General Project Information
The Project is located on State Route (SR) 128 at Post Mile (PM) 5.12 in Rutherford, an unincorporated census-designated place in Napa County, California. The Project limits extend from PM 5.0 to PM 5.2, a total of 0.2 mile.
Purpose and Need
The purpose of the Project is to address the deficiencies of the existing Hopper Slough Bridge using current Caltrans geometric standards that would provide the traveling public with a safer highway.
The Project is needed due to the bridge’s geometric deficiencies. The bridge rails, shoulder widths, and lane widths do not meet Caltrans standards (Photo 1), and the bridge approaches have differential settlement relative to the bridge. The current structure is not compatible with the Napa Countywide Bicycle Plan, which recommends Class II bike lane facilities throughout the Project limits.
The bridge was built in 1921 and has exceeded its service life. The current structure has required repairs to maintain its operation. An approximately 1.5-inch-wide crack and a loss of surface concrete measuring 3-feet long by 2.5-feet wide with a depth of 1.5 feet (Photo 2) was repaired on Abutment 1 on the western end of the bridge. The loss of surface concrete exposed one longitudinal and one transverse reinforcing bar . Currently, there are several spalls in the bottom face of Girder 2 near Abutment 1, with transverse rebar exposed at midspan, and one spall in the bottom face of Girder 1 at the quarter point and a similar spall near Abutment 1. The spall near Abutment 1 exposes rebar. During Caltrans routine inspection on April 15, 2021, the spalls in the bottom of Girders 1 and 2 on the superstructure were given a condition state rating of CS-3, which is described as “poor” in the Caltrans Bridge Element Inspection Manual. There are several spalls on the face of Abutment 2. During Caltrans routing inspection on April 15, 2021, the abutment cracking on the substructure were given a condition state rating of CS-4, which is described as “severe” in the Caltrans Bridge Element Inspection Manual. Both the superstructure and substructure display multiple structural deficiencies.
Photo 1: Nonstandard bridge features including: MBGR, no shoulders, and 10-foot-wide travel lanes
Photo 2: Abutment 1 with patched and repaired concrete areas and areas of damaged concrete (taken in 2015)
Caltrans proposes to replace the existing Hopper Slough Bridge with a new bridge of the same vehicular capacity. The Project would also replace an existing culvert with a 6-foot by 6-foot precast reinforced box culvert with natural creek bed material bottom.
There are two Build Alternatives for the Project.
Build Alternative 3F-6’ proposes to replace the existing bridge with a 120-foot-long, 40-foot-wide, three-span bridge, with 12-foot-wide travel lanes in each direction, 6-foot-wide shoulders, and 2-foot-wide type ST-75 steel barriers with tubular handrails. Retaining walls on the eastbound and westbound sides of SR 128 on both the east and west sides of the bridge would be constructed. The retaining walls would start at the bridge abutments and extend 490 feet to the northeast, 440 feet to the southeast, 455 feet to the northwest, and 455 feet to the southwest. The same 2-foot-wide type ST-75 steel barrier used on the bridge, would be constructed on top of the retaining wall. An 8-foot-wide ditch would be constructed on the south side for the full length of the retaining wall that would allow for drainage into Bale Slough.
Build Alternative 1F-6’ would also construct retaining walls with guardrails and would construct the same 8-foot-wide drainage ditch on the south side of the walls as Build Alternative 3F-6’. The retaining walls for Build Alternative 1F-6’ would start at the bridge abutments and extend 515 feet to the northeast, 465 feet to the southeast, 480 feet to the northwest, and 480 feet to the southwest. This alternative would also replace the existing bridge, but would be a single-span, 70-foot-long bridge.