The transferability of transportation planning data used to estimate travel-demand models is investigated. It is noted that several travel-demand models can be estimated by using aggregate data, such as trip rates, mode shares, and trip-length frequency distributions. Aggregate data of this type were extracted from the National Personal Transportation Survey of 1995 (NPTS 95) and the North Central Texas Council of Governments Survey of 1996 and compared with those from the Baton Rouge Personal Transportation Survey conducted in 1997. The measures were similar in certain cases and dissimilar in others. Bayesian updating was used to update values from the NPTS 95 survey with values from a small survey conducted in Baton Rouge in 1998. Transferability was marginally improved, although it is expected that the improvement would have been more pronounced if a larger sample of approximately 500 households were available. A panel of 500 households surveyed on an annual basis and used to update transferred data from a variety of sources appears to present a more cost-effective solution to the provision of urban transportation planning data for model estimation than a periodic full travel survey.