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9 transit to the greatest extent. In part, the article assesses whether are co-located with mass transit access, providing commuters or not casual carpools should be encouraged. Beroldo comes with the option to take transit if they cannot get a ride carpool- to mixed conclusions, tentatively contending that casual ing (Oliphant 2008). carpooling should be discouraged because it adds vehicles to the road. He qualifies this conclusion, saying it may only An additional document, Flexible Carpooling: Exploratory apply to the Bay Area. On the other hand, he suggests that Study (Dorinson et al. 2009), written by researchers at the casual carpooling could be encouraged if it reduces demand University of California at Davis, concludes that the circum- on transit service along a particular corridor, thereby allowing stances where casual carpooling would draw from public transit service to be increased along other corridors, which transit depend on the quality of the service available. For might attract new riders and take cars off the road. The article example, flexible/casual carpooling would be attractive if also provides insight into the effects of casual carpooling on the transit trip involved multiple providers and poor con transit agencies, citing several problems reported by BART nectivity. However, as a benefit to society, "the energy savings and AC Transit (AlamedaContra Costa Transit). These prob- of flexible carpooling are similar to what could be achieved by lems include a decline in public transit ridership and revenue an express bus service, but without the cost of providing the bus and a lack of parking available for roundtrip transit patrons. service." The authors recommend research trials to determine In response, the transit agencies have made changes to their whether flexible carpooling can reduce demand for peak hour operations, although attempts to control or discourage casual transit service, thereby also reducing overall transit costs. carpooling have been largely ineffective (Beroldo 1990): a survey conducted in 2010 by 511 Rideshare reported that Dynamic Ridesharing 47.3% of casual carpoolers indicated they previously com- muted by BART or AC Transit before they started casual Dynamic ridesharing is same day or "on the fly" ridesharing. carpooling. From November 2005 through May 2006, BART participated in a focused test of dynamic ridesharing at one of its stations On the other hand, a recent article, "Estimating the with impacted parking called RideNow! The results of the Energy Consumption Impact of Casual Carpooling" (Minett test are documented in a report to the Alameda County and Pearce 2011) notes that casual carpooling can reduce the Congestion Management Agency titled RideNow! Evaluation number of buses needed. The authors estimate that $30 million Final Report (Nelson\Nygaard 2006). Through the web or an a year could be saved from casual carpooling on the Bay automated telephone system, riders requested rides minutes Bridge leading to San Francisco in the morning commute. before leaving home or on the BART train in the evening. This conclusion is based on the need for fewer bus purchases Because eight partner agencies were involved, the project faced and paid drivers by AC Transit, which operates the transbay multiple challenges in implementation. Only 12% of the ride bus service across the bridge, as well as the value of time saved, requests were fulfilled. Recommendations for future projects lower emissions, and fewer accidents. included substantial simplification of the program, increased target marketing, and more time to build the volume of drivers The other articles are essentially case studies of specific and riders (2006). cities. "Slugging in Houston--Casual Carpool Passenger Characteristics" (Burris and Winn 2006) describes how casual "Markets for Dynamic Ridesharing? Case of Berkeley, carpooling in the Texas city occurs at three park-and-ride lots, California" (Deakin et al. 2010) is a study to assess the potential which are primarily used for transit. In the San Francisco area, of dynamic ridesharing to downtown Berkeley and the Univer- casual carpooling is a one-way phenomenon; most passengers sity of California. The area has high rates of walking, biking, carpool in the morning but take BART and AC Transit home and transit use, causing university and city officials to question in the evening, according to Casual Carpooling 1998 Update whether dynamic ridesharing would encourage undesirable (RIDES 1999). A 2010 update of that report confirmed this shifts away from these travel modes rather than reducing finding and further found that the vast majority of casual car the number of single drivers. The researchers found that "the poolers planned to continue their commuting practices despite potential market for dynamic ridesharing to the campus was a new toll on carpools (511 Rideshare 2010). According to up to 1,200 if no restrictions were placed on participation and another article "Slugging--The People's Transit," however, a more modest 700 if the program were limited to those who carpooling decreased 26% on area bridges a month after the were outside of walkbiketransit zones." The study concludes tolls were implemented (Badger 2011). with nine policy implications for consideration if a dynamic ridesharing program is to be implemented. Slugging reportedly began in Northern Virginia in the 1970s along Interstate 395 high-occupancy vehicle (HOV) Economic Considerations of Ridesharing lanes (Badger 2011). Today, it is estimated that roughly within Public Transit Agencies 10,000 people travel to Arlington and the District of Columbia by means of slugging. So-called slug lines form in areas that Some transit agencies consider the economics of supporting have ample parking and are close to HOV routes. Most slug vanpools over instituting more commute-hour bus service. lines, according to "The Native Slugs of Northern Virginia," A section of a 1978 document, Recent Developments in Bus