2.3 Other Enforcement Methods

Overall Effectiveness Concerns: In general, these technological measures have not been adequately studied to reliably determine their effectiveness.

Many traffic enforcement operations help to deter speeding and aggressive driving as well as other traffic offenses. In addition to HVE campaigns (the Speeding and Speed Management chapter, Section 2.2) and automated enforcement (Section 2.1), new technologies have been recommended to address speeding and aggressive driving (NHTSA, 2001a). LEAs around the country have also conducted innovative and effective aggressive driving enforcement programs (NHTSA, 2000).

Technology: Both external and in-vehicle technologies may help in several ways.

• In-car video equipment in patrol cars allows law enforcement to record aggressive driving actions and can enhance the ability to prosecute and convict offenders (NHTSA, 2001a).
• Laser speed measuring equipment can provide more accurate and reliable evidence of speeding (NHTSA, 2001a).
• Unstaffed speed display devices, also known as speed trailers, can show drivers that they are speeding and may encourage some drivers to slow down, but effects may last only as long as the devices are in place (Donnell & Cruzado, 2008). They may also suggest to drivers that speeds are being monitored or enforcement is nearby. Signs that provided either an implication that speeds were being monitored or a social norms message (average speed at the site; your speed) were effective at reducing speeds in a 50 km/h zone although not as much as in earlier studies (Wrapson et al., 2006). Other studies have shown that speed trailers or portable changeable message signs, which may include speed feedback plus other messages such as “Slow Down Now” can be effective in reducing speeds in work zones (Brewer et al., 2006; Mattox et al., 2007) and school zones (Lee et al., 2006). Automated speed display monitors also provide a method to collect location-specific travel speed data. Speed feedback devices are likely to be more effective on two-lane highways than multi-lane ones. In addition, they may not provide accurate speed indications if traffic volumes are too high (Ullman et al., 2013). Speeds seem to rebound quickly downstream and as soon as the devices are removed (Walter & Broughton, 2011; Hajbabaie et al., 2011).
• In work zones, a combination of a parked police vehicle and speed feedback trailer reduced average and 85th percentile traffic stream speeds and free flow speeds to a similar degree as automated camera enforcement, whereas the effect of speed trailers alone was the same as no treatment. Parked police alone was also effective, but to a lesser extent than the combination of police + trailer or the camera system. The number of speeders above 10 mph over the limit was essentially reduced to zero by both the automated enforcement and police + trailer combination. However, the treatment effects on speeds in work zones disappeared in 40 – 50 minutes of removal (Hajbabaie et al., 2011). See the Ullman et al. (2013) Report 746 for in-depth discussion of advantages, disadvantages and deployment considerations for  methods of traffic enforcement in work zones. According to this report, which provides state of the knowledge for work zone enforcement, there have been insufficient controlled trials to identify the optimal mix of enforcement types and other treatments for different highway types, geometries, and work zone situations. The report reiterates the importance of work zone speed limits that reflect the situation, including the presence of workers or alignment changes.
• Drone radar – A study of the use of this technology in work zones suggests that it may be effective at reducing overall speed of the traffic stream, with particularly large speed reductions among vehicles equipped with radar detectors (Eckenrode et al., 2007). Both in-vehicle driver warning systems, as well as traditional cruise control, are widely available technologies that may be well-accepted by drivers to help govern their own speeds (Sivak et al., 2007; Young & Regan, 2007).
• Intelligent speed adaptation (ISA) involves in-vehicle devices that “know” the speed limit through accurate digital maps of speed limits and GPS data of the vehicle location. ISA systems can either warn when the speed limit is being exceeded (i.e., open ISA) or apply active controls to slow the vehicle (i.e., closed ISA) (more details about levels of ISA can be found from European Commission, 2015). A pilot study was conducted in the United States among a group of repeat violators. (See section 3.1 for information about this study.) The devices have been widely studied in European countries for acceptability and effects on driver behavior with more widespread on-road trials currently underway. (See www.ec.europa.eu/transport/road_safety/specialist/knowledge/speed/new_technologies_new_opportunities/intelligent_speed_adaptation_isa_en for more information.) In Europe, the effects on speeding have been fairly dramatic for both warning and control type ISA systems, decreasing the amount of speeding and narrowing the speed distributions (Carsten, 2012; Lai & Carsten, 2012; van der Pas et al., 2014). These are very promising results for potential crash and injury reductions. However, a widespread implementation and trial have yet to be documented. While there remain issues to be resolved, including the extent to which behaviors in international trials are generalizable to the United States, the main roadblock to implementation may be political (Carsten, 2012) rather than safety or technological reasons. Some issues uncovered in trials include that serious offenders were more likely to disable or over-ride the devices than other drivers (van der Pas et al., 2014), and may be less likely to adopt ISA use, even with incentives (Chorlton et al., 2012; De Leonardis et al., 2014). It is not clear if drivers’ behavior may change after the devices are inactivated, or when they are disabled. Drivers’ intentions to speed and actual behaviors were assessed following driving with an Intelligent Speed Adaptation in-vehicle system that provided direct resistance to speeding (Chorlton & Connor, 2012). While measured intentions to speed and impressions of time-savings that could be gained by speeding were decreased among the participants, actual speeding behavior after the system was inactivated returned to pre-exposure levels within 4 weeks.
• According to researchers from the United Kingdom, the devices may potentially be over-ridden where they may be most needed (Lai & Carsten, 2012). Other uncertainties also still exist about driver behaviors or adaptations, and even external forces that may potentially affect the costs and benefits of ISA (van der Pas et al., 2012). Finally, there is a need to provide current and accurate maps of speed limits (Carsten, 2012).
• A study of the effects of in-vehicle warning and monitoring systems was disappointing with respect to speed control by young teens (Farmer et al., 2010). Even with parental notification (immediate or delayed) and with or without in-vehicle alerts, there was either no reduction in instances of teens exceeding the limit by more than 10 mph or initial declining trends reversed after a few weeks.
• Alerts or speed monitoring combined with rewards may work better than alerts and monitoring alone. Several field tests from Europe have found that drivers exceeded limits less when offered economic incentives such as reduced insurance premiums or discounts (for lease vehicles). Results were positive for lease car drivers in the Netherlands (Mazureck & van Hattem, 2006), young drivers in the Netherlands (Bolderdijk et al., 2011), and members of a large motor club in Sweden (Stigson et al., 2014).
• In the United States, several vehicles with intelligent speed adapation (ISA) capabilities (open ISA level) are currently available (see NTSB, 2017). A study (Blomberg et al., 2015) tested a half-open ISA system with young drivers (18-24 years old, N = 44) to examine its effectiveness in speed reduction. The results showed that the ISA significantly reduced the incidence of speeding episodes that exceed 5+ mph over the posted speed limit.

Many jurisdictions use some of the above technologies. Each has costs for new equipment, maintenance, and training, and perhaps other costs. In the case of ISA, accurate digital maps of speed limits are needed.

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