Keywords

1 Requirements Related to Energy Efficient Truck Platooning

Sustainable logistics demands for energy efficient transport of goods. In this context, energy-efficient transport needs to consider both (i) efficient and optimised transport plans/strategies as well as (ii) efficient transport execution (vehicles used, driving behaviour) itself.

Fig. 3.1
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Selected truck platooning requirement dimensions

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Regarding efficient and optimised transport plans/strategies, [4] review published platoon planning approaches. In their contribution, they present three different planning situations based on the availability of truck travel information (start-/endpoint, departure-/arrival time):

  • Scheduled platoon planning—truck travel information is available in advance and platoon plans may be developed and optimised off-line in a static way.

  • Real-time platooning—truck drivers provide information when they start their trip [online or dynamic planning].

  • Opportunistic platooning—truck that are nearby builds a platoon in a dynamic way without any plan in advance [ad hoc or on the fly platooning].

Bhoopalam et al. [4] state that truck platoon planning may serve different objectives, e.g. minimising system-wide fuel costs or maximising the number of platoons. Furthermore, efficient truck platoon planning needs to meet different requirements and constraints, e.g.:

  • temporal coordination of truck journeys,

  • regulations with respect to driving times,

  • technical compatibility of platooning systems,

  • constraints due to transport goods (e.g. dangerous goods),

  • regulations related to platoon length,

  • individual and organisational caveats,

  • vehicle properties.

With respect to efficient transport execution, different influence factors need to be considered. Influence factors related to energy efficient vehicles are, e.g.:

  • Drive technology

    • Increase efficiency of existing drive technologies versus alternative fuels.

  • Vehicle weight.

  • Aerodynamic drag.

  • Rolling drag.

Furthermore, influence factors related to energy-efficient driving are:

  • Driving behaviour, e.g.

    • driving foresighted, different driving manoeuvres for platoon building.

  • Given (road) infrastructure, e.g.

    • Road profile, available real-time traffic information services.

  • Current (road) traffic.

  • Driving situation (wind, weather, ...).

Truck platooning as a means for increasing efficiency aims to reduce fuel consumption and emissions. Previous related work regarding truck platooning investigated potential savings gained by slipstream effects via reducing the distance between trucks and optimising the aerodynamic drag (cf. [2, 15, 17, 23])

Actual savings will depend on aspects such as distance between trucks in a platoon, overall truck platoon length/number of trucks in platoon, position of truck in platoon or platoon formation strategy/manoeuvre. Related work addressing energy efficiency of truck platoons applies simulation approaches (computational fluid dynamics, traffic simulation) and tests under real-life conditions on specific test tracks.

Simulation-based results reveal potential savings of truck platooning. For example, the EU Project Companion found based on a simulation model that even the first truck in a platoon may save 4.7–7.7% fuel at a speed of 70 km/h depending on the distance (10, 12, 20 m) between the first and the second truck (cf. [17]). However, tests on a test track showed within the Companion project that only minimal (max. 1%) or even no savings for the lead truck could be measured. [10] state based on the tests that the fuel saving potential is 4.99% per truck within a truck platoon consisting of three trucks driving at a speed of 70–80 km/h in a distance between 10 and 20 m. The companion tests were performed on a test track under ideal conditions. Effects such as current traffic or diverse platoon building manoeuvres were not investigated on the test track and will likely reduce fuel saving potentials.

Since the early 1990s, diverse truck platooning projects were realised (cf. 2). Estimating and evaluating energy efficiency of truck platoons typically represented a core element of such projects. Subsequently, reported fuel savings from different truck platooning projects are compared in Fig. 3.2 and the underlying data set is depicted in Table 3.1. The majority of the fuel efficiency investigations conducted tests on specific test tracks without surrounding traffic. Only the results reported by the German project EDDI (cf. [5]) were gained on German highways under practical operation. The listed investigations were performed for cabover trucks. The results can be compared with respect to the speed (in kilometre per hour—kph), the distance (in metre) between trucks in a platoon and the fuel savings for each truck in a platoon.

Fig. 3.2
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Fuel savings comparison

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The comparison indicates different measured fuel savings across the projects. Differences may arise from different test situations (test settings, fuel measurement equipment, road profile, surrounding conditions). For example, the savings reported from tests under artificial conditions on test tracks are greater than those from tests under practical conditions:

  • Saving results from Energy ITS [13, 21] at a distance of 15 m are in average 8.55% versus

  • EDDI results (cf. [5]) gained under practical operation indicate fuel savings at a distance of 15 m in average of 2.4% for a platoon of 2 trucks.

However, valid (and agreed upon) criteria and data for assessing the energy efficiency of truck platoons are vital for decisions makers to make an informed decision when it comes to the deployment of truck platooning. Decisions in this case require multi-criteria decision making taking into account different objectives and requirements for truck platooning, for example defining reasonable distances between trucks that are fuel efficient, still safe and comfortable for the truck driver.

Table 3.1 Fuel savings comparison—data set
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Overall, the requirements related to energy-efficient truck platooning may be summarised as follows. Energy-efficient truck platooning needs to consider:

  • Platoon planning and formation strategies.

  • Driving behaviours.

  • Vehicle configurations, e.g.

    • max. speed, motor power, tyre pressure, vehicle weight incl. goods, braking profile, power train—diesel, liquefied natural gas, electric.

  • Platoon configuration, e.g.

    • Truck sequence in platoon, distance between trucks.

  • Road infrastructure.

  • Control technology for efficient formation, execution and resolving of truck platoons.

2 User and Other Road User Requirements

In this section, requirements related, especially related to truck drivers and other road users, are detailed. The results are either derived via literature reviews and/or dedicated studies within the Connecting Austria research project.

2.1 Truck Driver-Related Requirements

Following, the results of a literature review related to truck driver requirements are presented. The literature search focused on:

  • Technology acceptance + platooning.

  • Human–machine interface (HMI) + platooning.

  • Simulation + platooning.

  • Truck platooning deployment.

During the literature search, Google Scholar as search engine and digital libraries (ACM, IEEE, Springer) were used to find relevant references. In addition, forward- and backward-oriented search strategies based on the literature found were applied. The results of the literature review are summarised in Table 3.2. The results are structured according to (i) Reference (Ref.), (ii) Study type, (iii) Study focus and (iv) Requirements/Issues identified.

Table 3.2 Truck driver acceptance literature review
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In addition to the literature review, empirical studies on truck platooning acceptance in Austria were performed in Connecting Austria. In general, all participants of empirical studies conducted in Connecting Austria provided an informed consent to participate in the respective study and to publish the results. Furthermore, interview data were anonymised and securely stored internally in the University of Applied Sciences Upper Austria. In advance to the empirical studies, the authorisation of the involved parties related to the interviews was provided. In 2018, different empirical studies were performed together with Austrian fleet operators and their truck drivers with a special focus on the acceptance of level 1 platooning. In an initial endeavour, a questionnaire based on technology acceptance aspects presented by [24, 25] within the UTAUT and TAM model was conducted. In advance to the questionnaire, level 1 platooning was explained and demonstrated in a short presentation including texts, images and videos. Fifteen male truck drivers aged between 34 and 57 years participated in the questionnaire.

In a next step after the platooning acceptance questionnaire, semi-structured interviews with ten truck drivers aged between 33 and 54 years were conducted in order to gain deeper insights. The interviews were structured similarly to the questionnaire.

As reported in [16], the results of the questionnaire and the semi-structured interviews differ in some aspects. Compared to the questionnaire results, the interview results expect that platooning will be deployed within the next years successfully. Furthermore, the interview results show that drivers expect a benefit when using platooning, whereas the questionnaire results do rather indicate that drivers to not expect a benefit. Furthermore, the interview results related to the intention to use are far more positive than the questionnaire results.

Furthermore, an observation study was conducted in the Connecting Austria project to gain further insights in the everyday work of truck drivers. As reported in [16], an interesting initial finding is that experienced truck drivers tend to turn of driving assistance systems and state “I know how to drive, that’s my job”. Fleet operators also confirmed this finding. For this reason, it will be crucial to design proper deployment processes, actively inform about new features and explain their functionality as well as involve and train drivers when introducing platooning features.

Requirements related to truck drivers may be summarised as follows. Existing related work in the area of HMI provides insights in how interface designs for platooning should be designed and what are crucial acceptance factors, e.g. related to information provision or situation awareness. Furthermore, existing simulator studies and studies with research and development prototypes in real-world tests provide insights related to the application of platooning. These studies provide for example findings on acceptable distances between trucks, trust between truck drivers or trust in technology as crucial elements for deploying truck platooning. In general, the results of the empirical studies conducted in Austria in 2018 confirm the observations presented in the related work. However, there are some slight differences. For example, within the related work safety and comfort are identified as the main reasons for truck drivers to use automated driving functions (cf. [18]. The results of the empirical studies in the Connecting Austria project indicated that truck drivers do not think that platooning will increase safety. However, the truck drivers were asked before the actual use of such a system. Considering the findings within the real operation usage of platooning (cf. [5]) safety concerns could be eliminated during actual use. Beyond, the observation in the Connecting Austria project indicated that the general intention to use assistance systems may influence the adoption of truck platooning.

2.2 Other Road User-Related Requirements

The deployment of connected and automated vehicles will not appear from one day to another. Traffic situations in which vehicles at different automation levels and other road users need to interact are a major challenge for deploying automated driving solutions. Safe and smooth interaction among other road users and automated vehicles will play a crucial role when it comes to the acceptance of automated vehicles in real traffic situations.

Initial research regarding the communication between automated vehicles and other road users (e.g. pedestrians, bicyclists, SAE-level 0 vehicles) has already been presented. For example, [9] investigate “Automated Vehicle Interaction Principles” within four different scenarios:

  1. 1.

    A pedestrian encounters an automated passenger vehicle or a truck at a zebra crossing.

  2. 2.

    A pedestrian encounters an automated passenger vehicle at a parking lot.

  3. 3.

    A conventional passenger vehicle encounters an automated passenger vehicle or a truck at a symmetrically narrowed road.

  4. 4.

    A conventional passenger vehicle encounters a platoon of automated trucks on a highway.

Especially, scenario 1 and scenario 4 allow to convey requirements of other road users relevant in the context of truck platooning. Scenario 1 investigates the interaction between pedestrians and automated trucks at crossings, and scenario 4 is explicitly dedicated to truck platoons.

Related to the interaction at crossings [9] presents the following key requirements and challenges:

  • Mutual understanding between pedestrians and automated vehicles needs to be supported. However,

    • Mutual understanding is challenged by the complexity of interactions and external as well as internal and situational factors, e.g. way of communication between system and other road user—explicit versus nonverbal communication to clarify intentions.

    • Today, pedestrians and drivers use diverse signals to negotiate mutual understanding, e.g. eye contact, hand waving, posture, lights flashing.

  • Being aware of the vehicle mode (e.g. driving, stopping, accelerating) could allow pedestrians aligning their behaviour.

  • Knowing the intentions of the vehicle would eliminate possible ambiguities due to the lack of communication with the “driver”.

  • Minimalistic and generic external vehicle interface such as AVIP could have positive impact on interactions between AVs and pedestrians.

  • Ensure that pedestrians can interpret the signals displayed by an external vehicle interfaces.

  • Ensure that external vehicle interfaces will function in a multi-agent scenarios.

To explore the needs of external signalling for truck platoons, [9] used various highway scenarios (on-ramp, off-ramp, etc.) as a starting point for a series of workshop discussions and interviews involving truck drivers with platooning experience as well as passenger vehicle drivers, OEMs and other experts in the field. Related to scenario 4 (conventional passenger vehicle encounters a platoon of automated trucks on a highway) [9] present the following key requirements and challenges:

  • Inter-vehicle interactions are today affected mainly by traffic regulations. However, there traffic situations rely not only on regulations and depend on the perceptions and actions of traffic participants. In this respect, non-verbal communication aspects, such as eye contact or flashing the lights, need to be understood to be able to negotiate and align behaviour among traffic participants. Unfortunately, non-verbal cues may be ambiguous and situation dependent.

  • Traffic safety and efficiency as well as trust towards AVs may be enhanced if AVs are able to communicate information on their state and information that “replaces” driver-centric cues such as hand gestures.

  • External vehicle interfaces may be useful in solving ambiguities that drivers face today in unclear traffic situations.

  • For trucks involved in a platoon, the rationale of external signalling is to inform other road users in the vicinity that platooning is ongoing and that the trucks wish to stay together without interruption.

  • Most relevant situations for external signalling for platoons are highways at on-ramps, off-ramps, during overtaking and lane changes.

  • Barrier to implement external signalling on the trailer is the fact that trailers are often switched between different haulers. It will be unclear who should cover the cost for the installation and maintenance of the signalling system on the trailers.

  • The possibility of using existing positioning lights should be explored.

The research of [9] represents an initial approach to designing communication means and reveals the need for further research addressing the communication among automated vehicles and other road users. In addition, [3] performed a study of communication needs in interaction between trucks and surrounding traffic in platooning. They investigated “What information needs to be communicated from a platoon to the surrounding traffic to create safe and efficient interaction with the surrounding traffic”? As a result of workshops and interviews, they present a list of information items that may be relevant for exchange (cf. Table 3.3) between a platoon and the surrounding traffic.

Table 3.3 List of communication needs identified by [3]. © April 2021 Andersson, J., Englund, C., and Voronov, A., reproduced with permission
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In their study, [3] conclude that “the in Sweden, and during traffic conditions similar to today’s traffic, there is no urgent need to deploy external signalling for platoons with two trucks, neither if they are driving in ACC-mode with 1s headway or using V2V with 0.5s headway, since the traffic density in most cases will allow for other traffic to interact smoothly with platoons. In Europe, the situation is different because the traffic density is much higher. However, based on the current study, we can not conclude that external signalling is needed in Europe. The subjective data collected in the project support that cut-ins can be reduced to close to zero with a vehicle distance of 0.5 s headway.Footnote 1"

3 Road Safety Requirements

Road safety needs to be ensured when it comes to connected and automated driving solutions such as truck platooning. Thereby, road safety may investigate different objects of traffic systems, e.g.

  • Safe road design.

  • Safe vehicle design.

  • Safe driving.

Previous studies already investigated potential opportunities and risks of truck platooning as well required technical and infrastructural conditions. For example, in Switzerland, the federal office for roads (ASTRA) published a feasibility study, which assess the potential and risks of truck platooning on Swiss highways (cf. [12]). This study concludes that the potential of truck platooning in Switzerland is limited due to the restriction elicited within the study and the high number of tunnels and road accesses in Switzerland. As depicted in Fig. 3.3, the study recommends to resolve truck platoons 1200 m ahead of motorway access points and form 1100 m after motorway access points (compare Scenario C). Furthermore, truck platooning in motorway tunnels is not recommended (resolve 2800m in advance, (re-)form 2600 after tunnel) and bridges are also not recommended. Regarding bridges, the study indicates the need for further research addressing acceptable maximum weight and road wear. Further related work on regulations will be described in Chap.  13 as well as the need for the harmonisation of regulations.

Fig. 3.3
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Truck platooning regulation scenarios

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In the Connecting Austria project members of the Austrian Road Safety Board (KfV—Kuratorium für Verkehrssicherheit) assessed requirements and regulations with respect to safe truck platooning and defined the following constraints within the project based on literature research, workshops and interviews with road safety experts:

  • Motorway should comprise three lanes.

  • Width of lane should be greater than 3 m.

  • Platooning should be prohibited in tunnels (resolve platoon min 1000 m ahead).

  • Platooning should be prohibited at road works (resolve platoon min 1600 m ahead).

  • Platooning should be prohibited at declared dangerous spots (e.g. foggy areas, accident accumulation points).

  • Platooning should be primarily performed on road sections with little curves.

  • Platooning should be prohibited at motorway junctions (resolve platoon min 2000 m ahead).

  • The length of acceleration lanes and deceleration lanes needs to be assessed.

Scenario D in Fig. 3.3 adheres to the defined constraints of the KfV. In addition to this general regulations, the KfV recommends to assess road safety for dedicated platooning tracks. An established means to assess road safety is the “road safety inspection” method. The method has been adopted for truck platooning within the Connecting Austria project. The adoption as well as method application for a dedicated route will be described in Chap. 13.

Fig. 3.4
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Scenario-based assessment of truck platooning routes for a fleet operator, base map and map data from OpenStreetMap, ©OpenStreetMap contributors under the CC-BY-SA license, https://www.openstreetmap.org/copyright

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In order to assess the feasibility of truck platooning in Austria, additional scenarios next to the rather conservative constraints defined in scenario B,C,D were defined by the project partners.

Scenarios A, E and F are aimed at maximising the amount of “allowed” truck platooning kilometres on Austrian motorways applying different strategies:

  • Scen A—minimises area before and after potential dangerous spots to \({\pm }\)assumes that platoon may be safely operated on bridges and in tunnels and allows platooning on bridges and in tunnels (other parameters are similar to Astra study).

  • Scen F—assumes low traffic density at motorway access points (e.g. during night) and allows to drive in a platoon at this road sections.

The scenario restrictions are summarised in Fig. 3.3. Furthermore, a selected result of the scenario-based assessment of routes is depicted in Fig. 3.4. The assessment depicts typical routes of an Austrian fleet operator and the share of highway kilometres that are eligible for truck platooning within a certain scenario. The map in Fig. 3.4 depicts the results, especially for scenario A. However, the chart below the map depicts the differences between the defined scenarios for the given routes. A detailed route analysis with respect to fuel efficiency will be described in Chap. 11. In order to increase the number of in-platoon-driven-kilometres, dynamic platoon management strategies are recommended. A situation-based implementation aiming at dynamic platoon management on highways may be supported by C-ITS services (see Sect. 3.4).

4 Technical Requirements Related to C-ITS

Intelligent road infrastructures fuelled by C-ITS services may have a positive effect on the deployment of truck platooning with respect to safety and energy—as well as traffic-efficiency (cf. [1]). In the area of C-ITS communication, standards have been developed by ETSI. ETSI, a European Standards Organisation, already standardises communication means for Vehicle-to-Vehicle (V2V), Vehicle-to-Infrastructure (V2I) and Infrastructure-to-Vehicle (I2V) communication. Information exchange is standardised in ITS-G5 messages, which may have different types:

  • Cooperative Awareness Message (CAM).

  • Decentralised Environmental Notification Message (DENM).

  • In-Vehicle Information (IVI).

  • Signal Phase and Timing (SPAT).

  • MAP Topology Layer (MAPEM).

In the Connecting Austria project, relevant messages have been identified based on the defined truck platooning use cases. For such messages, the data profiles need to be defined. General information relevant for supporting truck platooning comprises:

  • Information for building a platoon (I2V).

  • Information for resolving a platoon (I2V).

  • Information related to dangerous areas (e.g. road works)(I2V).

  • Information related to the signalling of traffic lights (e.g. remaining green time) (I2V).

  • Information related to road profile (e.g. traffic lights on a track) (I2V).

  • Information related to the status of a platoon (V2I).

  • Information exchange within a platoon (V2V).

For forming and dissolving platoons, the following specific messages are relevant:

  • Minimal gap distance message—indicates to allowed distance between trucks in a platoon for a certain area. May depend on weather, traffic situation, regulations,...

  • Platooning allowed message—indicates if platooning is allowed in a certain area. May depend on weather, traffic situation, regulations,...

Such C-ITS messages will allow to support dynamic truck platoon management for road operators. Depending on a given situation, the minimal gap distance may be varied or platooning may even be prohibited. In comparison with static and restrictive platoon regulations, a dynamic truck platoon management could increase the number of platooning kilometres on specific motorways and thereby contribute to energy efficiency and sustainability. However, information security of ITS-G5 communication needs to be ensured in terms of:

  • Validation of message integrity.

  • Validation of message authenticity.

  • Availability of communication channels.

  • Availability of communicating actors (road-side units and on-board units).

5 Conclusion

In this chapter, selected deployment requirements for truck platooning are reported. Starting with an overview on related work with respect to energy efficiency, the results of fuel savings investigated in previous projects are compared and different strategies to form truck platoons are explained. Subsequently, truck driver-related requirements are summarised based on a literature review and empirical studies conducted in Connecting Austria. Furthermore, user requirements related to other road users are compiled based on related work. In addition to user requirements, road safety requirements are derived and relevant scenarios of the Connecting Austria project are depicted. Finally, technical requirements relevant for C-ITS-based truck platooning are described.