Mitigation Strategies For Design Exceptions - Safety

Mitigation Strategies

Table 22 lists potential mitigation strategies for FHWA&rsquo s 13 controlling criteria. Additional information is provided on the following pages. The list is not meant to include every possible mitigation strategy for each criterion. Rather, it is intended to initiate a thought process by presenting some common as well as innovative mitigation strategies to consider. Every design exception location is unique, so the photos and examples presented in this chapter and the case studies that follow are not meant to imply a best solution for any particular location. The recommended approach is to consider the mitigation strategies presented in this chapter as well as other ideas and new approaches. If available, consult current research to gain additional information. Then customize one or more strategies to address the unique concerns and site conditions at the design exception location.

The known effectiveness of the mitigation strategies varies. Some, such as shoulder rumble strips, have been used for many years and are well proven. Others are new ideas that have been tried, but their effectiveness is still being studied. The body of knowledge on these strategies will continue to grow, so designers should consult the most recent research available to assess the effectiveness of particular strategies.

TABLE 22 Potential Mitigation Strategies
Design Element	Objective	Potential Mitigation Strategies
Design Speed	Reduce operating speeds to the design speed.	Cross-sectional elements to manage speed.
Lane Width & Shoulder Width	Optimize safety and operations by distributing available cross-sectional width.	Select optimal combination of lane and shoulder width based on site characteristics.
	Provide advance warning of lane width reduction.	Signing.
	Improve ability to stay within the lane.	Wide pavement markings.
		Recessed pavement markings.
		Raised pavement markings.
		Delineators.
		Lighting.
		Centerline rumble strips.
		Shoulder rumble strips.
		Painted edgeline rumble strips.
	Improve ability to recover if driver leaves the lane.	Paved or partially-paved shoulders.
	Improve ability to recover if driver leaves the lane.	Safety edge.
	Reduce crash severity if driver leaves the roadway.	Remove or relocate fixed objects.
		Traversable slopes.
		Breakaway safety hardware.
		Shield fixed objects and steep slopes.
	Provide space for enforcement and disabled vehicles.	Pull-off areas.
Bridge Width	Provide advance warning and delineation of narrow bridge. Improve visibility of narrow bridge, bridge rail, and lane lines.	Signing.
		Reflectors on approach guardrail and bridge rail.
		Post-mounted delineators.
		Object markers.
		High-visibility bridge rail.
		Bridge lighting.
		Enhanced pavement markings.
	Maintain pavement on bridge that will provide safe driving conditions.	Skid-resistant pavement.
		Anti-icing systems.
	Reduce crash severity if driver leaves the roadway.	Crashworthy bridge rail and approach guardrail.
	Provide space for disabled vehicles or emergencies on long bridges.	Pull-off areas.
	Provide quick response to disabled vehicles or emergencies on long bridges.	Surveillance.
Horizontal Alignment & Superelevation	Provide advance warning.	Signing.
		Pavement marking messages.
		Dynamic curve warning systems.
	Provide delineation.	Chevrons.
		Post-mounted delineators.
		Reflectors on barrier.
	Improve ability to stay within the lane.	Widen the roadway.
		Skid-resistant pavement.
		Enhanced pavement markings.
		Lighting.
		Centerline rumble strips.
		Shoulder rumble strips.
		Painted edgeline rumble strips.
	Improve ability to recover if driver leaves the lane.	Paved or partially paved shoulders.
	Improve ability to recover if driver leaves the lane.	Safety edge.
	Reduce crash severity if driver leaves the roadway.	Remove or relocate fixed objects.
		Traversable slopes.
		Breakaway safety hardware.
		Shield fixed objects and steep slopes.
Vertical Alignment	See (8) Grade and (9) Stopping Sight Distance.
Grade	Provide advance warning.	Signing.
	Improve safety and operations for vehicles ascending or descending steep grades.	Climbing lanes.
		Downgrade lanes.
	Capture out-of-control vehicles descending steep grades.	Escape ramps.
	Improve ability to stay within the lane.	Enhanced pavement markings.
		Delineators.
		Centerline rumble strips.
		Shoulder rumble strips.
		Painted edgeline rumble strips.
	Improve ability to recover if driver leaves the lane.	Paved or partially-paved shoulders.
	Improve ability to recover if driver leaves the lane.	Safety edge.
	Reduce crash severity if driver leaves the roadway.	Remove or relocate fixed objects.
		Traversable slopes.
		Breakaway safety hardware.
		Shield fixed objects and steep slopes.
	Address drainage on flat grades.	Adjusting gutter profile on curbed cross sections.
	Address drainage on flat grades.	Continuous drains.
Stopping Sight Distance	Mitigate sight distance restrictions.	Signing and speed advisory plaques (crest vertical curves).
		Lighting (sag vertical curves).
		Adjust placement of lane within the roadway cross section (horizontal).
		Cross-sectional elements to manage speed.
	Improve ability to avoid crashes.	Wide shoulders.
	Improve ability to avoid crashes.	Wider clear recovery area.
	Improve driver awareness on approach to intersections.	Advanced warning signs.
		Dynamic warning signs.
		Larger or additional STOP/YIELD signs.
		Intersection lighting.
Cross Slope	Provide warning of slick pavement.	Signing.
	Improve surface friction.	Pavement grooving (PCC pavement).
	Improve surface friction.	Open-graded friction courses (HMA pavement).
	Improve drainage.	Transverse pavement grooving (PCC pavement).
		Open-graded friction courses (HMA pavement).
		Pavement edge drains.
	Mitigate cross-slope break on the high side of superelevated curves.	Modified shoulder cross slope.
Vertical Clearance	Advance warning.	Signing.
	Preventing impacts with low structures.	Alternate routes.
	Preventing impacts with low structures.	Large vehicle restrictions.
Lateral Offset to Obstruction	Improve visibility of objects near the roadway.	Delineate objects.
	Improve visibility of objects near the roadway.	Lighting.
	Optimize operations by distributing available cross-sectional width.	Provide full outside lane width and/or additional offset.
	Improve visibility of the lane lines.	Enhanced pavement markings.
Structural Capacity	Not addressed in this Guide.

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Page last modified on October 15, 2014