Senate Environment and Public Works Chairman Barbara Boxer (D-Calif.) was optimistic Tuesday that a deal on a transportation bill could be struck before the July 1 deadline.

Boxer said aides to top negotiators have moved beyond the organizational level and are now debating key elements of the bill. She and House Transportation and Infrastructure Chairman John Mica (R-Fla.) have been speaking regularly on the phone and plan to meet in person Thursday, after which Boxer will brief the rest of the panel.

However, the deal could face challenges given that the House and Senate calendars do not match up between now and the final deadline, when highway projects would lose funding.

The House will be in recess next week, and Memorial Day has pushed back votes until May 30 the following week; the chamber will recess again from June 9 to June 17. The Senate is in recess from May 28 to June 1.

It is not yet clear when talks will begin in earnest at the Member level, but staffers have put in more than 20 hours of work.

“I can’t really tell,” Senate Majority Whip Dick Durbin (D-Ill.) said when asked when Member-level negotiations would really begin.

“If the House would stick around, or at least the conferees, it would help,” he added, noting the difficulties of the schedule.

In addition to the scheduling conflicts, Senators are coming to the table with a two-year, $109 billion bill that passed on a broad bipartisan vote, while House conferees hope to work from a shell bill that did not have enough support to reach the House floor.

The conference itself was deliberately designed to be large and inclusive in the hope that significant support from the conferees could lead to easy approval from both chambers. But Speaker John Boehner (R-Ohio), in a bit of a gamble, appointed eight freshmen to his 20-
Member conference delegation. The support of those new Members, many of whom are averse to government spending, will be key to the success of the conference committee and the legislation itself.

Boxer has been holding office hours for conferees who have questions. And she said Tuesday she has met face to face with some GOP freshmen, though she declined to specify which ones.

“I’m not treating the freshmen any different,” Boxer said. “My door’s open to everybody, and I am having individual meetings with those who have asked for those and who have reached out to me, and a couple of those are freshmen.”

The California Democrat worked with the top Republican on her committee, Sen. James Inhofe (Okla.), to craft the Senate bill. Inhofe is one of the body’s most conservative Members, but he has steadfastly defended the infrastructure spending.

Boxer touted the support of the traditionally Republican-leaning U.S. Chamber of Commerce, which published an op-ed earlier this week stating “it’s still critical” to get the transportation authorization bill approved, despite some of its flaws.

And she’s hoping the relatively open and transparent process will lead to another completed bipartisan product. She intends to deliver weekly updates, much like the press conference she held Tuesday. Boxer indicated what several aides close to the panel have suggested: that at least so far, no Member has doubled-down on any single issue, and lawmakers are still fairly open-minded about what might be included in the final product.

One of the more controversial measures, for example, is language on the Keystone XL oil pipeline included in the House bill. The pipeline enjoys bipartisan support, but President Barack Obama has said he would veto any bill that includes its authorization. Boxer would not say definitively whether Keystone would be removed from the final report, but she did note that she represents the “will of the Senate” in the panel and that the Senate has rejected the pipeline.

Boxer also said that no one on the committee has indicated Keystone would be a deal-breaker.

“No. No one has laid a marker down or [drawn] a line in the sand,” she said.

Most of the staff work to date has come from aides to the committee chairmen. But there are smaller working groups within the larger, 47-member conference. Those working groups are being led by Members whose committees roughly match up to the issues at hand.

For instance, Senate Finance Chairman Max Baucus (D-Mont.) is working on finding offsets for the legislation and Senate Commerce Chairman Jay Rockefeller (D-W.Va.) is working on transportation safety provisions.

Other working groups are dealing with the reparations from BP to states affected by the 2010 oil spill, the Keystone pipeline and coal ash.