Horsley said the driver was taking students home following the first day of a four-week summer program at the Hartvigsen School for medically fragile and severely disabled students. District buses have an alarm that goes off when the back door is opened and preliminary reports indicate that the sensor on the rear emergency door was functioning, he said.
"It appears that the noise from the windows as well as the noise from the freeway may have impeded the driver's ability to initially hear the sensor or hear that the door had been opened," Horsley said.
Horsley said the attendant heard the sensor and looked back from her location on the bus to see if the door was open, but the door appeared to be closed. Reports from a district investigation said the turn on the freeway from eastbound I-80 to southbound Interstate 215 may have swung the door back into a position where it appeared to be closed.
The attendant walked back to check on the student, Horsley said, assuming that he had ducked down or leaned over against the window. But once she got closer, she could see that the door was slightly open.
The bus driver pulled over to the side of I-215 and called district and emergency officials. Horsley said between 60 to 90 seconds passed from the time the student fell to the time the bus pulled over around a mile to a mile and a half away.
A motorist who spotted the boy in a travel lane on I-80 stopped and called 911 around 11:30 a.m., according to UHP.
When emergency personnel arrived, the bus continued on I-215 and exited on 3300 South, where students were transported to another bus and police continued their investigation.
As part of district policy, the bus driver and attendant have been put on leave pending the completion of the investigation. The bus driver has also been tested for drugs in accordance with policy as well.
Horsley said students riding on the bus are required to wear seat belts, either on seats or while in a wheelchair. It wasn't immediately known if the boy, who did not use a wheelchair, opened the door himself.
The boy took part in the program last summer, Horsley said.