RSA No. 3 – Project Background

FHWA and the Oregon Department of Transportation (ODOT) partnered to conduct an RSA along US Highway 97 in south central Oregon, between Modoc Point and Algoma in Klamath County. In this area, the US 97 alignment passes along the east side of Upper Klamath Lake and the Union Pacific Railroad (see Figure 15). ODOT noted the presence of narrow shoulders, steep cut and fill slopes, and various fixed objects within the clear zone, including barriers, guardrail, and guardrail end terminals that did not meet current standards.

Figure 15: US Highway 97 Study Corridor.

Figure 16: Rockfall in US 97 RSA Study Area.

To address these and other concerns, a two-phase road improvement project was adopted by ODOT. The Phase One work began in early 2005 and was in progress at the time of the RSA; it included replacement/repair of four bridges, as well as rockfall work and widening on the east side of the highway. The Phase Two work, with a projected completion date of November 2009, would comprise improvements on the west side of US 97–between the highway and the adjacent railroad tracks. Constraints included topography and steep slopes, rockfall issues, the adjacent Union Pacific Railroad right-of-way and culturally sensitive sites of the area’s Native American tribes, and the need for the road to not only remain open to traffic during construction but also maintain certain minimum lane widths to accommodate heavy truck traffic.

RSA No. 3 – Use of IHSDM

The RSA team reviewed safety conditions on US 97 utilizing recent crash data, local and RSA team inputs, and IHSDM. IHSDM was used to help select sites for detailed review and to help identify priority areas where improvements should be considered. The project team utilized three IHSDM modules: the Policy Review Module (PRM), the Design Consistency Module (DCM), and the Crash Prediction Module (CPM).

The IHSDM analysis produced output tables and graphs that illustrate locations where stopping sight distance was not met, where the differential in speed from a tangent section to subsequent horizontal curve are a concern, and where crash potential is elevated. The results by module are summarized as follows:

PRM: The available stopping sight distance at two locations did not meet the minimum criteria set forth by the 2004 AASHTO "Green Book." In Figure 17 are the available sight in gold for the northbound direction and in blue for southbound). Note the circle on the graph indicates a location where a combination of critical elements identified by IHSDM are present. This location was one of the most critical based on PRM and DCM output.

Figure 17: A Section of US 97 IHSDM PRM Stopping Sight Distance Graph.

Figure 18: Sight distance is limited on horizontal curves with barriers.

DCM: The output from this module showed that the expected reduction in estimated 85th percentile speeds from an approach tangent to its succeeding horizontal curve were all flagged as "green," indicating the speed differential is less than 6 mph (in Figure 19, see 85th percentile speed plotted for the northbound direction with green flags indicating speed differential). Two horizontal curve locations that approached this threshold were noted, but overall design consistency was fairly uniform. Note the circle on the graph indicates a location where a combination of critical elements identified by IHSDM are present. This location was one of the most critical locations based on PRM and DCM output.

Figure 19: Summary of US 97 IHSDM DCM Results.

CPM – Five years of historical crash data–including 74 reported collisions from January 1, 2000 to December 31, 2004– were considered by the CPM analysis for the section of the alignment from milepost 262 to milepost 267.2. The expected crash rate (crashes/mi/yr) for each homogeneous roadway segment and horizontal design element was graphed as part of the default IHSDM output (see Figure 20). The results indicated that expected crash rates are higher at horizontal curves with short radii.

Figure 20: Summary of US 97 IHSDM CPM Results on Segment Evaluated as Part of RSA.

RSA No. 3 – Key RSA Findings and Suggestions

A summary of the key RSA findings and suggestions is shown in Table 7.

Table 7: US 97, Klamath County, Oregon: Key safety issues and suggested mitigating actions.

RSA No. 3 – Conclusions

IHSDM provided key inputs to the RSA team based on several modules that helped it to identify potential safety issues along the corridor. The use of IHSDM allowed a comparison between the existing available stopping sight distance and the stopping sight distance associated with the proposed design. It also predicted crashes along the future roadway based on its geometric characteristics and projected traffic volumes. IHSDM highlighted locations where drivers may need to decelerate to safely negotiate a horizontal curve, thereby assisting in the prioritization of locations for review by the RSA team.

The ability to quantify values associated with design issues (e.g., stopping sight distance) and to estimate future crash frequencies based on the road redesign enhanced the value of the RSA by demonstrating the magnitude of the 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 expected crash frequencies. Quantifying these 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.

Furthermore, opportunities for using IHSDM output beyond engineering were identified. Law enforcement indicated an interest in reviewing locations where speed may be a concern as identified by the DCM.