Pedestrian versus Auto

This article was written by my friend Mike Shertz, a former Special Forces medic and current ER doctor.

With the increasing frequency of vehicles being used as weapons by violent extremists, and ISIS’s encouragement of its followers to rent SUVs and trucks for this purpose, it is worth reviewing the trauma literature of pedestrians injured by automobiles. (UPDATED 04 March 2021)

There is little medical literature on casualties intentionally run over by vehicles. One study looked at the Israeli experience, as this method of attack first occurred there in 1987. One major difference between accidental auto versus pedestrian collisions and intentional attacks is the vehicle speed. In general, unintentional collisions involve the vehicle trying to decelerate rather than a deliberate acceleration in vehicle-ramming attacks.¹

Several patterns are clear from the existing literature on pedestrians injured by automobiles:

• A German² study of cars hitting pedestrians at speeds over 13 mph found the fatality rate was about 24%, with approximately 8% dead on the scene. Fatality rates significantly increase if the casualty was hit at speeds over 30 mph.
• The driver of the car used during the Westminster Bridge attack was traveling at 76 mph by the time he reached the end of the bridge. Five died (not including the attacker), and 49 were injured (9% killed).
• The truck attack in Nice in 2016 killed 85 and wounded another 434 (16% killed).
• In the 2016 Christmas-time Berlin attack, the driver killed 12 (including the registered driver of the truck who was kidnapped and killed as he tried to avert the attack) and left 56 wounded (17% killed). Witnesses estimated the truck was traveling 40 mph.
• August’s attack in Barcelona killed 13 and injured 131 (10% killed). Witnesses described the vehicle as driving at “high speeds.”

Injury Patterns in pedestrian vs. automobiles

Essentially, pedestrians who ultimately die from vehicle crashes have head injuries, largely subarachnoid bleeding, and brain contusions. This may be more likely in intentional ramming as the victim is hurled toward/into the vehicle by acceleration rather than pushed away by deceleration of the accidental, surprised driver.¹

Blunt chest and abdominal injuries were the next most frequent life-threatening conditions after a high-energy impact. Injuries to the chest, spine, and pelvis occurred in decreasing order of frequency.

• Most chest injuries included multiple rib fractures and lung contusions.
• Spleen and liver rupture were the most common abdominal injuries.
• Unstable thoracic and cervical spine fractures were the leading cause of spine injuries.
• Anterior pelvic ring fractures were the most common injury to the pelvis.

Head Injuries

The Israeli study showed a much higher rate of severe head injuries and a fourfold increase in prehospital intubation rates compared to accidental auto vs. peds (27% vs. 7%).

Prehospital management of head injuries largely is supportive and tries to avoid the “second injury” of hypoxia or hypotension (low oxygen levels and abnormally low blood pressure, respectively), both of which markedly increase the likelihood of death from an already injured brain. A single episode of hypotension in the head-injured increases their mortality by 2.5 times. A single recorded hypoxic oxygen saturation increases their death rate three times. If they have both hypotension and hypoxia, their mortality increases by six-fold.³

Torso Injuries

Multiple rib fractures can cause death by compromising the casualty’s respiratory function both mechanically (think flail chest) and through underlying hemo / pneumothorax, tension pneumothorax, and lung contusion. Imagine breathing through a wet sponge: Oxygen transport through blood-soaked bruised lungs is poor.

Liver and spleen rupture can cause substantial intra-abdominal bleeding with hypotension (making the associated head injury worse). Blood transfusions are often required, and surgery may be necessary to control the bleeding.

Pelvic fractures can be life-threatening because of the major vasculature that is often torn with a significant bony break and the large volume of the pelvis, allowing significant internal bleeding into what is essentially a large bowl.

Spinal Fractures

While unstable spinal fractures are rare in penetrating trauma, the bullet or fragment either touched your spine, or it didn’t, they are very common in pedestrians injured by automobiles. In the German study, unstable spinal fractures were the majority occurring in 9 of 11 spine fractures. What you need to know: All of this complicates casualty movement. With stable spinal fractures from penetrating trauma, moving a casualty without regard to spinal precautions rarely worsens their injuries. With unstable fractures from a vehicular crash, they are by definition fragile and any extra spinal motion increases the possibility of spinal cord injury.

While unstable spinal fractures are rare in penetrating trauma, the bullet or fragment either touched your spine, or it didn’t,⁴ they are very common in pedestrians injured by automobiles. In the German study, unstable spinal fractures were the majority occurring in 9 of 11 spine fractures. What you need to know: All of this complicates casualty movement. With stable spinal fractures from penetrating trauma, moving a casualty without regard to spinal precautions rarely worsens their injuries. With unstable fractures from a vehicular crash, they are by definition fragile, and any extra spinal motion increases the possibility of spinal cord injury.

Summing all this up, the majority of life-threatening injuries occurring in pedestrians hit by motor vehicles are blunt trauma injuries. TCCC and TECC guidelines are optimized largely for casualties of penetrating trauma. Fortunately, civilian prehospital providers have extensive experience dealing with blunt trauma, as it is the majority cause of trauma in developed nations. 

As a bystander, you must consider your safety first. Running to aid in a car crash may put you in the path of an oncoming attacker, as these attackers often exit their vehicles once they have crashed and begin stabbing people. If it is safe to help, your first priority is to ensure the EMS system has been activated: Call 911. Most of these injuries will require paramedic-level training and an ambulance of supplies to manage. Avoid moving casualties unless to prevent greater harm, such as from an encroaching fire or other vehicles. Then, work the MARCH pneumonic as best as you can: prioritize external bleeding control, maintain an open airway, and prevent hypothermia.

Notes:

¹Almogy, G., Kedar, A. & Bala, M. When a vehicle becomes a weapon: intentional vehicular assaults in Israel. Scand J Trauma Resusc Emerg Med 24, 149 (2016). https://doi.org/10.1186/s13049-016-0338-9

² Schmucker U, Beirau M, Frank M, Stengel D, Matthes G, Ekkernkamp A, Seifert J. Real-world car-to-pedestrian-crash data from an urban centre. J Trauma Manag Outcomes. 2010;4(1):2.[PMC free article] [PubMed]

³Spaite DW, Hu C, Bobrow BJ, Chikani V, Barnhart B, Gaither JB, Denninghoff KR, Adelson PD, Keim SM, Viscusi C, Mullins T, Rice AD, Sherrill D. Association of Out-of-Hospital Hypotension Depth and Duration With Traumatic Brain Injury Mortality. Ann Emerg Med. 2017 Oct;70(4):522-530

⁴Haut ER, Kalish BT, Efron DT, Haider AH, Stevens KA, Kieninger AN, Cornwell EE 3rd, Chang DC. Spine immobilization in penetrating trauma: more harm than good? J Trauma. 2010 Jan;68(1):115-20

US DHS has an overview of the topic in their Vehicle Ramming: security awareness for soft targets & crowded places