moment it moves away from it. This includes the transition time to that target number of glances 4.2.2 time interval consisting of two or more glances that are linked in a consecutive set of fixations to areas of interest in the visual scene mean glance duration 4.2.4 mean duration of all glance durations to an area of interest (or set of related of Interest) during a condition, task, subtask or sub-subtask maximum glance duration 4.2.7 mean duration of all glance durations to an area of interest (or set of related of Interest) during a condition, task, subtask or sub-subtask total eyes off the road time summation of all glance durations to areas of interest other than the road scene ahead during a condition, task, subtask or sub-subtask
medical products than say motor vehicles), and the user group (e.g., the standard of care is greater for children and babies because they are unable to protect themselves). What is the burden of proof? This topic is also addressed in detail by Green (2002). There may be legal precedents for the burden of proof required · Beyond any shadow of a · Beyond a reasonable doubt · The preponderance of evidence · The balance of the evidence · The most probable outcome · There is a reasonable chance · The possibility exists This too is a question for which there are often very different perspectives, with the pro-safety folks arguing for safety measures to be put in place when there is some evidence of risk. Others will argue against safety measures until enough people die and there is compelling evidence of a safety problem, sometimes referred to as a tombstone count. What Kinds of Data Can Be Used to Address the Main Question? The answer to the too long question depends on the measurement category used to answer the question and the method by which the data is collected. The measurement categories included crashes and near crashes, a close surrogate measure, driver performance, and driver comfortable (Table 4). Table 4. Methods and Measurement Categories. Measurement category Natural/uncontrolled Controlled (driving, task, both) occlusion, look away, driving experiment control vision or task or both Simulated/ estimated Crashes (& near) Re-analysis of FOT data (e.g., 100 car) How often do crashes occur as a function of glance characteristics? How many crashes or near crashes occurred in a simulation as a function of secondary task characteristics? How many crashes for various simulations of how people look and look away (scenario dependent)
For large commercial vehicles, the National Safety Council now recommends a minimum 6-s following distance under ideal conditions, in contrast to a 4-second rule used in the past (National Safety Council, 2012). These rules make good sense as guidance. However, it is unknown how effective they are in heavy traffic, where cut-ins occur when gaps between vehicles are large. Cut-ins are important because they can be crash inducing events. One use the 2 and 3 second rules as a basis for determining how long it is safe to look away from the road. Rockwell’s 2-Second Rule (1988) Rockwell (Rockwell, 1988) studied driver "in car" visual performance in 3 different experiments over a 6-year period involving 106 subjects participating in 200 test sessions. The sample was even divided between younger (less then 35 years old) and “mature” subjects (over age 45). Data were collected on expressways in light to moderate traffic. Many of the studies involved glances to “stereos,” AM/FM radios that were being sold in the 1980s, as well as glances to mirrors (Figures 7 and 8). Note that the mean duration for glances to the mirror was 1.1 s, vs. 1.44 s to the radio, with the standard deviation of glances to the radio being much larger. Mirror glance durations varied with the purpose of the glance (simple detection vs. traffic checks) and glances durations to the radio varied with the task and the design of the radio. The radio glance distribution appears to be log normal. Interestingly, the differences in radio glance durations between studies were not significant. Table ** shows some of these details and percentiles of interest. Figure 7. Distribution of Glance Durations Source: Rockwell, 1988, p. 321. Figure 8. Distribution of Left Mirror Glance Durations Source: Rockwell, 1988, p. 321. Table 5. Glance Statistics (s) from 3 Studies Source: Rockwell, 1988, p. 320. In discussion these data, Rockwell states the following, “For years researchers studying car following and eye movements have found a 2 second rule, i.e., drivers are loath to go without roadway information for more than 2 seconds (and rightly so)” (Rockwell, 1988, p. 322) which has led to what is known as “Rockwell’s Two-Second Rule.”