Tough to narrow this down, but at least a couple sources make what may be a useful comparison to more recent construction of Scottish military roads in the 1700s.
from The Secret History of the Roman Roads of Britain: And their Impact on Military History, By M.C. Bishop
Direct comparison is obviously difficult, not least because there
would inevitably be special circumstances surrounding the construction
of roads in highland terrain, but it can at least provide some hints
at what would have been possible in the Roman period. The expected
rate of construction was 1 1/2 yards (1.35m) per man per day (at 16ft
- 4.8m- most roads were just over 5 yards wide), and in at least one case 2 yards per man per day was achieved.
A second source , The Planning of Roman Roads and Walls in Northern Britain
By John Poulter, references the same Scottish constructions as a proxy, and gives some numbers on the crew sizes:
So the bottom line figures out to 1 1/2 yards (1.35m) to 2 yds per man per day, assuming a typical 16ft wide Roman style road.
Note the last figure speaks of building a road 28 miles long in a single work season, which the book mentions was April to October. Reasonably close to your requested 30 mile road.