ida-clear4783-1_PM 03-26 Dent Bridge Road Final Pavement Memo.pdf

158377846

M E M O R A N D U M Western Federal Lands Highway Division

610 E. Fifth Street Vancouver, WA 98661

DATE: January 16, 2026

TO: David Arena, Project Manager Thinh Phan, Designer

FROM: Jason Dietz Pavement and Materials Engineer

SUBJECT: Final Pavement Memo (PM 03-26) Dent Bridge Road Rehabilitation Project

ID FLAP CLEAR 4783(1)

Clearwater County, Idaho

To support developing 95% PS&E plans for this project, we are submitting our final pavement recommendations for the project ID FLAP CLEAR 4783(1). The project site encompasses a paved, rural two-lane, first 5-mile-long asphalt concrete roadway (MP 0.0 to MP 5.0) of Dent Bridge Road. Dent Bridge Road is a 15-mile-long route that connects Orofino, Idaho to Dent Bridge and the city of Elk River, Idaho. It provides access to Dworshak Reservoir, campgrounds, recreation trails, Canyon Creek, and the Clearwater National Forest. The road serves for a variety of users including adjacent communities, truckers, hikers, snowmobile riders, bikers, hunters, campers, ATV riders, fisherman, tourists, and equestrians. The project scope includes rehabilitation of the existing asphalt concrete pavement surface, ditch cleaning throughout, deep patch, and sections of existing guardrail which are structural deficient and improperly placed.

Recommendations for rehabilitation of Dent Bridge Road were provided based on field investigations conducted in June 2021, subsurface exploration conducted in April 2022, and December 2025 in which ground penetrating radar (GPR) was used to detect asphalt pavement thickness of MP 0.0 to 6.0 and measure every 0.5 mile. We also measured width of pavement striping every 0.5 mile due to the centerline strip not reflecting center of roadway. It was also noted that asphalt concrete pavement was fairly new just prior to MP 1, MP 5.0 to MP 5.4, and MP 6.0 to MP 6.2 that might have been caused by slide repairs. Right before MP

5.0 lies an intersection that would be a good stopping point if the work needed to tie in past the intersection to make a future connection. Safety edges for this project would not be needed due to shoulder drop offs but could be if millings were used to make up these drop offs.

Traffic Data and Design Analysis A final pavement recommendations report was provided by Nassim Sabahfar on July 13, 2023, in which she provided information for a pavement evaluation field visit conducted in June 2021, subsurface explorations conducted in April 2022, the result of tests conducted on extracted soil samples by the Western Federal Lands Highway Division Materials Laboratory, and the Final Geotechnical Engineering Report 02-26 dated January 2026.

The Federal Lands Access Program application estimates the current Average Daily Traffic as 1,223 at MP 0.0 and 236 at MP 11.0 on Dent Bridge Road with 12 percent trucks. Assuming ADT at 1,223 for the section between MP 0.0 and MP 5.0 and applying the 18-kip ESALs for a 20-year period design life is projected to be about 1,300,000.

Table 1: Parameters for Traffic Load Determination Parameter Value Reference

Performance Period 20 years PDDM1 11.2.1.1

Average Daily Traffic (ADT) 1,223 Final Pavement Structural Recommendation Memo

July 13, 2023 Percent Heavy Trucks (of ADT) 12.0%

Average Initial Truck factor (ESALs/truck) 2.3 PDDM1 11.2.1.2 Annual Traffic Volume Growth Rate 2% PDDM1 11.2.1.2 Growth Simple -

Table 2: 1993 AASHTO Flexible Pavement Design Parameter Value Reference

Initial Serviceability 4.2 PDDM1 11.2.1.1 Terminal Serviceability 2.5 PDDM1 11.2.1.1 Reliability Level 75% PDDM1 11.2.2 Overall Standard Deviation 0.49 PDDM1 11.2.2

Roadbed Soil Resilient Modulus

30,000 psi for MP 0.0 to MP 1.0 7,500 psi for MP 1.0 to MP 5.0

Final Pavement Structural Recommendation Memo

July 13, 2023 Design Structural Number 3.30 DARWin2

Asphalt concrete pavement 4 inches -

Aggregate base 8 inches - Calculated Structural Number 2.34 DARWin2

Notes:

1. PDDM = Federal Lands Highway Project Development and Design Manual (2008)

2. DARWin Pavement Design and Analysis System

PAVEMENT ASSESSMENT AND DESIGN RECOMMENDATIONS

From the December 2025, Ground Penetrating Radar (GPR) field investigation, the existing roadway currently consist of an average asphalt concrete (AC) surface from MP 0.0 to MP 6.0 of 8 inches with an average of 3.5 inches aggregate base course.

Overall, the pavement surface is in fair to poor condition with at least two sections of large patch areas caused by landslide repairs that might have taken place over the past five years.

There is no particular pattern of distresses decreasing or increasing in frequency and severity with increasing mile post and distance from the beginning and intersection of Dent Bridge Road in Orofino, ID. This is presumed due to tributary traffic load increasing with proximity to Orofino. There are some isolated areas where the pavement surface shows higher severity distress including potholes due to localized subgrade instability, which is likely related to poor drainage and moisture induced damage. Edge cracking is intermittently present throughout the roadway length due to insufficient shoulder support along with sloughing and erosion on fill slopes.

Observed distresses in order of descending significance and prevalence include:

• Medium severity fatigue cracking,

• High to medium severity longitudinal and transverse cracking,

• High to medium severity edge cracking,

• High to medium severity potholes that have been patched,

• High to medium raveling of surface treatment near potholes,

• Shoving of surface treatment

Based on the previous final pavement structural recommendations memo completed on July 13, 2023, we are providing the following recommendation as laid out in Table 3. Recommended asphalt binder grade for the project is PG 58-34 and it is recommended that asphalt concrete pavement layer be placed in two equal lifts and tack coat applied between the layers.

Table 3: Segment 1 - Project Start MP 0.0 to 5.0 Pavement Recommendations Layer Minimum Thickness

(in) Comments

Asphalt Concrete Surface Course

4 Asphalt Concrete Pavement or WMA, 0.3 to < 3 million ESAL’s as per Section 401 @ 1.94 tons/cy, 1/2-inch Nominal Maximum Aggregate Size (NMAS), Type III roughness

Tack Coat --- As per Section 412, est. 0.10 gal/sqyd Asphalt Pavement Milling

4 As per Section 413

Prime Coat, Method 1 --- As per Section 411, est. 0.25 gal/sqyd

Full Depth Reclamation (FDR) with Cement

8 As per Section 305, est. 1.5 ton/cy;

4.5% of the weight of blended FDR material

SPECIFICATIONS

WFL Materials will provide the required SCRs for inclusion in the final package.

CLOSING

Please notify Jason Dietz at (720) 810-0871 or Jason.Dietz@dot.gov if any questions regarding this memo or changes to the assumptions occur which may require revisions to this revised final pavement memo.

JD

cc: David Arena, Project Manager Thinh Phan, Designer Dave Mariman, Quality Assurance Specialist Nicholas Ferreira, Geotechnical Engineer Materials/Pavement File mailto:Jason.Dietz@dot.gov