Flexibility - Carpooling can struggle to be flexible enough to accommodate en route stops or changes to working times/patterns. One survey identified this as the most common reason for not carpooling.[5] To counter this some schemes offer 'sweeper services' with later running options, or a 'guaranteed ride home' arrangement with a local taxi company.
Reliability - If a carpooling network lacks a "critical mass" of participants, it may be difficult to find a match for certain trips. The parties may not necessarily follow through on the agreed-upon ride. Several internet carpooling marketplaces are addressing this concern by implementing online paid passenger reservation, billed even if passengers do not turn up.
Riding with strangers - Concerns over security have been an obstacle to sharing a vehicle with strangers, though in reality the risk of crime is small.[15] One remedy used by internet carpooling schemes is reputation systems that flag problematic users and allow responsible users to build up trust capital, such systems greatly increase the value of the website for the user community.
Overall efficacy - Though carpooling is officially sanctioned by most governments, including construction of lanes specifically allocated for car-pooling, some doubts remain as to the overall efficacy of carpool lanes. As an example, many car-pool lanes, or lanes restricted to car-pools during peak traffic hours, are seldom occupied by car-pools in the traditional sense[citation needed]. Instead, these lanes are often empty, leading to an overall net increase in fuel consumption as freeway capacity is intentionally contracted, forcing the solo-occupied cars to travel slower, leading to reduced fuel efficiency. Further, many of the vehicles are occupied by passengers that would nevertheless consist of multiple passengers, for example a parent with multiple children being escorted to school.
In 2012, the Queensland government announce it would end car pool lanes (known as Transit Lanes) claiming they were creating congestion and delays. The move was supported by the RACQ motoring group