U.S. automakers continued to narrow the productivity gap between them and Japanese manufacturers last year, with DaimlerChrysler AG's Chrysler Group (DCX) making the biggest strides, the authors of a closely watched study said Thursday.

Meanwhile, the assembly plant designated the most productive of 2005 by the Harbour Report is one that is scheduled to close: Ford Motor Co.'s (F) facility near Atlanta.

Click here to visit FOXBusiness.com's Autos page.

The annual study, which compares labor productivity at six companies with North American plants and is published by Troy-based Harbour Consulting, put Nissan Motor Co. in the lead with an average of 28.5 hours per vehicle. Ford was last at 35.8 hours.

Nissan's productivity figure compares with 29.4 hours in 2004 and does not include its plants in Mexico, which do not participate in the voluntary data-sharing on which the report depends.

Ron Harbour, president of Harbour Consulting, said Nissan's productivity lead amounts to a cost advantage of $300 to $450 per vehicle over less productive manufacturers.

The domestic Big Three have been steadily catching up to Japanese automakers. The difference between the most productive and the least productive narrowed to 7.3 hours in 2005 from 9.1 hours in 2004 and 16.6 hours in 1998.

Recent improvements in productivity have come largely from improvements in quality, Harbour said at the report's presentation in Detroit.

"We live in a world where we think quality costs more, and that's completely backwards," he said.

Because quality is up, plants are spending far less time repairing vehicles when they come off the line, he said.

Although the three major Japanese manufacturers stayed on top, two of them saw productivity fall.

Toyota Motor Corp. (TM), which took first place in 2004 at 27.9 hours, came in second in 2005 at 29.4 hours. Honda Motor Co.'s third-place score of 32.5 hours was half an hour more than last year's.

General Motors Corp. (GM) was close behind Honda at 33.2 hours, followed by Chrysler at 33.7 hours.

Chrysler improved 6 percent over its 2004 average of 35.8 hours, the biggest move of the six automakers.

The Harbour Report, first published in 1989, measures productivity at assembly, stamping and engine and transmission plants. It calculates the number of hours worked by salaried and hourly employees at a plant and divides that by the number of units produced.

Among assembly plants, the Ford facility in Hapeville, Ga., outside Atlanta, stood out with 15.4 hours per vehicle. The plant, which makes the Taurus, is one of seven Ford announced it is closing by 2008 as part of its restructuring.

"When you evaluate closing or retaining a plant, there's hundreds of criteria," Harbour said. "Productivity is only one of them — certainly an important one, but it's not the only one."

The plant's distance from major supply routes was likely a key factor, he said.

The No. 2 assembly plant for productivity, GM's Oshawa, Ontario plant, also is scheduled for closure.

Harbour noted that GM and Ford made productivity gains even as they cut their volumes, something that historically is difficult to do.

Despite the narrowing productivity gap, the automakers remain far apart by other measures, the study's authors noted. Capacity utilization ranged from 106 percent at Toyota's assembly plants to 79 percent at Ford's.

Another big difference is profitability. Nissan, Toyota and Honda each earned more than $1,200 before taxes on every vehicle they sold in North America in 2005, according to the study. In contrast, Chrysler Group earned $223, while Ford lost $590 and GM lost $2,496 on each vehicle. This reflects differences in health care and pension costs, as well as rebates and low-interest financing used to cut inventories, the report said.

In afternoon trading on the New York Stock Exchange, GM shares fell 24 cents to $26.69 while Ford gained 2 cents to $7.18. DaimlerChrysler's U.S. shares fell 21 cents to $52.40 on the NYSE while Toyota's U.S. shares rose 93 cents to $108.31 and Honda's U.SA. sales rose 25 cents to $33.28. Nissan's U.S. shares rose 31 cents to $24.56 on the Nasdaq Stock Market.

Click here to visit FOXBusiness.com's Autos page.