The Statement of Requirements leads to the development of the Functional and Technical Specifications for the transport model. It also enables the travel survey planning to commence, for which three sets of documents are likely to be needed:
Travel surveys can go badly wrong: samples are not achieved, survey questions are misunderstood by respondents, key items of data are omitted, expanding the sample to the full population turns out to be impossible etc. So my advice is to build yourself a safety net by appreciating the risks and drawing widely on expertise and experience. Some of my links provide formal travel survey design guidance and there are numerous textbooks on the subject.
A transport modeller must take responsibility for deciding what information should be collected to meet the transport modelling requirements, indeed this should be formally specified as a brief to the travel survey designer; the scope of this brief should include:
The transport modeller and travel survey designer must reconcile their differing experiences. There is no point in the transport modeller demanding data to be collected which cannot be achieved accurately or reliably in practice and there is no point including standard questions if these are not actually needed by the transport modeller - indeed any extraneous data will usually undermine the collection of the important data.
Where a standard form of travel survey is envisaged it is a good idea to obtain descriptions of similar successful travel surveys carried out elsewhere including the questionnaires. For complex or expensive travel survey programmes it is sensible to consult with the government organisations which have sponsored similar types of travel survey to gain an appreciation of their experiences.
A survey agency to execute the travel surveys is required. Here there are the major issues of supervision and quality control and, if your travel survey specification has significant deficiencies, they will be there when you take collection of the data.