Designed to deter: community perceptions of police vehicles, markings and the certainty of apprehension and punishment

Road traffic crashes are a leading cause of death and serious injury worldwide (World Health Organization, 2023), with speeding, impairment and other risky behaviours contributing heavily to the human and economic toll. Governments have responded with enforcement strategies to improve compliance and safety, with road policing central to both detecting and punishing offenders and shaping perceptions of risk. Road policing serves both reactive functions, such as responding to crashes and apprehending offenders, and proactive functions, including high-visibility enforcement operations designed to deter illegal driving behaviour (Hakkert and Gitelman, 2005; Prenzler, 2012). Through these activities, police play a key role in shaping drivers' perceptions of risk and reinforcing road rules across the road network. Within Australia, road policing also represents the most common context in which members of the public interact with police, with Roberts and Indermaur (2009) finding over one-half of police contact was during roadside encounters. This underscores the centrality of traffic-related interactions within policing and highlights the importance of understanding how drivers interpret and respond to police presence on the road.

Road policing is fundamentally grounded in the deterrence theory, which posits that offending declines when individuals perceive that a high likelihood of detection and sanction would result from illegal behaviour (Paternoster, 2019; Raskolnikov, 2020, 2021). Deterrence theory distinguishes three core dimensions: certainty, referring to the perceived likelihood of apprehension; severity, referring to the perceived harshness of the punishment and swiftness, referring to how promptly punishment follows the offence. General deterrence, which aims to shape broader public behaviour through the perceived risk of enforcement rather than solely targeting detected offenders, is the mechanism most directly relevant to road policing (Davey and Freeman, 2011; Nagin, 2013). Of these dimensions, certainty of apprehension has consistently been shown to exert the strongest influence on driver behaviour (Durlauf and Nagin, 2010; Nagin and Pogarsky, 2001). Road policing activities designed in accordance with deterrence theory principles are therefore primarily aimed to increase the perceived likelihood that traffic offending will be detected and sanctioned (Bates et al., 2012).

A critical mechanism through which deterrence operates in road policing is visibility. Visible enforcement increases drivers' awareness of police presence and can serve as a salient reminder of enforcement risk, reinforcing perceptions of certainty and therefore encouraging compliance with road rules. Research has consistently demonstrated that visible enforcement is associated with reductions in speeding and other risky behaviours, even when enforcement encounters are brief (Bates and Anderson, 2019; Freeman et al., 2015; Simpson et al., 2023a). Police vehicles represent the most prominent and frequently encountered form of visible enforcement presence, functioning as mobile symbols of police authority and enforcement capability.

Despite the importance of visibility in deterrence-based policing, limited research has examined how specific features of police vehicles, such as colour, markings, equipment and vehicle type, shape drivers' perceptions of enforcement risk. Existing work has tended to focus on the presence or absence of police, or on enforcement technologies, rather than on how drivers interpret the visual design of enforcement vehicles themselves (e.g. Simpson, 2019; Simpson, 2025). This represents a critical gap. Drivers must first recognise and interpret a police vehicle as an enforcement threat before deterrence mechanisms can operate, and a vehicle perceived as unlikely to enforce traffic laws may fail to generate the behavioural response that visible enforcement is intended to produce. Understanding the relationship between police vehicle design, perceived certainty of intercept and punishment and driver behaviour is therefore relevant for both theory and practice.

The current study addresses this gap by examining how Queensland-licensed drivers perceive different police vehicle designs, particularly in relation to key deterrence concepts (certainty of intercept and punishment) and behavioural responses to seeing police vehicles. Three research questions guided the study:

1. How do drivers perceive different roles or focus of police officers based on the visual characteristics (e.g. colour, markings, equipment, vehicle type) of their police vehicle?

2. How do drivers describe visual elements of police vehicles (e.g. colour, markings, equipment, vehicle type) as it relates to their perceived certainty of apprehension and punishment?

3. How do drivers describe these perceptions in relation to their perceived impact immediate and sustained changes in behaviour (i.e. the halo effect) after encountering police vehicles?

Road policing is a central pillar of road safety strategies, with a primary aim being to reduce road trauma (serious injury and fatal crashes) by deterring illegal driving behaviours (Australian Government, 2021; Bates et al., 2012; Davey and Freeman, 2011). Through both proactive and reactive enforcement activities, road policing serves to reinforce road rules, protect road users and maintain safety on the road network (Hinkle et al., 2020; Nagin, 2013). From a theoretical perspective, these functions align closely with deterrence theory, which posits the fact that individuals are less likely to offend when they perceive a high probability of apprehension and a meaningful punitive consequence (Paternoster, 2019).

Deterrence theory distinguishes three core dimensions that are proposed to reflect perceptions regarding the outcomes of engagement in illegal behaviour, including around the road. This includes dimensions of: certainty, referring to the perceived likelihood of apprehension; severity, referring to the perceived harshness of the punishment and swiftness, referring to how promptly punishment follows the offence (Paternoster, 2019; Raskolnikov, 2020, 2021). The overarching conceptualisation has distinguished concepts of specific and general deterrence. General deterrence aims to reduce offending among the broader population by shaping perceptions of enforcement risk and is most relevant to road policing. Specific deterrence instead targets detected offenders (Davey and Freeman, 2011; Nagin, 2013). Of the three dimensions, certainty of apprehension has been shown to exert the strongest influence on driver behaviour (Durlauf and Nagin, 2010; Nagin and Pogarsky, 2001). Any reduction in the perceived certainty of apprehension may therefore lead drivers to underestimate the likelihood of sanction and diminish compliance with road rules. Road policing activities are accordingly designed to increase the perceived risk of apprehension and sanction for traffic offending (Bates et al., 2012).

This study distinguishes certainty of apprehension into two related constructs: certainty of intercept (the perceived likelihood of being stopped) and certainty of punishment (the likelihood of a sanction following intercept). This distinction acknowledges that a driver may believe they could be stopped by police, or particular police officers, without necessarily expecting to be penalised. Differentiating these concepts allows a more precise examination of how police vehicle design and visibility shape perceptions and behaviour.

Research shows that visible enforcement strengthens deterrence by increasing the perceived certainty, severity and swiftness of sanctions (Bates and Anderson, 2019; Bates et al., 2017; Davey and Freeman, 2011; Freeman et al., 2015; Truelove et al., 2023). A visible police presence is associated with changes in driver behaviour, including reductions in speed (Megat-Johari et al., 2021; Simpson et al., 2023a). As drivers have limited time to detect and interpret enforcement cues, police vehicles serve as the primary means through which enforcement presence is communicated to road users, with rapid identification reinforcing the perception that violations are likely to be detected and sanctioned.

Police vehicles are more than just functional transport; they are symbolic representations of police authority, legitimacy and enforcement intent (Simpson, 2019). Across jurisdictions, police vehicle designs vary substantially in colour schemes, markings and mounted equipment, and these variations provide important context for understanding how police vehicles may be interpreted differently by members of the public.

Empirical research has shown that police vehicle design influences public perceptions of police officers and their intentions. In an experimental study conducted in Canada, Simpson (2019) found officers in marked vehicles were associated with more positive perceptions of legitimacy compared with those in unmarked vehicles, while unmarked vehicles were more frequently associated with aggression and reduced approachability. Specifically, when comparing an unmarked vehicle with marked vehicles, participants rated officers in the unmarked vehicle higher on aggression and significantly lower on approachability, friendliness and accountability. More recent experimental work has also demonstrated that marked vehicles are detected far more frequently than unmarked vehicles, particularly under low-visibility conditions (Simpson, 2025), underscoring the importance of vehicle design in the context of recognition and interpretation.

Simpson (2025) used a visual detection exercise and found that high-contrast liveries provide a recognition advantage when vehicles are partially obstructed or observed at a distance. Qualitative research by Simpson et al. (2023b) highlighted that highly visible and identifiable features, such as bright and reflective colouring, are perceived as important for police vehicle visibility. However, limited research has directly examined how these designs affect drivers' perceptions of enforcement risk, particularly certainty of intercept, certainty of punishment and the duration of deterrence.

Research examining the behavioural effects of overt enforcement presence suggests that visible police activity can produce immediate changes in driver behaviour (Simpson, 2025; Simpson et al., 2023a). Studies have found that drivers reduce speed and increase compliance in the presence of marked police vehicles, with behavioural effects often persisting for only a short duration after the police vehicles is no longer visible (Simpson et al., 2023a). Direct research on the behavioural effects of marked police vehicles specifically remains limited; much of the available evidence draws on studies of overt enforcement operations more broadly, including mobile speed camera deployments. For example, Gouda and El-Basyouny (2017) found that overt mobile speed camera enforcement produces a limited “halo” effect on driver speeds, with factors like frequency and duration of mobile speed camera operations associated with the observed duration of behaviour change. While speed cameras are a distinct enforcement tool from marked police vehicles, both function as overt, visible signals of enforcement presence on the road and are theoretically grounded in the same certainty of apprehension mechanism. The extent to which findings from speed camera research generalise to marked police vehicles remains an open empirical question and one this study seeks to address.

Existing research has examined road policing strategies such as random breath testing (RBT) ^[1], speed enforcement and high-visibility operations, and more recently, how police vehicle design shapes perceptions of police. However, police vehicle markings have traditionally served branding and identification purposes rather than being considered as a mechanism to achieve and sustain deterrence.

The study was undertaken in Queensland, Australia, the third-most populous state (approximately 5.7 million people as of 2025; Australian Bureau of Statistics, 2026), with a densely populated south-east metropolitan corner and large rural, remote and regional areas of lower density. In terms of road safety, Queensland's road fatality rate has consistently been above the national average (Department of Infrastructure, 2026), with more than 300 lives lost on Queensland roads in 2024 and 2025 and fatality rates of around 5.4 deaths per 100,000 persons, reflecting ongoing challenges across the state.

Like other Australian states, Queensland has only one policing agency that looks after all state-based law enforcement. Road Policing is undertaken through both general duties (GD) and specialist traffic enforcement units within the Queensland Police Service (QPS). A range of QPS vehicles were selected for use within this study (see Figure 1) included GD policing vehicles (including one with a transportation pod on the rear), highway patrol (HWP) vehicles (including a marked HWP motorcycle), an unmarked vehicle and “QPS FATAL5” vehicles. GD, commonly referred to as “patrol” in North America’, are frontline police who have a primary role in responding to calls for service from the public. Highway patrol (formally called Road Policing Command [RPC]) are specialist police units that proactively targeted traffic offending. Unmarked vehicles are typically used by detectives. The QPS have “Fatal 5” campaign-liveried police vehicles as a high-visibility road safety initiative intended to capture driver attention, promote safer behaviour and serve as high visibility enforcement driven by HWP officers that target the Fatal Five high-risk behaviours (Queensland Police Service, 2025); speeding, drink and drug driving, distractions, fatigue and seatbelts.

Forty Queensland-licensed drivers aged 18 years and over were purposively recruited to capture variation in age, gender and location (metropolitan, rural, regional areas of Queensland). Participant location was classified using the Accessibility/Remoteness Index of Australia Plus (ARIA+; Australian Bureau of Statistics, 2023) based on residential postcode provided by participants. Expressions of interest (EOIs) were obtained via social media, directing respondents to a Qualtrics survey for eligibility screening and consent form. Participants were selected from those who met eligibility criteria based on age, gender and location to ensure variation across the sample. EOIs matching required eligibility groups were invited for an interview, with 40 included in the final sample. Participants reconfirmed their consent to participate at the beginning of the interview. A $20 e-gift card was offered to participants who completed the interview, as a token of appreciation. This study received approval from the University Human Research Ethics Committee (Approval No. A242134).

After providing consent and contact information, participants were contacted by a research team member to schedule an interview via Microsoft Teams. Interviews lasted 33 min on average (ranging from 18 to 56 min). While reconfirming consent to participate in the interview, consent to record the interview was also obtained. Audio recordings of the interviews were then transcribed verbatim by an external transcription service. Recruitment continued until purposeful recruitment targets and thematic saturation was reached, defined as the point at which no substantively new themes relevant to the research questions were identified in successive interviews.

The semi-structured interviews explored perceptions of police vehicle design and deterrence. Participants first described police vehicles and their visual features (e.g. type, colour, decals, equipment). Participants were then asked about police vehicle designs related to their perceived certainty of intercept and punishment and impact that observing a police vehicle had on their driving behaviour.

In the next section of the interviews, participants were shown photographs of different police vehicles (see Figure 1) and asked to score their certainty of intercept and punishment using a Likert-type scale from 1 (not at all likely) to 10 (highly likely) based on their observations (and experiences if any) of the vehicle in the images. Following the rating, they were asked to describe their reasoning for the rating. Additional questions also probed whether the presence of each vehicle would change their driving behaviour and for how long they believed that observing this vehicle while driving would have an impact on their behaviour.

Transcripts were analysed thematically (Braun and Clarke, 2006) using a largely deductive approach guided by deterrence theory and the research questions. Qualitative data analysis software (Nvivo 20) was used during the coding process. An initial structured coding framework was developed deductively to capture key theoretical constructs relevant to road policing deterrence, including certainty of intercept, certainty of punishment, vehicle visibility, perceived enforcement role, immediate behavioural change and duration of behavioural impact (halo effect). All transcripts were coded using this framework. During coding, sub-themes were identified. An example of the sub-themes within certainty of punishment included perceptions of leniency versus strict enforcement, education-focused versus enforcement roles of police based on their vehicle. Sub-themes were generated through repeated patterns in participant interviews.

Themes were refined collaboratively by the research team and a subject-matter expert who did not conduct the interviews to ensure objectivity. Interpretations were compared through analytic discussion, with disagreements resolved iteratively until sub-themes were cohered and distinct. Illustrative quotes are provided to demonstrate the grounding of themes in participant responses.

Along with the participant characteristic information, two interview questions were quantitative in nature, with certainty of intercept and certainty of punishment being measured on a 10-point Likert-type scale. Mean scores for each scale were calculated for descriptive comparison across the eight vehicle images presented to participants. These descriptive statistics were computed manually. No inferential statistical analysis was conducted, consistent with the exploratory nature of the study.

Forty Queensland-licensed drivers participated in the study, distributed across age groups (18–24, 25–49, 50+; see Table 1) and locations (62.5% metropolitan, 37.5% regional). Most were male (62.5%). Just over half (52.5%) had received an infringement in the past five years, with more detected by cameras (57%) than police (43%). Police intercepts (excluding for the sole purpose of RBT ) were reported by 28% in the past year and 40% in the past five years; 38% had not been stopped in over five years, and 23% had never been stopped. Nearly half (45%) had been stopped for RBT in the past year.

Visual identification of police vehicles was the first topic covered during the interview. Without visual stimulus, participants consistently described relying on visual cues to identify police vehicles while driving. Markings, lighting and visible equipment were commonly cited as the primary features that enabled drivers to recognise a vehicle as belonging to police and to distinguish between different types of police vehicles.

Participants described police vehicle markings as central to identification with high-visibility markings such as blue and white checkers combined with bright contrasting striping in yellow, orange, red or blue were repeatedly referenced as the primary cue signalling that a vehicle was police. Prominent liveries, reflective or “iridescent” striping, and large, legible text such as “POLICE,” “Highway Patrol,” or “Road Policing Command” were also described as increasing both recognisability and perceived enforcement certainty. Several participants also suggested that bold decals or explicit messaging (e.g. camera warnings or road safety slogans) would further enhance salience and perceived enforcement presence.

Collectively, the findings indicate that conspicuous, high-contrast markings function as a key visual heuristic through which drivers identify police vehicles. This interpretation aligns with prior experimental research demonstrating that marked vehicles are more readily detected and recognised than unmarked designs, particularly under low-visibility conditions (Simpson, 2019, 2025), and with work highlighting the importance of distinctive visual components such as contrasting colour schemes and reflective elements in facilitating rapid categorisation (Thomas and Williams, 2012).

Participants discussed a range of lighting and enforcement hardware they have observed attached to police vehicles. Emergency lights, particularly red and blue roof-mounted lightbars, were seen as key features drivers use to identify police vehicles. Some participants noted that these lightbars were highly recognisable from a distance and they described immediate behavioural changes, including one participant who stated:

In addition to lighting, participants were asked if there was any equipment on the police vehicles that, if present, would increase their perceived certainty of intercept or punishment. A number of participants highlighted the importance of speed detection devices and cameras, with some specifically mentioning the visibility of automatic numberplate recognition (ANPR) cameras, radars or antennas as contributing to perceptions of traffic enforcement capability of police vehicles.

These responses suggest that both emergency lighting systems and the presence of specialised devices that assist the police in the detection of traffic offences can reinforce the visibility and perceived capability of police vehicles to enforce the road rules, potentially enhancing their deterrent impact. This finding is supported by previous research that identified lightbars as key identifiable features of a police vehicle (Thomas and Williams, 2012). However, the current study extends beyond emergency lighting equipment to the recognition of specific enforcement equipment, such as speed detection devices and onboard cameras (such as ANPR), which for some drivers elevates the perceived traffic enforcement capability of that police vehicles.

Beyond recognising police vehicles visually, participants made inferences on the operational role and enforcement focus of police vehicles based on their appearance.

When it comes to the colour of the police vehicle, the base colour was often discussed as a way that participants identify the role of the police within the vehicle. White police vehicles were consistently associated with GD policing and often perceived as less likely to enforce the road rules, with participants distinguishing these from more vibrantly coloured or purposefully marked HWP vehicles. Contrasting and high-visibility police markings (particularly the checkered pattern) were frequently discussed as key identifying features of police vehicles. One participant stated:

These results suggest that participants perceive police vehicle colour and markings as strong indicators or visual cues of the role of a police vehicle. White cars were commonly seen as GD vehicles, while brightly coloured or distinctively marked vehicles were viewed as traffic enforcement-focused. Such findings are supported by previous work on police vehicle design which has demonstrated that variations in colour and marking are associated with perceptual differences by members of the public (Simpson et al., 2023b; Thomas and Williams, 2012).

Many participants associated specific vehicle types (shape or make/model, including unmarked or less conventional vehicles such as those with a transportation pod) with particular policing functions, often describing them in terms of their overall build, style and perceived function. Sedans and marked sports utility vehicles (SUVs) were commonly recognised as GD vehicles, while sports cars (such as the Kia Stinger) and police motorcycles were recognised as having a traffic enforcement focus. Participants discussed how they perceived high-visibility vehicles as more authoritative and, therefore more effective in influencing their behaviour.

One of the most consistent perceptions related to vehicle type held by participants, was that police officers on motorcycles were overwhelmingly associated with having a road policing focus and only in rare cases would do any other policing duties. Participant descriptions of police motorcycles indicated that due to their agility, manoeuvrability and interception capabilities, they associated them with dedicated traffic enforcement roles:

Unmarked or less conventional vehicles (e.g. utility vehicles) were often seen as harder to identify compared with other police vehicles and often associated with duties other than traffic enforcement. However, there were two overall considerations with regard to unmarked vehicles. The first and most common theme was that they believed the unmarked vehicles were used by detectives, who are typically responsible for investigating more serious crimes, who would have little to no interest or time to conduct GD policing or detect and punish traffic offending.

However, other participants discussed unmarked police vehicles that are operated by the HWP and in that case, they perceive the focus of those unmarked vehicles as having a dedicated traffic enforcement role where they can covertly detect and punishing traffic offending.

A number of participant quotes highlighted this dichotomy of views between the use of unmarked cars by detective or GD officers and the HWP or traffic focused officers stating:

The perception of operational role attribution was particularly evident in participant discussions of police vehicles designed for the transport of persons in custody. A majority of the participants discussed the role of the paddy wagon (a term used to describe police vehicles with purpose built modules for the transport of a person in police custody) as a transport vehicle, and indicated that transport was its primary role and would be almost exclusively for that task.

These findings indicate that participants describe a form of visual profiling that occurs on the road while driving, categorising police vehicles based on observable characteristics (such as their size and perceived speed) to assess their likely role and the probability that they will enforce traffic laws. In a road policing context, these perceptions around police vehicles can serve as a visual clue to the enforcement focus and capability of police (such as specific HWP vehicles) which, based on the literature, may influence the certainty of punishment perceived by drivers and thus the deterrent effects (Truelove et al., 2017), with motorcycles functioning as a symbol of highly capable and dedicated traffic enforcement vehicles. The current study extends Simpson (2019) and Thomas and Williams (2012) by demonstrating that vehicle type, make and model recognition are linked not only to the perceptions of police occupying those vehicles, but also the perceived enforcement capabilities.

A unique design of some Queensland Police vehicles, FATAL5 vehicles, elicited mixed responses from participants, with some drivers perceiving them as highly recognisable and strict on the enforcement of the road rules (much like HWP cars), other participants perceived that their main purpose may be more educational or focused on communicating road safety messages and therefore more likely to give warning for traffic offences. Participants who believed the FATAL5 police vehicles were likely to be strict and there was very little chance of avoiding punishment for traffic offending include:

Whereas example quotes from participants who believed that the police vehicles with the FATAL5 design were education-focused or more likely to give out warnings stated:

While the intent behind the FATAL5 vehicle design may be to communicate a clear road safety message, the divergent interpretations among participants suggest that these designs have the potential for conflicting effects on perceived certainty of punishment. For some drivers, the prominent messaging about high-risk behaviours reinforced the impression that these vehicles were actively targeting traffic offences, thereby heightening the perceived likelihood of apprehension and punishment. For others, however, the same messaging appeared to soften the perceived punishment role, instead aligning it more with education, community engagement or public awareness campaigns. As such, policing organisations need to be cognisant of the visual design of police vehicles, especially when incorporating additional messaging, as it may inadvertently dilute the clarity of punishment purpose behind the vehicle.

Participants' interpretations of police vehicle roles were closely linked to their perceived certainty of being intercepted and punished for traffic offending. Ratings of CoI and CoP (see Figure 2) consistently associated the highest perceived deterrence with specialist enforcement vehicles (HWP Stinger, HWP Motorcycle), with the HWP motorcycle rated highest and described as highly agile, fast and traffic enforcement-focused:

Participants had mixed perceptions about GD police vehicles, with the GD Camry scoring higher for CoI compared to CoP. This relates back to the perceptions held around the operational role of the vehicle, that is, a GD vehicle may intercept you for a traffic offence, but it is less likely to issue an infringement during that traffic stop with participants stating:

Inversely, participants suggested the GD Paddy Wagon and the Unmarked Camry are unlikely to intercept, however, an offence serious enough to trigger one would likely to result in a punishment.

When it came to the use of police motorcycles, there was a consistent view that these vehicles were only for traffic enforcement and had no other operational policing role which means that their sole purpose is to intercept and punish offenders. This perceived focus was somewhat shared with the HWP Stinger and the RPC Levorg which also score highly for certainty of intercept and punishment, however possibly due to the agility and manoeuvrability of the motorcycle, scored slightly higher compared to the vehicles. Some of the quote discussing the certainty around motorcycles, HWP Stinger and the RPC Levorg include:

By consistently associating the visibility of HWP vehicles and the agility of motorcycles with heightened levels of certainty regarding interception and punishment, these findings suggest that the design and function of police vehicles can alter driver perceptions and their behaviour. However, when it came to the FATAL5 vehicles, as discussed above, there was some varied perceptions around their operational role and whether their purpose was as an enforcement or an educational vehicle.

These insights suggest that drivers form some assumptions about the likelihood of being intercepted or punished by police for traffic offences, based on the design and markings on the police vehicle the observe. However, road safety campaign markings (FATAL5) on enforcement vehicles are interpreted differently by drivers, and when these markings shift the perceived operational role of the police vehicle to educational rather than enforcement-focused, it may reduce the vehicle's deterrent effect, with potential unintended consequences for deterring traffic offending. Consistent with the general deterrence theory (Nagin and Pogarsky, 2001), and with prior work demonstrating that visible and clearly identifiable enforcement enhances perceived risk (Simpson, 2019; Simpson et al., 2023a), these findings suggest that ambiguity in operational messaging may attenuate the perceived certainty of sanction.

There was a consistent theme reported by a majority of the participants that seeing a police vehicle triggered an immediate change in their driving behaviour. This response was particularly evident when encountering highly visible or traffic enforcement focused vehicles, such as HWP cars and motorcycles. Commonly reported behavioural changes included reducing speed, checking mirrors, increasing following distance and generally driving more cautiously.

These findings align with deterrence theory, which posits that increased certainty of apprehension, that would result from the presence of police vehicles, serves as a mechanism that deters drivers from committing traffic offences, increasing compliance with the road rules (Nagin and Pogarsky, 2001; Truelove et al., 2021). Police vehicles such as motorcycles and HWP vehicles were described as eliciting stronger behavioural shifts due to their perceived agility and their operational focus on traffic enforcement. Participants stated:

These findings underscore the importance of highly visible police vehicle designs and distinct traffic-enforcement focused markings and vehicles, such as HWP cars and motorcycles, in shaping driver behaviour. Many participants reported that vehicles clearly associated with traffic enforcement elicited more immediate and pronounced behavioural adjustments, particularly reductions in speed, cessation of any other offending (mobile phone use) and increased vigilance. These findings are consistent with core principles of deterrence theory, which includes the perception or threat of punishment reduces the likelihood of individuals engaging in undesirable behaviour (Gibbs, 1968; Paternoster, 2019).

Of interest, not all police vehicles are perceived equally on the road with regard to the enforcement risk they pose; rather, it is the salience of enforcement-specific visual cues that amplifies the perceived certainty of apprehension. These results also align with traditional enforcement strategies and road safety countermeasures that are grounded in deterrence theory, particularly the notion that perceived certainty of being apprehended and punished by police may be a key factor of driver compliance with the road rules (Nagin and Pogarsky, 2001; Nagin et al., 2015; Truelove et al., 2021). The results also align with broader policing research suggesting that enforcement is most effective when it is seen as problem-oriented, targeted, and specific (Hakkert and Gitelman, 2005; Hinkle et al., 2020; Reisig, 2010). These findings have practical implications for police vehicle design and deployment strategy, highlighting that enhancing the visibility and recognition of police vehicles, especially those associated with traffic enforcement, can play a critical role in promoting safer driving behaviours through situational and vicarious deterrence.

While participants described an immediate behavioural change in the presence of a police vehicle, they also commonly reported that these behavioural adjustments were temporary, and in most cases, lasting only as long as the vehicle remained visible. Once the police vehicle was passed or out of sight most participants acknowledged that their driving returned to their previous behaviour within a short time frame.

In contrast, highly visible traffic enforcement-focused vehicles, particularly HWP cars and police motorcycles, were discussed as influential. Participants frequently noted that the behavioural changes initiated upon seeing these vehicles often persisted well beyond the initial encounter, for a longer duration compared with GD police vehicles and with some of the participants reporting that the effect persisted for the remainder of their journey that day.

The change in behaviour (primarily less speeding) that was described when participants viewed images of HWP vehicles and motorcycles can be understood as a stronger and more sustained halo effect. Gouda and El-Basyouny (2017) found that repeated exposure to overt enforcement operations can prolong the deterrent effects. In the current study, the interpretation of the vehicle, based on the visual assessment of the vehicle and its markings, as having a traffic enforcement role was associated with descriptions of longer deterrence. HWP cars and motorcycles were described as having “no leniency” and that “their main job, it's to enforce traffic”. These findings appeared to reinforce participants' higher certainty of apprehension and, thus, potentially reducing the likelihood of drivers resuming their traffic offences (a greater halo effect).

The findings of this study suggest that traffic enforcement specific police vehicle types, with a higher certainty of apprehension and punishment, not only produce stronger immediate behavioural changes but also extend the duration of compliance, consistent with deterrence theory (Freeman et al., 2015; Nagin and Pogarsky, 2001; Piquero and Pogarsky, 2002). From an operational perspective, this highlights the importance of visible, recognisable traffic enforcement police vehicles for sustaining safer driving behaviours beyond the moment of direct observation by a driver.

This study offers novel insights into how drivers describe police vehicle design and its relationship with perceptions of enforcement capability, certainty of apprehension and punishment. Several limitations should be noted. First, the study used a mostly qualitative design with 40 purposively sampled Queensland-licensed drivers where we cannot determine response rates (given social media recruitment). Although diversity across age, gender and location was sought, the small, non-random sample limits generalisability. Second, limitations arise from the vehicle types shown to participants and their familiarity with them. A range of QPS vehicles was included (e.g. GD, HWP cars and motorcycles, unmarked and FATAL5 designs), but prior knowledge or experiences likely shaped perceptions. As Simpson et al. (2023b) suggest, unfamiliar or ambiguous designs may weaken deterrence. Finally, the study relied on self-reported perceptions and behavioural intentions from semi-structured interviews. These methods may be affected by recall bias or social desirability, with some participants potentially overstating compliance or the deterrent influence of police vehicles despite confidentiality assurances.

Future research should employ larger, more representative samples, potentially incorporating stratified sampling to capture variation across demographic groups, driving experience and prior contact with police. To address concerns regarding the familiarity of participants with the police vehicles displayed, future research could explore these dynamics further by systematically comparing perceptions of known versus unfamiliar police vehicle designs, including cross-jurisdictional studies where police fleets and markings differ. Furthermore, an experimental trial of the impact of various police vehicle designs could be conducted (using a similar methodology to Simpson et al. (2023a)) to determine the impact of various police vehicles on driver behaviour, including different driver behaviours.

This novel study found that police vehicle designs are described by road users as having an impact on their certainty of intercept and punishment, and importantly, their behaviour as a driver. The results explore how drivers identify and differentiate between police vehicles based on visual cues (colours, markings, equipment and vehicle type), assigning specific roles and enforcement capabilities that directly impact their perceived certainty of apprehension and punishment. In doing so, the study extends deterrence theory by highlighting that certainty is not derived solely from police presence, but from how enforcement capability is perceived by road users. Critically, specialist or traffic enforcement-focused vehicles, in this case, motorcycles and HWP cars, particularly as bright and visible vehicles were rated and described as having substantially higher deterrent effects and extended behavioural compliance compared to general policing vehicles. The findings refine the deterrence theory by showing that targeted, recognisable traffic enforcement amplifies both immediate and lasting deterrent effects, highlighting the importance of enforcement salience and perceived certainty beyond what a generalised police presence achieves.

For policing organisations, these findings suggest that vehicle selection and design decisions can serve as force multipliers, maximising the deterrent impact of a limited police resource. This study also highlights the potential consequences of certain design choices, such as educational messaging that may inadvertently signal leniency or a diminished enforcement focus, possibly undermining the deterrent effect achieved regardless of the role of the vehicle in enforcement activities.

Importantly, this does not mean such a duality in designs are ineffective. Rather, from a deterrence perspective, the findings suggest the need for clear and consistent public messaging. HWP officers can and do play dual roles within the road safety space, enforcing road laws while also communicating and educating the public on vital safety messages their enforcement interaction and other community-policing activities (Anderson et al., 2020). To address this, policing organisations opting for vehicle designs with additional messaging should accompany these vehicles with broader media engagement strategies that clarify the purpose of the messaging, preserving the educative value of these designs while ensuring their enforcement capabilities remain prominent in the minds of drivers.

As police agencies face increasing pressure to demonstrate efficient resource allocation and measurable crime prevention outcomes, this research offers evidence to support policy that optimises police vehicle fleets. Aligning police vehicles and their livery designs with clear enforcement objectives, supported by communication strategies that reinforce their role on the road, may enhance both public safety and organisational effectiveness through the application of the deterrence theory and problem-oriented policing principles.

The Motor Accident Insurance Commission provided funding to the University of the Sunshine Coast to support the MAIC/UniSC Road Safety Research Collaboration to conduct research activities that aim to reduce the incidence of motor vehicle crashes.The authors would like to acknowledge Mr Peter Flanders for his operational expertise and valuable assistance with the data analysis for this study.