Democrats Dianne Feinstein and Barbara Boxer said Thursday the government needs to tighten vehicle inspections and safety rules to weed out potentially dangerous vehicles.
Their letter to Transportation Secretary Ray LaHood came four days after a tour bus carrying 38 lost control below the Big Bear resort area and collided with a sedan and a pickup.
Eight people were killed and dozens injured.
The driver told investigators the brakes failed.
The senators say many bus crashes are preventable. They say the government must do more to protect passenger safety. Proposed improvements have been stalled in Washington for years.