The methods used to develop a travel forecasting model for the Washington State Ferries (WSF) are described. The model is being used to develop ridership forecasts for the WSF Long-Range System Plan and other project planning efforts. The WSF model covers a 12-county ferry system service area, including the four counties within the central Puget Sound region. The model was designed to be sensitive to policy variables and to produce detailed ridership forecasts on each ferry route by ( a) boarding methods, ( b) mode of access and egress combinations for walk-on passengers, and ( c) vehicle occupancy for those persons boarding by vehicle. The model is fully incremental and uses observed travel patterns from a comprehensive on-board origin-destination survey of ferry riders conducted in 1993 for the afternoon peak period. Choice of terminal is an intermediate destination choice for walk-on ferry riders and is a prime example of trip chaining between an origin and destination. A new method involving matrix algebra has been used to formulate choice of terminal in terms of matrix products. This method estimates demand matrices corresponding to individual legs of the trip chain for each access and egress mode combination. The modeling system was validated for replication of ridership on each route by boarding methods and by mode of access and egress combinations.