Slugging is an informal carpooling arrangement that has developed over the past 30 years to meet High Occupancy Vehicle (HOV) highway restrictions that prevent single occupancy vehicles from using certain traffic lanes. Slugging increases access to ride sharing as it eliminates the need to plan formal carpools that can be difficult to maintain.  It helps reduce traffic and carbon emissions from cars, as well as save the participants gas money. With this practice comes a set of rules established through practice that compose a unique culture. Various organizations, such as the government, and the participants express particular opinions about slugging. The perspectives of each of these groups contribute to the overall success and growth of slugging.
Development of HOV Lanes
High Occupancy Vehicle (HOV) lanes were first developed in the 1970's as a response to several problems of the time: poor air quality, traffic, and a shortage of oil due to conflicts in the Middle East.  Today, HOV lanes are primarily promoted as a means of reducing congestion. 
HOV lanes began in Washington DC in the early 1970's along I-95 and I-395 and on I-66 in 1993. At first, 4 occupants were required in a vehicle to qualify for HOV status. In 1988 the standard was lowered to 3. In addition to I-95, I-395, and I-66, there are HOV lanes on I-270, 267/Dulles Toll Road, and I-50. All of these HOV roads are major arteries that allow people to travel long distances into the city. These other HOV roads are only HOV-2, likely due to the difficulty of organizing a carpool with 3 occupants. 
The highways only have HOV restrictions during the rush hour periods, typically around 5:30-9:00 AM and 3:00-7:00 PM on working days. The exact timing of HOV depends on how far away from the city the road is because this affects when the peak demand for the road will be. In addition, the HOV restrictions only apply in the direction of heavy traffic flow. The roads are regularly enforced with high fines and repeat HOV offenders may receive points on their license; this keeps the HOV lanes generally free of single occupancy vehicles. 
HOV lanes have been successful at getting people into the city. Including mass transit vehicles that use the lanes, HOV lanes account for 26% of morning rush hour traffic into Washington DC. A 2003 study indicated that trips on I-95/I-395 were twice as fast as non-HOV lanes and trips on I-66 were 50% faster in HOV lanes than in non-HOV lanes.  These massive time reductions have provided a strong incentive for commuters to obtain the necessary number of passengers to use the HOV lanes.
Critics have argued that HOV lanes are underutilized. It is unclear whether HOV lanes are sufficiently utilized to compensate for delays in the other mixed-use lanes.  Slugging has increased the use of HOV lanes in Washington; however, concerns about under-utilization have prompted an experiment with High Occupancy Toll (HOT) Lanes which allow single occupancy vehicles to use HOV lanes by paying a toll that varies to prevent congestion in the lanes. 
Gas Price Fluctuation
In 2005, studies show the first increase in shared rides since 1970.  This can be largely attributed to increases in fuel prices and limited resources, as an increase in price of $38.27 to $54.28 per barrel was observed between 2004 and 2005. The price of oil per barrel has continued to rise since then. Similarly, gas prices have fluctuated throughout history due to various world events that effect the availability of oil throughout the world. The first major event influencing the price of oil and HOV status was the OPEC Oil Embargo in 1973, increasing the price of crude oil from $4.65 to $8.05 per barrel between 1973 and 1974. Additionally, conflict in the middle east with the Iranian Revolution and the Iran-Iraq War led to the next major crude oil price increase; between 1978 and 1981 the price of oil increased from $10.75 to $36.67 per barrel. 
Although slugging has been documented in Houston, TX and San Franscisco, CA, the most popular slugging location is the Washington DC Metro Area..
Slug Lines & Maps
Pick up points for slug lines in the DC area generally lie near public transportation lines, like metro or bus stops. Originally, slugging was very informal and all of the pick up points were at bus stops along the I-95 corridor. People driving to work initiated the system by stopping at bus stops to pick up extra passengers so that they could drive in HOV lanes. Bus drivers nicknamed those waiting at bus stops (but not for the bus) slugs, as a slug is a counterfeit coin; in those days, a slug was essentially a counterfeit bus rider. There are currently 24 established slug lines in Northern Virginia; they are summarized on this map. Morning slug lines help commuters enter the city from the suburbs, while afternoon slug lines transport commuters from the city to their homes. Morning slug pick up points include locations in Washington DC, Springfield, Woodbridge, Stafford, and Fredericksburg. All afternoon slugs depart from various locations in Washington DC.
Although slugging is an informal practice, slugs and drivers follow a loose etiquette. Participants of slugging engage in the practice for the purpose of ride sharing and nothing else; similarly, the rules surrounding the symbiotic relationship between driver and slug promote simplicity not personality. This allows for mutual toleration of strangers in the car. At pick up points, slugs organize themselves by destination, and drivers call out their destination and offer rides on a first-come, first-served basis. Drivers generally only gather enough slugs in their car to meet HOV requirements; however, participants of slugging never leave a female slug alone at night. Since the relationship is mutually beneficial, both drivers and slugs must respect each other’s privacy and solidarity. Participants of slugging do not exchange names or talk unless the driver initiates conversation. Conversation is very limited and never includes controversial or personal subjects (politics, religion, family problems, etc.). The driver is the only person who can change the radio or temperature controls. It is common for drivers to play a neutral radio show or music, like the National Public Radio or smooth jazz music. Slugs also do not read or talk on the phone during the ride as a sign of respect for the driver. Drivers may not pick up additional slugs before the pick up point or drop off the slugs before reaching the destination. Both drivers and slugs thank each other at the destination, but the parties never exchange gifts or money. Compensation is neither offered nor desired by either party as both slugs and drivers benefit from the system. Slugs and drivers both reach their destination faster than otherwise as they can utilize HOV lanes .
Alternative Carpooling Initiatives
DC Metropolitan area transit authorities have created a program called Commuter Connections, which encourages commuters to use alternatives to single occupancy vehicle transit. Commuter Connections maintains a ride board that allows strangers to organize carpools to work, similar to slugging. Carpools can be organized in a variety of ways including alternating drivers and riders and pick-up at various locations. If there is a designated driver, the passengers are expected pay for gas and parking. Etiquette can also vary and is decided upon by each group of carpoolers. In addition, this program offers a guaranteed ride home to increase flexibility for participants. Commuter Connections offers tools and incentives for entire companies that join the program. They also disseminate information for commuters interested in bicycling, walking, or taking public transportation to work. 
Drivers & Riders
Slugging is seen as each group performing a service for the other. Passengers allow the driver get to utilize the HOV lanes and thus avoid traffic when commuting while the drivers offer riders a free trip. For this reason, it is rare that drivers pick up more slugs than is necessary to meet the minimum HOV requirement, as this would be viewed as a free handout. 
The response from slugging participants is overwhelmingly positive. Drivers cite reduced commuting time as the most important benefit to slugging. Riders mention lower gas costs, in addition to quick commutes, as their most important benefits.  Drivers and riders generally come from similar backgrounds as well. Most people involved in this form of transportation are between the ages of 25 and 34; people are also more likely to choose this form of transportation over public transit as their number of commutes per week increases .
Riders and drivers also mention the lack of formal carpooling arrangements and the lack of social interaction are benefits of the system. This is presumably because it lowers the overall costs associated with slugging. Neither party cites safety as a major concern.  In fact, there is little evidence of any crimes associated with slugging. 
Washington DC area governments generally approve of slugging. They see it as a similar system to public transit, as it reduces traffic during peak hours, except that it requires no additional funding. While the slugging system is dependent upon infrastructure paid for by the government (e.g. HOV lanes, Metro stations, etc.), once these structures are in place, slugging forms spontaneously. Therefore, most local transportation departments favor slugging and some actually work to support it. 
Some government officials are concerned that slugging does not actually reduce overall traffic. They claim that slugging merely steals riders off public transit systems, thereby not only reducing government revenue, but also remaining ineffective in the fight against road congestion. 
According to a 2011 study, slugging uses less energy per day for the same number of people than alternate methods of transportation.  In addition, it was estimated that in the San Francisco area, over half a million barrels of oil are conserved by slugging. Environmentalists who advocate a green lifestyle see slugging as a wonderful alternative to the traditional commute.
Why was carpooling unsuccessful despite numerous direct attempts to facilitate the process? People did not want to carpool before HOV lanes came around. Due to the inflexible nature of traditional carpools and the minor benefit of reduced gas costs, carpooling was not a feasible option for most commuters for many years. However, with the invention of HOV lanes, carpooling suddenly had the added benefit of reducing commute times. This additional benefit made carpooling a desirable commuting choice. Thus, we see that if government wants to implement a new public policy, it cannot simply give people the resources to change their behaviors, it needs to make people want to change their behavior.
The global warming movement shows an example of this lesson. Federal and state initiatives have attempted to tackle the problem but these efforts have had limited success. However, Al Gore's 2006 movie An Inconvenient Truth has had significant impact on the issue. By making people more aware of the global warming problem, the movie has convinced many people to act in a more environmentally friendly way; 74% of people polled stated they changed their behaviors to lower their carbon output after watching the movie.  By causing people to want to change their behavior, An Inconvenient Truth was able to get closer to its overall policy goal of reducing total greenhouse gas emissions.
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