Part III Special Topics in

Applied Psychology

IAAP Handbook of Applied Psychology, First Edition. Edited by Paul R. Martin, Fanny M. Cheung, Michael C. Knowles, Michael Kyrios, Lyn Littlefi eld, J. Bruce Overmier, and José M. Prieto.© 2011 Blackwell Publishing Ltd. Published 2011 by Blackwell Publishing Ltd.

22

Traffi c Psychology A State - of - the - Art Review

A. Ian Glendon

Extent of the Review

This chapter reviews a sample of refereed journal papers and book chapters on traffi c psychology topics published during the years 1998 – 2008. The start date was the year that the journal Transportation Research Part F: Traffi c Psychology and Behaviour ( TRF ) was initiated by IAAP ’ s Division 13 inaugural president, Talib Rothengatter who, with other like - minded traffi c psychology researchers, desired to see a specialist journal in this fi eld. Talib Rothengatter edited TRF until his untimely death early in 2009.

In this chapter “ traffi c psychology ” includes a range of behavioral and statistical approaches, but excludes engineering and environmental orientations. It is primarily concerned with cognitive, social, and behavioral relationships between people and vehicles. I reviewed 1472 empirical articles and chapters with a predominantly psy-chological or human factors/ergonomics approach. Nearly half ( n = 727) were published in Accident Analysis and Prevention ( AAP ). Two other journals published large numbers of traffi c psychology papers — TRF (247) and the Journal of Safety Research ( JSR ) (166). Three further journals — Human Factors ( HF ) (61) , Ergonomics (56), and Safety Science ( SS ) (37) were also well represented. Fewer papers appeared in Applied Ergonomics (9), Personality and Individual Differences (9), Work and Stress (2), and the Journal of Environmental Psychology (2). While every attempt was made to review all empirical papers on traffi c psychology published in these sources during the target years, papers on relevant topics that were not included have appeared, inter alia, in journals of experimental psychology, neuroimaging, alcohol and other drug use, and marketing. Only papers published in English - language journals and books were included, introducing a sampling bias.

IAAP Handbook of Applied Psychology, First Edition. Edited by Paul R. Martin, Fanny M. Cheung, Michael C. Knowles, Michael Kyrios, Lyn Littlefi eld, J. Bruce Overmier, and José M. Prieto.© 2011 Blackwell Publishing Ltd. Published 2011 by Blackwell Publishing Ltd.

546 Glendon

Book chapters were from volumes devoted to traffi c psychology topics with empiri-cal content broadly comparable with refereed journals. Chapters published in the two Traffi c and Transport Psychology volumes ( n = 82) (Rothengatter & Huguenin, 2004 ; Underwood, 2005 ) were based respectively on papers delivered at the 2000 and 2004 International Conferences on Traffi c and Transport Psychology (ICTTP). Chapters (64) in the three Driver Behaviour and Training volumes (Dorn, 2003, 2005, 2008 ) were based on papers presented at contemporaneous eponymous conferences. Hennessey and Wiesenthal (2005) comprised commissioned chapters (10) from traffi c psychology researchers. Other chapters on traffi c psychology topics published during the target years, reports and other publications in traffi c psychology were not reviewed, many of which might differ in their methodology and focus from most journal papers and book chapters. No attempt was made to chart changes over the time period encom-passed by this review on the grounds that it is too short to obtain meaningful results.

In the years 1998 – 2001, there were fewer than 100 traffi c psychology publications per year. Between 2002 and 2007, 100 – 200 publications per annum appeared, while in 2008 there were almost 300 publications. While there is a clear upward trend in published traffi c psychology research, it is instructive to examine the literature in disaggregated form in order to understand better how the fi eld is structured and how research is undertaken.

Patterns of Authorship

The mean number of authors per paper was three (range 1 – 11; mode 2), with well over 4,000 authors represented, not all of whom would acknowledge the label of “ traffi c psychologist. ” Many researchers authored multiple papers. As just over 10% of papers in the sample were written by researchers from more than one country, this raises the question of the extent to which this is a truly international fi eld. Of papers coauthored by researchers from more than one country, US researchers tended to coauthor papers with researchers based either in Canada or in a few developing countries. European - based researchers who coauthored papers across countries tended to do so with researchers from other countries in the broad European region — from the Scandinavian countries in the north to Spain, Greece, and Italy in the south, and from the UK and Ireland in the west to Turkey in the east. North American researchers published mainly in AAP, HF and JSR . European traffi c psy-chologists tended to publish in TRF, SS and the books based upon conference papers.

To determine relative contributions of researchers from different countries, one point was allocated to each publication to be shared among all the authors in respect of country of affi liation indicated on the paper and converting these into percentages of the total number of publications. In the few cases where authors reported multiple affi liations, fractions were distributed pro rata. This exercise revealed that researchers from 52 countries published traffi c psychology papers during the 11 - year period. That these 52 countries are home to 68% of the world ’ s population might suggest that traffi c psychology research is an international phenomenon. However, of those occupying the fi rst 20 places on this “ league table ” only Taiwan and Turkey were not OECD members, suggesting that traffi c psychology researchers

Traffi c Psychology 547

are overwhelmingly concentrated in relatively developed nations. One perspective on the disparity between countries ’ relative contributions may be gleaned from the fact that the fi rst three countries on this list (United States, United Kingdom, Australia) contributed 53.74% of publications during the sampled period. The US alone accounted for just over one third of the total. At the other end of the table, the last 14 places were occupied by countries whose contributions were based upon the equivalent of one sole - authored publication or less. Over 100 nations, containing almost one third of the world ’ s population, had no representation at all. These extremes are a reminder of the considerable imbalance between resources available for research between countries. Wealthy nations acting as a magnet for researchers can further increase disparities between developed and developing nations ’ relative research contributions. However, it also allows the possibility of researchers from developing countries sharing resources with those from wealthier nations to under-take comparative studies, including gathering data from their own countries. There is some evidence that this occurs to a limited extent in traffi c psychology.

Taking countries ’ relative populations into account — in this case by dividing each country ’ s relative contribution to the traffi c psychology literature by its percent of the world population, a different pattern emerges. Without implying any political intent in distributing such resources, this might be considered to be a proxy for resources devoted to traffi c psychology research as a ratio of population at risk. Half a dozen countries scored particularly highly on this index, with New Zealand, Sweden, Finland, Israel, Australia, and Norway occupying the top six positions — well ahead of the rest of the fi eld. Newcomers to this “ top 20 ” included Bahrain (rank 7), Hong Kong (15), Singapore (16), Qatar (17), and Kuwait (18). Taking popula-tion size into account tends to favor relatively smaller countries, which require only a few publications to make the upper reaches of this league table. It also provides a pointer as to where traffi c psychology is an emerging fi eld (e.g., some Gulf States). Larger countries tend to score poorly on this measure as they require a much larger proportion of publications to achieve a high ranking. Large developing countries score particularly poorly on this index, perhaps indicating where there is considerable scope for developing traffi c psychology (e.g., China, India, Indonesia).

Other ways of indexing a country ’ s performance in a fi eld of scientifi c endeavor include taking account of per capita income, which could be considered a proxy measure of a country ’ s wealth attributed to research in traffi c psychology. With per capita income as the indexing criterion, in this case by dividing the percent of traffi c psychology publications by per capita income for each country, the fi rst four rankings revert to their “ raw ” state, with the list headed again by the United States, United Kingdom, Australia, and Sweden, followed by New Zealand, Canada, and Israel, and the overall pattern very much resembling the raw data ranks.

Given that an ultimate objective of research in this fi eld is to reduce road casual-ties, it seems appropriate to use at least one road casualty measure. The author data can be indexed by reference to road deaths per 100,000 of population, which could be considered as a proxy measure of the extent to which a country devotes resources to research in traffi c psychology in relation to its road death toll — the higher the index the greater the willingness to devote resources to this fi eld of study compared with the “ magnitude ” of the problem. Obtaining accurate and reliable road casualty

548 Glendon

data across countries can be problematic, particularly where different reporting and recording systems exist and where a variety of statistical bases are employed to derive published fi gures. This, together with the small number of publications from many of the countries in the sample, means that only data for OECD countries were con-sidered. Again the rank order, particularly at the top of this table, bears a strong resemblance to the raw fi gures, refl ecting wealthy countries ’ ability to devote greater resources to both road safety interventions and traffi c research. However, it also revealed that even wealthy countries differ considerably in their willingness or ability to fund research in this domain, although it is quite possible that in some countries resources devoted to road safety issues are directed through channels not refl ected in publications sampled here. The English - language sampling bias also meant that countries where traffi c psychology researchers publish mainly or extensively in non - English - language journals and books were underrepresented in these calculations.

Theoretical Orientations

Theories or models developed specifi cally to describe driving behavior include N ä ä t ä nen and Summala ’ s (1976) classic work on zero risk (also Summala & N ä ä t ä nen, 1988 ), Heino ’ s (1996) risk perspective exposition, various descriptions of risk home-ostasis (also known as “ risk compensation ” or “ target risk ” and more generically as “ behavioral adaptation ” ), fi rst introduced into the driving domain by Wilde (1982, 2001) , Lajunen ’ s (1997) approach from personality and driving style, Groeger ’ s (2000) cognitive approach, the driver stress model (Matthews, 2001 ), and task - or threat - oriented approaches (Fuller, 1984, 2005, 2008 ). However, only a handful of the empirical papers reviewed used any of these models as a conceptual basis. Of the reviewed papers around 15% adopted some recognizable theoretical framework or model as the conceptual basis for their study, while the remaining 85% were driven by data exploration, correlational designs or statistical modeling.

Of the 224 papers that adopted a recognizable conceptual framework around 10% were based on a model originating within traffi c psychology (e.g., those listed above) — 22 such theories or models were identifi ed. A further 13 theoretical models were derived from other fi elds and modifi ed for a driving or other road user context. For example, the transactional stress model has been adopted for driving applications. These 35 driving specifi c and derivative models refl ected a broad range of conceptual frameworks for considering driving behavior, incorporating cognitive, visual, behav-ioral, social, individual, emotional, and human factors approaches, either singly or in some combination. Clearly driving and other road user behavior can be represented across and within multiple conceptual modalities.

A much larger number of papers among those adopting a conceptual basis for their empirical research applied an existing model from the literature to a driving context with little or no modifi cation. These conceptual models took a variety of forms. Those that were essentially cognitive ( n = 28) included such features as per-ception, appraisal, attention, memory, processing speed, or decision making. The largest category of theories or models ( n = 67) were extended cognitive models, for example incorporating additional emotional, attributional, social, human factors, or

Traffi c Psychology 549

behavioral components. Other models were derived from the broad social domain ( n = 22), including personality/individual differences, developmental and cultural approaches as well as from social psychology. Fourteen models were developed from behavioral, learning or organizational approaches, while eight papers were based upon a miscellany of conceptual approaches.

In summary 174 theories, conceptual frameworks, or models that had some identifi able psychological component or origin were identifi ed. Some two dozen of these frameworks were developed specifi cally to account for various aspects of driving or road use more generally. About half that number were derived from other psychological domains and applied to driving. Of models or conceptual frame-works that were applied from areas of psychology external to driving or road use, the largest number had a cognitive basis, either exclusively or in augmented form, for example to include social, behavioral or human factors aspects. Some form of augmented cognitive framework represented the largest category of applied concep-tual model in the studies reviewed. Within this category the theory of planned behavior (TPB) — including its predecessor, theory of reasoned action (TRA) — and TPB variants was the most frequently adopted conceptual framework. While most of the conceptual frameworks identifi ed appeared in only a single publication, the TPB was identifi ed as the conceptual basis in 33 studies and the TRA in a further fi ve studies.

Conceptual frameworks encompassing social, personality, cultural, and develop-mental approaches were fairly popular, while those based upon behavioral, learning, or organizational frameworks were also in evidence. Together these conceptual frameworks indicate both the richness and complexity of the subject material of driving and road use more generally, as well as the variety of theoretical and discipli-nary backgrounds of those who choose to study this important fi eld within applied psychology.

Methodology and Data

Study d esigns and d ata c ollection m ethods

The variety of methods available for studying driving behavior and road use more widely was described by Glendon (2007) . Study designs and data collection methods described in the 1,472 sampled publications revealed four multiple measure designs — laboratory experiments, fi eld experiments, quasi - experimental and cohort/epidemio-logical designs, each with a number of variants. However, single - measure cross - sectional designs were the most commonly adopted design for the widely - used questionnaire/survey data collection method. Only 28 studies were classifi ed as either intervention or evaluation studies — less than 2% of publications sampled.

Nine distinct data gathering methods were identifi ed, involving varying levels of participant involvement. At one extreme, mining existing databases (e.g., crash/col-lision data) required no active “ participant ” involvement. At the other end of the scale, taking neurological or neurophysiological measures requires a high level of participant agreement. Between these extremes were: indirect and direct observation

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methods, self - completion instruments, interviews, experimental tasks, simulations, and physical or physiological measures. Each basic method had two or more variants, refl ecting the rich diversity of data gathering techniques available to traffi c psycholo-gists, as well as their variety of disciplinary backgrounds. There was a strong bias towards quantitative data, with only 27 studies — less than 2% of the sample — using qualitative data gathering as the only or main approach.

Participants

In traffi c psychology research, participants can “ cooperate ” either actively or passively. Active participants agree to be surveyed, tested, or experimented upon, while passive participants ’ involvement does not require their personal agreement as data are gath-ered from such sources as anonymous roadside observations, archive data modeling — as in crash statistics — or analyzing data from other secondary sources. In the sampled period, the researchers studied some 875,000 active participants and accessed data on well over 50 million passive participants. Many of the latter were almost certain to have been included in multiple samples, while the real total is considerably larger than this fi gure, which was compiled only from studies reporting sample sizes — many did not do so. US researchers in particular can access extensive databases from which large samples may be drawn for statistical analysis, such access favoring data - driven modeling or exploratory approaches.

Unsurprisingly, the most commonly studied active road user participants were vehicle drivers or two - wheeled vehicle riders. Participants included 19 categories of car drivers (e.g., commuters, crash - involved, convicted, experienced, inexperienced, alcohol/drug users), 14 varieties of specialist drivers (e.g., bus/coach, commercial, police, taxi), fi ve rider types (e.g., cyclists, motorcyclists), 22 categories of non-drivers — participants recruited for something other than their driving ability, and eight grouped samples (e.g., couples, family dyads, matched samples).

As part of triangulating data in a number of studies, driving - related data were collected or calculated concurrently and analyzed as part of the research study. The 32 categories of concurrent data identifi ed were grouped under six main headings — moving traffi c (e.g., traffi c fl ows, driving speeds), geometric/environmental measures (e.g., road width, road curvature), vehicle characteristics (e.g., speed, distance trav-elled), historical records (e.g., medical), driver characteristics (e.g., mobile/cellular phone use), and crash data (e.g., on - site investigations).

Of the sampled studies, 146 identifi ed secondary data sources used to analyze or model patterns or trends. Nearly half of these used some form of database (e.g., census, vehicle registration data), while the other two main categories were various types of legal and crash databases. In addition to secondary sources of passive partici-pants, 87 studies used information from other sources as research variables. Economic, traffi c data and legal indicators headed the list of secondary data sources.

Tests and o ther i nstruments u sed

To collect data on a vast range of variables, 542 tests, questionnaires, and other measures were used in these studies. There were 152 driving - specifi c measures — the

Traffi c Psychology 551

remainder being generic measures. Driving - specifi c measures could be grouped at three levels. The fi rst level comprised instruments measuring a single entity, such as behavior — either by direct observation (35) or self - reported driving/riding behaviors (7). The greatest variety and depth of measures was at the second level in the cogni-tive domain (78), in which measures could be classifi ed as assessing knowledge (11), attributions (5), perception (5), attention (4), skills and abilities (4), and attitudes (3). Cognitive measures were also combined with self - reported behavior (3) and observed behavior (1) measures. Where separate cognitive measures were combined with behavioral measures at the third level, the largest number was classifi ed as cogni-tive/attitudinal along with reported behavior (34) — many driving questionnaires were of this type.

Most of the 13 driving personality measures had an emotion orientation (e.g., driving anger, aggression). Other aspects of driving included self - reported behaviors (8), ergonomic (6), clinical (2), health (1), medical (1), and physical (1).

There was great variety among the 390 nondriving measures. Cognitive measures accounted for 120 of these, distributed among 34 varieties. The most frequently encountered were skills and abilities tests (18), perception measures (11), measures of attention (10) and measures of attitudes and self - reported behaviors (10). The next largest broad category was personality tests (67), many of these addressing emotional aspects (23). This was followed by various measures of vision (48), clini-cal/diagnostic assessments (38), physiological measures (23), health assessments (21), and organizational measures (11). There were also auditory assessments (7), social measures (7), ergonomic assessments (6), physical measures (6), behaviors that were observed (6) and self - reported (5), medical assessments (5), neurological meas-ures (5), measures of emotions (4), motor skills measures (3), and biographical items (2), plus six unclassifi ed measures.

Data a nalysis t echniques

The rich variety of participant origins, data collection methods, and instruments employed was matched by considerable diversity in data analysis techniques. An initial listing of over 440 techniques identifi ed in the sampled papers was grouped into 19 types, with a residual unclassifi ed category. The main data analysis approaches identi-fi ed, with numbers of variants and examples of each were: assumption tests (6, e.g., Bartlett ’ s test), data classifi cation (20, e.g., cluster analysis), data reduction (9, e.g., factor analysis), derivative tests (20, e.g., post hoc tests), descriptive (23, e.g., percentages, rates), effect size (12, e.g., odds ratios), event/survival analysis (9, e.g., Cox model), general techniques (26, e.g., sign test, z - test), generalized linear modeling — comprising non - GLM regression - based models (82, e.g., binary probit modeling, ordered logit modeling), general linear modeling (GLM) (53, e.g., ANOVA, multivariable regression), non - parametric GLM (12, e.g., Mann - Whitney U test), structural equation modeling (GLM) (2, e.g., path analysis), panel general-ized linear modeling (9, e.g., multi - level modeling), panel GLM (15, e.g., generalized estimating equations), qualitative (20, e.g., inductive analysis, content analysis), reliability analysis (9, e.g., Cronbach ’ s alpha), spatial analysis (9, e.g., social area analysis), time series analysis (8, e.g., autoregressive integrated moving average

552 Glendon

models), validity checks (9, e.g., sensitivity analysis — for predictive validity), not otherwise classifi ed (87, e.g., Bayes analysis, Rasch analysis).

Traffi c Psychologists ’ Affi liations

Unlike national - level organizations that represent applied psychologists in many other fi elds, few national psychology or ergonomics/human factors societies have specialist divisions for traffi c psychologists. The prime organization for traffi c psychologists is the International Association of Applied Psychology ’ s Division 13 — Traffi c and Transportation Psychology. Where they belong to national - level bodies, traffi c psy-chologists tend to join specialist organizations, the great majority of whose members represent road safety practitioner and professional groups including engineers, police, driving instructors, government offi cials at various levels, and human factors special-ists. Opportunities exist in these forums for exchanging expertise and jointly concep-tualising road safety problems, for example through national conferences and journals.

Further Evidence on Future Directions for Traffi c Psychology

Delegates to the fourth International Conference on Traffi c and Transport Psychology (Washington, DC, September 2008) provided some information on traffi c psychol-ogy ’ s immediate future. A conference questionnaire item invited respondents to indicate the direction that research within this fi eld would develop within the next fi ve years. Seventy - fi ve delegates provided 127 interpretable responses, which were coded under six major headings.

The greatest number of responses concerned “ Methodology ” (33% of responses). The seven subheadings (N responses) were:

• naturalistic research/observation (9); studying “ naturalistic driving ” particularly prominent

• brain activity (8); neuroimaging was mentioned most frequently, plus cognitive factors associated with driving

• interventions (7); generic and specifi c intervention examples mentioned • greater focus on safety (7); including addressing organizational aspects of safety

related to driving • applications (e.g., simulation) (6); emphasising the importance of applying theo-

retical and empirical work • measurement (3); including improving existing techniques and developing new

measures • qualitative (2); pleas for more qualitative research.

The next category was “ Road user groups ” (21% of responses), divided into fi ve subcategories:

Traffi c Psychology 553

• older/less mobile drivers/road users (12); including general and specifi c examples • younger drivers (6); including parental involvement • commercial vehicle drivers (4); including reference to rules, training, monitoring,

and feedback • motorcyclists (3); training fi gured prominently here • vulnerable road users (2); generalized responses.

The third heading, “ Environmental infl uences ” (18% of responses), had four sub - headings:

• internal (8); included role of emotion, alcohol/other drugs, fatigue, and distraction

• training/education (8); included evaluation, graduated licensing and customization

• external (3); included community infl uence, external environment, and informa-tion presentation

• testing (3); included reference to fi eld operational tests, hazard perception tests, and psychological tests generally.

The fourth heading included “ Technology/automation ” items (14% of responses) relating to driving and road use generally. The diverse responses ( n = 18) included such topics as increased automated enforcement, in - vehicle assessment of driver impairment and investigation of possible hazards, and potential benefi ts of further automating driving tasks. The fi fth heading, “ Behavior change/transport mode ” (7% of responses), comprised responses ( n = 9) referring to changing behavior either in respect of driving or effecting change between transport modes (e.g., to more sustainable forms of transport). The sixth heading was “ Theory ” (5% of responses) with responses ( n = 6) requesting a more robust theoretical approach in developing models of driving and other road user behavior. The seventh heading (3 responses) included two pleas for some/any developments in the fi eld, one suggesting that extant efforts were too “ scattered, ” while the fi nal plea was for greater research emphasis in developing countries. Responses generally refl ected a wide spectrum of interests and approaches within traffi c psychology and were broadly consistent with the analyses of published work described above.

Conclusions and Future Challenges for Traffi c Psychology

From this overview of recently published English - language empirical research, a strong researcher base within a number of countries emerges. A few thousand traffi c psychologists and researchers in related fi elds, such as human factors/ergonomics, contributed to the scientifi c literature over the 11 - year period. Notwithstanding the current healthy state of this disciplinary domain, some future challenges emerged from reviewing this sample of published work.

554 Glendon

Internationalization

While many countries are represented in the traffi c psychology research literature, the overwhelming bias is towards research being undertaken in the most developed countries, with no representation at all from many nations and minimal representation from some others. Generalization from studies undertaken in one culture to jurisdic-tions with different driving styles, road rules, and enforcement practices is problem-atic. A challenge for traffi c psychology researchers is to obtain the necessary resources and collaborative partners to undertake research in traffi c psychology and related issues in developing nations, where, given the generally much higher crash and fatality rates, there is the greatest potential to develop this subject domain to infl uence policy and practice. Future cross - national research cooperation can build upon existing col-laborative networks to develop more comparative aspects in this fi eld of study and inform both theoretical and applied components of traffi c psychology. Cultural factors have been little studied within the traffi c psychology literature, which could also be remedied by more comparative research.

Theory and c onceptual m odels

Published research in traffi c psychology is primarily characterized by an atheoretical approach — some 85% of papers reviewed had no discernable theoretical or conceptual basis for data collection and analysis. The array of conceptual models adopted in the remaining 15% of papers was highly fragmented. A small proportion of papers adopted models or theories developed specifi cally within the fi eld of driving and other road user behavior, while the most frequently adopted model was from psychology ’ s sociocognitive domain. This plethora of conceptual frameworks refl ects the complex-ity and diversity of this fi eld as well as the multidisciplinary backgrounds of those who study it. However, the absence of a coherent body of theory — or a few compet-ing theories — that could underpin future research, may lead to further conceptual fragmentation on the one hand and continuing eschewing of theory altogether on the other. A comprehensive theory within traffi c psychology would almost certainly need to be broadly based so as to encompass not only sociocognitive aspects, but also emotional, individual differences (e.g., personality), human factors and cultural components — and where appropriate, organizational elements — for example as pre-dictors of behavioral outcomes. A major challenge for traffi c psychologists is to develop a coherent body of driver/road user testable theory that can both guide research and be relevant to road safety applications.

Bridging the r esearcher – p ractitioner d ivide

The researcher – practitioner divide phenomenon is common to several areas of applied psychology — for a review of the debate within organizational psychology see Glendon, Myors, and Thompson (2007) . The scientifi c literature is dominated by researchers based in universities and research institutes, while practitioners who publish articles on traffi c - related topics overwhelmingly do so in professional journals. The challenge here is to locate and develop appropriate relationships with collaborative practitioner

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partners, particularly to develop evaluation and intervention fi eld studies, which are currently represented in a small minority of research publications.

Methodological o rientation

Independently of practitioner collaboration, another major challenge is to obtain resources for more intervention and evaluation studies. While the range of study designs, data collection techniques, participants and analysis techniques represents considerable research diversity, the most powerful tools in our scientifi c armoury — for example, fi eld study interventions with comprehensive evaluation — have been very sparingly applied to many road transport problems involving human behavior and cognitions, particularly with safety outcomes. Longitudinal studies to evaluate inter-vention effects on vehicle and other road user crash/collision rates and injury reduc-tion require considerable resources, which can be diffi cult to obtain in straitened economic circumstances. Opportunities to effect and to measure such reductions might be more available in developing countries where crash rates are highest and where the potential impact on safety could be maximized.

Extending the r ange and n ature of v ariables s tudied and a nalyzed

The impressive range of data collection methods adopted within the sample of studies investigated belies the strong bias towards driver/other road user attitudes and per-ceptions, particularly gathered via questionnaire and other survey techniques. Attitude – behavior relationships have an extended history within psychology and criteria for establishing credible links have been known for more than 30 years (Ajzen & Fishbein, 1977 ). While behavioral fi eld observations — using either external or in - vehicle methodologies — may be more costly and time - consuming than attitude surveys, they can provide a valuable validity check on less direct data gathering tech-niques. Greater adoption of triangulated methodologies could also be valuable in extending our knowledge — for example collating measures of attitudes and behavior, cognitions and skills, perceptions and motives. Decisions about variables to be included within a research study may be driven by short - term pressures to produce scientifi c publications rather than to make demonstrable road safety improvements.

Quantitative research dominates the empirical literature and a larger number of rigorously conducted qualitative studies could assist not only in theory development but also in a more grounded understanding of psychological components of driver/other road user behavior and cognitions — for example, motives, emotions, peer and other social pressure, substance use, and skill acquisition/maintenance. Grounded research could help traffi c psychologists develop more user - defi ned variables, rather than adhering to those deemed appropriate by previous generations of researchers or pursuing content - free statistical modeling. Theoretical advances could also be made via this route.

Increasing opportunities exist to investigate neural processes associated with driving and other road user behaviors. While equipment and techniques currently available impose limitations on data that can be collected during naturalistic driving there would be opportunities to collect neural processing data in the course of

556 Glendon

driving simulations and experimental tasks relevant to driving (e.g., Calhoun, Pekar, & Pearlson, 2004 ).

Driving data are naturally hierarchical. Driving occurs within jurisdictions (nations, states, regions, etc.), on different road types (motorway, highway, suburban, rural, etc.) in a variety of vehicle types (passenger, work, private, etc.) driven by people with a range of individual characteristics (attitudes, perceptions, motives, etc.). Opportunities exist for multilevel modeling to represent these various features, esti-mated either as variable parameters or as fi xed components within hierarchical models. Within the sampled literature, despite the considerable range and variety of statistical techniques applied, only a tiny number adopted a hierarchical modeling approach. If appropriate data can be collected there is considerable scope for examining the level at which variables signifi cantly infl uence outcomes. This approach could also enhance theory building within traffi c psychology.

Training

Few training programs for traffi c psychologists exist; most researchers transfer from or straddle other psychological sub - disciplines (e.g., cognitive, social, organiza-tional) or operate from cognate fi elds (e.g., ergonomics/human factors). Many traffi c psychologists work in research units in which opportunities exist for new researchers to learn requisite competencies. Others may acquire relevant skills and techniques through mentoring by more experienced researchers. Training programs in traffi c psychology might include a broad theoretical base — incorporating many of the theo-retical approaches outlined in this chapter — introduce researchers to a range of direct and indirect measures of road user behaviors, cognitions, and emotions, and teach appreciation of the range of statistical techniques that can be applied to quantitative data. Special attention should be paid to designing and evaluating intervention studies focused on safety outcomes and on grounded qualitative approaches to data gathering and analysis. For graduate psychologists specialist masters programs could provide a springboard for traffi c psychology careers, while undergraduate programs could provide greater depth. A desirable development would see aspiring traffi c researchers from developing countries benefi t from study programs in research centers in devel-oped nations. A worthwhile initiative would be an international accreditation body for traffi c psychology educational programs.

Extending t raffi c p sychology to o ther t ransportation d omains and b eyond

While other transport modes were outside the sampling frame for this study, much may be learned by traffi c psychologists exploring other transportation domains, for example through cross - modal work, to determine the extent to which theories, methodologies, and data collection/analysis may be either commonly or uniquely applied. Traffi c psychology researchers whose interests extend to other fi elds of transportation psychology include Peter Hancock ’ s human factors work in aviation psychology (e.g., Andre & Hancock, 1995 ), John Groeger ’ s interests anchored within cognitive psychology, including how this might impact upon rail

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human factors (e.g., Groeger, Clegg, & O ’ Shea, 2005 ), and Ray Fuller, who in addi-tion to developing theory within the fi eld of traffi c psychology, has maintained a longstanding involvement in aviation psychology human factors (e.g., McDonald, Fuller, & White, 1991 ). My personal interests in transport psychology extend to rail (e.g., Glendon & Evans, 2007 ) and civil aviation sectors (e.g., Evans, Glendon, & Creed, 2007 ).

To what extent are theories and applications within traffi c psychology relevant across transportation modes — for example, civil aviation, rail, marine, space, military, transport on closed sites such as agriculture, construction, or mining, and transport involving animals? One potentially fruitful approach to cross - modal transport study may be through concepts and methodologies developed within cognitive ergonomics at the person – machine interface. Broader social and environmental factors are also known to have an impact, for example upon transport mode selection and individual commitment to environmental issues. The future may well witness further develop-ments along all or some of the lines suggested here.

Acknowledgments

For their expertise and assistance in preparing this chapter special thanks to Stephen Cox, Michele Dunbar, Cassandra Gordon, Tashaal Green, and Peter Macqueen. For helpful comments on an earlier draft I thank Bryan Porter, Jos é Prieto, and Joe Reser.

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