When you read the motorcyclist safety research posted in this PERCEPTION section you will encounter many different related words.  To aid your understanding of what you read we have developed a definitions of terms document that we recommend reviewing prior to reading the posted research.

The usual dictionary definitions of perception include:      The ability to see, hear, or become aware of something through the senses such as  “The normal limits to human perception” and  the state of being or process of becoming aware of something through the senses such as  “The perception of pain.”

A few similar words include: discernment, appreciation, recognition, realization, cognizance, awareness, consciousness, knowledge, acknowledgment, grasp, and understanding.

An additional part of the definition of perception includes:  A way of regarding, understanding, or interpreting something; a mental impression such as “Hollywood’s perception of the tastes of the American public” and  intuitive understanding and insight such as “He wouldn’t have accepted,” said my mother  with unusual perception”

A few similar words include: insight, perceptiveness, keenness, sharpness, sharp-wittedness, intelligence, intuition, cleverness, astuteness, shrewdness and thoughtfulness

It is clear the definition of perception includes both ability or process and a state of being.  In more simple terms perception is the process of getting, interpreting, selecting, and organizing sensory information.  It includes the collection of data from sense organs through to the interpretation made by the brain.  Perception is a lot more than just “information coming in.”

Humans get (perceive) the incoming information through the use of the five senses; touch, sight, taste smell and sound.  Perception also refers to the way the incoming sensory information is organized, interpreted, and consciously experienced.

Our perception affects our responses because we respond to stimuli differently based on how we perceive them. And how we perceive and respond to things is influenced by heredity, needs, peer group, interests, and expectations.

Most motorcycle riders have heard the expression “Safe riding is a skill more of the eyes and mind (mental) than the hands and feet (physical).”  This expression places the focus of safe riding on visual perception and cognition as compared to physical skills such as shifting, turning and stopping.

Visual perception may be defined as seeing and understanding accurately. For practical purposes, it is visually identifying clues in traffic that could affect speed, lane position or path of travel (Ochs, Buche 2010)

Cognition refers to the way in which we deal with information. Whereas visual perception refers to a way of obtaining information from our environment; cognition describes processes such as remembering, learning, solving problems and orientation.  The phrase hazard perception combines the obtaining of the information and the processing of the information.  Hazard perception is accurately recognizing and predicting the behavior of other road users, recognizing road-based hazards and how to select and implement the most appropriate response.

Perception in all its various definitions is obviously a critical topic in motorcyclist safety research.  On the physical incoming stimulus side it is mostly about visual perception.  On the cognitive side our higher-order brain/mind processes such as goal setting, planning, organizing, prioritizing, initiating, shifting and self-monitoring play a critical role.  These are the executive function processes involved in controlling behavior and reading a person for situations (Meltzer, 2007)

A key point to understand is the human eyes and brain is not the equivalent of the lens of a camera.  The common sense argument that “if it is visible, we will see it if we look hard enough” simply isn’t true.  The Four Chances for Error is an excellent article that describes the four chances for error and the research based perception  phenomena associated with the Looked But Failed to See (LBFTS) Right-of-way Violation (ROWV) motorcyclist/car collision scenario.  Recommended actions for both riders and drivers that will lessen the chance of these types of collision occurring are included.

Gaining a Background

In addition to reviewing the definitions of terms we have listed below three articles and a video that provide excellent background regarding the complicated subject of perception and motorcycle rider safety.   There are also connections between the research we have posted here under the heading PERCEPTION and the research posted in CONSPICUITY . 

These are external links so don’t forget to come back.

2019 – To Pay Attention, the Brain uses Filters, Not a Spotlight, Jordana Cepelewiez, 9-24

2018 – Invisibility Training for Motorcyclist

2016 – Vision and Motorcycling, Sandeep Goswami

2010 – Preparing Rider to S.E.E. Better: MSF Tools for Improving Hazard Perception,  Ray Ochs and Tim Buche, Motorcycle Safety Foundation

2022 – Inattentional Blindness video. This video was developed by the Michigan Department of State for driver education instructors for viewing by driver education students. The content of the video is based on a traffic search procedure developed by SMARTER which in turn is based on the perception research. The search procedure provides a specific process for looking for and identifying vulnerable road users, specifically motorcyclists.


Meltzer, Lynn (Editor) Executive function in education: From theory to practice. New York:  The Guilford Press, 2007

Ochs, R., Buche, T., Preparing Riders to S.E.E. Better: MSF Tools for Improving hazard Perception. Paper presented in support of the Vulnerable Road users Conference in Jerusalem, 2010.

Perception Studies

2021 – “The Science of Being Seen”

This is a SMARTER edited version of an 85 page review of the literature written by Kevin Williams on the subject of the motorcyclist/car crash scenario where the car driver violates the right-of-way of the motorcyclist.  In the U. S. this crash scenario is often called a Looked But Failed to See (LBFTS) crash. In the U.K, Australia, and New Zealand this scenario is called the SMIDSY crash for Sorry Mate, I Didn’t See You.  The research reviewed dispels the common assumption that car drivers simply don’t look or don’t look hard enough for motorcyclists and helps us understand why common countermeasures such as efforts to increase motorcyclist/motorcycle conspicuity and motorist awareness campaigns have not demonstrated effectiveness. The Science of Being Seen Key Points without references and explanation.

2020 – “Recording and Evaluating Motorcyclists’ Gaze Behaviour in Rural Roads”

The present study deals with motorcycle riders’ gaze behaviour due to out of the vehicle sources of distraction. The most generic conclusion of the analysis is that both at urban and suburban environment exist too many elements that attract the attention of the driver. Average distraction times differ among drivers but every one of them is being distracted for unsafe periods – more than 1 sec at suburban environments and more than 1.2 seconds for urban environments. These distractions last enough to create the circumstances for an accident to take place.  

2019 – “The ‘Saw but Forgot’ Error: A Role for Short-term Memory Failures in Understanding Junction Crashes?”

Here we show from a series of three experiments in a high-fidelity driving simulator, that when drivers’ visual attention towards and memory for approaching vehicles is experimentally tested, drivers fail to report approaching motorcycles on between 13% and 18% of occasions. These failures in reporting a critical vehicle were not associated with how long the driver looked at the vehicle for, but were associated with drivers’ subsequent visual search and the time that elapsed between fixating on the oncoming vehicle and pulling out of the junction. Here, we raise the possibility that interference in short-term memory might prevent drivers holding important visual information during these complex manoeuvres. This explanation suggests that some junction crashes on real roads that have been attributed to LBFTS errors may have been misclassified and might instead be the result of ‘Saw but Forgot’ (SBF) errors.  

2019 – “Dual-target Hazard Perception: Could Identifying One Hazard Hinder a Driver’s Capacity to Find a Second?”

Low-level cognitive processes like visual search are crucial for hazard detection. In dual-target searches, subsequent search misses (SSMs) are known to occur when the identification of one target impedes detection of another that is concurrently presented. Implications of SSMs in understanding the causes of some crashes are discussed, as well as future directions to improve ecological and criterion validity and to explore the roles of expertise and cognitive capabilities in multi-hazard detection.

2018 – “Why Do Drivers Pull Out In Front Of Motorcyclists?”

  This is an excellent current comprehensive review of the literature regarding the title topic.  The review is written March 5, 2018 by Nathan Rose, Director and Principal of Kineticorp, LLC., (303)733-1888, (720)839-1995,, Note:  SMARTER is providing this contact information as a thank you for the permission to post this article and no endorsement of the LLC or its staff should be implied.

2018 – “Allocating Attention to Detect Motorcycles – The Role of Inattentional Blindness

This research concludes inattentional blindness (IB) provides a good psychological framework for understanding looked-but-failed-to-see crashes that occur with motorcycles.  

2018 – “Meaning Guides Attention in Real-world Scene Images: Evidence from Eye Movements and Meaning Maps”

These researchers compared the influence of meaning and of salience on attentional guidance in scene images. The results showed that both meaning and image salience predicted the duration-weighted distribution of attention, but that when the correlation between meaning and salience was statistically controlled, meaning accounted for unique variance in attention whereas salience did not. The results strongly suggest that meaning guides attention in real-world scenes. The authors discuss the results from the perspective of a cognitive-relevance theory of attentional guidance.  The authors provide a review of their research approach here:

2017 – “Comparison of Glancing Behaviors of Riders and Drivers at Unsignalized Intersections Involving Right Turns”

This research was presented at the Ninth International Driving Symposium on Human Factors in Driver Assessment, Training and Vehicle Design and compares the scanning behaviors of  a ‘driver-rider’ group and ‘driver-only’ group. The results showed that driver-rider made significantly more glances to the left when riding compared when driving after the intersection than before, while they made more glances to the right after the entry than before the intersection. Accordingly, there is some potential for the development of training programs targeted at improving driver and rider behaviors.

2017 – “Interactions between Cars and Motorcycles: Testing Underlying Concepts through Integration of On-Road and Simulator Studies”

The first study revealed that motorcyclists’ SA comprises more elements than for car drivers, and strong themes emerged around motorcyclists checking for surrounding traffic and hazards. In study 2 an effect of prevalence on the time taken to detect targets was found, with drivers able to detect high-prevalence targets from significantly farther away than low-prevalence targets. The results show that drivers’ difficulty in perceiving motorcyclists is partially due to the fact that motorcycles are relatively rare on Australian roads and consequently drivers do not expect to see them.  Given that artificially increasing the prevalence of motorcycles on the roads is not a practical solution, in future research it would be worthwhile exploring other methods of eradicating prevalence effects.

2016 – “Size Speed Bias or Size Arrival Effect – How Judgments of Vehicles’ Approach Speed and Time to Arrival are Influenced by the Vehicles’ Size”

When asked to judge the time it takes an approaching object to arrive at a predefined position (time to arrival, TTA), observers tend to provide lower estimates for larger objects. In that case, road users' crossing decisions when confronted with larger vehicles should be rather conservative, which has been confirmed in multiple studies on gap acceptance. The aim of the experiment reported in this paper was to clarify the relationship between size speed bias and size arrival effect.  

2016 – “Long-lasting Virtual Motorcycle-riding Trainer Effectiveness”

This work aimed to test the long-lasting effects of learning acquired with a virtual motorcycle-riding trainer as a tool to improve hazard perception. Virtual training was found to be highly effective and long lasting.  This result should be compared to the mixed effectiveness found for traditional hands-on physical skills training.

2016 – “Perceptual Load Induces Inattentional Blindness in Drivers”

Perceptual load theory states that the level of perceptual load in a task predicts the processing of task‐irrelevant information. High perceptual load has been shown to result in increased inattentional blindness; however, there is little evidence that this extends beyond artificial computer‐based tasks to real‐world behavior. This study is the first to demonstrate perceptual load effects on awareness in an applied setting and has important implications for road safety and future applied research on the perceptual load model.  

2016 – “Judging Arrival Times of Incoming Traffic Vehicles is not a Prerequisite for Safely Crossing an Intersection: Differential Effects of Vehicle Size and Type in Passive Judgment and Active Driving Tasks”

  This research assessed the influences of actual arrival times (AT) as well as the size and the type of approaching vehicle(s) on AT judgments.  Overall, the results obtained in the two experiments do not provide evidence in favor of reliance on a common perceptual substrate in the two tasks. Use of successive AT estimates in the no-offset conditions of the active intersection- crossing task should therefore have led our participants to increase their speed early on during the approach, when AT was largely underestimated, followed by a decrease in speed as actual AT decreased and estimates became more accurate. The results of the present study do not fit these predictions.

2014 – “Safety in Numbers: Target Prevalence Affects the Detection of Vehicles during Simulated Driving”

The “low-prevalence effect” refers to the fact that observers often fail to detect rare targets (<5 % prevalence) during visual search tasks. Previous research has demonstrated robust prevalence effects in real-world tasks that employ static images, such as airport luggage screening. No published research has examined prevalence effects in dynamic tasks, such as driving. Overall, the results support the notion that increasing the prevalence of visual search targets makes them more salient, and consequently easier to detect.

2013 – “The Effect of Sight Distance Training on the Visual Scanning of Motorcycle Riders: A Preliminary Look”

This study collected naturalistic data from a mix of novice and experienced motorcycle riders on a closed course and an open course. A custom data acquisition system was developed that monitored the motorcycle rider’s head motions, visual behavior, motorcycle speed, GPS location, and motorcycle pitch, yaw, and roll. The preliminary findings suggest that there may be a relationship between training, experience, and visual behavior among motorcycle riders. It is feasible to collect naturalistic eye tracking data from motorcycle riders of varying experience levels using their own vehicles. Technical challenges of collecting data with this new technology are also discussed.  

2013 – “Motorcycling Experience and Hazard Perception”

Sixty-one motorcyclists, split across three groups (novice, experienced and advanced riders) were tested on a hazard perception test containing video clips filmed from the perspective of a motorcyclist.  The results demonstrate a link between advanced training and motorcycling hazard perception skill, but raise important concerns about the effects of mere experience on rider safety. This challenges previous conceptions that simply extrapolated from our understanding of the hazard perception skills of car drivers to this particularly vulnerable group of road users.  

2013 – “Effects of Size on Collision Perception and Implications for Perceptual Theory and Transportation Safety”

The size-arrival effect potentially can lead drivers to misjudge when a vehicle would arrive at an intersection and is considered a contributing factor in motorcycle accidents. In this article, the author reviews research on the size-arrival effect and its theoretical and practical implications.  

2013 – “Comparing the Glance Patterns of Older versus Younger Experienced Drivers: Scanning for Hazards while Approaching and Entering the Intersection”

This study attempts evaluated four hypotheses that attempt to explain the older drivers’ failure to properly scan in intersections: difficulty with head movements, decreases in working memory capacity, increased distractibility, and failure to recall specific scanning patterns. Our results suggest that none of these hypotheses can fully explain our finding that older adults are more likely to remain fixated on their intended path of travel and look less than younger drivers towards other areas where likely hazards might materialize.  

2013 – “Effects of Size on Collision Perception and Implications for Perceptual Theory and Transportation Safety”

One would expect people to rely on invariants rather than depth cues, but the size-arrival effect shows the contrary: People reported that a large far approaching object would hit them sooner than a small near object that would have hit first. This effect of size on collision perception violates theories of time-to-collision perception based solely on the invariant tau and suggests that perception is based on multiple information sources, including heuristics. The size-arrival effect potentially can lead drivers to misjudge when a vehicle would arrive at an intersection and is considered a contributing factor in motorcycle right-of-way violation crashes.  

2012 – “Training and Licensing Interventions for Risk Taking and Hazard Perception for Motorcyclists”

The Centre for Accident Research & Road Safety – Queensland.  This report identifies potential licensing components that will reduce the incidence of risky riding and improve higher-order cognitive skills in new riders. Collectively, the research findings indicate that evidence for the effectiveness of existing programs is sparse and implementation of interventions in licensing processes face several practical constraints. It was concluded that the process of addressing risk taking and hazard perception is qualitatively different to traditional rider training programs that focus on skill development for licensing purposes. The success of interventions to address risk taking and hazard perception within the licensing process is reliant not only upon program content, but also the teaching skills and support of instructors for face-to-face programs.

2012 – “Towards a Conceptual Model of Motorcyclists’ Risk Awareness: a comparative study of riding experience effect on hazard detection and situational criticality assessment”

This research investigates risk awareness abilities among different populations of motorcyclists. Risk awareness is defined here as an extension of the Situational Awareness theory applied to critical driving situations. This study is more particularly focused on two main cognitive abilities supporting risk awareness: hazard detection, corresponding to riders' skill to perceive critical event occurring in the road environment and to identify it as a threat, and situational criticality assessment, corresponding to a subjective assessment of the accident risk.  

2012 – “Some Hazards are More Attractive than Others – Drivers of Varying Experience Respond Differently to Different Types of Hazard”

The ability to detect hazards in video clips of driving has been inconsistently linked to driving experience and skill. One potential reason for the lack of consistency is the failure to understand the structural differences between those hazards that discriminate between safe and unsafe drivers, and those that do not. The current study used a car simulator to test drivers of differing levels of experience on approach to a series of hazards that were categorized a priori according to their underlying structure.

2012 – “Judgments of Approach Speed for Motorcycles across Different Lighting Levels and the Effect of an Improved Tri-headlight Configuration”

Incorporation of a tri-headlight formation onto the standard motorcycle frame resulted in improved accuracy of approach speed judgments, relative to the solo headlight motorcycle, as ambient light levels reduced.  

2012 – “Hazard Recognition Training Programs and Their Relationship to Executive Functions in Motorcyclists”

This is an abstract of a conference paper with similar content as 2010 – “Preparing Riders to S.E.E. Better: MSF Tools for Improving Hazard Perception.” The purpose of the paper is to illustrate how hazard recognition training can transcend perceptual processes by appealing to a rider’s executive functions, which refers to mindfulness associated with keeping safety a priority function of the riding task.

2011 – “A Comparison of the Hazard Perception Ability of Accident-involved and Accident-free Motorcycle Riders”

  This is an abstract of the report.  The results showed that both the divided and selective attention of accident-involved motorcycle riders were significantly inferior to those of accident-free motorcycle riders, and that accident-involved riders exhibited significantly higher driving violation behaviors and took longer to identify hazardous situations compared to their accident-free counterparts.  The results showed that an aggressive driving violation score significantly predicted both hazard perception and accident involvement of motorcycle riders. The most plausible explanation for the differences between them is their driving style (influenced by an undesirable driving attitude), rather than skill deficits per se.  

2011 – “Decisions about Objects in Real-World Scenes Are Influenced by Visual Saliency Before and During Their Inspection”

Evidence from eye-tracking experiments has provided mixed support for saliency map models of inspection, with the task set for the viewer accounting for some of the discrepancies between predictions and observations.  The saliency of a critical vehicle was varied in the present task, as was the type of vehicle and the preferred vehicle of the viewer. Decisions were influenced by saliency, with more risky decisions when low saliency motorcycles were present. Given that the vehicles were invariably inspected, this may relate to the high incidence of "looked-but-failed-to-see" crashes involving motorcycles and to prevalence effects in visual search.  

2010 – “The Visual Search Patterns and Hazard Responses of Experienced and Inexperienced Motorcycle Riders”

This is an abstract of the research in which an open-loop motorcycle simulator was used to examine the effects of motorcycle riding and car driving experience on hazard perception and visual scanning patterns. The results point to the potential benefit of training hazard perception and visual scanning in motorcycle riders, as has been successfully demonstrated in previous studies with car drivers.  

2010 – “Preparing Riders to S.E.E. Better: MSF Tools for Improving Hazard Perception”

This paper was presented in support of the Vulnerable Road Users Conference and provides the background for the Motorcycle Safety Foundations developed programs in hazard perception.  A unique aspect explored in this paper is the concept that hazard perception training should not only assist riders in developing their hazard perception skills, but to transcend the straightforward practice of hazard identification by expanding learning activities to address the human visual characteristics as well as executive functions. The idea of giving riders an awareness of the importance of executive functions like attention, prioritizing and strategizing would mean more meaningful hazard perception training.  Preparing Riders to SEE Better Presentation - PowerPoint

2008 – “Hazard Perception and Responding by Experienced and Inexperienced Motorcyclists”

This is the third connected research report posted here:  2004 literature review, 2006 comparison of car drivers and motorcyclists and this analysis of experienced and inexperienced riders.  The overall aim of the present project was to identify the fundamental skills that are required for expert hazard perception in motorcycle riding. In general, experienced riders were found to have better and faster hazard identification.  However while the authors found interesting preliminary results, they report the belief that considerably more research is needed in this area. Perhaps one of the more important outcomes from this research is the valuable insights gained regarding the requirements for a simulation facility to better support the conduct of motorcycle safety research.

2006 – “A Comparison of Hazard Perception and Responding in Car Drivers and Motorcyclists”

Poor hazard perception skills have been shown to contribute to novice driver crash involvement. Yet driving and riding differ in terms of hazards, responses and consequences and many novice motorcyclists are experienced drivers. This paper follows the 2004 literature review “Hazard Perception, Attitudes and Behaviors in Riding” and presents results from the first stage of a program of research to develop hazard perception training for motorcyclists. It is possible that the need for improved hazard perception and responding skills is not limited to riders entering the license process but may apply to many fully licensed riders (particularly returning riders) and how this could be done.   A Comparison of Hazard Perception and Responding in Car Drivers and Motorcyclist -Slides

2006 – “Investigation into ‘A’ Pillar Obscuration – A Study to Quantify the Problem Using Real World Data”

The scope of this study was to assess if there is a problem caused by car ‘A’ pillar obscuration in the real world and, if so, to start to quantify the size of that problem. This was achieved by using real world crash data to construct 3-D visualizations that would provide a graphical illustration of the obscuration caused by the car ‘A’ pillar. The report found there is not enough evidence at this stage to suggest changes to the current legislation. However, the EC legislation currently assesses cars based on a 50th percentile male and the visualizations have suggested consideration could be given to smaller and larger drivers. The study recommends that further work.

2005 – “Motorcycle Accident Risk Could Be Inflated by a Time to Arrival Illusion”

Drivers adopt smaller safety margins when pulling out in front of motorcycles compared with cars. This could partly account for why the most common motorcycle/car accident involves a car violating a motorcyclist’s right of way. One possible explanation is the size–arrival effect in which smaller objects are perceived to arrive later than larger objects. That is, drivers may estimate the time to arrival of motorcycles to be later than cars because motorcycles are smaller.

2005 – “Motorcycle Accident Risk Could Be Inflated by a Time to Arrival Illusion

This is an abstract of the research report. Drivers adopt smaller safety margins when pulling out in front of motorcycles compared with cars. This could partly account for why the most common motorcycle/car accident involves a car violating a motorcyclist’s right of way. This research investigates possible reasons for this error in judgment.  The authors conclude drivers estimate motorcycles will reach them later than cars across a range of conditions.  

2005 – “Hazard Perception and Responding by Motorcyclists: Background and Literature Review”

This project is the first stage of a larger program of research into hazard perception training for motorcyclists. Future stages of the project will investigate what type of environment can be used to teach hazard perception and responding, for example a simulator environment or combination of off-road and simulator training. This report summarizes the research that has been conducted into hazard perception and responding, assesses what can be learnt from motorcycle crash data and describes current motorcycle simulators.

2005 – “Best Training Methods for Teaching Hazard Perception and Responding by Motorcyclists”

The research suggests that simulators are best used as part of a comprehensive rider education system that includes classroom training and skills practice using real vehicles, with simulators being used to training riders in situations that are too dangerous to practice using a real vehicle. The cost of sufficient access to simulators may prevent this approach from being applied to the general motorcycle rider LEARNER population. However, simulators may be cost-effective for training particular groups, such as individuals with high accident rates or professional riders. In the short-term, simulators may provide a useful tool for conducting research into hazard perception and responding by riders.  

2004 – “Hazard Perception, Attitudes and Behaviors in Riding – Literature Review”

Motorcycle riders are subject to specific hazards in addition to those that they have in common with car drivers.  Riders’ evaluation of level of risk also needs to take account of the different performance characteristics of a motorcycle compared with a car and the lower levels of injury protection.  As the title indicates this report is a review of the literature available to the authors prior to 2004.    

2003 – “A Behavioral Comparison between Motorcyclists and a Matched Group of Non-motorcycling Car Drivers: Factors Influencing Accident Risk”

This is an abstract of the research.  Motorcyclists and a matched group of non-motorcycling car drivers were assessed on behavioral measures known to relate to accident involvement. The authors found that motorcyclists chose faster speeds than the car drivers, overtook more, and pulled into smaller gaps in traffic, though they did not travel any closer to the vehicle in front.  However, the authors suggest that the increased risk-taking behavior of motorcyclists was only likely to account for a small proportion of the difference in accident risk between motorcyclists and car drivers.  

2000 – “Hazard Perception by Inexperienced Motorcyclists”

This project by Monash University Accident Research Centre had two aims: (1) to investigate how hazard perception and responding is affected by level of experience as a motorcycle rider and (2) to assess the extent to which hazard perception and responding can be improved by specific training. This report presents the results of a literature review and re-examination of crash data as the first stages of an examination of the role of hazard perception in motorcycle safety. Based on the results of these first two stages, recommendations will be made about future directions for hazard perception training and testing of motorcyclists.

1997 – “To See or Not to See: The Need for Attention to Perceive Changes in Scenes”

This research shows that identification of changes in scenes (change blindness) becomes extremely difficult, even when changes are large and made repeatedly but with cues or when the changes are considered important they are identified much faster. These results support the idea that observers never form a complete, detailed representation of their surroundings. In addition, the results indicate that attention is required to perceive change, and that in the absence of localized motion signals, attention is guided on the basis of high-level interest.

1994 – “The Perception of Arrival Time for Different Vehicles at Intersections”

This is early research examining the factors related to decisions by drivers to make a left turn.  The perceptual information to turn left appears from this research to be related to (a) the relative size of the vehicle; (b) the visibility of other vehicles; (c) the relative paths of other vehicles; (d) whether a vehicle is approaching, stopped, or receding from an intersection; (e) the necessity for action by the driver; and (f) whether the driver is in motion or stopped.  This report is extensively referenced and provides an excellent review of relevant research published prior to 1994.