Drivers' reactions to sudden braking by lead car under varying workload conditions; towards a driver support system

At urban intersections drivers handle multiple tasks simultaneously, making urban driving a complex task. An advanced driver assistance system may support drivers in this specific driving task, but the design details of such a system need to be determined before they can be fully deployed. A driving simulator experiment was conducted to determine the relationship between different subtasks of driving at urban intersections. Participants completed four drives, each comprising 20 comparable intersections with different traffic situations and encountered one unexpected braking event during the experiment. The effects of varying levels of event urgency on the relationship between different driving subtasks were studied. Furthermore, the influence of workload on this relationship was determined by giving half of the subjects an additional cognitive task. After the lead car braked unexpectedly, participants reduced speed and increased headway depending on the urgency of the braking event. Depending on the workload, participants returned to the normal speed and headway again after a number of intersections. Participants experiencing a high-workload drove more smoothly, except for those who had experienced the most urgent unexpected event. High workload additionally affected the length of the adjustments to the unexpected even

Automatic segmentation, detection and quantification of coronary artery stenoses on CTA

Accurate detection and quantification of coronary artery stenoses is an essential requirement for treatment planning of patients with suspected coronary artery disease. We present a method to automatically detect and quantify coronary artery stenoses in computed tomography coronary angiography. First, centerlines are extracted using a two-point minimum cost path approach and a subsequent refinement step. The resulting centerlines are used as an initialization for lumen segmentation, performed using graph cuts. Then, the expected diameter of the healthy lumen is estimated by applying robust kernel regression to the coronary artery lumen diameter profile. Finally, stenoses are detected and quantified by computing the difference between estimated and expected diameter profiles. We evaluated our method using the data provided in the Coronary Artery Stenoses Detection and Quantification Evaluation Framework. Using 30 testing datasets, the method achieved a detection sensitivity of 29 % and a positive predi

3D fusion of intravascular ultrasound and coronary computed tomography for in-vivo wall shear stress analysis: A feasibility study

Wall shear stress, the force per area acting on the lumen wall due to the blood flow, is an important biomechanical parameter in the localization and progression of atherosclerosis. To calculate shear stress and relate it to atherosclerosis, a 3D description of the lumen and vessel wall is required. We present a framework to obtain the 3D reconstruction of human coronary arteries by the fusion of intravascular ultrasound (IVUS) and coronary computed tomography angiography (CT). We imaged 23 patients with IVUS and CT. The images from both modalities were registered for 35 arteries, using bifurcations as landmarks. The IVUS images together with IVUS derived lumen and wall contours were positioned on the 3D centerline, which was derived from CT. The resulting 3D lumen and wall contours were transformed to a surface for calculation of shear stress and plaque thickness. We applied variations in selection of landmarks and investigated whether these variations influenced the relation between shear stress and plaque thickness. Fusion was successfully achieved in 31 of the 35 arteries. The average length of the fused segments was 36.4 ± 15.7 mm. The length in IVUS and CT of the fused parts correlated excellently (R2= 0.98). Both for a mildly diseased and a very diseased coronary artery, shear stress was calculated and related to plaque thickness. Variations in the selection of the landmarks for these two arteries did not affect the relationship between shear stress and plaque thickness. This new framework can therefore successfully be applied for shear stress analysis in human coronary arteries

Drivers' behavioural reactions to unexpected events : Influence of workload, environment and driver characteristics

Many subtasks are relevant simultaneously when driving at urban intersections. Advanced Driver Assistance Systems (ADAS) can support the driver in this complex task. For a well-guided development and evaluatoin process of ADAS, insight into how different driving tasks influence each other is needed. Earlier research has shown that the interaction between different subtasks is changed by unexpected events. A driving simulator experiment was conducted to determine how gender, workload and event urgency influence this. Participants' reactions to two unexpected events were measured. Participants temporarily changed their driving behaviour in reaction to the event. Urgency of the event increased this effect; workload changed the length of adjustments to the event. An interaction effect was found between workload and urgency: participants with high workload drove smoother, unless urgency of the unexpected event reached a threshold. No influence of gender was found. Keywords Behavioural adaptation, workload, gender, levels of the driving tas

Influence of unexpected events on driving behaviour at different hierarchical levels: a driving simulator experiment

Computer based simulation models of human driving behaviour can be used effectively to model driving and behavioural adaptation to Intelligent Transport System (ITS). This can be a useful step in human centered design of ITS. To construct a comprehensive model of driving behaviour, the interaction between the three levels of the driving task has to be determined. This gives insight into how different driving tasks influence each other. A driving simulator experiment was conducted to determine the relationship between levels of the driving task. The influence of workload on this relationship was determined by giving subjects an additional cognitive task. Subjects had to drive many similar intersections, until an unexpected event occurred. Their reaction on the tactical level to the compensation on the control level was measured. Participants lowered speed and increased headway after having to brake; level of unexpectedness increased this effect. Workload decreased this effect on driving speed

Impact of different shopping stages on shopping-related travel behaviour: analyses of the Netherlands Mobility Panel data

From the moment e-shopping emerged, there have been speculations about its impact on personal mobility. A fair amount of research has already been carried out on Internet shopping itself as well as on its consequences for mobility. Most studies focus on the overall impact of online shopping on personal mobility. However, little is known about how personal shopping mobility can be characterised when differentiating its constituent stages, being browsing/orienting, comparing, selecting and purchasing products, and how this is affected by e-shopping. This will be the main topic of this paper. We will investigate this using recently collected data from the Netherlands Mobility Panel [in Dutch: MobiliteitsPanel Nederland (MPN)]. It is the unique combination of reported shopping trips in the three-day travel diary, the large amount of personal and household characteristics combined with the detailed information from the e-shopping questionnaire that enables us to perform this research. Using factor analysis, we explore the underlying factors related to the browsing and selection behaviour prior to the purchase of a product. Using these factors as a starting point, we apply cluster analysis resulting in three homogeneous groups of shoppers with different pre-purchase shopping behaviour. The groups differ clearly with respect to personal and household characteristics, in the frequency with which they buy and sell products online and in their perception of (dis-)advantages of online shopping. Once relevant groups have been distinguished and characterised, differences in shopping-related mobility between them are studied in two different ways. Firstly, we analyse statements from shoppers on how their shopping-related mobility has changed. Secondly, we analyse shopping trips reported in the three-day travel diary. Only one group, which consists of shoppers that rely on the Internet to search for product information, compare prices and get new product ideas, states that their shopping-related travel behaviour has changed since they started shopping online. Approximately 50% of all shoppers experienced no difference in their shopping mobility. The analysis of actual shopping mobility using the travel diary data showed only minor differences in shopping-related travel behaviour between the identified groups. Finally, we fit a multi-variate linear regression model of shopping trip distance to determine if (e)-shopping characteristics influence trip distances. The frequency with which people shop online as well as some stated changes in shopping-related travel behaviour (shopping in a similar manner and shopping longer) turn out to influence non-grocery shopping trip distance. No significant influence could be found of shopping cluster membership on shopping trip distances

The relationship between driver distraction and mental workload

Driver distraction and mental workload are two constructs that are closely related, but which are affected by different aspects of the driving situation and may also have different effects on driving performance. This chapter introduces the concept of latent driver distraction, a form of driver distraction that does not materialise in measurably unsafe driving behaviour, but that does impair being able to respond adequately to upcoming safety-critical situations. It proposes using one of the measurement tools for mental workload as an indication of latent driver distraction. It further raises the issue of evidence for increased mental workload being used often as a direct indication of all types of driver distraction. However, measurements should focus on the type of driver distraction that is measured, instead of translating an increase in one of the constructs into a supposed increase in the other construct. The relationship between mental workload and driver distraction is made explicit

The relationship between driver distraction and mental workload

Driver distraction and mental workload are two constructs that are closely related, but which are affected by different aspects of the driving situation and may also have different effects on driving performance. This chapter introduces the concept of latent driver distraction, a form of driver distraction that does not materialise in measurably unsafe driving behaviour, but that does impair being able to respond adequately to upcoming safety-critical situations. It proposes using one of the measurement tools for mental workload as an indication of latent driver distraction. It further raises the issue of evidence for increased mental workload being used often as a direct indication of all types of driver distraction. However, measurements should focus on the type of driver distraction that is measured, instead of translating an increase in one of the constructs into a supposed increase in the other construct. The relationship between mental workload and driver distraction is made explicit