Incentive-Based Carpooling Application Launched in Seattle Area Led to 85 Percent Reduction in Single Occupancy Vehicle Mode Share, Based on the Participants’ Survey Responses.
A Policy Experiment Facilitated by the Collaboration Between a Public Transit Agency in Seattle and a Dynamic Carpooling Service Provider Was Used to Evaluate the Impact of Monetary Incentives on Car-pooling Behavior Among Survey Participants.
Date Posted

Exploring partnership between transit agency and shared mobility company: an incentive program for app-based carpooling

Summary Information

Technological advancements and development of mobile information and communication has helped app-based shared mobility services emerge as a competing mode of urban transportation. This study conducted a data-based research to understand how public transit agencies can deliver mobility services with shared mobility and ride-hailing services on the rise. King County Metro – the primary transit agency in the Seattle region launched the Carpool Incentive Fund (CIF) program aimed towards building a shared mobility public-private partnership with a dynamic carpooling service provider in the region. As a part of the program, participants who commuted using the dynamic app-based carpooling service were offered monetary incentives. The five-month program offered up to $2 incentive to participant of each carpooling trip from December 2018 to April 2019. Statistical models were used to evaluate the effects of the monetary incentive in encouraging the use of app-based carpooling.


Data-based research is undertaken to evaluate the effects of various strategies that can facilitate carpooling through a collaboration between the public and the private sector in the transportation environment in Seattle. The research study integrated two types of data – a detailed data set that contained information regarding carpooling trips including trip duration, origin and destination at the census tract level, vehicle occupancy, trip cost and amount of incentive provided. The second type of data was collected through an electronic survey of carpool participants enquiring about their travel behaviors, socio-demographic characteristics, habits and preferences. Statistical models were developed using these two datasets to evaluate the CIF program using quantifiable metrics such as reduction in VMT and change in travel preferences before and after the introduction of the program. 


  • Nine percent of the survey respondents reported using single occupancy vehicles (SOV) as their primary mode after the availability of carpooling services as compared to 58 percent before the service was made available (a 85 percent reduction). The average carpool occupancy per trip was between 2.37 and 2.4 during the program period indicating that a large proportion of the carpooling trips were shared by three or more people.
  • The substitution effect on other modes was strong among the commuters who adopted carpooling. Only 7 percent of the survey respondents used public transit after the introduction of carpooling services as compared to 25 percent before the implementation.
  • The monetary incentive provided by the Kings County Metro resulted in a reduction of 900,000 – 1,000,000 vehicle miles traveled during the experiment period with an estimated cost of $0.40 per vehicle mile travelled. The reduction in VMT does not include long term impacts of the carpooling program after the monetary incentive had been removed. 
Results Type
Deployment Locations