Attention deficit hyperactivity disorder (ADHD) is typified by excessive levels of inattention, impulsivity, and hyperactivity, three characteristics collectively constituting the core symptoms of the disorder (American Psychiatric Association, 2013; Barkley et al., 2010). These traits extend into the domain of driving, elevating the risk of those with ADHD being involved in car crashes (Chang et al., 2017; Curry et al., 2017; Jerome et al., 2006; Vaa, 2014). In response to these observations, the Netherlands mandates individuals with ADHD to undergo a psychiatric evaluation before obtaining their driving licence, which is optionally supplemented with a driving test (CBR, 2024). This procedure concerns approximately 3.6% of the population (Have et al., 2023), corresponding to about 10,000 people annually (Gezondheidsraad, 2021).

Data from 2017, a period in which the driving test was also obligatory for all individuals with ADHD seeking to acquire their licence, suggest that 96% (1256/1307) of individuals receive an assessment which allows them to drive unrestrictedly (Piersma et al., 2019), raising questions about the effectiveness of the current approach. Consequently, this paper reviews three potential alternative regulation policies tailored specifically for ADHD drivers: mandatory behavioural training programmes, the compulsory usage of driver monitoring systems, and temporary driving restrictions. On the basis of information available, these measures are assessed for their potential impact on road safety and inclusiveness, recognising the need to carefully balance improvements in driving safety with their limitations on mobility and the risk of stigmatisation.

This paper presents the first analyses of the mandatory utilisation of in-car technology and mandatory driving restrictions as potential interventions for ADHD drivers. Overall, by utilising the Netherlands as a case study, the paper aims to provide insights into alternative potential driving regulation policies for individuals with ADHD, findings which may not only be applicable to the Dutch context but are also relevant for other countries grappling with similar challenges surrounding ADHD and driving.

A narrative literature review was conducted to investigate potential ADHD-specific driving interventions. Relevant scientific studies were identified from the PubMed and Google Scholar databases, while articles and reports from government agencies and associated research organisations were extracted from Google. Search strategies encompassed a diverse set of keywords and phrases, including variations and derivatives, to capture various aspects of ADHD and driving. These terms included: ADHD (and related terms, e.g., attention-deficit hyperactivity disorder); driving (risk, performance); crashes (motor vehicle crashes); restrictions (driving, night-time, passenger, alcohol); (behavioural) training; in-car technology (driver monitoring systems); graduated driver licensing (GDL); medication; age; compliance. Studies were considered for inclusion if they discussed ADHD-associated driving risks, explored relevant between- and within-individual factors impacting these risks, presented data relevant to potential driving interventions, or were otherwise deemed appropriately relevant to the discussion. Additional articles were identified through the reference lists of these initial studies. The available literature was analysed up until May 2024.

Numerous research methods have been applied to investigate the potential relationship between ADHD and an elevated risk of adverse driving outcomes. Reviews of self- and parent-report studies, including works by (Barkley & Cox, 2007), (Cox et al., 2011) and (Fuermaier et al., 2015) collectively suggest that adolescent and adult drivers with ADHD tend to report a higher frequency of collisions, traffic citations, and traffic violations. Expanding on this, a 2006 meta-analysis based on self-report studies indicated that young adults with ADHD faced an 88% higher risk of being involved in a motor vehicle crash (Relative Risk [RR], 95% CI [1.42–2.50]) and a 35% increased risk of receiving a citation [RR], 95% CI [1.20–1.50]) (Jerome et al., 2006), although the authors acknowledged methodological shortcomings in the selected studies, such as poor follow-up, the selection of clinical samples which do not reflect the general ADHD population, and the lack of control for both co-morbidities and driving experience. A more recent meta-analysis reaffirmed the heightened crash rates among ADHD drivers (RR, 1.36; 95% CI [1.18–1.57]); corrections for publication bias (RR, 1.29; 95% CI [1.12–1.49]) and driving exposure (RR, 1.23; 95% CI [1.04–1.46]) yielded slightly lower figures (Vaa, 2014). Notably, the reliability of self-report studies is constrained by the fact that both adolescents and adults with ADHD often underestimate their ADHD-related impairments and overestimate their competence (Manor et al., 2012; Owens et al., 2007). This tendency extends to driving-related settings (Fabiano et al., 2015; Hoza et al., 2013; Knouse et al., 2005; Weafer et al., 2008), potentially leading to conservative estimates of ADHD-related driving risks.

Studies based on official driving records circumvent these concerns by linking accident data with population-based health records. Employing this methodology, (Chang et al., 2014; Chang et al., 2017) conducted studies based on data from Sweden (2014) and the US (2017), with both studies estimating that ADHD drivers (diagnosed at a minimum age of 13; see Persisters and Desisters) had an approximately 47% higher risk of being involved in a traffic accident leading to an emergency room visit compared to a non-ADHD cohort (adjusted Hazard Ratio [HR], Sweden: 95% CI [1.32–1.63]; Odds Ratio (OR) (author calculated: average male/female), US: 95% CI [1.44–1.51]). Similarly,Curry et al. (2017) examined ten years of data from new licensees in New Jersey, finding that ADHD drivers, defined as individuals who received their diagnosis at ≥ 12 years of age, had a 36% higher first crash risk compared to non-ADHD drivers (adjusted HR, 95% CI [1.25–1.48]). While these studies provide consistent evidence of an increased crash risk among individuals with ADHD, research which makes use of official police and hospital records is dependent upon the reporting of the crash and the filing of the police report, and is thus inherently limited to severe crashes.

Driving simulators, on the other hand, allow for an analysis of vehicle control throughout an entire drive. Furthermore, they provide a controlled environment to assess car handling skills in risky driving situations. Simulator studies support earlier findings by identifying a deteriorated driving performance among individuals with ADHD, marked by higher frequencies of collisions, speeding, and driving errors, as well as increased steering variability and lane swerving (Fuermaier et al., 2015). However, concerns about the ecological validity of driving simulators exist (Fuermaier et al., 2015; Jerome et al., 2006; Vaa, 2014), with observed driving errors potentially linked to stress or unfamiliarity with the simulator setup (Jerome et al., 2006). Similar concerns apply to on-road driving studies, which also find substandard driving performances in individuals with ADHD (Fuermaier et al., 2015), where the presence of an evaluator in the car can be a stress- and motivation-inducing factor.

Finally, naturalistic driving studies offer insights into naturally occurring dangerous driving situations by installing video cameras in participants' cars for extended periods of time. In such a setup, whenever the in-car technology detects a significant change in g-force—indicative of a crash, strong swerving, or sudden acceleration or deceleration—a short video just before and after the event is saved, which can be analysed later. Klauer et al. (2017) illustrated this approach in a pilot study which followed 16-year-old drivers with ADHD (N = 10) for 15 to 24 months, finding an almost double crash/near-crash rate per 1 000 hours travelled compared to a control group free of ADHD symptoms (N = 45) (ADHD: 22.59, Control: 11.53; p = .039). Similarly, Aduen et al. (2018) reported a 46% (Incident Rate Ratio [IRR], 95% CI [1.17–1.83]) and 28% (IRR, 95% CI [1.04–1.58]) increased crash and near-crash risk, respectively, among drivers with ADHD who were studied for 1–2 years. In a third study, drivers with ADHD had significantly more collisions and produced approximately 2.5 times (Control: 649; ADHD: 1,590) the number of g-force events within a three-month period compared to controls (Merkel et al., 2013). However, this study did not control for driving activity and only included ADHD drivers who reported at least one citation or collision in the past two years, an inclusion criterion not enforced in the control group, making the comparison of driving risks between ADHD and non-ADHD drivers in this study improper. Overall, naturalistic driving studies consistently indicate that ADHD drivers are more frequently involved in (near-) crashes.

In summary, a wide array of research methods has explored the relationship between ADHD and driving risks, each offering unique benefits and limitations. Considering the findings collectively, it is evident that individuals with ADHD on average exhibit a substandard driving performance compared to their non-ADHD counterparts.

Having established a subpar driving performance in those diagnosed with ADHD, insight into the specific challenges faced by ADHD drivers is crucial for the development of effective interventions.

ADHD has been speculated to arise primarily from impairments in executive functions (Brown, 2009; Willcutt et al., 2005), which encompasses abilities such as working memory, impulse control and cognitive flexibility. These functions are essential for maintaining attention, problem-solving, planning and self-control - and ultimately pivotal for completing set tasks (Baggetta & Alexander, 2016). In the context of driving, they enable individuals to maintain attention, plan and execute actions, control impulses and constantly adapt their behaviour to changing road conditions, and are thus crucial to safe driving. A study by Barkley et al. (2002) highlighted the correlation between deficits in working memory, inhibition, and selective attention among individuals with ADHD and self-reported involvement in motor vehicle crashes and risky driving. Executive dysfunction, and its closely related three core symptoms of ADHD—inattention, impulsivity, and hyperactivity—have therefore been suggested to underlie the observed difficulties of ADHD drivers. Indeed,Aduen et al. (2018) identified a significant relationship between the severity of ADHD symptoms, determined via the Barkley Adult ADHD Quick Screen (BAQS) (Barkley et al., 2010), and the frequency of crashes and near-crashes. For each increase in symptom severity score, ADHD drivers had a 5% higher crash risk (IRR, 95% CI [1.02–1.09]) and a 6% higher near-crash risk (IRR, 95% CI [1.03–1.09]) (Aduen et al., 2018).

Numerous studies have focused specifically on these core ADHD symptoms and compared how ADHD and non-ADHD drivers exhibit behaviour which is closely related to these symptoms, both in the context of a crash and normal driving. In a study based on official driving records, Curry et al. (2022) found that ADHD drivers, defined as individuals who received their diagnosis at ≥ 12 years of age, were 15% more likely to be inattentive when involved in an accident compared to controls (adjusted Prevalence Ratio, 95% CI [1.07–1.23]), a perception reinforced by (Kingery et al., 2014), who observed more visual glances away from the road and a significantly higher percentage of time with the eyes diverted from the roadway in a driving simulator task. Fischer et al. (2007), on the other hand, found that young adults who had been diagnosed with ADHD between the ages of 4 and 12 made significantly more impulsive errors in an on-road drive and generated a higher frequency of impulsive- and inattention-related errors in driving simulator tests compared to controls. Two other studies, based on self-reports, have focused on how these ADHD symptoms function as crash-causing factors specifically in the ADHD group itself, providing opposing answers. Thompson et al. (2007) conclude that hyperactivity and impulsivity play a primary role in predicting diminished driving outcomes whereas Garner et al. (2012) suggest a stronger role of inattention. In conclusion, individuals with ADHD demonstrate a higher occurrence of behaviours related to the core ADHD symptoms during driving, yet the precise contribution of each symptom to crash risk remains uncertain.

Beyond examining how the underlying symptoms of ADHD function as crash-contributing factors, research has unveiled various problematic driving behaviours among ADHD drivers. On average, individuals with ADHD exhibit higher frequencies of driving anger, risky driving, driving without a licence, and speed violations (Barkley & Cox, 2007; Curry et al., 2019; Fuermaier et al., 2015; Jerome et al., 2006; Nada-Raja et al., 1997; Oliver et al., 2011; Richards et al., 2006; Vaa, 2014), show more sleepiness at the wheel (Philip et al., 2015), have a higher social media use while driving (Curry et al., 2019; Turel & Bechara, 2016), are less likely to wear a seatbelt (Curry et al., 2019; Nada-Raja et al., 1997), and are more often exposed to, or show a greater vulnerability towards, distracting factors like carrying passengers (Curry et al., 2019). Importantly, driving knowledge does not seem to be a significant factor underlying the substandard driving performance among ADHD drivers. BothAduen et al. (2018) and Barkley et al. (1996) found no differences in driving knowledge between ADHD and non-ADHD groups, with the former study notably not providing related data nor disclosure on the chosen questionnaire. In a second study by Barkley and colleagues, utilising the same questionnaire as in the 1996 paper, the authors did find a worse knowledge score in ADHD drivers, but it remained unclear whether this was a result of actually worse knowledge or the rapid application of this knowledge (Barkley et al., 2002).

In exploring the multifaceted challenges of ADHD drivers on the road, an aspect warranting deeper investigation is their communicative abilities behind the wheel (see also: (Bishop et al., 2018)). Driving involves constant social interactions with other road users, necessitating swift behavioural adjustments (Wilde, 1976). Actions like turn signalling, braking, horn usage, and mirror checks can all strategically be used to position oneself in a safe driving situation and effective communication therefore makes a key aspect of driving performance. Given that ADHD commonly co-occurs with language and communication problems (Green et al., 2013; Hawkins et al., 2016), individuals with ADHD may exhibit atypical communicative styles during driving, potentially compromising safety. Their typical inattentiveness may lead to missed signals from other drivers or lapses in signalling themselves, while their struggles with impulse control may lead to more frustration with other drivers and/or increase the frequency of risky driving manoeuvres. Groom et al. (2015) analysed several of these aspects in a driving simulator test and found that drivers with ADHD displayed significantly more impatience behind slow traffic and verbally expressed more frustration and anger towards other road users (see also: (Richards et al., 2006)). In addition, they exhibited trends of less safe driving during overtaking or lane changes, regularly neglecting to signal or check mirrors (Groom et al., 2015). These dynamics remain unexplored in a real-world driving context, underscoring the need for further investigation.

In summary, the substandard driving performance of individuals with ADHD stems from a multifaceted interplay of factors. The key symptoms of the disorder—inattention, hyperactivity, impulsivity—may each exert influence through their direct ties to behavioural tendencies related to unsafe driving. For example, the inattentive nature of an individual with ADHD may be directly linked to a higher frequency of looking away from the road, a higher phone usage, lower seat belt usage and more passenger interactions, while impulsivity may manifest as impatience in traffic, leading to behaviours such as speeding, tailgating, elevated horn usage and a higher frequency of risky overtaking manoeuvres. It should be emphasised that while these tendencies may be more frequently found in ADHD drivers on average, they are unlikely to be expressed in all individuals to the same degree. Moreover, even within individuals, driving performance fluctuates, based on factors such as fatigue (Sagaspe et al., 2008; Ting et al., 2008) and stress (Cunningham & Regan, 2016; Rowden et al., 2011). This inter- and intra-individual variability complicates the identification of a single trait as a robust predictor of the observed substandard driving statistics. Overall, tailored interventions for ADHD drivers should prioritise strategies which enhance attentional focus, mitigate impulsivity and manage hyperactivity. Before discussing such potential measures, however, between- and within-subject factors affecting ADHD driving performance are reviewed, further illuminating the intricate relationship between ADHD and driving.

With the recognition that the period shortly post-licensure presents an opportune time to address the subpar driving performance among individuals with ADHD with driving interventions, the discussion now shifts to explore these potential measures. However, before delving into these interventions, it is imperative to the discussion to evaluate current regulatory approaches in the Netherlands. Presently, individuals with ADHD are mandated to undergo a 15 to 30-minute interview conducted by an independent psychiatrist. This interview assesses factors such as medication usage, alcohol and drug intake, and the presence of other clinically diagnosed diseases and/or disorders. Based on the psychiatric evaluation, individuals may be required to undergo an additional driving test (CBR, 2024). However, the specific criteria which are used to assess an individual's driving ability remain unclear, as the evaluation forms for the psychiatric interview and driving test are not publicly available. A study conducted by (Piersma et al., 2019) does provide insight into this regulatory process by analysing data from 2017, a year in which both the psychiatric interview and the driving test were mandatory. The study examined 28 (partial) psychiatric reports of individuals who were either rejected or mandated to undergo a periodic re-evaluation. Reasons for exclusion included comorbidity, the severity of ADHD symptoms, immaturity, drug usage, limited medication adherence, the nature of the medication usage, recent diagnosis or establishment of comorbidity, and a recent diagnosis of ADHD. The effectiveness of this approach remains unclear as no (publicly available) studies have shed light on ADHD driving statistics in the Netherlands specifically. Nevertheless, an important observation is that in 2017, 96% (1256/1307) of individuals received an assessment which allowed them to drive unrestrictedly (Piersma et al., 2019), suggesting that current regulatory approaches may have limited impact. Consequently, given the reported challenges faced by ADHD drivers, alternative approaches warrant consideration. The current paper explores three such alternatives: behavioural training, the mandatory usage of driver monitoring systems, and temporary driving restrictions. Unlike current regulations, mandatory behavioural training and the mandatory usage of driver monitoring systems offer the advantage of training or assisting individuals in their driving behaviour, rather than focusing solely on exclusion. Additionally, temporary driving restrictions for ADHD drivers warrant consideration because their effectiveness has been demonstrated for general cohorts of novice drivers. These three alternative regulatory approaches are first considered for their potential impacts on driving safety.

The current regulatory approaches in the Netherlands aimed at addressing the substandard average driving performance of individuals with ADHD consist of a psychiatric interview and optional driving test, but are likely to have a limited impact on driving safety considering that a significant majority of individuals receive an assessment which allows them to drive unrestrictedly (96% (1256/1307)) (Piersma et al., 2019). By utilising the Netherlands as a case study, the current paper aimed to provide insights into alternative regulatory approaches for ADHD drivers. Three such measures were explored: a mandatory behavioural training programme, temporary driving restrictions and the mandatory installation of driver monitoring systems. To our knowledge, no country has yet implemented any of these considered approaches specifically for ADHD drivers, choosing instead, like current practices in the Netherlands, to rely on driving tests and assessments conducted by healthcare professionals (e.g. (Austroads & National Transport Commission, 2022; RoadSafetyBC, 2024)). All three interventions do show promising hints towards their potential impacts on driving safety, but studies specifically examining individuals with ADHD and long-term effects are scarce. These interventions hold the strongest promise in producing beneficial effects on driving safety when targeted at novice ADHD drivers, given that the period shortly post-licensure, characterised as the highest-risk driving period in non-ADHD cohorts, produces even higher crash rates among ADHD drivers (Curry et al., 2019) .

Before discussing the potential driving interventions, an overview was made of the literature pointing towards a substandard driving performance of ADHD drivers, along with an analysis of the mechanisms underlying these findings, and between- and within-individual factors affecting ADHD driving performance. This examination revealed a consistent pattern of substandard driving performance in those with ADHD, most likely a result of behavioural tendencies which are closely related to the core symptoms of the disorder and can be considered unsafe in the context of driving. Within this framework, two studies byCurry et al. (2017); Curry et al. (2019) suggested that, unlike in non-ADHD cohorts (Chapman et al., 2014; McCartt et al., 2009; Vlakveld, 2004), crash risks shortly after licensure are not diminished in individuals who obtain their licence at a later age, implying that there is no basis to exclude these individuals if driving interventions are implemented for novice ADHD drivers. Additionally, further research on the crash-risk differences between persisters and desisters is encouraged, considering how this impacts the size of the targeted population of potential driving interventions.

The topic of medication in this context is complex. While stimulant medication strongly reduces, though not nullifies, the elevated crash risks associated with ADHD (Chang et al., 2017; Fuermaier et al., 2015), the ADHD population is characterised by low medication usage rates. In the context of driving, (novel) strategies to improve ADHD medication adherence are therefore encouraged. It should, however, be stressed that the current paper focuses on only a single behavioural outcome (i.e. driving performance), whereas the consideration of taking medication is always based on a myriad of factors, among which there may be multiple valid reasons as to why not to take medication.

Behavioural training programmes have been investigated in two different formats: computer-based programmes and large in-person educational seminars. Various forms of the former format have been shown to improve driving behaviour in both driving simulators and on-the-road tests, whereby the study by (Epstein et al., 2022) stands out in particular, demonstrating that trained individuals were able to carry over trained skills long-term to real-life driving. The latter option, concerning in-person (single or multi-day) educational programmes, has also shown its potential in reducing crash risk, but has not yet been assessed in ADHD drivers. Overall, given the potential already shown, further studies assessing the long-term effects of behavioural training programmes are greatly encouraged.

The implementation of ADHD-specific driving restrictions makes up the second considered alternative regulatory approach. Temporary night-time and/or passenger restrictions aimed at all novice drivers are considered a success but seem to be especially impactful for individuals with ADHD, as they are more often involved in a crash late at night (Curry et al., 2019) and are more often engaging with, or in the presence of, passengers before a significant driving event (Klauer et al., 2017). Although these indications are promising, the low sample size (ADHD: N = 10) in the pilot study by (Klauer et al., 2017) highlights the importance of follow-up studies investigating the effectiveness of driving restrictions in ADHD drivers. Concerning the aspect of potential alcohol restrictions, although there is no scientific consensus on whether ADHD drivers are more often involved in an alcohol-related crash, this aspect would be indirectly combated by night-time and/or passenger restrictions (Fell et al., 2011; Foss et al., 2001; Williams et al., 2012). An alcohol interlock offers an effectively proven, more invasive alternative.

A concerning aspect regarding driving restrictions is non-compliance. While general cohorts of drivers follow passenger and night-time restrictions in > 90% of drives (Curry et al., 2017; Foss & Goodwin, 2014; Klauer et al., 2011; Williams, 2017), two studies indicate lower compliance rates in those with ADHD. Specifically, (Nada-Raja et al., 1997), found that male, but not female, ADHD drivers self-reported significantly more violations of GDL rules compared to controls (15% vs 1%, p < .001), while (Curry et al., 2019) observed that 4.4% of ADHD drivers violated GDL restrictions in the first 12 months post-licensure as opposed to 2.9% of non-ADHD drivers (p = .001). A significantly greater non-compliance with night-time and/or passenger restrictions in ADHD drivers is especially problematic, as enforcing these rules is challenging. Police officers often face difficulties in identifying individuals subject to these laws on the road. Although licence plate identifiers or ‘decals’ could assist in enforcement, they are both controversial and unpopular (Williams, 2017), and a non-viable measure for the ADHD driver group for reasons of privacy, discrimination and stigma. Further studies on ADHD compliance rates, including those which make use of techniques other than self-reports, are necessary to confirm the findings from (Nada-Raja et al., 1997) and (Curry et al., 2019).

The earlier discussed study by (Curry et al., 2019) shows that even when a range of measures are implemented in the first year post-licensure, including a zero-tolerance alcohol policy and passenger- and night-time restrictions, ADHD drivers still showed a significantly higher crash (1.27; 95% CI [1.12–1.43]) and traffic violation rate (1.36; 95% CI [1.23–1.50] compared to controls. While the nature of the study design unfortunately does not allow a perspective on the degree to which these implementations were successful both in the ADHD and non-ADHD cohort, the results do at the very least indicate that these restrictions did not equalise the driving risks of individuals with and without ADHD. In turn, additional or alternative interventions could complement the earlier discussed driving restrictions. First is the mandatory usage of a car with a manual transmission, with the idea of improving driver attention levels (Cox et al., 2006; Randell et al., 2016), although the usage of a manual clutch may only be beneficial in circumstances where frequent gear-shifting is required (Aduen et al., 2019). A second option is a temporary ban on highway driving, which is already active for novice drivers in Ontario, Canada (MTO, 2022). ADHD drivers exhibit a lower driving performance on highways (Biederman et al., 2007; Fried et al., 2006; Randell et al., 2016; Reimer et al., 2010), possibly because the lack of stimuli ignites impulsive- and inattention-related behaviours. No studies have yet proven the effectiveness of this intervention, but a highway ban is likely to lead to a shift toward the lower road network, a network which is considered less safe as crashes are more frequent and severe (Elvik, 2010; SWOV, 2024).

Importantly, it should be emphasised that the current analysis on temporary driving restrictions is limited by the fact that many of the cited studies examined 16- and 17-year-old drivers. Temporary night-time and/or passenger restrictions are only likely to produce beneficial effects in the Netherlands for individuals above the age of 18, since 16- and 17-year-old drivers are only allowed to drive while supervised (Netherlands Enterprise Agency, 2024), which is a period characterised by low driving activity (Chapman et al., 2014) and thus limitedly affected by potential restrictions. This discrepancy is important, because these effects on driving safety may not be as strong in older drivers, as enforcement of these restrictions is majorly influenced by parents (Curry et al., 2017; Williams, 2017), who may have weaker effects on older individuals as these are for example less often residing in their parental home. Contradicting this notion, 18- to 21-year-old drivers do not seem to show lower compliance rates (Curry et al., 2017).

The third considered driving intervention for individuals with ADHD concerns the mandatory usage of driver monitoring systems. Two different measures, a PAYD system and ISA, have both been demonstrated to improve overall driving behaviour, but are yet untested in ADHD drivers. Naturally, mandating the usage of driver monitoring systems raises cost concerns, as most advanced systems are typically only available in new, expensive cars. However, rapid developments in smartphone applications could circumvent these issues (Botzer et al., 2017; Peer et al., 2020). Of note, if such driver monitoring systems were to be made obligatory for individuals with ADHD, ideally this would be of a temporary nature, such that individuals who make use of such a system may show long-term improvements in driving behaviour when this enforcement would be removed. However, individuals who make use of ISA seem to return to their old behaviour once systems are turned off (Doecke et al., 2021; Pas et al., 2014; Stephan et al., 2014), a finding which has been repeated for another driver monitoring system (Toledo & Lotan, 2006).

Importantly, even though these driving interventions may show promising potential in improving road safety, these measures also need to be considered for their potential costs, as any measure which specifically excludes the partial freedom of an entire group of individuals (i.e. ADHD drivers) bears costs in terms of potential stigma and hindrance in societal integration, participation, and acceptance. Among the three evaluated driving interventions, driving restrictions may in particular impose significant burdens by limiting an individual's ability to drive with passengers or during certain hours, affecting societal participation and potentially increasing stigma. Behavioural training programmes, on the other hand, would not restrict mobility but require (multi-)day participation. Computer-based programmes offer advantages in terms of accessibility, while large-scale, in-person educational programmes might encourage participation, but require significant collaboration and expenses (Bruce et al., 2014). In this context, the mandatory usage of driver monitoring systems does seem to be the most user-friendly option. These systems do not restrict mobility but rather assist or enforce adherence to traffic rules. Estimating the potential costs in terms of these approaches is difficult before their implementation, but is evidently affected by the strictness of the intervention. Both for a mandatory behavioural training programme and temporary driving restrictions, careful consideration must therefore be made of the length of these interventions. Moreover, if such interventions are implemented, their associated benefits and costs must be carefully tracked and monitored.

In summary, mandatory behavioural training, the obligatory usage of driver monitoring systems and temporary driving restrictions all show promising hints as potential regulatory measures for ADHD drivers, although ADHD-specific research is needed to further establish their potential. In particular, there is a need for research which examines the effectiveness of driving restrictions and driver monitoring systems in individuals with ADHD, as well as more studies assessing the long-term, within-individual effects of behavioural training on driving performance. Lastly, on grounds of inclusion and discrimination, a valid argument could be made that implementing driving interventions for all individuals with ADHD is unfair. Even though the percentage of individuals involved in multiple crashes is greater in ADHD than in non-ADHD drivers (see Proportions), there is large inter-individual variability in driving risks and the elevated crash risks observed are a result of only a subgroup of drivers. The development of a time-efficient screening method appears to be a valuable and economic alternative approach, which identifies those individuals with ADHD who are at risk for unsafe driving (with high sensitivity on the cost of specificity), on which more elaborate assessments can be performed. A study which identifies ADHD drivers who have recently been involved in multiple car crashes and retrospectively seeks risk factors which could have predicted these substandard driving outcomes constitutes a valuable first step in this direction.

The authors acknowledge that no external funding or financial support was received for the conduct of this study and the preparation of this manuscript.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.