1. Introduction
It is estimated that 10–15% of all crashes and 30% of all fatal accidents are a direct result of speeding or inappropriate speed [
1]. Increased speed increases not only the chance of an accident but also the severity of the crash. Because of trucks’ large size and heavy weight, this is especially true for them. Therefore, when searching for effective ways to improve traffic safety, trucks are a good choice to focus on. In general, trucks annually travel a greater distance than any other type of road vehicle. This assumption is backed by traffic safety numbers. Records from 2015 show that trucks were responsible for 8.3% of the distance traveled by vehicles registered in Belgium, while only 2% of the total number of registered vehicles were trucks [
2]. This suggests that with the same resources (i.e., number of target vehicles), a greater impact can be achieved by focusing on trucks. Traffic accident numbers for 2019 also show that a truck was involved in 5.2% of injury accidents, while only 1.9% of all registered vehicles were trucks [
3]. Accidents involving trucks are were also deadlier: a truck was involved in 17% of all traffic fatalities in Belgium during 2019, and in most cases (15.3% of fatalities), as the opposing vehicle [
4,
5]. Similar numbers have been reported by the European Union (EU), where in 2018, 14.5% of all fatalities resulted from accidents involving heavy transport vehicles [
6].
1.1. Intelligent Speed Assistance (ISA)
Intelligent speed assistance (ISA) is a type of advanced driver assistance system (ADAS) that aims to reduce speeding behavior by providing drivers with feedback about the enforced speed limit. Additionally, some ISA systems also can intervene by cutting engine power or by providing real-time feedback in the form of real-time interventions. From 2022 onward, the European Commission had mandated ISA for all new vehicles (including trucks) [
7]. Different technologies are used to determine speed limits within ISA systems [
8]. Camera-based technology can be used to recognize traffic signs, or speed maps can be used in combination with geolocation to determine speed limits. Some systems also use data-fusion techniques to use a combination of camera-based recognition and speed maps, such as to override speed map data in the case of roadworks [
9]. The European legislation also states that the correct speed limit must be determined with 90% accuracy, although special conditions that extend beyond knowing the country of operation and current road type are exempt from this rule [
10]. Apart from ISA systems installed by the original equipment manufacturer, aftermarket ISA solutions exist as dedicated units that can be installed in older vehicles.
1.2. Real-Time Interventions
Real-time interventions are part of an ADAS system and warn the driver on the threat of a specific event by using visual, auditory, and/or haptic feedback. Alternatively, the intervention system can also be used to inform the driver of the current driving parameters and persuade and nudge them toward safer driving [
11,
12]. To guarantee the optimal acceptance and effectiveness of the system, interventions should be designed with great care. A poorly designed intervention system might yield the opposite result of what it intends to achieve by annoying, confusing, and/or distracting the driver with the intervention itself [
13,
14].
Various studies and guidelines have suggested that a carefully designed multimodal, multistage warning system provides good results. Nonintrusive visual warnings can be used during a low-risk stage to nudge, persuade, or inform the driver, while more-urgent warnings should be multimodal and more intrusive [
15,
16,
17,
18]. The semantics of the warning message should also be easy to understand and preferably also trigger the desired reaction from the driver as a reflex (i.e., displaying a stop sign when necessary to stop); this is especially true for warnings that have higher urgency [
19,
20].
1.3. i-DREAMS Technology
A Horizon 2020 project, i-DREAMS is funded by the European Union. The project aims to set up a platform that provides interventions and automated coaching to keep the driver within boundaries of safe operation, conceptualized by the project as the safe tolerance zone (STZ). These interventions are provided to the driver both post-trip and in real time. The post-trip interventions aim to motivate sustained behavioral change in the long term, while real-time interventions have the purpose of nudging a driver toward safer decision-making or demand immediate action from the driver when the STZ is being exceeded and thus dangerous driving or an avoidable accident is detected. The i-DREAMS real-time intervention technology includes an ISA system that provides drivers with real-time information about speed limits but also provides warnings when exceeding speed limits. To determine the thresholds, several modifying conditions are considered, including distraction, sleepiness, weather, and time of day. The i-DREAMS technology was developed for different vehicle types (car, truck, bus, tram, train) and will be deployed and validated in multiple European countries (Belgium, Germany, Greece, Portugal, the United Kingdom)
Driving simulators are commonly used in the automotive industry to develop human–machine interfaces (HMIs) [
21]. They provide a risk-free environment in which driver behavior can be monitored under highly relevant, controlled, and repeatable conditions. To validate the i-DREAMS technology before usage during field trials, simulator experiments are performed to validate the technology. This paper describes an i-DREAMS simulator experiment in Belgium and aims to assess the effectiveness of the ISA system, for different road types on speeding behavior for professional truck drivers. To the best of our knowledge, the effectiveness of an ISA system for trucks as the one studied here, while accounting for differences in road type, has not yet been done before.
4. Discussion
The purpose of this experiment was to analyze the effect of an ISA system on speeding behavior for different road types. A significant reduction was found for almost all relevant driving parameters between a drive without ISA or speeding interventions and between a drive with ISA and speeding interventions, but only for road sections with a speed limit of 60 km/h and not on road sections with a speed limit of 90 km/h. Before any conclusions on this effect can be drawn, it is useful to consider common reasons for speeding. Previous research has indicated that drivers might engage in a riskier driving style when they are stressed [
30], which is often caused by organizational factors such as just-in-time delivery and long working hours [
31]. During the experiment, no initiatives to create time pressure for the drivers were created; instead drivers were asked to drive as they would normally drive. Therefore, it seems unlikely that drivers were exceeding the speed limit because of time pressure during the experiment, so on the basis of the current experiment, no conclusions can be drawn on the effectiveness of the ISA system to reduce speeding caused by time pressure.
Sleep quality and sleep deprivation may also be related to the speeding behavior of truck drivers [
32]. This behavior might be attributed to drivers’ becoming more impatient or being less aware of the surrounding environment. To cope with the additional risks caused by sleepiness, the ISA system was made “smart” in way that thresholds are modified when sleepiness is detected among drivers. To validate the acceptance of these stricter thresholds, a third drive was included to simulate the condition (in terms of thresholds only) where drivers were sleepy. Because of ethical and practical limitations during this pilot test of the presented ISA system, actual sleepiness could not be induced among drivers. Instead, drivers were asked to self-report sleepiness during each drive. The levels of sleepiness that were monitored were very low for almost all drivers. Therefore, according to the collected results, it is not possible to draw conclusions on how the presented ISA system, with modified thresholds for sleepiness, influences speeding behavior among sleepy drivers. The results do, however, indicate that acceptance of the presented ISA system was still high, even with the stricter thresholds that were set during the third drive.
Speeding might also occur because drivers are unaware either of their current speed or of the current speed limit. This type of speeding is mostly unintentional and limited in terms of speed limit exceedance [
33]. Additionally, speeding might be normative, where it is the norm among drivers, influenced by peers or surrounding traffic to drive above the speed limit [
34].
Given the abovementioned reasons for speeding, this study tried to explain the speeding behavior and effect of the ISA system that was monitored during the experiment. First, an ISA system may be most effective in situations where the driver is unaware of the speed limit because the speed limit signs contradict the enforced speed limit. On the road sections with a speed limit of 60 km/h, traffic signs with a speed limit of 70 km/h were placed along the road. For road sections with a speed limit of 90 km/h, there were no contradicting traffic signs. This is a realistic situation for trucks in Belgium on these types of roads. The ISA system used and displayed the enforced speed limits; for instance, the ISA system enforced the speed limit of 60 km/h for trucks where a speed sign of 70 km/h was shown. It is possible that participants were not aware of the enforced speed limit of 60 km/h without ISA. This is relevant as many truck drivers are operating in international transport and might not be fully aware of the many rules for enforced speed limits for trucks in Europe. Therefore, these results may suggest that ISA can be a useful tool for truck drivers, by apprising them of local speed limits. Of course, this is under the condition that the used ISA system has the capabilities of displaying speed limits for trucks, which requires at least some sort of speed mapping because it cannot be performed by camera-based traffic sign recognition alone. This raises the question of what the effect would be of an ISA system that does not display the correct speed limits for trucks, as it could increase driving speeds. More research is needed to investigate the effect of inaccurate ISA systems on speeding behavior.
The mean values for maximum and average speeds suggest that most participants were aware of the 60 km/h speed limit given that they mainly stayed below 70 km/h during the baseline drive for road sections with a speed limit of 60 km/h. Additionally, driving parameters for road sections with a speed limit of 90 km/h indicate that even during the baseline drive, participants were above the speed limit only for a limited percentage of distance, and in general, speeds were already below the speed limit, leaving very little room for improvement when using an ISA system. This leads to another possible explanation: truck drivers might be more inclined to speed on road sections with lower speed limits because it is the norm among drivers. An ISA system is an effective way of reducing speed on these road sections. This also makes sense given that trucks rarely exceed 90 km/h as they are normally equipped with a speed limiter that limits engine power when speed exceeds 80 km/h or 90 km/h (depending on the country: 90 km/h in Belgium), although no speed limiter was active during this simulation experiment.
The results also suggest that the modification of thresholds for speed warnings that were used in this experiment has very little effect on speeding behavior. A statistical analysis found no relevant significant effects on driving parameters between drive 2 (less strict threshold setting) and drive 3 (stricter threshold setting). Within i-DREAMS, the threshold modification that was used for this experiment would be aimed at drivers with high levels of sleepiness. However, participants were asked to self-report their level of sleepiness during the experiment, and none of the participants reported any score high enough to trigger the modification of thresholds, meaning that according to the collected dataset, it is impossible to draw conclusions on the effectiveness of modifying thresholds for sleepy drivers. Trends in driving parameter means seem to indicate increased speed for drive 3, where thresholds were stricter. This might be explained by the fact that drive 3 was always performed as the final drive, so participants could have been more confident in the driving simulator environment or might have been less motivated to showcase “good” driving behavior after several sessions.
Limitations and Future Work
This experiment was certainly subject to limitations. First, drivers were not actually in a sleepy condition when testing the thresholds for sleepiness during the third drive. Additionally, 15 min drives without time pressure might not be representative of the actual driving conditions experienced by truck drivers. Notwithstanding, as a pilot test for the presented ISA system, this experiment proved it could help to reduce speeding in certain conditions. Future work should focus on exposing truck drivers to more-challenging conditions, including induced sleepiness, adverse weather, longer trip durations, and increased time pressure. Additionally, future work could focus on determining whether the differences in speeding behavior between road types with a speed limit of 60 km/h and road types with a speed limit of 90 km/h can be attributed to the road type itself or to the fact that for trucks the actual speed limit is different from that posted on the speed signs on the road. As a next step, it would also be useful to examine how drivers interact with the ISA system and how the ISA system might influence speeding in a more naturalistic driving environment over longer time periods. This would reduce the possibility that drivers change their driving behavior because they are exposed to an unfamiliar environment (driving simulator) and know they are being monitored. Moreover, it would help to provide insight into how the ISA system influences speeding behavior in the long term.
5. Conclusions
Speeding is one of the leading causes of traffic accidents. ISA systems are designed to reduce speeding by providing drivers with warnings and feedback. From 2022 onward, these systems will become mandatory for new vehicles in the European Union. As part of the i-DREAMS project, this study aimed to investigate the effectiveness of an ISA system, specifically for trucks. A simulator experiment was held with 34 professional truck drivers in Belgium, where speeding behavior during a drive without ISA was compared with drives where ISA was enabled for different road types. The ISA system provided warnings when speeding was detected, and two sets of thresholds were tested. Each drive consisted of four road sections: two rural sections where the enforced speed limit for trucks (60 km/h) was different from the speed limit displayed on traffic signs (70 km/h), one rural section with a speed limit of 90 km/h, which was also indicated by speed limit signs; and one motorway section where the speed limit was 90 km/h for trucks. The driving parameters were collected from the driving simulator, and a statistical analysis was performed by using a repeated-measures analysis of variance. The results indicated that the ISA system that is part of the i-DREAMS set of technologies significantly reduced the average speed, maximum speed, minimum speed, and percentage of distance above the speed limit for both rural road sections with a speed limit of 60 km/h, suggesting that the ISA system is an effective method of reducing speeding behavior for this specific type of road. However, no significant effects were found for the road sections where the speed limit was 90 km/h. Using stricter thresholds also did not cause any significant effects. Although this study has some limitations, mostly in terms of the driving conditions and challenges commonly faced by truck drivers, it was still useful as a pilot test of the i-DREAMS ISA system for truck drivers.
It can be concluded that the tested ISA system, tailored for trucks, was effective on rural roads with a speed limit of 60 km/h where the speed limit is inferred from context rather than speed signs. To confirm these findings and to further assess the effectiveness of ISA systems for trucks, more research is needed to compare road types, with lower speed limits, that were not considered in this experiment. Additionally, more research is also required to validate the effectiveness of the ISA system under more-realistic and more-challenging driving conditions.