Keywords

1 Introduction

While decreasing transportation costs and reducing greenhouse gas emissions are explicit goals of platooning, many truck platooning initiatives so far have neglected the potential effects on road safety or merely assumed positive effects without providing sound evidence. Therefore, Connecting Austria committed to focusing on potential road safety costs and benefits from different perspectives. Four distinct topics were subject to the analyses, considering legal, statistical, infrastructural and human aspects. (1) The legal situation in Austria regarding automated driving in general and platooning in particular was reviewed, and requirements for testing platooning as a use case are discussed. (2) HGV accident figures of recent years are used to explore the safety potential of platooning: in the period of 2014–2018, inattention/distraction and insufficient safety margins were the leading causes of crashes, comprising two-thirds of accidents involving HGVs on Austrian motorways and expressways. The promise of these figures, indicating great potential to prevent injuries and damages, is tied to the assumption that automated and cooperative platooning systems are widespread and active at all times and failsafe. Furthermore, when accounting for safety gained through ADAS, the benefits of platooning itself are less obvious and harder to quantify. It will become increasingly important to not only document actual crashes but other relevant indicators for safe platooning such as the interaction between human and machine too. (3) Road infrastructure conditions on relevant Austrian motorways were assessed in terms of suitability for platooning by means of adapted Road Safety Inspection (RSI). One part of a traditional RSI is an on-road assessment. To this effect, more than 700 km on motorways, expressways and federal roads were evaluated, with a stretch of 190 km on the motorways A1 and A21, being used as an example for detailed discussion in this chapter. (4) Eventually, an outline of an on-road study with 96 participants is given, aiming at explaining car drivers’ subjective acceptance of gaps when merging between two HGV, which is an important measure for determining the minimum and maximum distance at which trucks should operate cooperatively.

2 Legal Aspects for Platooning in Austria

For the assessment of legal requirements for platooning in Austria, a platoon of two to three HGVs, equipped with advanced driver assistant and control systems as well as car-to-car communication technically allowing automated close following of the second and third vehicle on motorways, is assumed. Furthermore, it is assumed that each of the following vehicles is manned with conductors who supervise the vehicle and traffic and who take over manual driving if needed.

2.1 Acquiring a Test Permission According to the Austrian Regulation on Automated Driving

Testing (partially) automated systems on road is a necessary step towards eventual admission and registration in Austria or may serve mere research purposes. Prior to testing on public roads, virtual or on-road tests on private property roads are required. Testing on public roads can also be staged, for example, with tests under ideal conditions (good weather and road conditions) followed by increasingly adverse conditions.

Legal requirements for automated driving in Austria are regulated in the Automatisiertes Fahren Verordnung—AutomatFahrV [1]. While the AutomatFahrV regulates the requirements for automated systems to be tested on public roads, § 102 KFG (Austrian act on motor vehicles) provides the possibility for absolving the driver for certain responsibilities and transfers them to assistance and automated systems (e.g. keeping at least one hand on the steering wheel) per ordinance, in the first place.

The Austrian testing procedure of (partially or highly) automated vehicles is overseen by the Department for Transport (Federal Ministry “Climate Action, Environment, Energy, Mobility, Innovation and Technology"). A fundamental prerequisite is that the driver remains ready to resume control at all times—in accordance with the Vienna Convention on Road Traffic. Moreover, the automated systems must have the ability to comply with specifications of the StVO [2] (Austrian road traffic act), the EisbKrV [3] (Austrian regulation for level crossings) and the IG-L (Austrian act on air pollution control). Vehicles must be roadworthy and safe to operate and must meet certain other criteria for admission, such as insurance and data recording requirements. The AutomatFahrV contains provisions for (1) driver assistance systems which are already approved and in series production (parking assistant, motorway assistant with automatic lane guidance) and (2) systems which are used for test purposes and which can be assigned to one of three predefined use cases (autonomous minibus, motorway pilot with automatic lane changing, autonomous military vehicle and motorway assistant with automatic lane changing). The Federal Ministry “Climate Action, Environment, Energy, Mobility, Innovation and Technology" is the authority which issues the permission to test on public roads for a limited period of time, given the requirements are met. By the end of the testing period, a full report on the knowledge gained has to be submitted to the ministry and immediate notice has to be given in cases of critical situations or crashes including the underlying cause. Furthermore, the Department for Transport issued a “Code of Practice" [4] which aims at additionally increasing the safety level of testing.

2.2 Does the Current Law Facilitate Testing of Platoons on Austrian Roads?

One of the test use cases according to the AutomatFahrV is “motorway assistant with automatic lane changing", which refers to systems which can guide the longitudinal movements (accelerating, decelerating, complete stop, keeping distance) and lateral movement (lane keeping, lane changing, overtaking) of the vehicle. The respective system can only be tested by vehicle manufacturers, system developers and research institutions on motorways and express roads (once the vehicle has merged into the flow of traffic) in a defined set of vehicle types (M1, M2, M3, N1, N2 and N3 Motor Vehicle Act). Furthermore, the system must have been tested for at least 10,000 km on private property and have proper insurance through a liability insurer. A trained test driver is indispensable and must be able to resume the driving tasks and stop the automated system at all times. In case of an emergency or critical situation, the obligatory emergency mechanism also is activated, and the driver resumes control. They have to resume control well ahead of an exit as well. A black box has to be installed. The obligatory self-commitment to the “Code of Practice" aims at risk mitigation (contingency plan, risk management, etc.). Handling a critical situation must be subject to the training of test drivers, who are obliged to hold a valid driving licence and have several years of experience driving the respective vehicle.

This use case may apply to the system which was subject to the Connecting Austria project (HGV). The specifications above are indicators that the project’s endeavour is potentially in line with the motorway assistant use case. However, the ordinance refers to systems which feature longitudinal and lateral control, while the Connecting Austria project aims at building, maintaining and resolving platoons through intelligent V2V without targeting automated lane change and overtaking manoeuvres. The vehicles are supposed to drive back to back with reduced distance between them. Carefully considering the aim and focus of platooning and the legal texts lead to the conclusion that platooning and the motorway assistant are two different use cases with different aims, especially since (1) platooning involves more than one vehicle, (2) the requirements for road safety and infrastructure are different (short distance between trucks), (3) the platooning system aims at additional tasks (V2V) and (4) the road types for platooning ideally are not limited to motorways, to name but a few.

2.3 Requirements for Platooning Tests in Austria from a Legal Point of View

If a testing scheme does not fit the current regulations, potential test cases can be suggested to the Kontaktstelle Automatisierte Mobilität (contact point for automated mobility). Should the proposal be sufficiently legally and technically sound, the ministry can issue an amendment to the ordinance, accordingly.

However, one major barrier on the path towards testing of truck platooning relates to the StVO (Austrian Road Traffic Act). The AutomatFahrV requires conformity with the StVO which regulates under § 18 Abs 1 StVO a safe distance that allows a following vehicle to stop safely in case of sudden braking of the lead vehicle. Thus, a safe distance is dependent on speed, road and vehicle conditions, driver attention as well as the current distance. Generally, a two-second rule applies: two times the reaction distance, which increases especially for speeds over 100 km/h (three seconds) and hazardous circumstances (three to four seconds time headway) (e.g. [5]). Moreover, vehicles of bigger dimensions—such as trucks—are required to keep a minimum safety gap of 50 m to vehicles of the same kind on rural roads and motorways (§ 18 Abs 4 StVO).

Since platooning per definition is expedient when the distance between the single trucks is reduced, conformity with the StVO cannot be assumed. In order to resolve this discrepancy, an amendment of the StVO (§ 18 Abs 4) towards an exemption for truck platooning would be necessary. Furthermore, from a road safety perspective it remains to be considered if novel traffic signs should be incorporated into the StVO and if vehicles should be prohibited from merging between the vehicles in a platoon.

3 Considerations for the Safety Potential of Platooning

One of the major advantages (or hopes) of driving assistant systems such as electronic distance control is the lack of some of the human drivers’ flaws and weaknesses like error-proneness due to fatigue, sleepiness, distraction, substance impairment, etc. Electronic control will also be much more accurate with much less variation compared to human driving. For the purpose of estimating the crash reduction potential, HGV accidents of the past years (2014–2018) on Austrian motor and expressways will be looked at, considering vehicles \({>}3.5\) tonnes [6].

Usually, the accident type is one of the standard parameters to look at. However, due to the focus on motor and expressways, it is not surprising that the large majority of \(82\%\) of HGV accidents is classified as same direction accidents involving other road users and another \(9\%\) are single vehicle accidents. Looking at the causes of HGV accidents is more revealing (Table 13.1). The top five accident causes are linked to human errors, with inattention and distraction being the lead causes, making up around half of HGV crashes. Ranked number six, technical defects or insufficient cargo security represents only \(4\%\) of the analysed accidents.

Table 13.1 Causes of HGV accidents on Austrian motor and expressways from 2014 to 2018 (top eight = \(96\%\) of accidents)
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Although it should be noted that the classification of the accident cause is based on the law enforcement agent’s assessment and not a thorough accident investigation, the potential of crash reduction when eradicating human errors seems to be vast. In the context of automated and connected driving in general, it will become more and more important to adapt the accident classification scheme accordingly. However, when anticipating a potential admission of platooning, a more detailed reporting of incidents regarding the systems, the driver and the interaction with the environment is desirable. Asare et al. for example proposed in [7] twelve safety performance measures for truck platooning, including not only rates of crashes, near-crashes and safety critical conflicts but also the number and types of system failures, the conditions under which they occur, fails to notify the drivers about loss of control, V2V signal loss, disengagement of the driver, episodes and levels of fatigue, levels of vigilance and distraction of the driver, cut-ins of other vehicles.

Overall, the potentials for road safety due to platooning stand and fall with the reliability of the implemented ADAS and the proper use by operators. Based on these assumptions, platooning could substantially contribute to safer HGV traffic.

3.1 Safety Potential of Platooning Compared to Existing Safety Assistance Systems

Previous observations have clearly shown that there is considerable potential in the use of platooning technology regarding the avoidance and mitigation of traffic accidents. However, the extent of the improvement depends strongly on the reference scenario. To answer the question of a potential safety gain through platooning, the underlying assumptions must be clearly defined. For this discussion, a platoon is assumed consisting of a lead vehicle and two following vehicles, all equipped with the same accident preventing assistance systems as three HGV driving alone. Differences are therefore only taken into account to the extent that they result from the “platooning" function, i.e. the electronic connection and the possibility for the drivers in the following vehicles to divert their attention away from overseeing the traffic environment. When controlling for the effect of ADAS used in platoons, the safety benefits of platooning lie in shared information between the trucks. The following vehicles in the platoon have a head start concerning relevant information: they “know" about dangers at almost the same time as the lead vehicle and therefore react earlier and, if necessary, even use this time advantage flexibly for themselves or other road users following the platoon (V2V given). The reduced collision speeds due to faster reaction in case of rear-end collisions would result in decreased severities of collisions.

4 Assessment of Road Infrastructure with Respect to Safe Platooning

Providing safe road infrastructure is an important goal of public agencies. Road Safety Inspection (RSI) is one of many tools used to identify potential deficiencies and safety risks in the road network and to address them with appropriate countermeasures to prevent accidents or to mitigate accident consequences [8]. In 2011, the EU Directive 2008/96/EC (Infrastructure Directive) was implemented in Austria by amending BStG (Austrian Highway Act), which now details the RSI and requirements for becoming a certified inspector (RVS 02.02.35 Certification of road safety inspectors). The procedure of the RSI is four-part: (1) “preparatory work such as review of the existing documents, collection of accident data, etc.”, (2) “site visit including discussions with people responsible for the road”, (3) “creation of the RSI report” and (4) “implementation of the proposed measures, monitoring” [8, p. 4]. Checklists are available for different road types to support identifying safety-relevant features.

For the purpose of assessing Austrian roads with regard to the suitability for platooning, a team of experts of the Austrian Road Safety Board (KFV) adapted the RSI to the project’s needs. In a first step, the expert team defined a set of criteria which can serve as a basis for future evaluation of road sections and which are required for safe platooning in the experts’ view:

  • Minimum of two lanes (two lanes are considered sufficient if all of the other criteria apply).

  • Shoulder width of \({\ge } 3\) m.

  • Dissolution of platoons 1000 m ahead of tunnels.

  • Dissolution of platoons 1600 m ahead of construction sites.

  • Dissolution of platoons 1000 m ahead of hazard points such as accident black spots.

  • Route is characterised by only few bends (curve radios \({>} 1000\) m).

  • Dissolution of platoons 1000 m ahead of motorway junctions (on-/off-ramps), motorway stations and rest areas (the merging of traffic requires complex orientation tasks and masking information aiming at support of orientation for drivers should certainly be avoided).

  • Sufficient length of acceleration and deceleration lanes.

The following aspects of a classic RSI were assessable within the project: (1) presence and visibility of lane markings and influence of moisture, fog, wind, etc., (2) distance between direction signs and motorway exit (distances potentially have to be increased), (3) distance between motorway junctions, (4) road’s gradient and (5) accident analysis including accident black spots (beforehand assessment).

4.1 Performance of the On-Road Assessment

Subject to the assessment were sections of the Austrian motorways A1, A2, A7, A10, A21 and A25 as well as selected expressways and national roads which represent some of the typical routes of the carrier and project partner Transdanubia. For the analysis in this contribution, the following route is included (one direction only, from East to West): A21 motorway junction Vösendorf till junction Steinhäusl, continuing on A1 till junction Haid.

The respective road network was segmented into meaningful geographic units marked with motorway kilometrage before the on-road assessment started. Both directions were considered and part of the on-road assessment. The evaluation was based on the on-location sighting as well as video recordings and was conducted in December 2018. It is assumed that a potential platoon drives on the rightmost lane. As detailed in the list of criteria, above sections in the proximity to motorway junctions (on-/off-ramps) were excluded from a positive evaluation at the outset.

4.2 Analysis of Road Segments and Considerations for Platooning

A total stretch of 190.54 km was assessed in terms of suitability for platooning, segmented into 68 units. Table 13.2 gives an overview of the main characteristics of the route, for both positively and negatively evaluated route segments. About half of the segments are suitable for platooning; this half accounts for \(43.6\%\) of the route in length. Suitable stretches show a mean of 3.37 km and a median of 2.05, with a range of 0.3–10.2 km. See Fig. 13.1 for the distribution of segment lengths.

Table 13.2 Characteristics of the assessed segmented route on the Austrian motorways A1 and A21
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Fig. 13.1
figure 1

Distribution of segment lengths for positively evaluated route segments on Austrian motorways A1 and A21 (between A21 junction Vösendorf and A1 junction Haid), \(n=68\) motorway segments

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Since the segments were chosen according to motorway junctions as points of reference, there are no segments back to back which are suitable for platooning: each positively evaluated segment is interrupted by either a motorway junction or service stations/rest areas. The longest identified segment suitable for platooning on the reference route therefore is 10.2 km long and is located on the motorway A1 between the service stations St. Pölten and the junction Loosdorf. Not accounted for was the distance needed for building and dissolving a platoon. Dependent on the initial speeds of the HGVs as well as the compression and decompression pace and protocol, the processes combined require distances between 0.8 and 3.5 km (see Tables 11.3 and 11.4). Nine out of 32 route segments are 5 km or longer, and 20 are 3.6 km or shorter. All the route segments which resulted in a negative evaluation are characterised by on-/off-ramps (motorway junction, service station, rest area or a combination of those three). Furthermore, for three of those road segments a spike in truck accidents between 2015 and 2017 was observed (junction St. Pölten, Linz/Ansfelden and Traun/Haid).

5 Gap Acceptance of Car Drivers for Merging Between Trucks

One of the questions within the platooning discourse is the ideal distance between the trucks of a platoon. Alongside economic and environmental considerations, this is also an important road safety question. Not only in terms of potential malfunction of the used technical equipment but also for the perception of other road users. Car drivers for example have to decide at which gap sizes between trucks they would merge onto the rightmost lane for the purpose of exiting the motorway or merge into traffic coming from an on-ramp. While it is argued above that a platoon should dissolve well ahead of a motorway junction, it also is undesirable to have car drivers merge between the trucks and thereby break off the connected platoon. While it is known that some drivers are more and some drivers are less inclined to take risks, the roads must be safe for all drivers. To gain knowledge about the drivers’ decision-making regarding the acceptance of different gap sizes between trucks, an on-road driving study was conducted in summer 2020. However, in this contribution only a basic outline of the study design will be given since the data analyses were still ongoing.

About one hundred participants were recruited to drive an instrumented vehicle on an approximately one-hour route in and around Vienna with stretches characterised by a high share in trucks due to a nearby goods distribution centre. Besides recording a multitude of CAN bus-derived driving parameters such as speed, acceleration and deceleration, the test vehicle was equipped with two roof-mounted lidar sensors for measuring gap sizes between trucks. Before the test drives started, participants were informed of their task during the test drive, which was to assess whether they hypothetically would merge from the second lane between two trucks upon request of the test administrator on the passenger seat (leaving the participants the options of a definitive “yes" or “no" and the third category “in case of need"). The tasks of the test administrator were to give directions to the participants, to identify gaps of interest between trucks on the expressway as well as to record the participants’ answers and the timestamps for their decisions. Data of \(n=96\) participants was successfully collected and is subject to comprehensive analyses, considering a wide range of covariates such as speeds, sociodemographic factors, private car use, risk-taking proneness, comfort while driving, truck types and others.

6 Discussion

The discussed topics in this contribution are indicative of the fact that road safety is a multi-layered concept requiring interdisciplinarity: legal, technical, infrastructural and human aspects were touched upon, which represent only a few factors to be considered for the safe introduction of platooning. With this in mind, this text does not claim to provide an exhaustive overview but rather a discussion of selected road safety topics which were subject to the Connecting Austria project.

On the way to testing platooning in Austria, the required safety margin of at least 50 m between trucks seemingly represents one of the largest obstacles at this point from a legal perspective. This required distance is defined in the StVO (Austrian road traffic act), which cannot easily be circumvented by the Austrian Ordinance on Automated Driving. However, there are promising and realistic approaches to overcoming this obstacle. A more challenging discussion lies ahead concerning a potential market introduction, with potential impact on a variety of federal and EU laws and regulations, such as the KFG (Austrian Act on Motor Vehicles), FSG (Austrian Act on Driver Licensing), the Vienna Convention on Road Signs and Signals, regulations on driving time and resting periods, etc. Defining requirements and behavioural guidelines for drivers as well as parameters for the road infrastructure will be especially interesting. The latter will be crucial not only for road safety but also for the profitability of platooning in Austria, since long road stretches between single motorway junctions are rather rare. Allowing other vehicles to safely enter and exit motor or expressways is certainly a priority. To which extent this can be supported by means of V2V or I2V as a mitigation measure needs to be investigated further.

Although it is fair to say that road safety is not the primary motivation for proponents of platooning, it is worth discussing potential safety benefits. Human errors are without a doubt a leading cause of road accidents, with inattention and distraction alone accounting for \(51\%\) of HGV crashes on Austrian motor and expressways between 2014 and 2018. Thus, it can be assumed that platooning has the potential to prevent accidents. However, one unknown factor in the equation is the reliability of systems that control the connected/automated driving function as well as the assumed penetration rate. Furthermore, the effect most likely would be attributable to ADAS, meaning that single trucks with the same technical equipment would perform just as well. A safety consideration unique to platooning is the shared information within the platoon, which is not dependent on the platoon being connected to outside information systems for a head start concerning safety-relevant information in front of the lead vehicle. Regarding the impact on road accident statistics, it must always be considered that it is impossible to anticipate all potential factors compromising road safety. Especially when introducing new technology, a close observation of a range of parameters is desirable. In the case of platooning, this is not only referring to the automated system but also to the temporarily inactive driver and the interaction with other road users. The impact on driver attention and effects of risk compensation or adverse behavioural changes of other road users in reaction to platoons, etc., cannot be ruled out yet. Either way, systematic collection of a wide range of safety-relevant indicators will be key for platooning and the safety of all road users involved.