The Impact of Vehicle Size on Pedestrian Fatalities Since 2009

Pedestrian Fatalities Surge Due to Increasing Vehicle Size

Pedestrian fatalities in the United States have increased by 75% since 2009. A study by The New York Times and the Insurance Institute for Highway Safety indicates that the rise of larger vehicles, specifically SUVs and pickup trucks, is a primary driver of this trend. It is estimated that between 200 and 400 pedestrian deaths annually could have been avoided if vehicle dimensions had remained constant over the last 25 years, accounting for approximately 10% of the recent increase in fatalities.

Regulatory Drivers of Vehicle Growth

The shift toward larger vehicles was accelerated by specific regulatory changes and economic events following the 2008 financial crisis:

• The Footprint Model: An Obama-era revision to fuel economy calculations classified vehicles by physical dimensions and tire size. This "footprint model" effectively allowed automakers to emit more pollutants provided the vehicle was larger, inadvertently incentivizing the production of larger cars.
• Market Shifts: The "Cash for Clunkers" program removed nearly 700,000 older cars from the used market, pushing consumers toward newer, larger, and ostensibly more fuel-efficient crossover models.
• Consumer Trends: The crossover has largely supplanted the midsize sedan as the preferred family vehicle in the American market.

The Physics of Pedestrian Impact

Vehicle size affects pedestrian survival through two primary physical mechanisms: mass and impact area.

Mass and Force

According to the formula $F=ma$ (Force equals mass times acceleration), a heavier object moving at a given speed exerts more force upon impact. As the average mass of new vehicles increases—both through the growth of individual models and the disappearance of smaller cars—the force of collisions has increased.

Impact Area and Pressure

Pressure is defined as force divided by area ($P = F/A$). While a larger contact area can distribute force more widely (reducing the pressure on any single point of the body), this benefit is offset by the increased height of modern vehicles.

The Danger of Vehicle Height and Blind Spots

Increased vehicle height significantly alters the outcome of a collision. When a pedestrian is hit below their center of mass, they are more likely to be pushed away or fall toward the vehicle. However, when hit at or above the center of mass—which is more common with taller SUVs and trucks—the pedestrian is often "punted" forward.

This mechanism increases fatality rates because the pedestrian's head often ends up under the wheels before the driver can react. This risk is compounded by the inherent blind spots associated with the higher hoods and larger frames of modern trucks and SUVs.