After months, years really, of trailing designers in other U.S. regions, Midwest architects are not only seeing improving business conditions, but collectively leading the nation in backlogs, as measured by the American Institute of Architects Architectural Billing Index.

On Wednesday, AIA reported that while the overall index fell from 53.2 in November to 52.0 in December, the Midwest index rose from 50.8 to 55.7 over the same time period. By comparison, the Northeast index measured 53.1, followed by the South (51.2) and West (49.6).

As a leading economic indicator of construction activity, the ABI reflects the approximate nine- to 12-month lag time between architectural billings and construction spending. Any score above 50 denotes an increase in billings.

The industrial sector is the engine that continues to rev the Midwest, as nationwide demand for automobiles continues to drive plant construction in Indiana and Ohio.

Key metro areas also are showing signs of life. Chicago's long-moribund office sector received a kick start last week with the groundbreaking of River Point, a $300-million project that will add 850,000 square feet to the city's financial district when completed in 2016. It's the largest commercial project to rise in Chicago in five years.

Other key findings in AIA's December report:

Sector index breakdown: commercial/industrial (53.4), mixed practice (53.0), institutional (50.9), multi-family residential (50.5)

• Project inquiries index: 59.4

“While it’s not an across-the-board recovery, we are hearing a much more positive outlook in terms of demand for design services,” says AIA Chief Economist Kermit Baker. “Moving into 2013 we are expecting this trend to continue and conditions improve at a slow and steady rate. That said, we remain concerned that continued uncertainty over the outcomes of budget sequestration and the debt ceiling could impact further economic growth.”