The Role of Human Factors and Nighttime Visibility in a Pedestrian Accident Reconstruction
Author’s note: this article is derived from the forthcoming book, Pedestrian Accident Reconstruction.
In analyzing or reconstructing a vehicle vs. pedestrian accident, some or all of the following questions may arise:
A qualified accident reconstructionist will be able to answer many of the above questions. However, questions may remain related to the visibility of pedestrians and the factors to be evaluated in assessing a driver’s ability to avoid a collision with a pedestrian. Often, pedestrian collisions will involve some level of limited visibility, either from geometric obstructions (a parked vehicle, for instance) or from low light or nighttime conditions. This article will provide a brief review of the analysis concepts and techniques used to address these situations.
During daylight conditions, evaluating a pedestrian’s visibility to a driver, or conversely, an approaching vehicle’s visibility to a pedestrian, is often a matter of pure geometric visibility. The analyst determines if physical objects were obstructing the view of either party and when those objects would have ceased to obstruct a view relative to when the collision occurred. This analysis is often independent of the distance separating one of the parties from the other, except for specific cases such as fog, dust, or smoke. Under night or low light conditions, however, the light that reaches a pedestrian and is reflected from the pedestrian to a driver may not be sufficient to make the pedestrian detectable to a driver. The distance from the driver to the pedestrian through time is relevant, and the lighting conditions must be considered in addition to geometry obstructions.
The visibility of a pedestrian at night for an approaching driver will be affected by the illumination from the vehicle’s headlamps, by streetlamps, by ambient lighting, by oncoming traffic, and by characteristics of the weather. Primarily, it is the luminance contrast between an object and its background that makes an object visible to an observer at night [1]. Luminance is the amount of light that is reflected off a surface, and the luminance contrast, or difference in luminance between two objects, is dependent on surface properties such as color and reflectivity, as well as the amount of illumination arriving at that surface by light sources. In reconstructing a nighttime crash, the analyst may need to evaluate the limits of visibility to determine the distance from which a pedestrian is visible.
Lighting Sources
Ambient Light
During daytime conditions on a roadway, the majority of illumination comes from natural lighting via the sun. As the sun sets, the lighting conditions change from daytime to twilight. Twilight refers to the period after sunset and before sunrise during which the atmosphere is partially illuminated by the sun. Early astronomers defined civil twilight as the time period after sunset or before sunrise when normal outdoor activities could be conducted without artificial illumination. Civil twilight is currently defined as the period of time when the sun is from 0º to 6º below the horizon. Civil twilight occurs in the evening after sunset (civil dusk) as the sun descends from the horizon to 6º below the horizon, and in the morning before sunrise (civil dawn) as the sun ascends from 6º below the horizon to the horizon. Similarly, nautical twilight refers to the period when the geometric center of the sun is between 6º and 12º below the horizon, and astronomical twilight refers to the period when the sun is between 12º and 18º below the horizon. The diagram in Figure 1 depicts these phases.
Figure 1 - Twilight Phases
The reconstructionist may be interested in evaluating the ambient lighting that was present during a crash. This necessarily involves an accurate assessment of the time at which the crash occurred. Police records, fire records, dispatch records, and timestamped videos may all give an indication as to the time of the crash. The sun’s illumination changes most rapidly during civil twilight and civil dawn, so the sun’s illumination during these phases will be particularly sensitive to the determined time of the accident.
Often, a site inspection or study at a time with similar ambient lighting conditions is desired. The use of a sun calculator will inform the analyst of the altitude and azimuth of the sun at a given location and at a given time. One such calculator is on the website suncalc.org. Adequate matches of the solar altitude and azimuth can be achieved around the anniversary date of the crash, as well as on days equidistant from the summer solstice (June 20 or 21) and winter solstice (December 20 or 21).
Auxiliary Lighting Sources
In addition to lighting from the sun, a crash scene may be illuminated by nearby light sources, such as overhead lights, illuminated signs, or lights from nearby buildings. These auxiliary light sources can be documented and accounted for in an accident reconstruction. Often, photographs taken near the time of the accident will document these additional lighting sources. When evaluating external lighting sources, take note of which lighting sources were activated at the time of the crash. Lamps will sometimes burn out between the time of the accident and the time of a site inspection; or, they will have been burnt out at the time of the crash and replaced by the time of the inspection. Take note of the type of light as well. Prior to the prominence of LED lighting, many overhead streetlights were sodium vapor lights. Many municipalities are now transitioning from sodium vapor streetlights to LED lighting, given the energy efficiency improvements of LED lighting systems. A situation may arise where the accident occurred under sodium vapor streetlights and at the time of the inspection those lights have been upgraded to LED lighting. The two lighting types are usually distinguishable by the color temperature of the lights. Sodium vapor lighting has a warm yellow color, whereas LED lighting has a whiter or bluer appearance.
Vehicle Headlamps
The primary source of illumination in a nighttime pedestrian crash is often the headlamps of a driven vehicle. Thus, an understanding of vehicle headlamp illumination patterns is useful to a nighttime pedestrian accident reconstruction. As a vehicle approaches, the headlamps will illuminate the pedestrian to provide contrast to the driver between the pedestrian and the background. Each headlamp model has a unique beam pattern. Generic headlight models have been proposed [2], or for greater fidelity the accident reconstructionist may choose to measure the headlight beam pattern of the subject vehicle or a suitable exemplar [3,4]. Figure 2 depicts the mapped illumination pattern at various levels for a 2015 GMC Savana 2500 from a top-down perspective. In this figure, the longitudinal and lateral distances from the front left corner of the vehicle are depicted on the horizontal and vertical axis, respectively, in feet.
Figure 2 – Headlamp Illumination Distribution
Assessing the Nighttime Visibility of Pedestrians
An accident reconstructionist is often tasked with evaluating when an attentive driver would have been able to detect the presence of a pedestrian. The likelihood a driver will detect a pedestrian is influenced by the contrast between the pedestrian and their surroundings. Contrast is defined as the amount of light (luminance) reflecting from a subject compared to the luminance of the area surrounding that subject. In some situations, vehicle headlights or other lighting sources will illuminate a subject so that it is brighter than its background, which is known as positive contrast. An example of positive contrast is depicted in Figure 3. Other times, the background of the subject will appear brighter than the subject itself, which is known as negative contrast. An example of negative contrast is depicted in Figure 4. Negative contrast may occur when a pedestrian crosses in front of the headlights of a vehicle.
Figure 3 – Pedestrians Crossing a Roadway: Positive Contrast
Figure 4 – Pedestrians Crossing a Roadway: Negative Contrast
Researchers have proposed models to evaluate object visibility under nighttime conditions. One such model [2] evaluates the time at which a pedestrian is subject to a specific level of illuminance from vehicle headlights. This threshold illumination level in the model is based on the shade of clothing that the pedestrian is wearing. The model further correlates headlight illumination with driver response distances. The model necessarily requires two elements – an estimate of headlight illuminance as a function of the pedestrian location relative to the vehicle, and an estimate of when drivers tend to respond to pedestrians based on the reflectance of the pedestrian and their clothing. In this model, headlight illumination levels can be estimated from generic models or measured through mapping of the subject vehicle or suitable exemplar.
To correlate headlight illumination levels to driver response distances, the authors analyzed the results of previous nighttime driver response distance experiments and determined a threshold value for headlight illuminance. The authors noted that the shade of clothing had a significant influence on a driver’s detection distance. Combining a headlight model that is dependent on vehicle characteristics and a recognition model that accounts for pedestrian clothing shade and driver responses allows for a reconstructionist to estimate when a driver would be expected to react to a pedestrian in a path intrusion scenario. These models are incorporated into a widely utilized software package called Response [5].
Nighttime or Low-Light Studies
When practical for a nighttime pedestrian collision reconstruction, it may be valuable to perform a site visit and a nighttime study to evaluate the site-specific lighting conditions. Under equivalent ambient light, observations on lighting conditions can be recorded. These are often in the form of observations of objects that are visible from a viewpoint of interest that corresponds to a relevant moment prior to the collision. For instance, a position where a driver would have needed to detect the pedestrian in order to avoid the impact. From this position, observations can be made on the illumination in the area where the pedestrian would have been at that time. These observations can include luminance or illuminance measurements, photographs, and/or video.
Calibrated vs. Uncalibrated Photographs and Video
Sometimes, a photograph taken just after a crash will be used to illustrate “how dark it was” at the time of the accident or alternatively how “visible” an object or pedestrian was. This is likely to be inherently flawed. In taking the photograph, investigators or witnesses will most likely have their camera (or phone with integrated camera) set to an “auto” mode that will adjust exposure setting to minimize the portions of the photograph that are underexposed or overexposed. In doing so, the camera inaccurately depicts the actual lighting conditions at the scene. When an accident reconstructionist wishes to accurately portray the lighting conditions taken during a low-light or night-time study, a procedure is needed to verify that objects of interest that are visible during the study are visible in the photograph or video, and likewise, objects of interest that are not visible during the study are not visible in the photograph or video. Such a process is referred to photograph calibration or video calibration.
To create calibrated photographs or video, the analyst makes observations and/or measurements of relevant objects at a nighttime study. At the study, photographs and/or video are taken in a way that emulates the observed lighting conditions while also allowing for adjustments after the study. Then, adjustments are made to the raw media and or display medium to reasonably match the relevant observations and measurements. When displaying calibrated digital media, the use of an Organic Light Emitting Diode (OLED) screen may be useful. OLED screens have an advantage over traditional LED or LCD screens in that they do not require a backlight source to display. Therefore, dark areas of the media can be displayed much darker on an OLED screen than on a backlight screen. This technology works particularly well for displaying accurate calibrated images.
Case Study #1 – Night Pedestrian Accident with Unknown Impact Location
A collision involving a Ford SUV and a pedestrian under nighttime conditions was reconstructed. The traffic accident report indicated that the Ford SUV was driving southbound and the pedestrian was crossing the roadway from west to east in an area that was not near an intersection. The roadway was dry, and the surrounding area was unlit. The Ford was traveling in the leftmost southbound lane prior to the impact. The Ford driver stated that there were no streetlights or crosswalks in the area of the impact, his headlights were on, and he saw a black silhouette just prior to impacting the pedestrian.
Law enforcement officers documented the physical evidence and rest positions with photographs, marked evidence with paint, took measurements, and mapped the evidence and roadway geometry with a total station. The photographs in Figure 6 are a sampling of the photographs taken by law enforcement.
Figure 6 – Photographs of Physical Evidence
As part of the reconstruction, the subject Ford and the area of the crash were inspected, photographed, and digitally mapped using a laser scanner and a drone. The photographs taken at the scene were analyzed and the scaled diagram in Figure 7 was created. This diagram depicts the police paint, the Ford’s rest position, and the pedestrian rest position. There was no documented physical evidence to indicate the precise position on the roadway where the impact occurred, so a reconstruction was performed that determined that the impact occurred between 80 and 128 feet from the pedestrian’s point of rest, and that the Ford was traveling between 31 and 43 mph at impact.
Figure 7 – Evidence Diagram
To evaluate the distance at which the pedestrian would have been detectable to the driver of the Ford, a nighttime visibility study was performed at the crash site. During this study, the travel lanes were closed, and a surrogate pedestrian stood at the approximate location of the impact. The surrogate pedestrian was of similar height to the subject pedestrian and was dressed in similar clothing. A Sony A7S II camera was mounted to the interior windshield of the subject vehicle. A nighttime scene equivalent contrast gradient panel was utilized at the scene to make contrast and lighting observations. The subject Ford was positioned at various locations along the roadway and the visibility of the surrogate was evaluated and documented photographically at each location. At a distance of 50 feet, the pedestrian shoes and jeans were clearly visible, as was the bottom portion of the pedestrian’s jacket. At a distance of 100 feet, the pedestrian jeans and shoes were visible. At a distance of 150 feet, portions of the jeans were barely visible, and at distances of 200 feet and beyond, no portion of the surrogate pedestrian was visible. Figures 8 through 11 depict photographs taken at 50 feet, 100 feet, 150 feet, and 200 feet, respectively. These photographs were calibrated to give a fair and reasonable depiction when viewed on a specific monitor with documented settings. However, these images may not provide accurate depictions of the view when viewed in print or on other monitors.
After the visibility study, the degree to which the involved parties could have avoided the crash was analyzed. It was determined that the 85th percentile perception response time for drivers in a situation similar to the Ford driver would be 2.5 seconds. In other words, 85% of drivers would respond in 2.5 seconds or less. In those 2.5 seconds, the Ford would travel between 145 and 159 feet. Further, it would take between 68 and 78 feet of braking to bring the Ford to a stop. The total stopping distance, therefore would be between 213 and 237 feet. This indicates that, in order to brake to a stop and avoid the impact, the driver of the Ford would have had to begin detecting and reacting to the pedestrian at a time when the pedestrian would not have been visible, and thus, the driver of the Ford could not have avoided this collision.
Figure 8 – Photograph of Surrogate Taken at 50 feet from Impact Location
Figure 9 - Photograph of Surrogate Taken at 100 feet from Impact Location
Figure 10 – Photograph of Surrogate Taken at 150 feet from Impact Location
Figure 11 – Photograph of Surrogate Taken at 200 feet from Impact Location
During the visibility study, it was also documented that headlights of approaching southbound vehicles were visible when the vehicles were well north of the impact location. It was determined that a vehicle traveling at the speed limit would be visible for at least 10 seconds. The pedestrian in this case would have had a clear view of the approaching vehicle for at least 10 seconds prior to the impact and thus would have had adequate visibility to avoid the accident by waiting for the Ford to pass.
References
Neal Carter is a Professional Engineer and Principal Accident Reconstructionist at Explico Engineering. Mr. Carter has expertise, experience, and training in accident reconstruction, with an emphasis in pedestrian accident reconstruction, forensic photography, and nighttime or low-light photographs and video. Mr. Carter has conducted testing involving vehicle dynamics and acceleration, nighttime visibility, on-vehicle data recorders, passenger vehicle braking, pedestrian impacts, and motorcycle dynamics, braking, and sliding deceleration. Mr. Carter also regularly publishes technical articles related to vehicular accident reconstruction. Mr. Carter has authored publications based on his testing that have been published by the Society of Automotive Engineers International Journal of Transportation Safety, in the Society of Automotive Engineers Technical Paper Series, in Collision: The International Compendium for Crash Research, in the Annals of Biomedical Engineering and in Electric Energy.
In analyzing or reconstructing a vehicle vs. pedestrian accident, some or all of the following questions may arise:
1) Where on the road did the collision occur?
2) What was the impact speed of the vehicle?
3) How fast was the pedestrian moving at the time of the collision? Were they walking or running?
4) Are the descriptions of the crash given by witnesses and involved parties accurate?
5) Were there visibility obstructions that contributed to the crash?
6) What actions would have been needed by the driver to avoid the pedestrian?
7) What could the pedestrian have done to avoid the collision?
8) At what time did the collision occur?
9) What were the lighting conditions at the time of the collision?
2) What was the impact speed of the vehicle?
3) How fast was the pedestrian moving at the time of the collision? Were they walking or running?
4) Are the descriptions of the crash given by witnesses and involved parties accurate?
5) Were there visibility obstructions that contributed to the crash?
6) What actions would have been needed by the driver to avoid the pedestrian?
7) What could the pedestrian have done to avoid the collision?
8) At what time did the collision occur?
9) What were the lighting conditions at the time of the collision?
A qualified accident reconstructionist will be able to answer many of the above questions. However, questions may remain related to the visibility of pedestrians and the factors to be evaluated in assessing a driver’s ability to avoid a collision with a pedestrian. Often, pedestrian collisions will involve some level of limited visibility, either from geometric obstructions (a parked vehicle, for instance) or from low light or nighttime conditions. This article will provide a brief review of the analysis concepts and techniques used to address these situations.
During daylight conditions, evaluating a pedestrian’s visibility to a driver, or conversely, an approaching vehicle’s visibility to a pedestrian, is often a matter of pure geometric visibility. The analyst determines if physical objects were obstructing the view of either party and when those objects would have ceased to obstruct a view relative to when the collision occurred. This analysis is often independent of the distance separating one of the parties from the other, except for specific cases such as fog, dust, or smoke. Under night or low light conditions, however, the light that reaches a pedestrian and is reflected from the pedestrian to a driver may not be sufficient to make the pedestrian detectable to a driver. The distance from the driver to the pedestrian through time is relevant, and the lighting conditions must be considered in addition to geometry obstructions.
The visibility of a pedestrian at night for an approaching driver will be affected by the illumination from the vehicle’s headlamps, by streetlamps, by ambient lighting, by oncoming traffic, and by characteristics of the weather. Primarily, it is the luminance contrast between an object and its background that makes an object visible to an observer at night [1]. Luminance is the amount of light that is reflected off a surface, and the luminance contrast, or difference in luminance between two objects, is dependent on surface properties such as color and reflectivity, as well as the amount of illumination arriving at that surface by light sources. In reconstructing a nighttime crash, the analyst may need to evaluate the limits of visibility to determine the distance from which a pedestrian is visible.
Lighting Sources
Ambient Light
During daytime conditions on a roadway, the majority of illumination comes from natural lighting via the sun. As the sun sets, the lighting conditions change from daytime to twilight. Twilight refers to the period after sunset and before sunrise during which the atmosphere is partially illuminated by the sun. Early astronomers defined civil twilight as the time period after sunset or before sunrise when normal outdoor activities could be conducted without artificial illumination. Civil twilight is currently defined as the period of time when the sun is from 0º to 6º below the horizon. Civil twilight occurs in the evening after sunset (civil dusk) as the sun descends from the horizon to 6º below the horizon, and in the morning before sunrise (civil dawn) as the sun ascends from 6º below the horizon to the horizon. Similarly, nautical twilight refers to the period when the geometric center of the sun is between 6º and 12º below the horizon, and astronomical twilight refers to the period when the sun is between 12º and 18º below the horizon. The diagram in Figure 1 depicts these phases.
Figure 1 - Twilight Phases
The reconstructionist may be interested in evaluating the ambient lighting that was present during a crash. This necessarily involves an accurate assessment of the time at which the crash occurred. Police records, fire records, dispatch records, and timestamped videos may all give an indication as to the time of the crash. The sun’s illumination changes most rapidly during civil twilight and civil dawn, so the sun’s illumination during these phases will be particularly sensitive to the determined time of the accident.
Often, a site inspection or study at a time with similar ambient lighting conditions is desired. The use of a sun calculator will inform the analyst of the altitude and azimuth of the sun at a given location and at a given time. One such calculator is on the website suncalc.org. Adequate matches of the solar altitude and azimuth can be achieved around the anniversary date of the crash, as well as on days equidistant from the summer solstice (June 20 or 21) and winter solstice (December 20 or 21).
Auxiliary Lighting Sources
In addition to lighting from the sun, a crash scene may be illuminated by nearby light sources, such as overhead lights, illuminated signs, or lights from nearby buildings. These auxiliary light sources can be documented and accounted for in an accident reconstruction. Often, photographs taken near the time of the accident will document these additional lighting sources. When evaluating external lighting sources, take note of which lighting sources were activated at the time of the crash. Lamps will sometimes burn out between the time of the accident and the time of a site inspection; or, they will have been burnt out at the time of the crash and replaced by the time of the inspection. Take note of the type of light as well. Prior to the prominence of LED lighting, many overhead streetlights were sodium vapor lights. Many municipalities are now transitioning from sodium vapor streetlights to LED lighting, given the energy efficiency improvements of LED lighting systems. A situation may arise where the accident occurred under sodium vapor streetlights and at the time of the inspection those lights have been upgraded to LED lighting. The two lighting types are usually distinguishable by the color temperature of the lights. Sodium vapor lighting has a warm yellow color, whereas LED lighting has a whiter or bluer appearance.
Vehicle Headlamps
The primary source of illumination in a nighttime pedestrian crash is often the headlamps of a driven vehicle. Thus, an understanding of vehicle headlamp illumination patterns is useful to a nighttime pedestrian accident reconstruction. As a vehicle approaches, the headlamps will illuminate the pedestrian to provide contrast to the driver between the pedestrian and the background. Each headlamp model has a unique beam pattern. Generic headlight models have been proposed [2], or for greater fidelity the accident reconstructionist may choose to measure the headlight beam pattern of the subject vehicle or a suitable exemplar [3,4]. Figure 2 depicts the mapped illumination pattern at various levels for a 2015 GMC Savana 2500 from a top-down perspective. In this figure, the longitudinal and lateral distances from the front left corner of the vehicle are depicted on the horizontal and vertical axis, respectively, in feet.
Figure 2 – Headlamp Illumination Distribution
Assessing the Nighttime Visibility of Pedestrians
An accident reconstructionist is often tasked with evaluating when an attentive driver would have been able to detect the presence of a pedestrian. The likelihood a driver will detect a pedestrian is influenced by the contrast between the pedestrian and their surroundings. Contrast is defined as the amount of light (luminance) reflecting from a subject compared to the luminance of the area surrounding that subject. In some situations, vehicle headlights or other lighting sources will illuminate a subject so that it is brighter than its background, which is known as positive contrast. An example of positive contrast is depicted in Figure 3. Other times, the background of the subject will appear brighter than the subject itself, which is known as negative contrast. An example of negative contrast is depicted in Figure 4. Negative contrast may occur when a pedestrian crosses in front of the headlights of a vehicle.
Figure 3 – Pedestrians Crossing a Roadway: Positive Contrast
Figure 4 – Pedestrians Crossing a Roadway: Negative Contrast
Researchers have proposed models to evaluate object visibility under nighttime conditions. One such model [2] evaluates the time at which a pedestrian is subject to a specific level of illuminance from vehicle headlights. This threshold illumination level in the model is based on the shade of clothing that the pedestrian is wearing. The model further correlates headlight illumination with driver response distances. The model necessarily requires two elements – an estimate of headlight illuminance as a function of the pedestrian location relative to the vehicle, and an estimate of when drivers tend to respond to pedestrians based on the reflectance of the pedestrian and their clothing. In this model, headlight illumination levels can be estimated from generic models or measured through mapping of the subject vehicle or suitable exemplar.
To correlate headlight illumination levels to driver response distances, the authors analyzed the results of previous nighttime driver response distance experiments and determined a threshold value for headlight illuminance. The authors noted that the shade of clothing had a significant influence on a driver’s detection distance. Combining a headlight model that is dependent on vehicle characteristics and a recognition model that accounts for pedestrian clothing shade and driver responses allows for a reconstructionist to estimate when a driver would be expected to react to a pedestrian in a path intrusion scenario. These models are incorporated into a widely utilized software package called Response [5].
Nighttime or Low-Light Studies
When practical for a nighttime pedestrian collision reconstruction, it may be valuable to perform a site visit and a nighttime study to evaluate the site-specific lighting conditions. Under equivalent ambient light, observations on lighting conditions can be recorded. These are often in the form of observations of objects that are visible from a viewpoint of interest that corresponds to a relevant moment prior to the collision. For instance, a position where a driver would have needed to detect the pedestrian in order to avoid the impact. From this position, observations can be made on the illumination in the area where the pedestrian would have been at that time. These observations can include luminance or illuminance measurements, photographs, and/or video.
Calibrated vs. Uncalibrated Photographs and Video
Sometimes, a photograph taken just after a crash will be used to illustrate “how dark it was” at the time of the accident or alternatively how “visible” an object or pedestrian was. This is likely to be inherently flawed. In taking the photograph, investigators or witnesses will most likely have their camera (or phone with integrated camera) set to an “auto” mode that will adjust exposure setting to minimize the portions of the photograph that are underexposed or overexposed. In doing so, the camera inaccurately depicts the actual lighting conditions at the scene. When an accident reconstructionist wishes to accurately portray the lighting conditions taken during a low-light or night-time study, a procedure is needed to verify that objects of interest that are visible during the study are visible in the photograph or video, and likewise, objects of interest that are not visible during the study are not visible in the photograph or video. Such a process is referred to photograph calibration or video calibration.
To create calibrated photographs or video, the analyst makes observations and/or measurements of relevant objects at a nighttime study. At the study, photographs and/or video are taken in a way that emulates the observed lighting conditions while also allowing for adjustments after the study. Then, adjustments are made to the raw media and or display medium to reasonably match the relevant observations and measurements. When displaying calibrated digital media, the use of an Organic Light Emitting Diode (OLED) screen may be useful. OLED screens have an advantage over traditional LED or LCD screens in that they do not require a backlight source to display. Therefore, dark areas of the media can be displayed much darker on an OLED screen than on a backlight screen. This technology works particularly well for displaying accurate calibrated images.
Case Study #1 – Night Pedestrian Accident with Unknown Impact Location
A collision involving a Ford SUV and a pedestrian under nighttime conditions was reconstructed. The traffic accident report indicated that the Ford SUV was driving southbound and the pedestrian was crossing the roadway from west to east in an area that was not near an intersection. The roadway was dry, and the surrounding area was unlit. The Ford was traveling in the leftmost southbound lane prior to the impact. The Ford driver stated that there were no streetlights or crosswalks in the area of the impact, his headlights were on, and he saw a black silhouette just prior to impacting the pedestrian.
Law enforcement officers documented the physical evidence and rest positions with photographs, marked evidence with paint, took measurements, and mapped the evidence and roadway geometry with a total station. The photographs in Figure 6 are a sampling of the photographs taken by law enforcement.
Figure 6 – Photographs of Physical Evidence
As part of the reconstruction, the subject Ford and the area of the crash were inspected, photographed, and digitally mapped using a laser scanner and a drone. The photographs taken at the scene were analyzed and the scaled diagram in Figure 7 was created. This diagram depicts the police paint, the Ford’s rest position, and the pedestrian rest position. There was no documented physical evidence to indicate the precise position on the roadway where the impact occurred, so a reconstruction was performed that determined that the impact occurred between 80 and 128 feet from the pedestrian’s point of rest, and that the Ford was traveling between 31 and 43 mph at impact.
Figure 7 – Evidence Diagram
To evaluate the distance at which the pedestrian would have been detectable to the driver of the Ford, a nighttime visibility study was performed at the crash site. During this study, the travel lanes were closed, and a surrogate pedestrian stood at the approximate location of the impact. The surrogate pedestrian was of similar height to the subject pedestrian and was dressed in similar clothing. A Sony A7S II camera was mounted to the interior windshield of the subject vehicle. A nighttime scene equivalent contrast gradient panel was utilized at the scene to make contrast and lighting observations. The subject Ford was positioned at various locations along the roadway and the visibility of the surrogate was evaluated and documented photographically at each location. At a distance of 50 feet, the pedestrian shoes and jeans were clearly visible, as was the bottom portion of the pedestrian’s jacket. At a distance of 100 feet, the pedestrian jeans and shoes were visible. At a distance of 150 feet, portions of the jeans were barely visible, and at distances of 200 feet and beyond, no portion of the surrogate pedestrian was visible. Figures 8 through 11 depict photographs taken at 50 feet, 100 feet, 150 feet, and 200 feet, respectively. These photographs were calibrated to give a fair and reasonable depiction when viewed on a specific monitor with documented settings. However, these images may not provide accurate depictions of the view when viewed in print or on other monitors.
After the visibility study, the degree to which the involved parties could have avoided the crash was analyzed. It was determined that the 85th percentile perception response time for drivers in a situation similar to the Ford driver would be 2.5 seconds. In other words, 85% of drivers would respond in 2.5 seconds or less. In those 2.5 seconds, the Ford would travel between 145 and 159 feet. Further, it would take between 68 and 78 feet of braking to bring the Ford to a stop. The total stopping distance, therefore would be between 213 and 237 feet. This indicates that, in order to brake to a stop and avoid the impact, the driver of the Ford would have had to begin detecting and reacting to the pedestrian at a time when the pedestrian would not have been visible, and thus, the driver of the Ford could not have avoided this collision.
Figure 8 – Photograph of Surrogate Taken at 50 feet from Impact Location
Figure 9 - Photograph of Surrogate Taken at 100 feet from Impact Location
Figure 10 – Photograph of Surrogate Taken at 150 feet from Impact Location
Figure 11 – Photograph of Surrogate Taken at 200 feet from Impact Location
During the visibility study, it was also documented that headlights of approaching southbound vehicles were visible when the vehicles were well north of the impact location. It was determined that a vehicle traveling at the speed limit would be visible for at least 10 seconds. The pedestrian in this case would have had a clear view of the approaching vehicle for at least 10 seconds prior to the impact and thus would have had adequate visibility to avoid the accident by waiting for the Ford to pass.
References
- Muttart, J., Bartlett, W., Kauderer, C., Johnston, G., et al., “Determining When an Object Enters the Headlight Beam Pattern of a Vehicle,” SAE Technical Paper 2013-01-0787, 2013, https://doi.org/10.4271/2013-01-0787.
- “Response” software, Driver Research Institute, Hampton, CT, https://driverresearchinstitute.com/software/.
- Funk, C., Vozza, A., and Petroskey, K., “An Optimized Method for Mapping Headlamp Illumination Patterns,” SAE Technical Paper 2021-01-0886, 2021, https://doi.org/10.4271/2021-01-0886.
- Funk, C., Petroskey, K., Arndt, S., and Vozza, A., “Vehicle-Specific Headlamp Mapping for Nighttime Visibility,” SAE Technical Paper 2021-01-0880, 2021, https://doi.org/10.4271/2021-01-0880.
Neal Carter is a Professional Engineer and Principal Accident Reconstructionist at Explico Engineering. Mr. Carter has expertise, experience, and training in accident reconstruction, with an emphasis in pedestrian accident reconstruction, forensic photography, and nighttime or low-light photographs and video. Mr. Carter has conducted testing involving vehicle dynamics and acceleration, nighttime visibility, on-vehicle data recorders, passenger vehicle braking, pedestrian impacts, and motorcycle dynamics, braking, and sliding deceleration. Mr. Carter also regularly publishes technical articles related to vehicular accident reconstruction. Mr. Carter has authored publications based on his testing that have been published by the Society of Automotive Engineers International Journal of Transportation Safety, in the Society of Automotive Engineers Technical Paper Series, in Collision: The International Compendium for Crash Research, in the Annals of Biomedical Engineering and in Electric Energy.