Traffic is the single most dangerous hazard at most incident scenes. Whether you’re a first responder, a tow truck driver, or a bystander who stopped to help, the greatest threat usually isn’t the original emergency itself. It’s the vehicles still moving around it. Nationally, 1,234 people were killed in crashes involving parked or working vehicles at roadsides in 2022 alone. That number includes emergency workers, roadside assistance crews, and ordinary motorists who pulled over.
The answer might seem counterintuitive. You’d expect fire, structural collapse, or hazardous materials to top the list. Those are serious dangers, but they’re also predictable and contained. Traffic is relentless, hard to control, and affects every type of incident that occurs on or near a road.
Why Traffic Outranks Every Other Hazard
Between 2011 and 2015, roadway vehicle incidents accounted for nearly one-third of all fatal work injuries among law enforcement officers and one-fifth of fatalities among fire and rescue workers (a category that includes paramedics and ambulance crews). For law enforcement specifically, being struck or involved in a vehicle crash killed 192 officers in that five-year window, making it the second leading cause of on-duty death after shootings.
What makes traffic so lethal is that it’s present at almost every scene. A car accident on a highway, a medical call on a shoulder, a structure fire near a busy road: all of them put people in the path of drivers who may be distracted, impaired, or simply not expecting stopped vehicles and pedestrians. The problem compounds at night, in rain, or on curves where sight lines are short. Drivers approaching at highway speed have seconds to react, and many don’t.
Every U.S. state now has some version of a “Move Over” law requiring drivers to change lanes or slow down when passing emergency vehicles. But compliance remains low. A Government Accountability Office report found that the biggest challenge is simple awareness: many motorists don’t know the law exists or what it specifically requires. The laws also vary from state to state in which vehicles they cover, making public education even harder.
Hazards That Are Hard to See
Some of the most dangerous threats at an incident scene are invisible. Downed power lines can energize the ground around them without any visible sparks. Leaked fuel vapor can pool in low areas and ignite from a source hundreds of feet away. Carbon monoxide from running engines or smoldering materials has no color or smell at dangerous concentrations. These silent hazards are particularly risky because responders and bystanders may not recognize them until symptoms appear or something ignites.
Electric vehicle fires have introduced a newer invisible threat. When a lithium-ion battery is damaged in a crash, its cells can enter a chain reaction called thermal runaway, heating uncontrollably and potentially releasing toxic, flammable gases. Even after the fire appears to be out, energy trapped inside the damaged battery pack can reignite the vehicle days or even weeks later. Firefighters typically use massive amounts of water to cool the battery’s metal casing from the outside, but the unpredictability of stranded energy makes these scenes harder to declare safe.
Environmental Conditions That Multiply Risk
Weather doesn’t just cause incidents. It makes existing scenes more dangerous for everyone present. Extreme heat increases the risk of heat-related illness for responders wearing heavy protective gear. Cold temperatures reduce dexterity and slow reaction time. Sudden shifts between temperature extremes can cause additional health problems, particularly for people on certain medications.
Low visibility from fog, heavy rain, or blowing snow is especially dangerous because it amplifies the traffic hazard. Drivers approaching an incident scene in poor visibility have even less time to react to flashing lights and lane closures. Strong winds can spread fire, carry airborne contaminants in unpredictable directions, and make vehicle doors and equipment harder to manage safely.
The Scene Itself Changes Over Time
An incident scene isn’t static. What starts as a single-car accident can escalate into a multi-vehicle pileup if traffic isn’t controlled. A small fire can grow into a structure collapse. A chemical spill can spread with wind or water runoff. This is why professional incident management treats hazard assessment as a continuous process rather than a one-time check.
Safety officers at managed scenes follow a structured approach: identify hazards associated with the incident, ensure protective equipment is available and being used, flag potentially unsafe actions, and build a formal risk analysis into the response plan. But many roadside incidents don’t have a formal safety officer present, especially in the early minutes before additional resources arrive. That gap is when people are most vulnerable.
Crowd Behavior Adds Unpredictability
Bystanders create a layer of risk that’s easy to underestimate. Crowds gathering near a scene can block access for emergency vehicles, wander into traffic lanes, or interfere with responders. “Rubbernecking,” where passing drivers slow down to look, creates secondary congestion and raises the chance of rear-end collisions in the approach zone.
Bystanders who attempt to help can sometimes worsen injuries through incorrect first aid, and witnessing those mistakes makes other bystanders hesitant to assist at all. In rare cases, bystanders become hostile or agitated, particularly at scenes involving law enforcement. Any of these behaviors can distract responders from the primary hazard or pull resources away from the people who need them most.
How Responders Prioritize Scene Safety
The standard principle taught across fire, EMS, and law enforcement training is that scene safety comes before patient care. You can’t help anyone if you become a casualty yourself. In practice, this means the first arriving unit’s job is to assess what can kill them before they assess what’s wrong with the patient.
For roadside incidents, that assessment almost always starts with traffic. Positioning a fire engine or patrol car as a physical barrier between the scene and approaching traffic (sometimes called “blocking”) is one of the most effective protective measures. High-visibility clothing, early placement of cones or flares, and requesting lane closures from traffic control are standard steps. OSHA is currently working on a modernized emergency response standard that would expand federal safety requirements to cover the full range of hazards responders face, replacing a decades-old rule that focused primarily on fire brigades.
For scenes involving hazardous materials, the priority shifts to identifying the substance, establishing a safe perimeter, and approaching from upwind. For structural incidents, it’s assessing collapse potential. For EV crashes, it’s recognizing the vehicle type and preparing for the possibility of thermal runaway. Each scene type has its own hierarchy of threats, but the one hazard that cuts across nearly all of them is the flow of traffic that doesn’t stop just because an emergency is happening.