SAN FRANCISCO — It's becoming a familiar scene in everybody's favorite city — luxury shuttles with Wi-Fi and plush seats barreling past sluggish, dilapidated city buses crammed with local residents standing elbow to elbow.
The nerd convoy, ferrying workers to technology companies in Silicon Valley, has raised the ire of civic activists who see it as a symbol of a divide between the haves and have nots as the region's tech boom has sent housing costs and evictions soaring.
But as heated as that backlash has become at times, it has obscured a much broader story that these buses have to tell about changes sweeping across not just San Francisco but also the entire Bay Area.
Tech giants are building massive new headquarters to the south of this city in communities with no ability or desire to create additional housing. With the region's public transportation systems unable to keep pace with this growth, the tech boom has led to a private transportation boom.
Tech companies are spending tens of millions of dollars on hundreds of shuttles that transport thousands of increasingly far-flung employees to their Silicon Valley offices. In just a few years, this network has blossomed into what many transportation experts believe is the largest of its kind in the country.
For tech companies, the shuttles are key to competing for talent. And they are part of broader, environmentally focused efforts to get employees out of their cars and into traffic-reduction programs often required by local communities as a condition for approving expansions.
Yet critics are questioning whether this ad hoc system is the best way to solve the region's transportation woes. Some argue the private mass transit system is taking money away from public transportation while enabling municipalities in Silicon Valley to greenlight major tech expansions without building housing.
San Francisco, increasingly attractive to the young workers tech companies covet, can expect to see more of these shuttles barreling down its streets in the coming years, the critics say.
"I assume these companies were well-intentioned when they designed these programs," said Susan Shaheen, co-director of the transportation sustainability research center at UC Berkeley. "But this is what happens when something scales. The impact is very different."
Just about every major tech company in Silicon Valley now operates its own shuttle fleet, both long-haul buses that take riders from San Francisco, Oakland or Marin to Silicon Valley, and short-haul shuttles that pick up employees at train stations and carry them the last few miles to work.
By far the largest fleet is operated by Google Inc. So much so that "Google Buses" has become the default name for these private transportation networks.
Google operates about 100 buses on 40 routes across the Bay Area. The buses carry about 4,000 passengers a day from seven Bay Area counties.
The evolution of Google's transportation program demonstrates just how rapidly these programs have grown in recent years.
In 2004, the year the Mountain View company went public, Google had an informal van pool program in which employees volunteered to drive small vans. But that year the company decided that using 35-passenger buses with professional drivers would be more efficient.
In 2007 Google hired Kevin Mathy to be its first transportation manager. Mathy had previously overseen shuttle networks for UC Berkeley, Genentech Inc. and Stanford University.
In an effort to get employees out of cars, Google's transportation program now includes the largest electric corporate car sharing program in the country as well as an on-demand taxi service and bikes for getting around the Googleplex.
But as Google's workforce has ballooned, the shuttle service has grown as large as the fixed-route suburban bus service of the Central Contra Costa Transit Authority. Biodiesel shuttle buses are free for employees.
Nathalie Criou of San Francisco loved riding the Google bus so much that after she left, she decided to create a Google bus "for the rest of us."
In 2011, the former Google product manager launched RidePal, a start-up that provides shuttle services for smaller Silicon Valley companies that can't afford their own fleet or for technology workers looking for an easier way to get to work.
"If Google can do it, then it should be possible to do it for everyone else," she said.