Congress worked harder in the first six months of its session, outpacing the last several legislatures, according to a new report.

The Senate in particular seems to be running on the fast track. The Senate has clocked 86 working days from when Republicans took control of the chamber in January until the end of June. That's a double-digit increase in the number of days worked from the two previous sessions, when Democrats were in control. There were 71 working days in the first six months of the 2013-15 Congress and 73 during the 2011-13 Congress.

But there is still room to improve, according to the Bipartisan Policy Center. On Tuesday, the center released the second quarterly installment of its "Healthy Congress Index," featuring a series of metrics by which the effectiveness of Congress is evaluated. The index looks at 65 recommendations written by the the center's Commission on Political Reform on how to bridge the partisan divide and improve the effectiveness of the legislative branch.

While 86 working days is an improvement, the "Healthy Congress Index" recommends 90-100 working days in a six-month period, not achieved since the 2009-10 Congress.

"There's room for improvement," former Sen. Olympia Snowe, R-Maine, who retired in 2013, said at an event to discuss the release of the index in Washington. "The legislative process was moribund. At least we have a legislative pulse now."

The House had 70 working days, a tick above the two sessions that preceded it, but was below the number recommended by the index.

Further signs of productivity came from the number of bills being advanced out of committee. Senate panels advanced 102 bills, by far exceeding each of the last three Democrat-led Congresses. The House stood at 145, beating the number reported by all previous sessions of Congress examined by the center, which includes the 1995-97 Congress and all sessions from 2007 to the present.

"For the second quarter in a row, the Congress is soaring over the very low bar set by its predecessors," said Jason Grumet, founder and president of the Bipartisan Policy Center. "We're actually starting to see results."

A relatively large number of bills were brought to the House floor, but the the center is concerned about how strict the Republican majority has been about allowing amendments. Twenty-six closed rules were brought to the House floor in the first six months, a record among all the Congresses that were studied. Closed rules do not allow for amendments to be brought on the floor, which can be abused by the majority party. However, more Democratic amendments were considered in the last six months — 136 — than that of Republicans, who had 106.

Congress is making "legitimate connections between process and outcome," Grumet said. "From the effort to improve and repair our Medicare 'Doc Fix,' that embarrassing 18-year can-kicking exercise, to trade legislation, to fixing the big challenge over our government surveillance program, to efforts that are in the pipeline right now on 21st Century Cures, on education reform, on energy reform on the Toxic Substances Control Act. We have a Congress that is meeting and deliberating and arguing and actually legislating. So to be clear, there is a lot of work left to do. Frustration with Congress remains absolutely appropriate."

Polls show the public still has a negative perception of Congress. An aggregate of polls by RealClearPolitics on congressional job approval shows that 75.4 percent disapprove while a mere 15.2 percent approve.

The Bipartisan Policy Center is a Washington think tank, established in 2007 by former Senate Majority Leaders Howard Baker, R-Tenn., Tom Daschle, D-S.D., Bob Dole, R-Kansas, and George Mitchell, D-Maine, that "actively promotes bipartisanship," according to its website.