Road Safety Audits (RSA)


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APPENDIX A
RSA CASE STUDIES

RSA NUMBER 2

OKLAHAMA DEPARTMENT OF TRANSPORTATION:
RSA OF IMPROVEMENTS TO CLEAR LAKE AVENUE AND DIRKSEN PARKWAY

Project: widening and resurfacing a two-lane rural highway
Planned Improvements:
  • replacement of three bridges over two creeks
  • shoulder widening to provide a continuous 8-foot paved shoulder
  • intersection improvements (one intersection)
  • resurfacing of improved section as well as an adjacent 1.2-mile section
Project Environment:   urban   suburban x rural
Project Design Stage:   conceptual (0 to 30%)   preliminary (40 to 80%) x advanced (over 80%)
Project Cost:   < $100,000   $100,000 - $1,000,000 x >$1,000,000
Project Owner: Oklahama Department of Transportation
Road Safety Audit
Date of RSA: 1-3 February 2005
RSA Stage(s): x design stage   RSA of existing roads
RSA team: staff from Federal Highway Administration Oklahoma Field Office, Oklahoma DOT, and Opus Hamilton

PROJECT BACKGROUND:

US 60 is a US numbered highway (part of the National Highway System) extending for 350 miles across northern Oklahoma. The RSA team reviewed detailed (90 percent) design stage drawings of upgrades to a 2.9-mile stretch of US 60 in Osage County. Along the upgraded section, US 60 has a posted speed limit of 65 mph, and a reported AADT of 3,500 vehicles. The existing roadway, shown in FIGURE A.3, is a two-lane rural roadway having 12-foot driving lanes with narrow or absent paved shoulders. In addition to resurfacing, the upgrades included:

  • replacing existing bridges over Buck Creek and Turkey Creek, including reconstructing the approach roadways as two 12-foot lanes with 8-foot paved shoulders;
  • between the bridges, widening shoulders to provide a continuous 8-foot paved shoulder and adding one channelized right turn lane at the unsignalized intersection with Bowring Road, a section-line road;
  • resurfacing a 1.2-mile “incidental section” west of Buck Creek (12-foot lanes with 2-foot paved shoulders) to connect with an adjacent segment of US 60 further west that had been recently overlaid.

The RSA team also reviewed proposed construction-stage detours.

The photo shows US 60 crossing the Buck Creek bridge. The roadway is a two-lane rural road with no shoulders and poor pavement conditions. The RSA Team is shown at the side of the road. The photo shows US 60 in the segment known as the incidental section. The roadway is a two-lane rural road with no shoulders and horizontal and vertical curves. A guardrail is provided to protect drivers from a steep embankment on one side.
Buck Creek bridge
(planned improvements include repaving, bridge
improvements, and 8’ paved shoulders)		 adjacent “incidental” section
(planned improvements include repaving
and 2’ paved shoulders)

FIGURE A.3 VIEWS OF RSA SITE (OKLAHOMA DOT RSA)

KEY RSA FINDINGS AND SUGGESTIONS:

The key findings and suggestions of the RSA are summarized in TABLE A.2. The DOT responded that changes would be made as suggested except for changes that would involve re-negotiation with property owners or utility relocation (Issue 1), since these processes were already complete, or changes that would entail substantial delay or additional expense (redesign of cross-section elements on the incidental section, Issue 2D). The DOT also declined the suggestion to install rumble strips, since they are not typically used on Oklahoma highways.

KEY LESSONS LEARNED:

It is important to identify the safety benefits of the design as part of the RSA process. The improvements to US60 were motivated largely by safety, to provide a consistent and high-quality roadway where the existing roadway was characterized by poor pavement and roadside conditions. As part of the RSA process, the RSA team identified how the elements of the Design Team’s proposed improvements were expected to positively address existing safety concerns. Examples cited in the RSA report included the following:

  • Paved 8-foot shoulders and shallower fill slopes will reduce the risk and severity of off-road collisions.
  • Resurfacing will improve the travel surface, and new pavement markings will improve driver guidance.
  • Bridge reconstruction will increase the clearance distance to roadside safety issues, and provide the opportunity to improve barrier end treatments.

Acknowledging the safety benefits of the original design put the RSA findings in an appropriate context.

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

TABLE A.2 SUMMARY OF SELECTED SAFETY ISSUES AND SUGGESTIONS
OKLAHOMA DOT RSA
SELECTED SAFETY ISSUE
(Number and Description)		 RISK RATING SUGGESTIONS
1 Vertical crest curves limit drivers’ advance view of the intersection of US60 with Bowring Road. C
  • “Intersection Ahead” warning signs
  • relocate private driveways to minor approach
  • provide acceleration lane
2 The safety impacts of improving the incidental section should be reviewed:
2A The overlay may reduce the effectiveness of an existing guardrail. C
  • Reinstall guardrail at an appropriate height.
2B The shoulder width will drop from 8 feet to 2 feet for westbound traffic.
  • Provide appropriate tapers at transition point.
  • Provide appropriate delineation.
2C Westbound drivers may fail to follow the horizontal curve near the east end of the incidental section.
  • Provide appropriate signs and delineation.
2D The improved overlay surface may encourage higher prevailing speeds along the incidental section, which may be designed to an outdated standard.
  • Confirm that existing design elements are consistent with likely speeds and current geometric standards.
  • Introduce edgeline and/or centerline rumble strips.
3 Potential roadside safety issues may be present during construction. C
  • Consider reduction in construction speed limit.
  • Flare or protect ends of temporary barrier.
  • Introduce temporary barrier near 2:1 slope.
4 A proposed guardrail ends at a private driveway. B
  • Wrap guardrail around driveway.


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