Real-time ridesharing (also known as instant ridesharing, dynamic ridesharing, ad-hoc ridesharing, or 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:
- GPS navigation devices to determine a driver's route and arrange the shared ride
- Smartphones for a traveler to request a ride from wherever they happen to be
- Social networks to establish trust and accountability between drivers and passengers
These elements are coordinated through a network service, which can instantaneously handle the driver payments and match rides using an optimization algorithm.
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. It is also capable of serving one-time trips, not only recurrent commute trips. Furthermore, it can serve to limit the volume of car traffic, thereby reducing congestion and mitigating traffic's environmental impact.
One potential drawback may be economic harm to the auto industry due to sharing; however, some auto companies such as Daimler are quite supportive of real-time ridesharing research. Opposition may also come from taxi companies and public transit operators.
Potential market 
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.
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.
Most instant ridesharing services are still in their early stages. Successful pilot projects have been completed, but no real-time ridesharing company seems to have yet reached a critical mass of users.
The following organizations exhibit some of the characteristics of real-time ridesharing:
- CoWaG (All Smartphones in Germany)
- flinc (with GPS navi integration, social network, running on smartphones etc. german article)
- Smart Route (Android Application)
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.
In France, real-time ridesharing is provided by Geocar from Villefluide, which focuses on the commute market and utilizes a cluster model and algorithms.
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.
See also 
- Amey, A., J. Attanucci, and R. Mishalani. "'Real-Time' Ridesharing – The Opportunities and Challenges of Utilizing Mobile Phone Technology to Improve Rideshare Services." TRB Annual Meeting, 2011.
- Ecosummit TV – ECO11 – Young Future Mobility Leaders – Panel - ECOSUMMIT - Smart Green Economy Network and Conference
- Ecosummit TV – ECO11 – Klaus Dibbern – Flinc – Ride Sharing - ECOSUMMIT - Smart Green Economy Network and Conference
- Levofsky, Amber and Allen Greenberg. "ORGANIZED DYNAMIC RIDE SHARING: THE POTENTIAL ENVIRONMENTAL BENEFITS AND THE OPPORTUNITY FOR ADVANCING THE CONCEPT." Transportation Research Board, 2001.
- Elizabeth Deakin, Karen Trapenberg Frick, and Kevin Shively. 2012. "Dynamic Ridesharing." Access, 40: 23-28.
- Chan, Nelson and Susan Shaheen. "Ridesharing in North America: Past, Present, and Future." Transportation Research Board, 2010.
- United States Department of Transportation. "ADVANCED PUBLIC TRANSPORTATION SYSTEMS: THE STATE OF THE ART UPDATE 2006."
- Avego Ltd
- HentMEG.no website
- Sharepool website (Norwegian)
- Australian Ride share service
- Ride share website for North America an Australia
- MIT "Real-Time" Rideshare Research Page
- MIT "Real-Time" Rideshare Research Page
- Washington Post, 8/31/2012. Ride-Sharing Apps Take Off.
- Presentation on demand for real-time ride-sharing and its simulation in metropolitan Atlanta
- SocioTechnical Support for Ride Sharing
- Study on real-time ridesharing concepts, prior art, pilots and service introduction options
- Report of the Real-Time Rideshare Matching Problem, January 2011
- Study of real-time ride sharing from University of Zürich (Switzerland), August 2007 (German)
- A compendium of current and past ride sharing efforts
- A long analysis and partial design of a real-time system