Software engineers, designers and other employees of technology companies board shuttle buses to Silicon Valley, April 14, 2014, in San Francisco. Approximately 35,000 employees use shuttle buses each day to be dropped off at Google, Facebook, Yahoo and Genentech corporate headquarters in Silicon Valley. Robert Nickelsberg/Getty Images

Shuttle bus drivers for some of the biggest companies in Silicon Valley have scored a boost in working standards. Nearly 100 workers at Compass Transportation, a firm that provides bus service for companies like Apple, eBay and Yahoo, approved a labor agreement Sunday that includes significant pay raises and new benefits. It comes months after the drivers voted to join the Teamsters union.

The Teamsters had raised the possibility of a strike if Compass did not agree to a contract.

The contract ratification sheds light on the plight of low-wage labor in Silicon Valley -- the service workers who form the underside of the region’s booming technology economy. Many white-collar tech employees earn large salaries while the bus drivers who provide them with daily transportation from San Francisco make substantially less.

The median income for a high-skilled worker in Silicon Valley is $119,000 a year, compared to $27,000 for low-skilled workers, according to a report from Joint Venture Silicon Valley, a regional think tank.

Teamsters | Graphiq

In September, the San Francisco Chronicle profiled one shuttle bus driver for Apple who lived in his car, and found several other Compass Transportation employees who were homeless or on the brink of homelessness. Rents have skyrocketed in the Bay Area, rising nearly 50 percent since 2010.

Workers at Compass voted to join the Teamsters in February. At the time, they earned around $17 to $21 an hour. Since then, some of the companies that have contracts with Compass have rolled out pay raises for the drivers, in some cases by up to $9 an hour. The new contract solidifies those advances over the next three years and includes other benefits like paid holidays and improved health insurance.

Labor unions have increasingly sought to make inroads among Silicon Valley’s service workers. Facebook shuttle bus drivers voted last fall to join the Teamsters and approved a labor contract earlier this year. In March, Apple succumbed to demands from the Service Employees International Union and agreed to directly employ security guards at its Cupertino campus rather than continuing to use a third-party contractor.