Real-time ridesharing (also known as instant ridesharing, dynamic ridesharing, ad-hoc ridesharing, on-demand ridesharing, and dynamic carpooling) is a service that arranges one-time shared rides on very short notice. This type of carpooling generally makes use of three recent technological advances:
These elements are coordinated through a network service, which can instantaneously handle the driver payments and match rides using an optimization algorithm.
Like carpooling, real-time ridesharing is promoted as a way to better utilize the empty seats in most passenger cars, thus lowering fuel usage and transport costs. It can serve areas not covered by a public transit system and act as a transit feeder service. Ridesharing is also capable of serving one-time trips, not only recurrent commute trips or scheduled trips.
In the early 2010s, several transportation network companies were introduced that were advertised as ridesharing, but in fact dispatched commercial operators similar to a taxi service. The first such service to appear on the market was the San Francisco based company Sidecar (launched in 2011). Transportation experts have called these services "ridesourcing" to clarify that drivers do not share a destination with their passengers; the app simply outsources rides to commercial drivers.
"Ridesharing" has been controversial, variously criticized as lacking adequate regulation, insurance, licensure, and training. One of the main so-called ridesharing (but actually ridesourcing) firms, Uber, has been banned in major cities such as Frankfurt, Barcelona, Vancouver, Buffalo and a number of other cities around the world. Opposition may also come from taxi companies and public transit operators, because they are seen as alternatives.
A 2010 survey at the University of California, Berkeley found 20% of respondents willing to use real-time ridesharing at least once a week; and real-time ridesharing was more popular among current drive-alone commuters (30%) than transit or non-motorized commuters. The top obstacles to using real-time ridesharing were short trip lengths and the added time of ride logistics.
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Early real-time ridesharing projects began in the 1990s, but they faced obstacles such as the need to develop a user network and a convenient means of communication. Gradually the means of arranging the ride shifted from telephone to internet, email, and smartphone; and user networks were developed around major employers and universities. As of 2006, the goal of taxi-like responsiveness still generally eluded the industry; "next day" responsiveness was considered the state of the art. More recently taxi-sharing systems that accept taxi passengers’ real-time ride requests via smartphones have been proposed and studied.
A number of technology companies based in San Francisco premiered apps for real-time ridesharing around 2012. However, in the fall of 2012, the California Public Utilities Commission issued a cease and desist letter to rideshare companies Lyft, Uber, Wingz, and Sidecar, and fined each $20,000. In 2013 an agreement was reached reversing those actions, creating a new category of service called "Transportation Network Companies" to cover both real-time and scheduled ride-sharing companies. Transportation Network Companies have faced regulatory opposition in many other cities, including Los Angeles, Chicago, New York City, and Washington, D.C.
Two dynamic ridesharing pilots in Norway received government funds from Transnova in 2011. One pilot in Bergen had 31 passenger in private cars during one day. Thirty-nine users acted as drivers or passengers between June 30 and September 15 with four ridesharing episodes or more. The phone apps that was used was Avego Driver and HentMEG.no cell client, a prototype developed for the NPRA of Norway. The other pilot is run by the company Sharepool.
Some more advanced real-time ridesharing features have been proposed but not implemented. For example, longer trips might be facilitated using "multihop" matches in which passengers change cars to reach their final destination.