The 54-year-old father of four navigates busy, narrow city streets in the 45-foot-long bus, picking up Facebook employees at stops all over San Francisco, before merging into rush hour traffic on Highway 101.

An hour's drive south, he deposits his passengers on Facebook's leafy suburban campus, then reverses his route to fetch the next busload.

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Maerina works a split shift, so when his morning duties end around noon, he heads home to take a nap so he can be alert for the evening shift. By 5:15 p.m., Maerina is on the road again to take Facebook workers home.

It's not until late evening that he gets home, in time to say goodnight to his kids, but not to eat dinner with them or help them with their homework.

Maerina says he makes $18 an hour for nine hours of driving. Each paycheck covers his family's basic living expenses — mortgage, utilities, health insurance, a modest contribution to a retirement account — but not much more.

"We are just barely making it," Maerina said.

Maerina is one of a growing number of contract workers in Silicon Valley who work inside high-tech companies but are not on the payroll at Facebook or Google. Instead, they are employed by outside contractors.

For the most part, they earn low wages and benefits. They have little in the way of job security or protections. Some don't earn sick or vacation leave.

Of all the contract workers in high-tech, bus drivers are the most visible.

Tech companies are spending tens of millions of dollars on hundreds of shuttles that transport thousands of far-flung employees. The shuttle services help companies compete for top engineers and other key talent who prefer to live in San Francisco and commute to Silicon Valley.

Many of the high-tech companies own the buses but they contract with bus operators to oversee the workers who drive them.

Maerina and his fellow drivers work for Loop, which is run by SFO Shuttle Bus. It has contracts with Bay Area technology companies.

CEO Jeff Leonoudakis did not return phone calls from USA TODAY. Facebook declined to comment.

Shuttle drivers say they are proud that busloads of commuters keep cars off congested roads and reduce harmful emissions. They don't even mind the daily gridlock. They say they just want to get their passengers to the office safely and on time.

But resentment is percolating about pay and working conditions, as they watch the fortunes of the technology industry soar. Shuttle drivers say they received a 75 cent raise, not enough to cover the rising cost of living.

With heavy traffic and tight schedules, drivers say they rarely have time to take a break, not even to take a sip of water — which they are not permitted to drink on the bus — or to go to the bathroom.

Perhaps the toughest part of the job: long days spent away from family.

"My kids are asleep when I leave in the morning, and they are asleep when I get home at night," said Cynthia Goolsby, 35, a Facebook driver who lives in Dublin, Calif. "It's hard. I miss a lot."