Engineers find serious deck and beam deterioration; Chapel Lane Bridge to be load-posted and rebuilt if grant awarded

Bros Engineering told the Rapid City Public Works Committee on Aug. 12 that inspections of three city bridges — Chapel Lane, Somerset Drive and Creek Drive — revealed significant deterioration that will reduce allowable loads and, in one case, requires closing half the bridge.

The firm’s Spencer Doctor and inspector Josh Hertel said a roughly 3-foot-diameter hole was discovered in the Chapel Lane deck in April and that the deck shows widespread spalling and efflorescence. In their recommendation, Bros Engineering concluded the Chapel Lane Bridge should be load-posted at a 25% reduction of the Federal Highway Administration’s legal-vehicle loads. The city said those load ratings would go into effect on the 20th after required reporting to the South Dakota Department of Transportation and the FHWA.

The engineers also reported severe corrosion at the abutment cap under the Somerset Drive bridge, with exposed, section‑loss rebar, and progressive spalling and a severed bottom strand on double‑T beams at the Creek Drive structure. City staff said the Creek Drive bridge’s east half is closed and will remain so until repair or replacement.

The committee heard public comment from Brian and Joyce Kringen, managing directors of Chapel in the Hills, who said the posted weight limits could prevent tour buses (they estimated roughly 100 buses per season) from reaching the chapel and asked whether temporary accommodations could let scheduled tours finish this season. Council members and staff noted school buses are lighter and not affected; staff said they have met with Visit Rapid City, Rapid Transit, emergency services and area schools to coordinate impacts.

City staff said the Chapel Lane Bridge was built in 1974, the deck hole appeared in April and that the city has already begun design work and renewed grant applications. Staff said the state DOT’s bridge grant is typically 80% state/20% local; if the city’s score is sufficient they will bid the project in the next cycle and aim to begin construction in late 2026, with an estimated construction duration of about 18 months. The city also reported constraints that the replacement must generally be built in the same footprint because of flood‑plain and wildlife protections (staff noted an osprey nest adjacent to the site).

Committee members asked about interim public‑safety implications, including fire and ambulance access. City staff said emergency services protocol (sending both engine and ambulance due to staffing norms) will be reviewed with the fire chief and that staff are exploring a rough emergency ingress/egress route for residents if needed. Council members also asked whether the bridge materials used today are more durable; Bros Engineering said modern designs typically reduce joints where deicing salt and water penetrate and that repainting and cathodic protection can prolong life, but the damage observed at several locations is already advanced.

Why this matters: The bridges carry local traffic, emergency services and tourist buses; load postings and lane closures alter travel and service patterns for residents and businesses. The city is pursuing state grant funding to cover most construction costs but said the replacement schedule and funding depend on scoring and grant awards.

Details from the meeting: Engineers described taking the FHWA-specified hypothetical trucks and reducing allowable weights by 25% to set the Chapel Lane posting. The Somerset Drive structure still meets current postings (single units SU30 and combinations 50) but will be monitored. For Creek Drive, the city has started a replacement process to switch to a box culvert. City staff said they have been applying for grants on Chapel Lane “for years,” and that the recent critical findings should raise the project’s score enough to be competitive.

The committee voted to acknowledge the bridge inspection presentation.