Professor Heikki Summala
heikki.summala [at]

Traffic Research Unit
Traffic Psychology Chair
Institute of Behavioural Sciences
P.O. Box 9
Siltavuorenpenger 1 A
FI-00014 University of Helsinki

Researchers currently (2014) associated with Traffic Research Unit

Traffic Research Unit

The Traffic Resarch Unit of the University of Helsinki was founded in 1971.

The Unit’s mission is to conduct high quality basic research in behavioural science, to provide research-based higher education, and to produce and disseminate research results conducive to the well-being of people on the move.

The object of our research is human behaviour in a natural hazardous activity, and the cognitive and neural mechanisms behind it.

The reseach methods used include quantitative measurements in the field with instrumented cars, laboratory experiments and simulations, psychological tests, accident analysis, and computational modeling of road-user behaviour and traffic cognition.

We study human behaviour across the entire life span, and at all levels of skill and learning, from novice to expert.

The research has applications in driver education, driver assessment and licensing, road and traffic design, vehicle design, legislation, and in the prevention of road fatalities.

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Recent articles from Traffic Research Unit

Summala, H., Rajalin, S., Radun, I. (2014). Risky driving and recorded driving offences - 24 years follow-up study. Accidental Analysis and Prevention 73, 27-33, doi: 10.1016/j.aap.2014.08.008

Permanent individual differences in driver behavior and accident risk have long been under active debate. Cognitive and personality factors have correlated with risky driving indicators in cross-sectional studies, and prospective cohort studies are now increasingly revealing early antecedents of risky behavior and injury mortality in adult age, with connections to stable personality traits. However, long-term stability in driver behavior or accident involvement has not been documented in a general driver population.This study reports 24-year follow-up data from a study that compared the recorded offenses between 134 drivers stopped by the police because of sustained risky driving and 121 control drivers stopped at the same locations at the same time in 1987 (Rajalin, 1994. Accid. Anal. Prev., 26, 555–562). Data were compiled from national driver records and accident statistics for the same drivers again 24 years later, and their yearly mileage and speed behavior was requested in a mail survey. The results showed that the two groups of drivers sampled on one trip a quarter of a century ago still differ from each other. The offenders still have more entries in their driver record, also when adjusted for age and mileage (OR = 1.59, CI = 1.03–2.46), they still report in the survey that they drive faster and overtake other cars more often. The results show that individual differences in driver behavior persist for decades, perhaps for life. However, in this on-road sample, the effect seems to be moderated by occupation which also presumably explains the lower mortality among the offenders during this 24-year follow-up.

Lehtonen, E., Lappi, O., Koirikivi, I., Summala, H. (2014). Effect of driving experience on anticipatory look-ahead fixations in real curve driving . Accidental Analysis and Prevention 70, 195-208, doi: 10.1016/j.aap.2014.04.002

Anticipatory skills are a potential factor for novice drivers’ curve accidents. Behavioural data show that steering and speed regulation are affected by forward planning of the trajectory. When approaching a curve, the relevant visual information for online steering control and for planning is located at different eccentricities, creating a need to disengage the gaze from the guidance of steering to anticipatory look-ahead fixations over curves. With experience, peripheral vision can be increasingly used in the visual guidance of steering. This could leave experienced drivers more gaze time to invest on look-ahead fixations over curves, facilitating the trajectory planning.

Eighteen drivers (nine novices, nine experienced) drove an instrumented vehicle on a rural road four times in both directions. Their eye movements were analyzed in six curves. The trajectory of the car was modelled and divided to approach, entry and exit phases.

Experienced drivers spent less time on the road-ahead and more time on the look-ahead fixations over the curves. Look-ahead fixations were also more common in the approach than in the entry phase of the curve. The results suggest that with experience drivers allocate greater part of their visual attention to trajectory planning.

Mattsson, M. (2013). On testing factorial invariance: A reply to J.C.F. de Winter. Accidental Analysis and Prevention, doi: 10.1016/j.aap.2013.10.031

Since its publication, the Driver Behavior Questionnaire (DBQ) has been used for comparing subgroups of respondents on the constructs formed through factor analyzing the questionnaire items. However, not enough attention has been paid to ascertaining that the instrument actually measures the same constructs in the same way in all respondent groups. I recently published an article (Mattsson, 2012) that aimed to do this for the Finnish 28-item version of the DBQ using the stage-wise factorial invariance approach in the Exploratory Structural Equation Modeling (ESEM) context. de Winter (2013) commented on the publication, arguing that the results were artifacts due to measurement error that too many factors were extracted and that too strict criteria for invariance were applied. In this contribution, I reply to each criticism and suggest methodological approaches for ensuring the measurement invariance of self-report instruments such as the DBQ.

Lappi, O., Lehtonen, E., Pekkanen, J., Itkonen, T. (2013).Beyond the tangent point: Gaze targets in naturalistic driving. Journal of Vision 14(13) doi: 10.1167/13.13.11

Open access

Moving in natural environments is guided by looking where you are going. When entering a bend, car drivers direct their gaze toward the inside of the curve, in the region of the curve apex. This behavior has been analyzed in terms of both “tangent point models,” which posit that drivers are looking at the tangent point (TP), and “future path models,” which posit that drivers are visually targeting a point on the desired trajectory or future path (FP). This issue remains unresolved, partly due to the challenge of representing the changing visual projection of the trajectory into the driver's field of view. This paper reports a study of naturalistic driving, in which the FP in the field of view is explicitly modeled, and the TP and reference points on the FP are simultaneously analyzed as potential gaze targets. We argue that traditional area-of-interest methods commonly interpreted as supporting the TP hypothesis are problematic when the interest is contrasting multiple gaze targets. This prompts a critical reassessment of the empirical case for the ubiquity of looking at the TP and the generality of the TP hypothesis as an account of where people look when they steer. As a basis for representing driver gaze behavior, the FP is an equally valid point of departure. There are no overwhelming theoretical or empirical reasons for favoring the TP models over the FP models.

Cengiz, C., Kotkanen, H., Puolakka, M. Lappi, L., Lehtonen, L., Halonen, L., Summala, H. Combined eye-tracking and luminance measurements while driving on a rural road: Towards determining mesopic adaptation luminance Lighting Research and Technology doi:10.1177/1477153513503361

In collaboration with Aalto University Lighting Unit

In order to implement the recommended Commission Internationale de l'Eclairage (CIE) system for mesopic photometry to roads, it is necessary to define the relevant visual field and adaptation luminance in night-time driving conditions. We measured three drivers’ eye tracking on a rural road at night and in daytime, and the simultaneous luminance for the corresponding parts of the scene on lit and unlit sections of the road at night. Fields of view with circular sizes of 1°, 5°, 10°, 15° and 20°, with the centre point at the mode of the gaze distributions of the drivers, were used as initial estimates of the visual adaptation field. In both the lit and unlit sections, the variation within subject and between subjects in the mean luminance decreased as the size of the circular field increased. However, the mean luminances of all of the circular fields in the unlit section were higher than in the lit section due to the use of high-beam headlights in the unlit section.

Lappi O, Pekkanen J, Itkonen TH (2013) Pursuit Eye-Movements in Curve Driving Differentiate between Future Path and Tangent Point Models. PLoS ONE 8(7): e68326. doi:10.1371/journal.pone.0068326

Open access

For nearly 20 years, looking at the tangent point on the road edge has been prominent in models of visual orientation in curve driving. It is the most common interpretation of the commonly observed pattern of car drivers looking through a bend, or at the apex of the curve. Indeed, in the visual science literature, visual orientation towards the inside of a bend has become known as “tangent point orientation”. Yet, it remains to be empirically established whether it is the tangent point the drivers are looking at, or whether some other reference point on the road surface, or several reference points, are being targeted in addition to, or instead of, the tangent point. Recently discovered optokinetic pursuit eye-movements during curve driving can provide complementary evidence over and above traditional gaze-position measures. This paper presents the first detailed quantitative analysis of pursuit eye movements elicited by curvilinear optic flow in real driving. The data implicates the far zone beyond the tangent point as an important gaze target area during steady-state cornering. This is in line with the future path steering models, but difficult to reconcile with any pure tangent point steering model. We conclude that the tangent point steering models do not provide a general explanation of eye movement and steering during a curve driving sequence and cannot be considered uncritically as the default interpretation when the gaze position distribution is observed to be situated in the region of the curve apex.

Lappi, O. & Lehtonen, E., (2013) Eye-movements in real curve driving: pursuit-like optokinesis in vehicle frame of reference, stability in an allocentric reference coordinate system. Journal of Eye Movement Research 6(1):4, 1-13.

Open access

Looking at the future path and/or the tangent point (TP) have been identified as car drivers’ gaze targets in many studies on curve driving. Yet little is known in detail about these "fixations to the road". We quantitatively analyse gaze behavior at the level of individual fixations in real on-road data. We find that while gaze tracks the TP area, this pattern consists of fast optokinetic movements (smooth pursuit and fast resetting saccadic movements). Gaze is not “fixed” to the TP. We also relate eye-movements to a reference direction fixed to a point on the trajectory of the vehicle (curve exit), showing that fixations lose their pursuit-like character in this rotating system. The findings are discussed in terms of steering models and neural levels of oculomotor control.

Lehtonen, E., Lappi, O. Kotkanen, H., & Summala, H. (2013) Look-ahead fixations in curve driving. Ergonomics, 56(1), doi:10.1080/00140139.2012.739205

Open access version available

Two functionally distinct types of fixation, guiding fixations and look-ahead fixations, have been identified in naturalistic tasks based on their temporal relationship to the task execution. In car driving, steering through a curve is guided by fixations toward a region located 1–2 s in the future, but drivers also make fixations further along the road. We recorded drivers' eye movements while they drove an instrumented vehicle on curved rural roads and developed a method to quantify lead time and distance of look-ahead fixations. We also investigated the effect of cognitive load on look-ahead fixations. The look-ahead fixations appear to have a pattern which is connected to the sequential structure of a curve. This suggests that they have a role both in advance planning of the driving line and in the anticipation of oncoming vehicles. Cognitive load led to a shorter look-ahead lead time and distance.

Lehtonen, E., Lappi, O. & Summala, H. (2012). Anticipatory eye movements when approaching a curve on a rural road depend on working memory load. Transportation Research Part F 15(3), doi:10.1016/j.trf.2011.08.007

Open access version available

Where do drivers look when approaching curves on a winding road? Existing models on visual processes in curve driving have focused on path-controlling behavior. Another aspect in curve driving is the visual anticipation of potential oncoming vehicles, obstacles and road alignment. We define the occlusion point of a curve as the nearest point where the view of the road is blocked by some obstacle (e.g. vegetation). Monitoring the occlusion point is relevant for safe driving because potential oncoming vehicles or obstacles on the road will come into view on the occlusion point.

In the current on-road study, 10 participants drove an instrumented car at their own pace on a low standard rural road while their eye-movements were recorded. We investigated anticipatory glances towards the occlusion point while approaching open sight curves and how anticipatory glances are affected by a cognitive secondary task without explicit visuo-spatial or motor components.

The results demonstrate that drivers indeed look at the occlusion point while approaching open curves on rural roads, and that working memory load leads to a significant decrease in visual anticipation. Previously, it has been shown that cognitive secondary tasks lead to reduction of looking at the speedometer and mirrors and of safety critical visual scanning at street crossings. We show that the effect is also present in the anticipation of road curvature and hazards on rural roads.

Mattsson, M. (2012). Investigating the factorial invariance of the 28-item DBQ across genders and age groups: An Exploratory Structural Equation Modeling Study. Accid. Anal. Prev., doi:10.1016/j.aap.2012.02.009

The Driver Behaviour Questionnaire (DBQ) is perhaps the most widely used questionnaire instrument in traffic psychology with 174 studies published by late 2010. The instrument was developed based on a plausible cognitive ergonomic theory (the Generic Error Modeling System, GEMS), but the factor structure obtained in the original study (Reason et al., 1990) did not mirror the theory's conceptual structure. This led to abandoning GEMS and adopting the obtained factor structure as a starting point for further DBQ research. This article argues that (1) certain choices in the original study, concerning statistical methodology and the wording of individual question items, may have contributed to the ways the obtained factor structure deviated from the underlying theory and (2) the analysis methods often used in DBQ studies, principal components (PC) analysis and maximum likelihood (ML) factor analysis, are not optimal choices for the non-normally distributed categorical data that is obtained using the instrument. This is because ML produces biased results when used with this type of data, while PC is by definition unable to uncover latent factors as it summarizes all variation in the measured variables. (3) Even though DBQ factor scores have been routinely compared in subgroups of men and women and respondents of different ages, DBQ's factorial invariance in these groups has not been rigorously tested. These concerns are addressed in this article by framing the results of certain previous DBQ studies as a structural equation model (SEM) and an Exploratory Structural Equation Model (ESEM) and testing measurement model fit in subgroups of respondents. The SEM analyses indicate that the model does not fit data from the whole sample of respondents as it stands, while the ESEM analyses show that a modification of the model does. However, the ESEM analyses indicate the DBQ measures different underlying latent variables in the different subgroups. Based on the analyses and a review of recent advances in attention and memory research, an update to the theory underlying the DBQ is suggested.