Officer Scott Hermon prepares to pilot the first drone operated by the police department in Streetsboro, Ohio. The agency says it can't afford a helicopter, but a drone provides many of the same capabilities at a fraction of the price. (Dake Kang/Associated Press)

When police investigators tried to figure out what caused a multivehicle crash that killed an elderly woman in Morton, Ill., in July, they looked to the sky for help.

Like a growing number of police agencies throughout the country, the sheriff’s office in Tazewell County relied on a drone to quickly take photographs of the scene from on high to help investigators reconstruct the crash.

“It’s about a hundred times more detailed than what we could do with people taking the measurements,” Chief Deputy Jeff Lower said. “And it means that there’s much less time for the road to be closed and traffic to be backed up.”

For decades, police investigators at crash scenes used chalk marks, tape measures and roller wheels to record measurements and skid marks to help them assess what happened. More recently, many have used a ­laser-scanning tool to map the scene. But often those measurements can take hours, during which lanes may need to be shut down or the road closed entirely, putting emergency responders and crash investigators in harm’s way near traffic whizzing past.

Now, more police agencies are turning to unmanned aerial vehicles to do that work. Remote pilots send up the drones, which take high-resolution photos that are fed into a computer and run through software. That creates 3-D models that piece everything together for investigators.

And while advocates for privacy and civil rights strongly oppose law enforcement using drones for mass surveillance, such as at a protest rally, or for gathering criminal evidence without a warrant, they generally are not as concerned when the technology is used for car crashes.

“Filming a traffic accident overhead to get a better view, if it’s strictly limited to that purpose, is not the sort of thing that we would necessarily object to,” said Chad Marlow, a senior counsel at the American Civil Liberties Union in New York.

Jeramie D. Scott, national security counsel for the Electronic Privacy Information Center, a Washington-based nonprofit, agreed that it is less likely his group would be concerned about using drones for crash reconstruction, as long as it didn’t involve some type of surveillance to collect information about individuals.

Emergency-response agencies use drones in a variety of ways, such as tracking wildfires and conducting search-and-rescue missions.

At least 910 police, fire and emergency-services agencies have drones, according to an estimate by the Center for the Study of the Drone at Bard College in New York. About two-thirds of the state and local agencies with drones are in law enforcement.

While the study doesn’t break out how many police agencies use drones specifically for crash reconstruction, Dan Gettinger, co-director at the center, said the idea is spreading.

Lower, of the Tazewell sheriff’s office, said his department started using drones about a year ago for accident reconstruction, and has deployed them in six crashes. It has spent about $15,000 for the program, including training.

In the crash that killed the elderly woman, Lower said it took only 45 minutes to gather information using a drone, rather than the three hours it would have taken on the ground. The woman’s car hit the rear of a semi tractor-trailer and the side of another vehicle nearby. She died at the scene.

Last year, North Carolina’s transportation department and highway patrol conducted a study using a simulated two-car crash. It took the reconstruction team an hour and 51 minutes to collect the data using a laser scanner. It took 25 minutes using drones.

Maine State Police bought three drones for reconstruction last year and has used them more than 30 times. to investigate crashes. The agency paid about $40,000 for the drones, software and training. “We’ve probably saved twice that in overtime alone,” said Lt. Bruce Scott, the traffic safety unit’s commander.

Drones can be controversial, and many states have passed legislation to regulate or restrict their use.

At least 18 states require law enforcement agencies to get search warrants to use drones for surveillance or for conducting a search, according to the National Conference of State Legislatures.

But some of those states have specifically exempted crash reconstruction. In Maine, for example, state police worked with legislators to make sure the exemption was included in drone legislation enacted in 2015, according to Sgt. Darren Foster, who oversees his agency’s drone program.

In Virginia, the Stafford County Sheriff’s Office wanted to start a drone crash-reconstruction program using drones but was hampered by a state law requiring police to get a warrant except in certain circumstances.

The sheriff’s office contacted Republican state Del. Robert M. “Bob” Thomas (R-Stafford/Fredericksburg), who introduced a bill allowing drones for crash reconstruction without a warrant.

The legislature unanimously passed the measure, which was signed into law in March. It went into effect in July.

While the program has just started, Capt. Ben Worcester of the Stafford sheriff’s office said he expects it to revolutionize the way investigators capture crash-scene evidence and help protect emergency workers and the public.

“The benefits are undeniable,” he said.

Bergal is a reporter for Stateline, an initiative of the Pew Charitable Trusts.