Koorey (2007) asserts “…passing opportunities generate economic benefits by reducing travel times, as they release impeded vehicles from platoons. …When drivers cannot overtake slower vehicles owing to a lack of passing opportunities, they are likely to become frustrated. This can lead to an increase in unsafe passing manoeuvres, which in turn can lead to crashes”. This quote not only summarises the engineer’s viewpoint but that of many others, professional and public. Even a brief search of the internet reveals that driver frustration is a deep-seated issue. However, despite, or possibly because of, the widely held belief that frustration can lead to dangerous overtaking, the empirical evidence for this is sparse. Furthermore, the antecedents of driver frustration itself are not understood. In 2012, Transport Scotland commissioned a review of the international literature on frustration and overtaking. This review (Grayson, Kinnear & Helman, In press) concluded that the concept of frustration appears in historic traffic modelling work that attempts to quantify drivers’ perceptions of service quality. However, it tends to have been inferred from traffic variables rather than being measured directly. Two exceptions to this are the work of Gunatillake, Carnew and Akçelic (2000), and Koorey, Farrelly, Mitchell and Nicholson (1999), although these are in contexts not necessarily applicable to the A9. Gunatillake et al. (2000) measured self-rated levels of frustration in response to a variety of urban video-filmed traffic situations in Australia. They found that frustration did vary with driving situations (‘slow travel’, such as congestion, being the main situation that led to a marked increase in frustration) but that there was little increase in frustration over time. Frustration ratings for the various driving situations were incorporated into a model (the Traffic Frustration Index or TFI) which was then validated on a variety of additional routes and times of day. Gunatillake et al. concluded that the TFI did a reasonable job of modelling driver frustration, but that it did not add much (if anything) beyond what could be achieved simply by measuring travel speed. Koorey et al. (1999) used willingness to pay techniques to calculate an economic value for reduced frustration accruing from the provision of passing places on roads in New Zealand. They concluded that a value of NZ$0.035 (per vehicle per kilometre of passing opportunity) was robust and could be included in models along with the values for safety and journey time. Both of these studies (albeit in different driving contexts to the A9) show that it is possible to measure frustration directly (in these cases using self-report survey techniques) and to consider it in road design and traffic modelling. Grayson et al. nevertheless concluded that evidence focusing on frustration and overtaking behaviour directly is sparse. Only one study was found that directly addressed the issue. Kaub (1990) examined the effect of traffic flow on overtaking behaviour on a road in the United States, and found that as traffic flow went up, drivers were prepared to accept more risk in terms of the overtaking manoeuvres they attempted. This study demonstrates the potential for overtaking propensity to vary with traffic conditions believed to impact on frustration. Other studies using simulation (e.g. Pollatschek & Polus, 2005) have supported the general assertion that delays can lead to an increase the level of risk that at least some drivers are willing to accept in their overtaking decisionsKoorey (2007) asserts “…passing opportunities generate economic benefits by reducing travel times, as they release impeded vehicles from platoons. …When drivers cannot overtake slower vehicles owing to a lack of passing opportunities, they are likely to become frustrated. This can lead to an increase in unsafe passing manoeuvres, which in turn can lead to crashes”. This quote not only summarises the engineer’s viewpoint but that of many others, professional and public. Even a brief search of the internet reveals that driver frustration is a deep-seated issue. However, despite, or possibly because of, the widely held belief that frustration can lead to dangerous overtaking, the empirical evidence for this is sparse. Furthermore, the antecedents of driver frustration itself are not understood. In 2012, Transport Scotland commissioned a review of the international literature on frustration and overtaking. This review (Grayson, Kinnear & Helman, In press) concluded that the concept of frustration appears in historic traffic modelling work that attempts to quantify drivers’ perceptions of service quality. However, it tends to have been inferred from traffic variables rather than being measured directly. Two exceptions to this are the work of Gunatillake, Carnew and Akçelic (2000), and Koorey, Farrelly, Mitchell and Nicholson (1999), although these are in contexts not necessarily applicable to the A9. Gunatillake et al. (2000) measured self-rated levels of frustration in response to a variety of urban video-filmed traffic situations in Australia. They found that frustration did vary with driving situations (‘slow travel’, such as congestion, being the main situation that led to a marked increase in frustration) but that there was little increase in frustration over time. Frustration ratings for the various driving situations were incorporated into a model (the Traffic Frustration Index or TFI) which was then validated on a variety of additional routes and times of day. Gunatillake et al. concluded that the TFI did a reasonable job of modelling driver frustration, but that it did not add much (if anything) beyond what could be achieved simply by measuring travel speed. Koorey et al. (1999) used willingness to pay techniques to calculate an economic value for reduced frustration accruing from the provision of passing places on roads in New Zealand. They concluded that a value of NZ$0.035 (per vehicle per kilometre of passing opportunity) was robust and could be included in models along with the values for safety and journey time. Both of these studies (albeit in different driving contexts to the A9) show that it is possible to measure frustration directly (in these cases using self-report survey techniques) and to consider it in road design and traffic modelling. Grayson et al. nevertheless concluded that evidence focusing on frustration and overtaking behaviour directly is sparse. Only one study was found that directly addressed the issue. Kaub (1990) examined the effect of traffic flow on overtaking behaviour on a road in the United States, and found that as traffic flow went up, drivers were prepared to accept more risk in terms of the overtaking manoeuvres they attempted. This study demonstrates the potential for overtaking propensity to vary with traffic conditions believed to impact on frustration. Other studies using simulation (e.g. Pollatschek & Polus, 2005) have supported the general assertion that delays can lead to an increase the level of risk that at least some drivers are willing to accept in their overtaking decisions. (Author/publisher)
Abstract