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A "slug line" of passengers waiting for rides

Slugging,[1] also known as casual carpooling, is the practice of forming ad hoc, informal carpools for purposes of commuting, essentially a variation of ride-share commuting and hitchhiking. A driver picks up these non-paying passengers (known as "slugs" or "sluggers") at key locations, as having these additional passengers means that the driver can qualify to use an HOV lane or enjoy toll reduction. While the practice is most common and most publicized in the congested Washington, D.C. metropolitan area, slugging also occurs in San Francisco, Houston, and other cities.


In order to relieve traffic volume during the morning and evening rush hours, high-occupancy vehicle (HOV) lanes that require more than one person per automobile were introduced in many major American cities to encourage carpooling and greater use of public transport, first appearing in the Washington D.C. metropolitan area in 1975. The failure of the new lanes to relieve congestion, and frustration over failures of public-transport systems and high fuel prices, led to the creation in the 1970s of "slugging", a form of hitchhiking between strangers that is beneficial to both parties, as drivers and passengers are able to use the HOV lane for a quicker trip. While passengers are able to travel for free, or cheaper than via other modes of travel, and HOV drivers sometimes pay no tolls, "slugs are, above all, motivated by time saved, not money pocketed". Concern for the environment is not their primary motivation.

In the Washington area—with the second-busiest traffic during rush hour in the United States and Canada as of 2010[2]—slugging occurs on Interstates 95, 66 and 395 between Washington and northern Virginia.[3] As of 2006, there were about 6,459 daily slugging participants there.[4]

In the San Francisco Bay Area, with the third-busiest rush hour,[2] casual carpooling occurs on Interstate 80 between the East Bay and San Francisco. As of 1998, 8,000 to 9,000 people slugged in San Francisco daily.[4] However, after bridge tolls were levied on carpool vehicles in 2010, casual carpooling saw a significant decline and etiquette became more uncertain.[5] Among the effects of the COVID-19 pandemic in the San Francisco Bay Area was the end of casual carpooling in March 2020.

As of November 2022 the tradition has not materially resumed; although drivers continue to hope to see waiting passengers at designated pickup spots, the spontaneous nature of the program means that there is no one to officially restart it,[6] although several smartphone apps have been developed.[7]

Slugging also occurs in tenth-busiest[2] Houston,[8][9][10] at a rate of 900 daily in 2007,[4] and in Pittsburgh.[11]

Slugging is shown to be effective in reducing vehicle travel distance as a form of ridesharing.[12]

Slugging is more used during morning commutes than evening commutes. The most common mode that slugging replaces is the transit bus.[13]

David D. Friedman's The Machinery of Freedom proposed a similar system (which he referred to as "jitney transit") in the 1970s. However, his plan assumed that passengers would be expected to pay for their transit, and that security measures such as electronic identification cards (recording the identity of both driver and passenger in a database readily available to police, in the event one or both parties disappeared) would be needed in order for people to feel safe.[14] Although slugging is informal, ad hoc, and free, in 30 years no violence or crime was reported from Washington D.C. slugging[10] until October 2010, when former Sergeant Major of the Army Gene McKinney struck one of his passengers with his car after they threatened to report his reckless driving to the police.[15]


The term slug (used as both a noun and a verb) came from bus drivers who had to determine if the people waiting at the stop were genuine bus passengers or merely people wanting a free lift, in the same way that they look out for fake coins—or "slugs"—being thrown into the fare-collection box.[16]

General practices

In practice, slugging involves the creation of free, unofficial ad hoc carpool networks, often with published routes and pick-up and drop-off locations. In the morning, sluggers gather at local businesses and at government-run locations such as park and ride-like facilities or bus stops and subway stations with lines of sluggers. Drivers pull up to the queue for the route they will follow and either display a sign or call out the designated drop-off point they are willing to drive to and how many passengers they can take; in the Washington area the Pentagon—the largest place of employment in the United States, with 25,000 workers—is a popular destination. Enough riders fill the car and the driver departs. In the evening, the routes reverse.[16][10]

Many unofficial rules of etiquette exist, and websites allow sluggers to post warnings about those who break them.[10] Some Washington D.C. rules are:

Government involvement

While local governments sometimes aid sluggers by posting signs labeled with popular destinations for people to queue at, slugging is organized by its participants and no slug line has ever been created by government. Slug lines are organized and maintained by volunteers. Government officials have become more aware of sluggers' needs when planning changes that affect their behavior, and solicit their suggestions.[10] The Virginia Department of Transportation even includes links on their governmental webpage regarding slugging.[18]

Other examples

In France, spontaneous carpool lines have been established in rural municipalities by Ecov using electronic signs and smartphone apps to alert drivers of waiting riders.[19]

In Jakarta, "car jockeys" had been paid by commuters to ride into the center of the city to permit the use of high-occupancy vehicle lanes[20] until the lanes were eliminated in 2017.[21]

In India, it is illegal for drivers to randomly pick up commuters from the public roads and there is evidence that such drivers have been fined.

In the Polish People's Republic, hitchhiking was officially supported by the government (and formalized), and in Cuba, government vehicles are obligated to take hitchhikers, but these systems have nothing to do with high-occupancy lanes.

See also


  1. ^ "What are Sluglines". Sluglines.
  2. ^ a b c Quain, John R. (2010-11-24). "New York Has Worst Traffic in U.S. and Canada, Report Says". The New York Times. Retrieved March 8, 2011.
  3. ^ "Map of Slugging Sites in Washington DC". Retrieved March 7, 2011.
  4. ^ a b c Chan, Nelson and Susan Shaheen. "Ridesharing in North America: Past, Present, and Future." Transportation Research Board, 2010. Archived 2011-06-26 at the Wayback Machine
  5. ^ Lee, Linda and Karen Frick. "San Francisco-Oakland Bay Bridge Congestion Pricing." Bay Area Toll Authority, 2011.[permanent dead link]
  6. ^ Savidge, Nico (2022-11-20). "Casual Carpool was a Bay Area tradition before COVID. Can it make a comeback?". Berkeleyside. Retrieved 2023-06-30.
  7. ^ Brekke, Dan (October 19, 2023). "What Happened to Casual Carpool?". KQED.
  8. ^ Falkenberg, Lisa (July 2, 2007). "Slugs avoid the slow lane". Houston Chronicle.
  9. ^ Burris, Mark W. and Justin R. Winn (2006). "Slugging in Houston—Casual Carpool Passenger Characteristics". Journal of Public Transportation. 9 (5): 23–40. doi:10.5038/2375-0901.9.5.2.
  10. ^ a b c d e Badger, Emily (2011-03-07). "Slugging — The People's Transit". Miller-McCune. Archived from the original on March 8, 2011. Retrieved March 7, 2011.
  11. ^ News Story – Slugs and Bodysnatchers
  12. ^ S. Ma, O. Wolfson. (2013) Analysis and Evaluation of the Slugging Form of Ridesharing. Proceedings of the 21st ACM SIGSPATIAL International Conference on Advances in Geographic Information Systems, 2013.
  13. ^ Mark W. Burris and Justin R. Winn. Slugging in Houston—Casual Carpool Passenger Characteristics. Archived 2014-08-13 at the Wayback Machine Journal of Public Transportation, Vol. 9, No. 5, 2006.
  14. ^ Friedman, David D. (1989). "99 and 44/100ths Percent Built". The Machinery of Freedom. pp. 75–77. ISBN 0-8126-9068-0.
  15. ^ Augenstein, Neal (2011-12-11). "Sergeant Major Gets Weekend in Jail for Slugging Incident". Retrieved March 17, 2012.
  16. ^ a b Clarke, Rachel (October 15, 2003). "'Slugging' to avoid Washington slog". BBC News.
  17. ^ Etiquette and Rules of Slug Lines
  18. ^ High Occupancy Vehicle (HOV) Lanes - Rules and FAQs. Retrieved on 2013-08-15.
  19. ^ "Reducing commuter traffic in Val de Saône with carpooling (France)". June 13, 2019.
  20. ^ Jakarta's jockeys in demand as gridlock drives city to despair. (2012-02-04). Retrieved on 2013-08-15.
  21. ^ McFarland, Matt (July 6, 2017). "A city scraps its HOV lanes. Disaster ensues".

Further reading