County engineers report good bridge deck ratings, debate capacity standards as severe crash rate rises

Mark Peterson, county engineer, and Justin Hirsch, assistant director for Road and Bridge, briefed commissioners July 21 on transportation performance measures and safety trends.

Peterson said the county follows a standard that compares traffic volume to road capacity. He warned that the newest Highway Capacity Manual gives higher capacity values to some narrow, two‑lane mountain roads than earlier guidance, which will raise the computed percent of roads providing "free‑flow" capacity when the county recalculates measures for the transportation plan. "We've potentially given those roads credit for double the capacity," Peterson said, noting the change is a national standard the county will use but that it may not reflect local driving conditions on steep, narrow routes.

On bridges, Peterson said the county tracks deck area for structures with spans of 20 feet or greater and currently has about 200 such structures. Roughly 52% of bridge deck area is rated "good" and about 2.3% is rated "poor;" CDOT hires a consultant to inspect major structures on a two‑year cycle and the county is having all bridges inspected this year.

Hirsch described pavement‑condition measures and a forthcoming methodology change for unpaved roads. The county uses Pavement Condition Index (PCI) targets of 75–85 for paved roads and 80–90 for non‑paved roads, and he said the paved network is in a strong state overall. Road & Bridge has moved its chip‑seal program from a seven‑year cycle to a nine‑year cycle after internal review and will monitor results over several years; Hirsch said national chip‑seal life commonly ranges five to seven years and local practice has been delivering longer life.

For non‑paved roads, Hirsch said the department will transition from PCI‑style visual distress measures to the International Roughness Index (IRI), measured by mobile sensors, to reduce subjectivity and better represent drivability. He explained that IRI collects ride‑quality data and can be weighted for vehicle suspension to address how different vehicles perceive roughness.

Safety trends: Peterson reported that the county recorded zero fatalities on the unincorporated county road system in 2024 but that the severe crash rate (injury or crash requiring medical response) increased roughly 17% from the prior year and about 20% over a five‑year trend. Staff attributed part of the safety work to broader system measures in the county's safety action plan and noted recent investments in low‑cost safety measures such as curve signage, widened edge‑line striping, and other countermeasures.

Why this matters: recalculating capacity using the new Highway Capacity Manual will change where capacity needs are identified and could change prioritization of projects; the IRI transition aims to provide a more objective measure of non‑paved road condition. Commissioners asked how capacity changes affect safety and funding; staff said capacity changes do not directly change road safety but may affect where shoulder widening and multimodal improvements are prioritized.

Ending: Road & Bridge and Engineering will incorporate the new capacity metrics into the transportation master plan footnotes, continue bridge inspections and issue the county safety report when complete, and roll out the IRI‑based KPI for non‑paved roads in the next KPI cycle.