck Platooning Challenge, human error is responsible for more than 90% of road accidents and the human factor is decisive when it comes to traffic efficiency. Several projects examined the advantages, disadvantages, impact and safety effects of truck platooning in simulation studies, on test tracks as well as in real traffic situations in the last two decades. Subsequently, results from selected projects that evaluated interactions with other road users and driver perception are described.

The focus of the KONVOI project (cf. [3]) was on impact analysis (driver acceptance, traffic flow, environment) and the investigation of legal and economic implications of truck platooning. During the project a platoon of four trucks of the brands MAN and IVECO was formed and tested in real traffic for the first time worldwide in 2009. The participating vehicles were equipped with vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communication, a mono-camera as well as a lidar and radar sensor and could thus travel at distances of 10 m between each other. Based on real-life traffic (a total of 3100 km were covered), the project claims to have demonstrated safe traffic flow. However, no details on the results (methods, parameters, design, etc.) are publicly available. The German project EDDI (cf. [8, 9]) was able to analyse the experience of truck drivers and their interaction with other road users as well as psychosocial and neurophysiological effects of truck platooning on truck drivers. The project involved seven months of testing with two linked vehicles on the motorway between Nürnberg and München (approximately 165 km). The results indicate a significant change in the previously partly critical attitude of the drivers. The project was tested for the duration of seven months with two linked vehicles. For the international use, the scientists recommend further investigations with longer platooning phases. In the PLATOON project (cf. [10]), the advantages and disadvantages of truck platooning regarding transport operations were investigated to understand the effects of platooning strategies on transport operations on freeways. To this end, these effects were theoretically analysed to determine the limits of truck platooning and thus to decide when and how the formation of a platoon can improve motorway traffic operation. Traffic performance and safety effects of different platooning strategies and platoon configurations using microscopic simulation have been analysed in the paper “Benefits and risks of truck platooning of freeway operations near entrance ramp” (cf. [11]). The driving behaviour of truck platoons and conventionally controlled vehicles was also modelled for the same paper. The simulation showed that truck platoons may lead to problems at freeway entrances: The greater the traffic volume and the higher the number of truck platoons, the more vehicles may not be able to fit into the flow of traffic within the length of the acceleration lane. These vehicles must either stop at the end of the acceleration lane or continue along the hard shoulder. These manoeuvres are associated with a higher risk of accidents and affect the fluidity of the traffic. Therefore, it is recommended to allow truck platooning on on-ramps only under certain conditions (e.g. only at certain times of day). In case of higher traffic volume—especially at on-ramps—the use of truck platoons is not recommended.

2.3 Operation Costs and Fuel Consumption

The use of platooning technology/systems in the truck industry can help vehicle manufacturers and transport service providers to reduce fuel costs. According to Scania, fuel costs account for more than 30% of operating costs in normal European transport operations. Reducing fuel consumption would therefore have a significant impact on total freight costs in the transport industry. For example, tests conducted by Scania in December 2015 showed that a truck platoon can reduce fuel consumption by up to 12%. According to Peloton Technology, reducing drag on two-truck platoons offers fuel savings for both the trailing and the leading truck. However, the reduction in fuel consumption is highly dependent on the speed of the trucks. On European motorways, the speed of trucks is limited to 80 km/h, while in the USA, trucks travel at the same speed as cars for most motorway kilometres. Since air resistance increases with speed, fuel savings in the USA and in countries with similar truck driving patterns, such as Australia, are expected to be greater than in Europe. A detailed comparison of fuel savings reported in diverse truck platooning projects is provided in Chap.  3. Thereby, the comparison considers different following distances within a truck platoon and the speed of a truck platoon.

2.4 Reduction of CO\(_{2}\) Emissions

The International Transport Forum (ITF) estimates that international trade-related freight transport is currently responsible for around 30% of all transport-related \({\text {CO}}_{2}\) emissions from fuel combustion and for more than 7% of global emissions. In order to achieve the Parisienne climate targets, OEMs and Tier 1 suppliers are expected to comply with climate protection requirements. The European Parliament is calling for a 30% reduction in \({\text {CO}}_{2}\) values for trucks and buses by 2030 (reference year 2019). The reduction of the fuel consumption is directly related to the reduction of \({\text {CO}}_{2}\) emissions. As such, truck platooning may represent one means to reduce \({\text {CO}}_{2}\) emissions. An assessment of the emission reduction potential for a certain case is detailed in Chap. 12.

2.5 Shortage of Professional Drivers

According to the German Federal Motor Transport Authority, about 20% of professional drivers are over 55 years old and about to retire in the years to come. Only 40% of the vacant positions due to retirement can be reoccupied (67,000 professional drivers retire annually and only 27,000 junior drivers follow (cf. [12]). For this reason, a higher degree of automation in the transport sector is considered to solve the shortage of professional drivers. At the same time, the increasing level of automation is expected to rise the attractiveness of the profession, as the latest technology will require drivers with new skills and thus open new areas of responsibility. To solve the driver shortage issue, the Japanese government plans to commercialise unmanned trailing platooning vehicles by 2022.

2.6 New Requirements for Vehicles and the Infrastructure

The transition from conventional transport systems towards automated and connected mobility (digitalisation of the traffic system) sets new challenges, which require constant adjustments to both vehicles and infrastructure. On the vehicle side, the installation of advanced automated driving features from different OEMs and vehicle generations will lead to a huge range of different versions of software capability, which must be able to communicate and interact with each other and the infrastructure (V2V, V2I and V2X). The interaction of vehicles and infrastructure is achieved by collecting, processing and intelligently linking data (cf. “Strategy for Automated and Connected Driving” defined by the German government in 2015). The basic prerequisite is the generation of secure and fast data transmission, which results in high functional and qualitative demands on the communication technology and infrastructure. Most of the current road infrastructure (globally) is not sufficiently well equipped and thus restricts the formation of routes for long-distance truck platoons. Furthermore, unsuitable road markings and bridges hamper an optimised route for truck platooning. Therefore, before truck platoons can become a common sight on Europe’s road, the road infrastructure needs to be upgraded (cf. [1]).

ASFINAG, the Austrian motorway operator, is equipping the Austrian freeway network with C-ITS starting in November 2020 (cf. [13]). The C-ITS rollout has been coordinated in Europe with operators in 18 member states and automobile manufacturers. The goal is to network directly with vehicles and to be able to support future applications from electromobility to highly automated driving. In 2018, the Korean government set up a 7.7 km long test track on the Yeonju Smart Highway for the development of automated driving technology. Hyundai Motors was able to use the test environment on the Yeonju Smart Highway for its first truck platooning demonstration under real traffic conditions, using Xcient trucks. Efforts to digitalise the infrastructure are also being made in other countries. Among other things, Japan is working on preparing the infrastructure for a mixed traffic of truck platoons and conventional car traffic.

3 Conclusion

Truck platooning studies have shown that truck platooning facilitates increasing energy efficiency, may reduce costs and may improve road safety. Furthermore, studies provide information about socio-economic benefits such as congestion mitigation, traffic efficiency, better lane usage and driver safety. Although research and development as well as test results have been provided, the deployment remains open as well as further research and long-term impacts evaluations. Standards for multi-brand and multi-fleet platooning adopting C-ITS, clear platooning regulations and policies as well as safe and efficient operation strategies will be key for the adoption and deployment of truck platooning within the next years.