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          For More Info Visit the Office of Safety's Horizontal Curve Safety website

              Enhanced Delineation for Horizontal Curves
U.S. Department of Transportation logoU.S. Department of Transportation
    Federal Highway Administration
    FHWA-SA-21-035

          PDFEnhanced Delineation for Curves_508.pdf (PDF, 172.21 KB)


        Enhanced delineation at horizontal curves includes a variety of potential strategies that can be implemented in advance of or within curves, in combination, or individually.

Potential strategies that can be implemented in advance of or within curves, in combination, or individually.
	**Potential Strategies**
			**In advance
			of curve**
			**Within curve**Pavement markings
			(standard width or wider)
			X
			XIn-lane curve warning pavement markings
			XRetroreflective strips on sign posts
			X
			XDelineators
			
			XChevron signs
			
			XEnhanced Conspicuity
			(larger, fluorescent, and/or retroreflective signs)
			X
			XDynamic curve warning signs
			(including speed radar feedback signs)
			XSequential dynamic chevrons
			
			X

Enhanced delineation treatments can alert drivers to upcoming curves, the direction and sharpness of the curve, and appropriate operating speed.

Agencies can take the following steps to implement enhanced delineation strategies:

Review signing practices and policies to ensure they comply with the *Manual on Uniform Traffic Control Devices* (MUTCD) principles of traffic control devices. Consistent practice for similar curves sets the appropriate driver expectancy.
	Use the systemic approach to identify and treat problem curves. For example, Minnesota uses risk factors that include curve radii between 500 and 1,200 ft, traffic volumes between 500 and 1,000 vehicles per day, intersection in the curve, and presence of a visual trap.1
	Match the appropriate strategy to the identified problem(s), considering the full range of enhanced delineation treatments. Once the MUTCD requirements and recommendations have been met, an incremental approach is often beneficial to avoid excessive cost."A two-lane undivided roadway bearing to the left. On the outside of the curve, to the right, is a clear grassy area least 20 feet in width, featuring a gentle foreslope and steeper backslope."

**Chevron signs with retroreflective strips on sign posts installed along a curve.**
Source: FHWA

        Sources
        1. (CMF ID: 2439, 2431, 2432) Albin et al. Low-Cost Treatments for Horizontal Curve Safety 2016. FHWA-SA-15-084, (2016).

2. (CMF ID: 2438) Srinivasan et al. Safety Evaluation of Improved Curve Delineation. FHWA-HRT-09-045, (2009).

3. (CMF ID: 8978) Lyon et al. Safety Evaluation of Two Curve Warning Treatments: In-Lane Curve Warning Pavement Markings and Oversized Chevron Signs. Presented at the 96th TRB Annual Meeting, Paper No. 17-00432, (2017).

4. (CMF ID: 10362) Hallmark, S. Evaluation of Sequential Dynamic Chevrons on Rural Two-lane Highways. FHWA, (2017).

5. (CMF ID: 10312, 9167) Donnell et al. Reducing Roadway Departure Crashes at Horizontal Curve Sections on Two-lane Rural Highways. FHWA-SA-19-005, (2019).

**Note:** With the 2021 update of the PSCi, HFST is now included in Pavement Friction Management.
    
    Safety Benefit IconSafety Benefits:
              
Chevron Signs
          **25%** reduction in night-time crashes1

**16%** reduction in non-intersection fatal and injury crashes2
          Oversized Chevron Signs
          **15%** reduction in fatal and injury crashes.3
          Sequential Dynamic Chevrons
          **60%** reduction in fatal and injury crashes3
          In-Lane Curve Warning Pavement Markings
          **35-38%** reduction in all crashes. 4-5
          New Fluorescent Curve Signs or Upgrade Existing Curve Signs to Fluorescent Sheeting
          **18%** reduction in non-intersection, head-on, run-off-road, and sideswipe in rural areas.1 U.S. DEPARTMENT OF TRANSPORTATION

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