It’s a U.S. phenomenon that’s happening in just three cities. Tens of thousands of people congregating in crowded parking lots. In some circles they call themselves either “body snatchers” or “slugs,” and their motive is simple: they want to save time and money.

It’s called casual carpooling. It occurs in Washington, D.C., San Francisco and Houston. Every morning and evening, the slugs gather in park-and-ride lots, transit stations or other designated public areas waiting for a ride from a body snatcher. Two slugs get into a stranger’s car and head for the highway’s high-occupancy vehicle (HOV) lane, which requires at least three people per vehicle (also known as HOV3+).
“The slugs pool their money and pay for all three if there’s a toll. The body snatcher supplies the vehicle, and working together like this, they arrive at their destination much sooner than if they drove themselves or used city transit,” Texas Transportation Institute (TTI) Associate Research Engineer Mark Burris explains. Burris researched Houston “slugging” more than a decade ago, and last year he was part of a Federal Highway Administration scan tour of the three cities. In the case of Washington, D.C., and San Francisco casual carpooling, it’s been going on for more than 30 years.
“It’s an amazingly well-organized event that is extremely efficient, saving fuel and time. We estimated that 25,000 people casual carpool in D.C. each day. That takes a lot of cars off the road,” Burris notes. On the day he slugged in D.C., his trip into the city took 30 minutes in the HOV lane, but another scan team member who used the congested general-purpose lanes took 90 minutes.
Among one of the more unusual stories Burris heard during his research involved an elderly woman who would pick up slugs and, instead of using the HOV lane, insisted on using the congested general-purpose lanes. Turns out the woman was lonely and wanted the additional time with the strangers. Word spread like wildfire, and the woman and her car were quickly avoided by the slugs.
Last month, TTI Senior Research Engineer Ginger Goodin was in San Francisco for a conference on managed lanes and became a slug in order to take part in the casual carpooling experience firsthand. “There is a whole set of understood and accepted protocols and rules of etiquette governing the casual carpooling culture, without any government involvement,” she says. “I was one of about 20 people who took a casual carpooling technical tour as part of the conference. I rode across the Oakland Bay Bridge into the city with two people I had never met.” The tour participants were all asked to write about their experiences.

Goodin entitled her story “A Texan’s First Experience as a Slug,” describing her trip with a driver and a fellow slug who had been getting across the bridge this way for more than 20 years. “In my story I called him pro-slugger because he had been doing this for so long. He wasn’t concerned about the safety issue of riding with a stranger — other than riding with some erratic drivers over the years. It seems that the sluggers and the body snatchers learned about casual carpooling from friends and family.”
So, why isn’t casual carpooling occurring in other places?
Goodin thinks it’s because of the unique situation in each of the three cities. “For one thing, there has to be a centralized activity center for a destination location, and there has to be an HOV3+ lane that provides a time-saving advantage. If only two people were required in a car, I think a rider would be less likely to get in a car with just one stranger. There’s a perceived measure of safety with three strangers,” she says.