About 30 people were injured after a PSV bus they were traveling in over turned along Waiyaki way at Waruku stage.
They were among passengers on board a Climax bus traveling from Usenge in Siaya county to Nairobi.
NTSA officials said the accident happened after the driver of the ill-fated bus applied emergency brakes as he tried to bump into another vehicle that was joining the highway from the stage.
They said the driver of a Latema Sacco mini-bus was to blame for the accident as he was dangerously carrying passengers in the road.
"The driver of that Latema bus KBX was just carrying passenger in the road as this stretch is somehow sloppy and narrow. When the driver of the climax bus tried to signal for him to pave way, he immediately joined the road and sped off," one of the NTSA officers at the scene told reporters.
He said the conductor of the Latema mini-bus has been arrested to help police hunt for the driver.
The officer said the rest of the passengers sustained minor injuries.
"Those with serious injuries have been taken to Kenyatta National Hospital, while those who had no injuries at all will be taken to Kabete Police station to clear before collecting their luggage ," he said.
He said the injuries though serious they are not life threatening and thus there should be no cause for alarm.