WASHINGTON (Reuters) - Major automakers on Monday joined forces with tech companies and a variety of interest groups to urge the U.S. Senate to take up, before the end of May, a stalled bill aimed at speeding the deployment and testing of self-driving cars.

In a letter to U.S. Senate leaders that was signed by more than 100 groups and companies, and seen by Reuters, the automakers and other advocates of the bill cited the “potential lives that could be saved” in urging quick action, noting human error is a factor in about 94 percent of all U.S. vehicle crashes.

The bill would clear hurdles for automakers to get thousands of cars on the road without human controls.

A handful of Senate Democrats including Dianne Feinstein have raised concerns about the bill and whether self-driving cars are ready for rapid deployment. Without their assent, the bill could require several days of time on the Senate floor – and many issues and nominations are vying for limited floor time.

"Lack of congressional action on this important legislation will only cause uncertainty and delays in the development and ultimate deployment of such life-saving technologies," said the letter, signed by nearly ever major automaker including General Motors Co, Volkswagen AG VOWG_p.DE, Toyota Motor Corp and Hyundai Motor Co.

Other companies and groups backing the effort include Harley-Davidson Inc, Intel Corp, Denso Corp and Lyft Inc, as well as associations representing motorcyclists, drone manufacturers, auto suppliers, senior citizens, the disabled and tech companies.

In September, the U.S. House of Representatives unanimously passed a measure that would allow automakers to win exemptions from safety rules that require human controls. The Senate Commerce Committee approved a similar bill in October, and it is that bill whose passage has been stalled.

The Senate bill would allow automakers to each sell up to 80,000 self-driving vehicles annually within three years if they could demonstrate to regulators the vehicles are as safe as current ones. States could set rules on registration, licensing, liability and insurance, but not performance standards.

The National Highway Traffic Safety Administration is holding a public hearing Tuesday on what regulatory changes will be needed to eventually allow self-driving cars without human controls on U.S. roads.