Geography can influence social behavior and that’s the case with slug lines. This has nothing to do with bugs, rather it’s a commuting method originating organically without any type of government involvement or sanction in the Washington, DC area (and since spreading to other cities). Also sometime called “casual carpooling,” it’s an efficient arrangement that matches drivers with enough passengers to use High Occupancy Vehicle (HOV) lanes on instant, adhoc basis.
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First, understand the geography. The Potomac River separates the Commonwealth of Virginia from the District of Columbia. The only direct way to drive from Virginia into the District involves bridge crossings so by definition the river serves as a barrier. Traffic backs up after exceeding bridge capacity and there are no alternate routes. Drivers can’t take a secret shortcut or a side streets because they still can’t get across the river
It gets more insidious. Washington was consciously placed as far upstream as a ship could reach. That was great for 19th Century commerce when rivers served as the primary inland highways, but it’s generally irrelevant to the economy of the area today. As the Piedmont gives way to the Coastal Plain the river increases in width and takes a jog to the south. It quickly becomes too broad for additional bridge crossings after the Beltway and makes it impossible for vehicles to swing to the east to help dissipate traffic. Commuters from Virginia towns towards the south such as Fredericksburg, Stafford and Woodbridge funnel directly down the Interstate 95 / 395 corridor on a straight line shot directly towards the District. Gridlock ensues.
Traffic planners created carpool lanes as one way to take automobiles off the road. If people shared cars, the reasoning goes, savvy commuters could use the HOV and bypass the majority of the traffic. Everyone wins: fewer cars; less stress on the environment; and fewer hours in traffic. However it’s not that easy. Few individuals know a steady group of people who just happen live and commute to similar places on the same schedule everyday, even if inclined to carpool.
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The biggest bottleneck developed right here along the Henry G. Shirley Memorial Highway, or Interstate 395 inside the Beltway. Starting in the 1970’s, local drivers began cruising past bus stops in Springfield, asking if anyone wanted a free lift into the city so they could use the HOV lanes. Bus drivers disdainfully referred to those lost passengers as “slugs,” a slang term for fake coins placed in collection boxes used to avoid paying fares.
Over time the practice began to organize more formally. Specific, regular slug lines formed in the mornings and evenings. Elaborate social contracts, cultural norms and commonly understood ground rules developed. For instance, it’s considered impolite to talk, change the radio, adjust the heating or air conditioning, or use a mobile phone during the ride, unless expressly granted permission by the driver. It’s like riding in an elevator. Anything more than a quick acknowledgment is considered obtrusive. In the Internet age this hidden movement became more visible, with the inevitable website devoted to the practice. If you look at the website forums you’ll notice lots of angst among longtime practitioners as their system strains under the weight of newbies who don’t understand the rules, driven to slug lines by rising gasoline prices. How or whether slugging adjusts to this influx will be an interesting topic to follow.
If there were no river there would be no need for slugging. The practice does not exist on the other side of the river where a similar number of commuters arrive from Maryland.
UPDATE (November 10, 2008): Slugging depends upon a delicate balancing of nearly unique conditions. Recent proposals to change I-395 from HOV to HOT lanes has raised concerns about whether slug lines may be able to adapt or not, as described in a recent Washington Post article – ‘Slugs’ Fear HOT Lanes Will End Free Rides.