Now several years since the recession hit, business continues to improve for most firms. Seven of the top 10 firms that responded to the survey in the last two years saw regional revenue increase in 2014.

Despite uncertainty about long-term federal transportation funding, many firms that work in that sector reported growth in 2014. Seven of the top 10 firms on this year's list said that they brought in more revenue from transportation than any other sector. All but one firm—Arcadis—listed transportation as one of their top two sectors in terms of revenue.

Joe Makar, managing partner at Whitman, Requardt & Associates, Baltimore, says that, although the future of federal aid is an ongoing concern for firms, the market is "reasonably solid" with "steady opportunities for growth." Last year, WRA's revenue increased 4%, to $109.9 million, with 51% of that revenue generated in the transportation sector.

Some firms benefited from transportation megaprojects. Dewberry's revenue rose to $136.1 million last year from $120.8 million in 2013. Kurt Thompson, executive vice president, says one important reason for the gain was the firm's work on the $1.2-billion Phase 2 of Metro's Silver Line project, underway near Dulles International Airport.

Impact of Oil

The oil and gas market, particularly work related to natural gas activity in the Marcellus Shale region, helped some firms in 2014. Civil & Environmental Consultants, Cardno, Hatch Mott MacDonald and Dawood Engineering each reported more revenue from the petroleum sector than any other line of business. But the impact of lower energy prices on design firms' results in 2015 and beyond remains to be seen.

Several other firms banked on oil and gas opportunities last year. STV reported revenue was up 21%, to $111.4 million, from $92.3 million in 2013, which the firm credited to "an uptick in the volume of work relating to infrastructure to support the fuel transportation market."

Some general building firms also experienced an uptick in 2014. Gensler reported $79.6 million in general building revenue in 2014, up from $70.8 million in the previous year.