The modeling of long-distance trips in statewide models differs from that of urban and regional models that focus on differentiating home-based from nonhome-based trips. Long-distance trips are more likely to be divided into categories by frequency of travel or by purpose such as recreational/tourist versus business-oriented. Such considerations are more likely to be indicative of long-distance variations by trip length, mode choice, and other aspects of travel. The American Travel Survey (ATS) was originally designed to obtain information on long-distance travelers; however, this survey was later discontinued and the most recent National Household Travel Survey (NHTS) is not structured for a targeted sample size of long-distance trips.

Also, statewide models in smaller and more urbanized states do not typically distinguish between urban and rural travel. However, it is generally accepted that rural area trip patterns differ from intra-urban travel, and so statewide models should attempt to distinguish between urban and rural trip-makers. While trip rates are readily available for transferability from urban and regional models, there are relatively few rural trip rates available to transfer for use in statewide travel demand models. Statewide models with trip generation rates derived from statewide surveys or National Household Travel Survey (NHTS) Add-On samples stratified into urban and rural respondents are worth evaluating as a potential source of transferable parameters.

Another issue is that most statewide travel demand forecasting models are built upon practices originally developed for urbanized area modeling. In the context of statewide forecasting, long-distance intercity and rural travel constitute important market segments; much more so than in urban models. Information describing these markets, and how these markets vary from state-to-state, is somewhat sparse, and many states do not have the resources to initiate original data collection to develop a set of model parameters.

While documentation related to the validation of statewide models is available, no comprehensive research assessing recent national datasets had previously been performed, and there has been no prior analysis of the transferability of parameters among statewide models. For urban models, there are also several sources of validation and reasonableness checking. These documents provide a set of excellent resources to evaluate urban models but do not provide any guidance on how superregional, intercity, and statewide travel parameters should be used or reasonable ranges of resulting long-distance travel parameters. The documents also do not provide guidance on how non-urban parameters should be used, reasonable ranges of those parameters, and how those parameters should be modified for rural areas.

The objective of NCHRP 8-84 was to develop and document transferable parameters for both long-distance and rural trip-making for statewide models. The recently published final report entitled NCHRP Report 735, Long-Distance and Rural Transferable Parameters for Statewide Travel Forecasting Models is a supplement to NCHRP “quick response” guidance on urban model parameters (e.g., NCHRP Report 716) and highlight reasonable sets of parameter ranges for rural and long-distance trip-making.