231.2 Clear Zones - Revision history

Smithk: /* 231.2.1 Introduction */ Per TS, minor clarifications

2021-02-16T14:51:15Z

231.2.1 Introduction: Per TS, minor clarifications

← Older revision		Revision as of 09:51, 16 February 2021
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	Where resources and safety benefits justify the use of clear zones, clear zone concepts may be applied to existing roads to address roadside obstacles and non-traversable terrain. Clear zones are reviewed and/or selected based on the RDG guidelines during the preparation of the location/conceptual study report.		Where resources and safety benefits justify the use of clear zones, clear zone concepts may be applied to existing roads to address roadside obstacles and non-traversable terrain. Clear zones are reviewed and/or selected based on the RDG guidelines during the preparation of the location/conceptual study report.

	The clear zone concept shall be applied with engineering judgment including ~~a safety analysis (Highway Safety Manual or HSM)~~ and be balanced with project costs. Limited right of way or high construction costs may lead to the installation of a barrier or possibly no protection at all if justified through a safety analysis. The designer should consider site specific characteristics of the roadway at issue including, if appropriate, the location of the object or area in relation to the roadway, road width, lane width, traffic volume, design speed, roadway geometry, and the crash history (including severity) involving the roadside object or area when analyzing whether or not to install a barrier. Documentation of decisions regarding clear zone strategies shall be included in the project conceptual study report, project core team minutes, or design exception forms, and shall be filed in eProjects.		The clear zone concept shall be applied with engineering judgment including consideration of severe crash risk and be balanced with project costs. Resources to assist this decision-making includes the ''Roadside Design Guide'', history of run-off road crashes, and the ''Highway Safety Manual'' (HSM). Limited right of way or high construction costs may lead to the installation of a barrier or possibly no protection at all if justified through a safety analysis. The designer should consider site specific characteristics of the roadway at issue including, if appropriate, the location of the object or area in relation to the roadway, road width, lane width, traffic volume, design speed, roadway geometry, and the crash history (including severity) involving the roadside object or area when analyzing whether or not to install a barrier. Documentation of decisions regarding clear zone strategies shall be included in the project scoping, conceptual study report, project core team minutes, or design exception forms, and shall be filed in eProjects.

	Maintenance staff may remove trees, boulders, or other obstacles on existing roads where right-of-way is available. This cleared area shall not be assumed a designed clear zone as used in the EPG. If a safety concern is identified during a roadway safety audit or a project core team meeting, then the safety concern should be considered and discussed with the core team in the context of project budget and scope.		Maintenance staff may remove trees, boulders, or other obstacles on existing roads where right-of-way is available. This cleared area shall not be assumed a designed clear zone as used in the EPG. If a safety concern is identified during a roadway safety audit or a project core team meeting, then the safety concern should be considered and discussed with the core team in the context of project budget and scope.

Kleins1: /* 231.2.4 Ramps */

2021-02-02T14:41:37Z

231.2.4 Ramps

← Older revision		Revision as of 09:41, 2 February 2021
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	===231.2.4 Ramps===		===231.2.4 Ramps===

	Clear zones should be considered on ramps ~~when~~. Shielding may ~~also~~ be applicable with engineering judgment at these locations. Special consideration should be given at ramp termini where stop conditions exist. It may be acceptable to leave a non-traversable slope unshielded when operating speeds that approach zero are to be expected, especially when barriers in those areas become obstacles and receive continual damage from low speed, turning, commercial vehicle traffic.		Clear zones should be considered on ramps. Shielding may be applicable with engineering judgment at these locations. Special consideration should be given at ramp termini where stop conditions exist. It may be acceptable to leave a non-traversable slope unshielded when operating speeds that approach zero are to be expected, especially when barriers in those areas become obstacles and receive continual damage from low speed, turning, commercial vehicle traffic.

	===231.2.5 Unusual Conditions===		===231.2.5 Unusual Conditions===

Kleins1: /* 231.2.3 For Bridges and Culverts */

2021-02-02T14:39:59Z

231.2.3 For Bridges and Culverts

← Older revision		Revision as of 09:39, 2 February 2021
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	Where the existing roadway is to be incorporated into a newly constructed facility as part of the main roadway, the use of clear zones will be considered on individual projects. For “spot improvements” such as bridge replacements, the designer may determine to use less than the prescribed clear zone for new construction. This decision should be based on engineering judgment, giving consideration to crash history, roadway characteristics, access issues, project scope, and budget.		Where the existing roadway is to be incorporated into a newly constructed facility as part of the main roadway, the use of clear zones will be considered on individual projects. For “spot improvements” such as bridge replacements, the designer may determine to use less than the prescribed clear zone for new construction. This decision should be based on engineering judgment, giving consideration to crash history, roadway characteristics, access issues, project scope, and budget.

	The use of [[:Category:231 Typical Section Elements for Roadways\|clear zone typical sections is not applicable to small culvert replacement projects where the intent is to continue the service of the road without upgrading it. In such cases, the typical sections in the original construction are to be used except the roadway width is not to be narrower than the template of the roadway approaching the improvement.		The use of [[:Category:231 Typical Section Elements for Roadways\|clear zone typical sections]] is not applicable to small culvert replacement projects where the intent is to continue the service of the road without upgrading it. In such cases, the typical sections in the original construction are to be used except the roadway width is not to be narrower than the template of the roadway approaching the improvement.

	In shallow fills and in cuts where box or pipe culvert normally require a headwall to be located in the clear zone, the location of the headwall will be determined after an appropriate safety analysis is conducted. The culvert extension, shielding, audible warnings (rumble strips), delineation and the like (or combination of these) should be considered within the scope and budget of the project.		In shallow fills and in cuts where box or pipe culvert normally require a headwall to be located in the clear zone, the location of the headwall will be determined after an appropriate safety analysis is conducted. The culvert extension, shielding, audible warnings (rumble strips), delineation and the like (or combination of these) should be considered within the scope and budget of the project.

Kleins1: /* 231.2.3 For Bridges and Culverts */

2021-02-02T14:39:05Z

231.2.3 For Bridges and Culverts

← Older revision		Revision as of 09:39, 2 February 2021
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	Where the existing roadway is to be incorporated into a newly constructed facility as part of the main roadway, the use of clear zones will be considered on individual projects. For “spot improvements” such as bridge replacements, the designer may determine to use less than the prescribed clear zone for new construction. This decision should be based on engineering judgment, giving consideration to crash history, roadway characteristics, access issues, project scope, and budget.		Where the existing roadway is to be incorporated into a newly constructed facility as part of the main roadway, the use of clear zones will be considered on individual projects. For “spot improvements” such as bridge replacements, the designer may determine to use less than the prescribed clear zone for new construction. This decision should be based on engineering judgment, giving consideration to crash history, roadway characteristics, access issues, project scope, and budget.

	The use of [[:Category:231 Typical Section Elements for Roadways\|clear zone typical sections]] is not applicable to small culvert replacement projects where the intent is to continue the service of the road without upgrading it. In such cases, the typical sections used in the original construction are to be used except that the roadbed width is not to be more narrow than 24 feet.		The use of [[:Category:231 Typical Section Elements for Roadways\|clear zone typical sections is not applicable to small culvert replacement projects where the intent is to continue the service of the road without upgrading it. In such cases, the typical sections in the original construction are to be used except the roadway width is not to be narrower than the template of the roadway approaching the improvement.

	~~The use of~~ clear zone typical sections is not applicable to small culvert replacement projects where the intent is to continue the service of the road without upgrading it. In such cases, the typical sections in the original construction are to be used except the roadway width is not to be narrower than the template of the roadway approaching the improvement.

	In shallow fills and in cuts where box or pipe culvert normally require a headwall to be located in the clear zone, the location of the headwall will be determined after an appropriate safety analysis is conducted. The culvert extension, shielding, audible warnings (rumble strips), delineation and the like (or combination of these) should be considered within the scope and budget of the project.		In shallow fills and in cuts where box or pipe culvert normally require a headwall to be located in the clear zone, the location of the headwall will be determined after an appropriate safety analysis is conducted. The culvert extension, shielding, audible warnings (rumble strips), delineation and the like (or combination of these) should be considered within the scope and budget of the project.

	===231.2.4 Ramps===		===231.2.4 Ramps===

Smithk: Per DE, guidance now incorporates additional Roadside Design Guide (RDG) verbiage, RDG tables, and recommends a safety analysis as a means of documenting decisions for safety strategies.

2021-02-01T18:53:02Z

Per DE, guidance now incorporates additional Roadside Design Guide (RDG) verbiage, RDG tables, and recommends a safety analysis as a means of documenting decisions for safety strategies.

Show changes

Smithk at 15:09, 25 January 2019

2019-01-25T15:09:43Z

← Older revision		Revision as of 10:09, 25 January 2019
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	\|[[:Category:231 Typical Section Elements for Roadways\|Roadway Typical Sections]]		\|[[:Category:231 Typical Section Elements for Roadways\|Roadway Typical Sections]]
	\|-		\|-
	\|[[media:231.2 Clear Zone Distance.~~pdf~~\|RDG Table 3-1 "Suggested Clear-Zone Distances from Edge of Through Traveled Lane"]]		\|[[media:231.2 Clear Zone Distance 2019.docx\|RDG Table 3-1 "Suggested Clear-Zone Distances from Edge of Through Traveled Lane"]]
	\|-		\|-
	\|[[media:231.2 Horizontal Curve Adjustments.jpg\|RDG Table 3-2 "Horizontal Curve Adjustment Factor"]]		\|[[media:231.2 Horizontal Curve Adjustments.jpg\|RDG Table 3-2 "Horizontal Curve Adjustment Factor"]]

Smithk: Per Chuck Schumann, updated RDG Table 3-1 to reflect July 2015 errata

2018-09-14T15:04:52Z

Per Chuck Schumann, updated RDG Table 3-1 to reflect July 2015 errata

← Older revision		Revision as of 10:04, 14 September 2018
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	\|[[:Category:231 Typical Section Elements for Roadways\|Roadway Typical Sections]]		\|[[:Category:231 Typical Section Elements for Roadways\|Roadway Typical Sections]]
	\|-		\|-
	\|[[media:231.2 Clear Zone Distance.~~docx~~\|RDG Table 3-1 "Suggested Clear-Zone Distances from Edge of Through Traveled Lane"]]		\|[[media:231.2 Clear Zone Distance.pdf\|RDG Table 3-1 "Suggested Clear-Zone Distances from Edge of Through Traveled Lane"]]
	\|-		\|-
	\|[[media:231.2 Horizontal Curve Adjustments.jpg\|RDG Table 3-2 "Horizontal Curve Adjustment Factor"]]		\|[[media:231.2 Horizontal Curve Adjustments.jpg\|RDG Table 3-2 "Horizontal Curve Adjustment Factor"]]

Smithk: /* 231.2.1 Introduction */

2018-08-14T18:25:21Z

231.2.1 Introduction

← Older revision		Revision as of 13:25, 14 August 2018
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	\|[[:Category:231 Typical Section Elements for Roadways\|Roadway Typical Sections]]		\|[[:Category:231 Typical Section Elements for Roadways\|Roadway Typical Sections]]
	\|-		\|-
	\|[[media:231.2 Clear Zone Distance.docx\|RDG Table 3.1 "Suggested Clear-Zone Distances from Edge of Through Traveled Lane"]]		\|[[media:231.2 Clear Zone Distance.docx\|RDG Table 3-1 "Suggested Clear-Zone Distances from Edge of Through Traveled Lane"]]
	\|-		\|-
	\|[[media:231.2 Horizontal Curve Adjustments.jpg\|RDG Table 3.2 "Horizontal Curve Adjustment Factor"]]		\|[[media:231.2 Horizontal Curve Adjustments.jpg\|RDG Table 3-2 "Horizontal Curve Adjustment Factor"]]
	\|-		\|-
	\|[[media:231.2 Clear Zone for Non-recoverable.jpg\|RDG Figure 3-2 "Clear Zone for Non-Recoverable Parallel Foreslope"]]		\|[[media:231.2 Clear Zone for Non-recoverable.jpg\|RDG Figure 3-2 "Clear Zone for Non-Recoverable Parallel Foreslope"]]

Smithk: Per EPS, clarified clear zone guidance

2018-08-14T18:17:10Z

Per EPS, clarified clear zone guidance

← Older revision		Revision as of 13:17, 14 August 2018
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	===231.2.1 Introduction===		===231.2.1 Introduction===

	The [[media:231.2 Examples of a Parallel Foreslope Design.pdf\|clear zone]] concept is the road design principle of providing an unobstructed, traversable area beyond the edge of the through traveled way for the recovery of errant vehicles. The concept was developed in the 1960s and later incorporated into the ''Roadside Design Guide'' (RDG). The RDG ~~recommends~~ distances ~~for particular design conditions~~. These distances are neither absolute nor precise and, in some cases, it may be reasonable to leave a fixed object or non-traversable terrain within the clear zone area. The clear zone concept ~~is '''mostly'''~~ applicable to new construction and ~~major~~ reconstruction. ~~In limited circumstances, specific fixed~~ objects and non-traversable terrain features may be addressed on existing roads as part of resurfacing (1R) or resurfacing and restoration (2R) projects (see [[:Category:128 Conceptual Studies#128.2 Preventive Maintenance Projects (1R and 2R)\|EPG 128.2 Preventive Maintenance Projects (1R and 2R)]]). On existing roads, primarily those of an older or lower-order nature, a clear area may be established through maintenance activities. While this practice is strongly encouraged, these areas should not be construed as providing the same safety benefit as clear zones.		The [[media:231.2 Examples of a Parallel Foreslope Design.pdf\|clear zone]] concept is the road design principle of providing an unobstructed, traversable area beyond the edge of the through traveled way for the recovery of errant vehicles. The concept was developed in the 1960s and later incorporated into the ''Roadside Design Guide'' (RDG). The RDG suggests clear zone distances based on traffic volumes and speeds. These distances are neither absolute nor precise and, in some cases, it may be reasonable to leave a fixed object or non-traversable terrain within the clear zone area. Roadside design strategies involve the following:
	{\|style="padding: 0.3em; margin-left:15px; border:1px solid #a9a9a9; text-align:center; font-size: 95%; background:#f5f5f5" width="~~220px~~" align="right"
			:1. Remove the obstacle
			:2. Redesign the obstacle for safe traversal
			:3. Relocate the obstacle further from the roadway
			:4. Reduce obstacle severity (make it breakaway)
			:5. Shield the obstacle
			:6. Delineate the obstacle (when we must leave the obstacle)

			The clear zone concept guidelines in the RDG may be most applicable to new construction and reconstruction/rehabilitation projects. Fixed objects and non-traversable terrain features may also be addressed on existing roads as part of resurfacing (1R) or resurfacing and restoration (2R) projects (see [[:Category:128 Conceptual Studies#128.2 Preventive Maintenance Projects (1R and 2R)\|EPG 128.2 Preventive Maintenance Projects (1R and 2R)]]). Every roadside should be made as safe as practical. On existing roads, primarily those of an older or lower-order nature, a clear area may be established through maintenance activities. While this practice is strongly encouraged, these areas should not be construed as providing the same safety benefit as clear zones.
			{\|style="padding: 0.3em; margin-left:15px; border:1px solid #a9a9a9; text-align:center; font-size: 95%; background:#f5f5f5" width="280px" align="right"
	\|-		\|-
	\|'''Figures'''		\|'''Figures'''
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	\|[[:Category:231 Typical Section Elements for Roadways\|Roadway Typical Sections]]		\|[[:Category:231 Typical Section Elements for Roadways\|Roadway Typical Sections]]
	\|-		\|-
	\|[[media:231.2 Clear Zone Distance ~~Curves~~.~~pdf~~\|RDG ~~Figure~~ 3.1 "Clear-Zone ~~Distance curves~~"]]		\|[[media:231.2 Clear Zone Distance.docx\|RDG Table 3.1 "Suggested Clear-Zone Distances from Edge of Through Traveled Lane"]]
	\|-		\|-
	\|[[media:231.2 Horizontal Curve Adjustments.~~pdf~~\|RDG Table 3.2 "Horizontal Curve ~~Adjustments~~"]]		\|[[media:231.2 Horizontal Curve Adjustments.jpg\|RDG Table 3.2 "Horizontal Curve Adjustment Factor"]]
	\|-		\|-
	\|[[media:231.2 ~~Examples of a Parallel Foreslope Design~~.~~pdf~~\|RDG Figure 3.2 "~~Example of a~~ Parallel Foreslope ~~Design~~"]]		\|[[media:231.2 Clear Zone for Non-recoverable.jpg\|RDG Figure 3-2 "Clear Zone for Non-Recoverable Parallel Foreslope"]]
	\|-		\|-
	\|[[media:231.2 Preferred Cross Sections ~~for Channels with abrupt slope changes~~.~~pdf~~\|RDG Figure 3.6 "Preferred Cross Sections for Channels with Abrupt Slope Changes"]]		\|[[media:231.2 Preferred Cross Sections.jpg\|RDG Figure 3-6 "Preferred Cross Sections for Channels with Abrupt Slope Changes"]]
	\|}		\|}
	Clear ~~zone widths~~ are ~~most affected by the traffic’s speed~~ and ~~volume and the slope of the area adjacent to the travelway. Appropriate clear zones are~~ selected ~~for new construction or major reconstruction projects using [[media:231.2 Clear Zone Distance Curves.pdf\|Figure 3.1]] from~~ the RDG after consulting the [[:Category:126 Location Study and Alternatives Analysis\|location study report]].
			Clear zones are reviewed and/or selected based on the RDG guidelines after consulting the [[:Category:126 Location Study and Alternatives Analysis\|location study report]].

	Clear zones are designed into a project when the anticipated posted speed of the roadway is 45 mph or more. When the anticipated posted speed is less than 45 mph, clear zones are still beneficial, but they are to be considered only if economically feasible. Non-traversable slopes or fixed objects are to be removed, redesigned, relocated or shielded by a barrier if they are within the indicated minimum clear zone width and it is cost effective to do so.		Clear zones are designed into a project when the anticipated posted speed of the roadway is 45 mph or more. When the anticipated posted speed is less than 45 mph, clear zones are still beneficial, but they are to be considered only if economically feasible. Non-traversable slopes or fixed objects are to be removed, redesigned, relocated or shielded by a barrier if they are within the indicated minimum clear zone width and it is cost effective to do so.
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	Clear zones, when used, shall extend full-width to bridge ends. Where the existing roadway is to be incorporated into the completed facility as part of the main roadway, the use of clear zones will be considered on individual projects.		Clear zones, when used, shall extend full-width to bridge ends. Where the existing roadway is to be incorporated into the completed facility as part of the main roadway, the use of clear zones will be considered on individual projects.

	The use of [[:Category:231 Typical Section Elements for Roadways\|clear zone typical sections]] is not applicable to small culvert replacement projects where the intent is to continue the service of the road without upgrading it. In such cases, the typical sections used in the original construction are to be used except that the roadbed width is not to be more narrow than 24 ft.		The use of [[:Category:231 Typical Section Elements for Roadways\|clear zone typical sections]] is not applicable to small culvert replacement projects where the intent is to continue the service of the road without upgrading it. In such cases, the typical sections used in the original construction are to be used except that the roadbed width is not to be more narrow than 24 feet.

	In shallow fills and in cuts where box or pipe culvert normally require a headwall to be located in the clear zone, the structure should be extended to place the headwall at the outside of the clear zone or a safety appurtenance (guardrail or barrier) should be provided. The slope of the clear zone will then require modification over the entire surface.		In shallow fills and in cuts where box or pipe culvert normally require a headwall to be located in the clear zone, the structure should be extended to place the headwall at the outside of the clear zone or a safety appurtenance (guardrail or barrier) should be provided. The slope of the clear zone will then require modification over the entire surface.
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	===231.2.5 In Unusual Conditions===		===231.2.5 In Unusual Conditions===

	When a standard clear zone width and slope will not properly terminate on the existing ground surface because of hilly conditions, steeper slopes must be used. In this case, the clear zone may be omitted and guardrail used at the shoulder line. The desirable minimum length for the elimination of clear zone is 500 ft. but in no case less than 250 ft.		When a standard clear zone width and slope will not properly terminate on the existing ground surface because of hilly conditions, steeper slopes must be used. In this case, the clear zone may be omitted and guardrail used at the shoulder line. The desirable minimum length for the elimination of clear zone is 500 ft. but in no case less than 250 feet.

	For long fill sections through a reservoir project, clear zones can be eliminated and guardrail used at the shoulder lines.		For long fill sections through a reservoir project, clear zones can be eliminated and guardrail used at the shoulder lines.
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	===231.2.6 Maintenance===		===231.2.6 Maintenance===

	District personnel shall be responsible for maintaining clear zones on ~~highway improvement projects~~.		District personnel shall be responsible for maintaining clear zones on highways.

	[[category:231 Typical Section Elements for Roadways\|231.02]]		[[category:231 Typical Section Elements for Roadways\|231.02]]

EPGsysop: /* 231.2.1 Introduction */ Per EPS and CCO, condensed and clarified guidance regarding clear zones and roadside hardware for 1R and 2R projects

2018-02-01T20:53:56Z

231.2.1 Introduction: Per EPS and CCO, condensed and clarified guidance regarding clear zones and roadside hardware for 1R and 2R projects

← Older revision		Revision as of 15:53, 1 February 2018
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	===231.2.1 Introduction===		===231.2.1 Introduction===

	The [[media:231.2 Examples of a Parallel Foreslope Design.pdf\|clear zone]] is an unobstructed, traversable area ~~provided~~ beyond the edge of the through traveled way for the recovery of errant vehicles. The ~~provision of~~ a clear zone is ~~only~~ applicable to new construction and re-~~construction~~ projects ~~pursuant to guidance outlined in the Roadside Design Guide~~. On existing roads, primarily those of an older or lower-order nature, a clear area ~~has been~~ established through maintenance activities. While this practice is strongly encouraged, these areas should not be construed as providing the same safety benefit as clear zones.		The [[media:231.2 Examples of a Parallel Foreslope Design.pdf\|clear zone]] concept is the road design principle of providing an unobstructed, traversable area beyond the edge of the through traveled way for the recovery of errant vehicles. The concept was developed in the 1960s and later incorporated into the ''Roadside Design Guide'' (RDG). The RDG recommends distances for particular design conditions. These distances are neither absolute nor precise and, in some cases, it may be reasonable to leave a fixed object or non-traversable terrain within the clear zone area. The clear zone concept is '''mostly''' applicable to new construction and major reconstruction. In limited circumstances, specific fixed objects and non-traversable terrain features may be addressed on existing roads as part of resurfacing (1R) or resurfacing and restoration (2R) projects (see [[:Category:128 Conceptual Studies#128.2 Preventive Maintenance Projects (1R and 2R)\|EPG 128.2 Preventive Maintenance Projects (1R and 2R)]]). On existing roads, primarily those of an older or lower-order nature, a clear area may be established through maintenance activities. While this practice is strongly encouraged, these areas should not be construed as providing the same safety benefit as clear zones.
			{\|style="padding: 0.3em; margin-left:15px; border:1px solid #a9a9a9; text-align:center; font-size: 95%; background:#f5f5f5" width="220px" align="right"
	~~In general, the clear zone, or forgiving roadside concept is the preferred method of achieving roadside safety. The four methods of establishing a clear zone are listed here in order of preference:~~

	~~:1) Eliminate obstacles.~~
	~~:2) Redesign obstacles so they can be safely traversed.~~
	~~:3) Relocate obstacles to a location where they're less likely to be struck.~~
	~~:4) Reduce the impact severity of obstacles by using appropriate breakaway devices~~.
	{\|style="padding: 0.3em; margin-left:15px; border:1px solid #a9a9a9; text-align:center; font-size: 95%; background:#f5f5f5" width="~~160px~~" align="right"
	\|-		\|-
	\|'''Figures'''		\|'''Figures'''
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	\|[[media:231.2 Preferred Cross Sections for Channels with abrupt slope changes.pdf\|RDG Figure 3.6 "Preferred Cross Sections for Channels with Abrupt Slope Changes"]]		\|[[media:231.2 Preferred Cross Sections for Channels with abrupt slope changes.pdf\|RDG Figure 3.6 "Preferred Cross Sections for Channels with Abrupt Slope Changes"]]
	\|}		\|}
	Clear zone widths are most affected by the traffic’s speed and volume and the slope of the area adjacent to the travelway. Appropriate clear zones are selected for projects using [[media:231.2 Clear Zone Distance Curves.pdf\|Figure 3.1]] from the RDG after consulting the [[:Category:126 Location Study and Alternatives Analysis\|location study report]].		Clear zone widths are most affected by the traffic’s speed and volume and the slope of the area adjacent to the travelway. Appropriate clear zones are selected for new construction or major reconstruction projects using [[media:231.2 Clear Zone Distance Curves.pdf\|Figure 3.1]] from the RDG after consulting the [[:Category:126 Location Study and Alternatives Analysis\|location study report]].

	Clear zones are ~~provided where~~ the anticipated posted speed of the roadway is 45 mph or more. When the anticipated posted speed is less than 45 mph, clear zones are still beneficial but they are to be considered only if economically feasible. Non-traversable slopes or fixed objects are to be removed, relocated or shielded by a barrier if they are within the indicated minimum clear zone width and it is cost effective to do so. Higher speeds result in vehicles traveling farther off the travelway before control is recovered. Horizontal curvature increases the likelihood of a vehicle leaving the travelway and increases the distance it travels. The designer may choose to modify the clear zone distance obtained from RDG Figure 3.1 by using [[media:231.2 Horizontal Curve Adjustments.pdf\|Table 3.2]] (adjusting the values for horizontal curvature as necessary). These modifications are normally only considered where accident histories indicate a need, or a specific site investigation shows a definite accident potential which could be significantly lessened by increasing the clear zone width and such increases are cost-effective. Steeper slopes adjacent to the travelway increases the distance the vehicle travels beyond the travelway. In the implementation of the clear zone concept it is important for clear zone distances to not be used as boundaries for introducing roadside hazards such as bridge piers or trees. These are to be as far from the travelway as practical.		Clear zones are designed into a project when the anticipated posted speed of the roadway is 45 mph or more. When the anticipated posted speed is less than 45 mph, clear zones are still beneficial, but they are to be considered only if economically feasible. Non-traversable slopes or fixed objects are to be removed, redesigned, relocated or shielded by a barrier if they are within the indicated minimum clear zone width and it is cost effective to do so.

	~~[[image:231.2.1 Cut Section.jpg\|right\|175px\|thumb\|<center>'''Cut Section'''</center>]]~~		The clear zone width is to be applied with good judgment and should be balanced with project costs. Limited right of way or high construction costs may lead to the installation of a barrier or possibly no protection at all.
	The clear zone width is to be applied with good judgment~~. If an obstacle lies just beyond the clear zone, it is to~~ be ~~removed or shielded if~~ costs ~~are reasonable~~. ~~Conversely, the clear zone is not to be obtained at all costs.~~ Limited right of way or high construction costs may lead to the installation of a barrier or possibly no protection at all.

	As may be noted, roadside slopes apply an important part in the clear zone width determination. Fill slopes of 1V:6H/1V:3H are preferred in areas of high fill, that is, a 1V:6H slope extending from the shoulder line out for a distance necessary to obtain the clear zone then break the slope to 1V:3H or flatter. If feasible, the flattening of slopes is preferable to installation of guardrail. In cut sections, the roadside ditch is likely to be located within the clear zone. Therefore, the configuration of the ditch and the type of [[:Category:806 Pollution, Erosion and Sediment Control\|erosion control treatment]] used in the ditch must be viewed with respect to clear zone requirements. Namely, side slopes of the ditch and the method of erosion control used in the ditch must be traversable by vehicles that leave the roadway. [[media:231.2 Preferred Cross Sections for Channels with abrupt slope changes.pdf\|Figure 3.6]] in the RDG is to be checked for preferred ditch cross-sections. Ditch sections must be within the shaded portions of the guides for use with clear zones. Background for this procedure is contained in Appendix A of the RDG. Any deviation from the preferred slope will be considered a special condition and is to be justified by costs or other considerations.

	===231.2.2 Clear Zone Perception Issues===		===231.2.2 Clear Zone Perception Issues===