SALEM — The driver of a dump truck has been charged with negligent driving after an accident with a pickup truck and school bus that injured more than 20 people last week, police said.

Police said Wednesday that Jeremy McNally, 37, of Concord rear-ended a Nissan pickup truck on North Broadway near Lake Street on Aug. 1. The pickup then hit the rear of a school bus carrying 43 children and adults from the Little Sprouts summer camp in Lawrence, Mass., who were on a field trip to a Salem bowling alley, police said.

The charge against McNally alleges he was transporting 73,750 pounds in a three-axle truck, “thus significantly impairing the vehicle’s ability to brake.” Police said the accident happened when McNally tried to brake behind vehicles stopped at a red light.

According to court documents, state law requires a load of 65,000 pounds or more to be transported by a four-axle vehicle.

Emergency crews triggered a “level-two mass casualty” alert to treat the large number of injured people after the crash.

While all the injuries were minor — ranging from bumps and bruises to whiplash — 17 children and four adults were taken to hospitals.

All the children were discharged from Lawrence General Hospital in Lawrence, Mass. within hours.

The driver of the pickup truck suffered minor injuries, though his vehicle suffered heavy damage, police said.

McNally, who was driving a truck owned by A.E. Gidley LLC, was uninjured.

A person answering the phone at A.E. Gidley declined to comment.

McNally, truck driver charged, will be arraigned in Salem Circuit Court Sept. 23.