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Increase of Car Occupancy through Innovative Measures and Technical Instruments

European Union
Complete with results
Project Acronym
STRIA Roadmaps
Smart mobility and services (SMO)
Transport policies
Environmental/Emissions aspects,
Societal/Economic issues
Transport sectors
Passenger transport


Background & Policy context

The growth of traffic in cities is leading to rising levels of congestion. The provision of new infrastructure is often not a solution, since it can generate more traffic and make the urban environment less attractive. Another approach is to make better use of the existing infrastructure, by filling the unused space in vehicles. For example, in peak period commuter traffic, average car occupancy rates may be as low as 1.2. Therefore car-pooling seems attractive, where at least two people ride in a private car usually owned by one of the occupants. (This is also known as car sharing in the UK.) However, little is known about people's attitudes towards car-pooling and how best to promote this behaviour.


The aims of ICARO were to evaluate measures for increasing car occupancy rates in European countries and to provide guidelines for policy development and implementation strategies.


Parent Programmes
Institution Type
Public institution
Institution Name
European Commission; Directorate-General for Energy and Transport (DG TREN; formerly DG VII)
Type of funding
Public (EU)


Through surveys, demonstrations and modelling in eight countries, ICARO identified the success factors for car-pooling, including the effectiveness of supporting measures such as parking restrictions/incentives and high occupancy vehicle (HOV) lanes.


Car-pooling was found to be the most successful for employees from the same work place. Therefore, initiatives to promote this behaviour are best targeted on the workplace, particularly by working with companies. The willingness to car-pool increases with the distance between home and work.


The majority of people looking to car-pool were found to be drivers, particularly those with regular working hours. Experience with matching centres, set-up to put drivers and passengers in touch, showed that they need at least 500-800 clients to provide an effective service - or at least 100 clients in a single company scheme.


One of the most effective ways of increasing car occupancy is through the provision of infrastructure measures such as HOV lanes. Test site experience showed that car-poolers cut their travel time by 3.5 minutes using a 1.5km HOV lane in Leeds. Preferential parking for HOVs at the workplace has limited impact, especially where parking is readily available and free of charge. ICARO found no convincing evidence that guaranteed ride home schemes are influential on the decision of people to car-pool. Public acceptance is greater for incentive measures than for restrictions like HOV lanes or banning single occupancy vehicles from the city centre.


ICARO estimated that perhaps 30% of car users have the freedom to choose car-pooling as an option. However, this potential is reduced particularly where there is a tendency towards flexible working hours, which is a serious obstacle to car-pooling.

ICARO produced a number of publications on the introduction of car-pooling, available from the project web site.

Policy implications

Test site experiences showed that general promotion campaigns for car-pooling are not effective. ICARO recommended focusing on companies and commuters at the workplace, by embedding car-pooling in 'Green Commuter Plans' or 'Travelwise' campaigns.

There are various legal barriers to car-pooling and the development of HOV lanes that need to be overcome. ICARO recommended that:

  • The terms car-pooling and HOV should be defined in national legislation for policy and insurance use.
  • In many countries, the tax treatment for reimbursement of costs between car-poolers needs to be defined.
  • The insurance situation for car-pooling should be clarified.
  • For most countries, HOV lane regulations still need to be included in the national traffic regulations. Linked to this, a harmonised European car-pooling sign for HOV infrastructure should be agreed.

Project results indicated that measures to make car-pooling more attractive run the risk of attracting people from public transport. However, restrictive measures tend to promote both car-pooling and public transport, and are more effective in increasing the car occupancy rate than incentives alone.


Lead Organisation
EU Contribution
Partner Organisations
EU Contribution


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