Preliminary design is the process of advancing preliminary engineering and obtaining formal community and environmental approval of the Initially Preferred Alternative. PD denotes preliminary design by NJDOT; LPD denotes local preliminary design by a local entity (MPO, county, municipality).

During preliminary design, the Project Manager who was liaison for the Feasibility Assessment phase will assume full control of the project. A number of activities will be simultaneously set in motion, based on the Initially Preferred Alternative (IPA): community involvement, environmental documentation, and design services.

To obtain the formal community involvement buy-in, a public meeting will generally be arranged, which may lead to some minor adjustments to the project's scope. Ultimately, the local officials will be asked to provide a resolution of support endorsing the project.

To obtain the environmental approvals for the IPA, consultation with outside agencies, such as the State Historic Preservation Office may be necessary. The approved environmental document will be based on technical studies conducted by the environmental teams within the Division of Environmental Resources, and will generally consist of a Categorical Exclusion. The preliminary design phase will not be considered complete until the environmental document is approved.

The preliminary design conducted during this phase will be initiated to facilitate later final design activities. They will be based on the IPA, and consist of, among other things: development of base plans for final design; development of geometric design sufficiently to clarify environmental impacts and to define right-of-way parcels; utilities discovery and verification; geotechnical studies (soil borings and analysis); preliminary drainage work; and development of property acquisition cost estimates.