Road Safety Audits (RSA)

APPENDIX A
RSA CASE STUDIES

RSA NUMBER 3

OREGON DEPARTMENT OF TRANSPORTATION:
RSA OF IMPROVEMENTS TO US 97 (MODOC POINT TO SHADY PINE ROAD)

PROJECT BACKGROUND:

The project, along US Highway 97 between Modoc Point and Algoma, was located in Klamath County in South Central Oregon. In this area, the US 97 alignment passes along the east side of Upper Klamath Lake and the Union Pacific Railroad (FIGURE A.4). The Oregon Department of Transportation (ODOT) identified several safety issues along this section of US 97, including a fatality rate of 5.3 per million vehicle miles, almost double the average rate for similar Oregon highways. The DOT noted the presence of narrow substandard shoulders widths, substandard cut and fill slopes, and unprotected safety issues within clear the zone, including barriers, guardrail, and guardrail end terminals that did not meet current standards.

To address these and other concerns, a two-phase road improvement program was adopted by ODOT. Phase One work, which began in early 2005 and was in progress at the time of the RSA, included replacement/repair of four bridges as well as rockfall work and widening on the east side of the highway. Phase Two work, which was to be let in September 2007 with a projected completion date of November 2009, was expected to take place on the west side of US 97, between the highway and the adjacent railroad tracks.

The improvement projects were subject to several conditions that imposed unique and substantial constraints on design and construction:

• Topography and slope stability were challenging constraints. Steep, unstable slopes were present on both sides of the highway (FIGURE A.4). The project limits included six rockfall sites, one of which would be affected by construction.
• To the west of the roadway, the Union Pacific Railroad imposed right-of-way constraints that affected road design. In addition, the railroad’s rockfall warning system affected construction methods.
• Cultural sites associated with the area’s Indian tribes affected slope stabilization efforts.
• The roadway, which was to remain open during construction, must accommodate mobility needs. ODOT required that the construction design maintain specified minimum lane widths and that average traffic delay not exceed six minutes. In addition, US 97 is a designated truck corridor, and was expected to accommodate additional truck traffic diverted from nearby construction works on Interstate Highway 5.

This RSA incorporated the use of the Interactive Highway Safety Design Model (IHSDM), a suite of software analysis tools³ being developed by the FHWA to provide an explicit, quantitative evaluation of safety and operational effects of geometric design on two-lane rural highways. IHSDM was used to evaluate the elements of the existing and proposed design against design policy values, design consistency, and to predict the expected safety of the future road. IHSDM may be downloaded free of charge at http://www.ihsdm.org.

KEY RSA FINDINGS AND SUGGESTIONS:

The key findings and suggestions of the RSA are summarized in TABLE A.3.

KEY LESSONS LEARNED:

The Interactive Highway Safety Design Model (IHSDM)is a useful tool toquantify safety issues associated with the audited design.

This RSA usedIHSDM to evaluate design consistency, compliance withselected design policy values,and to predict the expected safety of the future roadway. Specifically, theproposedalignment was analyzed using:

• the IHSDM Policy Review Module (PRM) to identify two locations where stopping sight distancedid notappear to meetminimum sight distance requirements. It is important to note that an RSA is not simply a check that design standards have been met. Therefore, minimum policy checks using IHSDM were limited to sight distance policy checks. This enabled the RSA team to observe conditions in the field that IHSDM identified as having a sight distance issue.
• theIHSDM Crash Prediction Module (CPM) and five yearsof crashdata (2000-2004) to identify the potential fora futureincrease incrash frequency attwo intersections along the alignment;
• the IHSDM Design Consistency Module (DCM) to estimatefree flow 85th percentile operating speeds betweensuccessive alignment elements, as a measure of design consistency. The results from the DCM suggested that, with the proposed improvements, the alignmentof US 97 was reasonably consistent.The DCM found no locations requiring speed reductions greater than 6 mi/hr entering a curve, whichwasconsidered the upper limit for good consistency. There were however, two horizontal curves where theDCM module identified speed differentials approachingthis limit,andthe PRM module identified insufficient stopping sight distances. The RSA team flagged the locations where the combination ofdesign-consistency and sight-distance issueswas found for the Design Team's further consideration.

The ability to quantify values associated with design issues such as stopping sight distance, and to estimate futurecrash frequencies based onthe road re-design, enhanced thevalue of the RSAby demonstrating themagnitude ofthe safety issues identified by the RSA team. Without IHSDM estimates, the RSA team could identify, but could not necessarily quantify, expected changes in safety parameters such as operating speeds or in expected crash frequencies. Quantifyingthese parameters and frequencies provided a higher level of confidence to all parties (the RSA team, Design Team, and Owner) concerning the magnitude and importance of the safety issues identified in the RSA.

See also the discussion of “Key Factors for Success” and “Lessons Learned” in the main text.

³IHSDM currently includes five evaluation modules: Crash Prediction Module (CPM), Design Consistency Module (DCM), Intersection Review Module (IRM), Policy Review Module (PRM), and Traffic Analysis Module (TAM).