Commentary

One of the most technically challenging accident reconstruction analyses is the vehicle-pedestrian collision. Occasionally, the facts are clear and the pedestrian or vehicle can be held fully liable, but there are often conflicting accounts regarding the events leading up to a collision.

The safety of pedestrians and the prevention of these collisions are shared by the actions of both the motorist and the pedestrian. A common assumption made by pedestrians is that because they can see the approaching car, the approaching driver can see them. Of course, this has repeatedly been proven false, especially at twilight or nighttime.

While a motorist may not typically be looking for a pedestrian, the pedestrian may sometimes expect a vehicle to yield the right-of-way regardless of the situation and fail to assess the likelihood of interaction with the vehicle. State laws vary and most give the right of way to the pedestrian. However, this is usually only applicable at intersections and crosswalks.

If the pedestrian is not crossing at an intersection or crosswalk, laws usually require that the pedestrian must cross the road at a right angle, which results in the least time exposure in the roadway. Many non-intersection pedestrian collisions occur because the pedestrian crossed the roadway at an angle, therefore increasing his or her time exposure in the roadway. Because the pedestrian needs more time to clear the roadway, the approaching vehicle that he or she initially perceived as “off in the distance” has now become an unexpected and significant hazard.

Right-of-way questions at traffic-signal-controlled intersections can sometimes be resolved by outside sources, such as clear witness statements or a chance video recording by traffic cameras, surveillance or personal video cameras.

There are some instances, however, when some or all of this potential information is unavailable. An examination of the traffic signal sequence at the site can assist in determining whether the pedestrian actually had a clear “walk” signal. Any witness statements regarding the condition of the traffic signal for the pedestrian can be compared to its actual operation, such as a pedestrian-activated call button for a walk signal or a multiphased sequencing with a left turn arrow that may have delayed the walk signal.

“Dart-out,” or an unexpected emerging pedestrian situation in urban driving, presents an unforeseen hazard that may not give the motorist time or distance to react. This classification of pedestrian behavior can generally be attributed to the pedestrian failing to check for cross traffic, poor sight lines or visibility or simply pedestrian distraction. This may be particularly applicable to skaters, skateboarders and bicyclists.

Vehicle approach speeds can be an important factor in helping to reconstruct the events leading up to a vehicle-pedestrian collision. In some cases, the vehicle speed can be calculated from the pedestrian “throw distance,” which is the distance from the point of impact to the point of final rest for the body of the pedestrian. Several studies have been performed on the pedestrian’s airborne portion and total distance of projection. Of the available calculations for speed versus throw distance, it is important that the reconstructionist be attentive to detail and use the most applicable studies to deduce speed from the available physical evidence.

The overall visibility of the pedestrian can be a major factor in evaluating the cause of the accident. One aspect of visibility is the available ambient lighting. After sunset on a clear day, daylight remains for normal activities for about a half hour. This period is known as civil twilight. During civil twilight, some light remains for normal outdoor activities but diminishes to a level where reading would require an additional light source. For a motorist, objects become harder to recognize and take longer to mentally process. Nearby street lights may or may not effectively illuminate a pedestrian for a motorist. These factors should be recognized in the vehicle-pedestrian collision evaluation.

Similar to ambient lighting levels decreasing during civil twilight, the headlights of a car at night will project a beam of light in front of the car with diminishing intensity. As you move farther away from the front headlights of a vehicle, the headlight intensity decreases to make objects harder to recognize for the driver. This increases the driver’s response time, because hazards come into view only within the headlight illumination area.

Headlight illumination varies with the automobile and type of headlight, i.e., sealed beam, halogen and projector lights. The effective zones of these headlights can be a significant factor in the investigation of the nighttime pedestrian collision, and the reconstructionist must pay careful attention to these details.

Important information to gather during the initial investigation of a vehicle-pedestrian collision includes:

• Location of the point of impact between the vehicle and the pedestrian.

• Locations of the car and pedestrian post-impact relative to lane markings, crosswalks, curbs or other available reference points.

• Roadway evidence, e.g., skid marks, pedestrian’s shoes or other possessions.

• Topography and terrain of the roadway and the surrounding area that may affect lines of sight.

• Traffic conditions, e.g., the adjacent lane of traffic was stopped and the pedestrian stepped from between cars.

• Type of vehicle and condition of the vehicle’s headlights.

• Point(s) of impact on the vehicle.

• Injury patterns on the pedestrian.

• Time of day, considering sun location/glare and sunrise/sunset.

• Weather conditions, i.e., cloudy, foggy, bright, snow or ice on the ground or sidewalks.

• Event data recordings (EDR) from a crash data retrieval (CDR) system.

While the vehicle’s airbag system typically does not deploy in a pedestrian collision, the EDR data can be helpful. EDR data can contain pre-impact speeds of the vehicle, braking status and other relevant information that can be useful in reconstructing a vehicle-pedestrian collision. Some vehicles are equipped with an onboard airbag control module that records nondeployment events (an event when a vehicle senses a collision but does not deploy the airbag) and these events are downloadable by commercial means.

To determine which vehicles are commercially downloadable, consult the ARCCA iPhone/iPad app.

If the airbag was deployed in one of these vehicles, the EDR should have a locked record of the event. However, the recording of a nondeployment event like a vehicle-pedestrian collision is transient and may be lost by continued use of the vehicle. In this case, it is important that the reconstructionist access the vehicle and the EDR as soon as possible after the collision. This nondeployment event data can be read by a CDR system and may contain helpful information in reconstructing the collision.

An inspection of the accident site will gather other important data. A 3-D survey of the site will enable features to be accurately mapped. This computerized mapping will enable a sight-line analysis to account for the terrain, vegetation and other conditions that will assist in reconstructing the accident. Positions of lighting in the area can be evaluated and augmented by light-level measurements during the inspection. Backgrounds for contrast and conspicuity can be observed and evaluated during the site visit. Sometimes, an inspection of the site is not necessary for a specific case. For these cases, publically available mapping software can be used to gather the information needed.

Case Study Number 1

For analysis of a pedestrian collision, the driver’s statement can be critical. Often, a driver will state, “I never saw him until impact.” This statement should be explored in light of the evidence available to the reconstructionist. Braking by the vehicle prior to, or at, the moment of impact would refute the testimony that the driver did not see the pedestrian until impact. The evidence of pre-impact braking would, however, support that the driver actually saw the pedestrian but did not have the time and distance to avoid the collision.

A driver’s perception of the direction of approach of the pedestrian can also be important. A pedestrian stepping from behind a parked car to the driver’s right gives far less time to react than a pedestrian who has crossed the opposite lane and entered the driver’s path from his left.

The authors have encountered certain vehicle-pedestrian collisions where, after the initial analysis of the case facts, circumstances were not what they originally appeared to be. In one example, a southbound pedestrian was struck by an eastbound car on a sunny day in an area that, upon inspection, appeared as a wide, flat, open, two-lane roadway.

The pedestrian would have had to cross the westbound lane to reach the eastbound lane where he was struck, leaving the shaken driver to explain how he did not see the pedestrian. Further investigation showed that the seemingly open roadway encountered a backup of traffic from a signal to the west at the time of day of the incident. The pedestrian had stepped from between stopped westbound cars and gave the eastbound driver no chance to avoid the collision.

Case Study Number 2

In another incident, a pedestrian was walking along a sidewalk when he was struck by a four-door sedan backing out of a blind driveway. The driver claimed that the pedestrian had been running down the sidewalk and had tried to cross the driveway while his car was slowly backing out. The evidence gathered at the scene indicated that the pedestrian had been thrown a known distance into the street from the point of impact with the sedan. In addition, the pedestrian had contact injuries to his back at a height consistent with the rear profile of the vehicle. Testing demonstrated that the vehicle was traveling at an excessive speed in order to vault the pedestrian the known distance he was thrown.

The pedestrian had actually been walking across the driveway and had turned defensively away from the fast-moving car at the time of impact, resulting in the contact injuries to his back. A line-of-sight analysis demonstrated that the driver of the sedan could not see the pedestrian walking along the sidewalk from where the sedan started to rapidly accelerate in the driveway. Conversely, the sedan was not visible to the pedestrian while he was walking along the sidewalk and approaching the driveway. The testing proved that the car was traveling at an excessive speed, failed to stop at the sidewalk of a blind driveway and failed to yield the right of way to the pedestrian.

Often, vehicle-pedestrian collisions are more challenging to reconstruct than other types of vehicular collisions. Scientifically valid results depend on the proper application of the laws of physics and the quality of the available physical evidence, witness statements and site conditions.

Investigators, claims adjustors and attorneys can assist in the process by considering the factors listed above and gathering this information early on in the case. A thorough analysis of the available case facts combined with the proper application of the laws of physics will result in conclusions to a reasonable degree of engineering certainty as required by courts today. •

Donald K. Eisentraut is vice president of safety restraint engineering at ARCCA Inc. and is well known as an expert in the forensic analysis of occupant protection and vehicle motion in crash environments.

Michael L. Markushewski is a recognized leader in the field of crashworthiness and occupant protection and is a senior engineer and chief technical officer for ARCCA.

Shawn F. Harrington is an engineer at ARCCA specializing in accident reconstruction, with a focus on dynamic crash testing and pedestrian impact trajectory analysis.