Stewart Tunnel

Located north of Exeter, this tunnel carries the former Illinois Central Railroad Madison Branch underneath an unnamed hill. Due to the hilly terrain in the area, construction of railroad lines was difficult, often requiring vast amounts of earthwork, large viaducts and tunnels. As the Chicago, Madison & Northern Railroad constructed the line between Freeport and Madison, several sections of steep grades would be required, particularly in Green County. It was decided to construct a tunnel north of Exeter to help minimize steep grades at the largest hill. Construction on the tunnel began in December 1886, with construction progressing from the north and south ends. Camps were set up at "Tunnel City", and approximately 125 men worked for $1.50 a day to construct the tunnel. Throughout 1887, work continued to progress, with only minor disruptions due to unstable rock. On December 1, 1887; the two bores met, and the tunnel was completed soon after. Construction of the tunnel was completed by Drake & Stratton, the contractor which received the contract for grading from Monroe to the tunnel. Isham Randolph served as Chief Engineer for the CM&N, and oversaw the progress on the tunnel.

The completed tunnel consists of 1,280 feet of tunnel bored through blue limestone. The tunnel is also located on a 2-degree curve. To stabilize the entrances, a brick arch portal was constructed on the north end and a stone arch portal was constructed on the south end. The north portal does not use wing walls, while the south portal uses stepped wing walls constructed parallel to the track. At the ends, the tunnel is approached by steep limestone bluffs, which were carved to allow for construction of the railroad. Due to the horizontal stone planes that the tunnel is constructed through, the ceiling of the tunnel has been somewhat unstable since it first constructed. Four sections of brick lining were installed in the tunnel in the late 19th or earth 20th Century. It appears that an additional concrete lining section was installed sometime in the mid-20th Century. After the railroad line was acquired by the State of Wisconsin, some concrete repairs were made in the 1980s. Further repairs were made in 2005, when an additional section of corrugated metal plate and concrete walls were added to stabilize the tunnel. The most recent alterations involve the addition of rock netting, which was added in 2017. Due to falling rocks, the tunnel was closed in 2019. Funding has been allocated to repair the tunnel, which will involve placing a corrugated metal plate and concrete lining through the entire structure. Currently, the tunnel is closed to all traffic, but has been used by the Badger State Trail. Overall, the tunnel is in poor condition, with several areas of poor drainage and falling rock. The author has ranked the tunnel as being moderately significant, due to the age and limited number of similar structures in Wisconsin.