Walker also told Gottlieb to hold new bonding to a "reasonable level."

Nygren said Wednesday it's "unrealistic" to expect the department to be able to identify nearly $1 billion worth of efficiencies to address the projected shortfall.

He also noted that Walker has previously said he won't approve any tax or fee increases without an offset somewhere else in the budget. Given other budget necessities, Nygren said, it's also not realistic to expect any additional transportation revenues could be offset with a cut elsewhere.

Walker has instructed Gottlieb to submit a complete budget by the Sept. 15 deadline "in order to allow for a full public discussion," rather than submitting a partial budget in September and a full budget in November as the DOT traditionally does.

Nygren said he doesn't have a specific level of bonding in mind with which he would be comfortable, and added that he doesn't want to advocate specific policy proposals just yet. Rather, he said, he wants to start the discussion well in advance of the budget process.

That conversation should take place beyond the walls of the state Capitol, Nygren said.