Manual for Selecting Safety Improvements on High Risk Rural Roads - Safety

Program Contact

James Dahlem
james.dahlem@dot.gov
(202) 366-9265

4. Selecting Safety Treatments (continued)

4.9. Vertical Curves

Safety improvement treatments on vertical curves range from low-cost improvements (such as signing) to high-cost improvements (such as modifying road geometry). This section covers safety improvement treatments that can be applied at vertical curve locations. Some treatments in this section also appear in the sections on intersection improvements, signing, and roadside safety.

Safety Treatment	For more information, visit page	Cost		Frequency of Maintenance (years)	Safety Benefit		Benefit Cost Ratio³⁸
Safety Treatment	For more information, visit page	Initial Implementation	Ongoing Maintenance	Frequency of Maintenance (years)	NCHRP 500 Performance Rating	Crash Modification Factor (CMF)	Lower Volume, Optimal Conditions**	Higher Volume, Optimal Conditions*	Lower Volume, Narrower Conditions***	Higher Volume, Narrower Conditions**
Install Advanced Intersection Warning Signs	143	$			P
Install Dynamic Advanced Intersection Warning System	144	$$			P	0.10-0.76
Modify Horizontal/Vertical Geometry	145	$$$$$			P
Relocate Driveways, Entrances, and Intersections	146	$$$$$			T
Cost: $ = $0 to $5,000 $$ = $5,001 to $20,000 $$$ = $20,001 to $50,000 $$$$ = $50,001 to $100,000 $$$$$ = $100,001 and up NCHRP 500 Performance rating³⁹ P – Proven T – Tried E – Experimental U – Unknown Lower Volume ≤ 1000 vpd Higher Volume = Between 1,001 and 8000 vpd Optimal Conditions = 12-foot lanes, 6-foot paved shoulders **Narrower Conditions = 10-foot lanes and no shoulders

Install Advanced Intersection Warning Signs

Advanced intersection warning signs can help alert drivers to the presence of an intersection ahead. Signs can be placed with sufficient distance prior to the intersection to allow drivers to perceive and react. They can also be installed on both sides of the roadway to solicit greater awareness.

Diagram shows positioning of advanced warning signs on the approach to a cross street.

Where to Use: Advanced intersection warning signs are to be applied predominantly on single through lane, high-crash, stop-controlled State intersections in both rural and urban areas. They may also be applied on dual through lane, high-crash, stop-controlled intersections with lower traffic volumes (less than about 25,000 average annual daily traffic (AADT)) where the use of J-treatments is not appropriate and the frequency of acceptable gaps for entering traffic is such that long waiting and higher risk taking are present at the intersection.

Safety Treatment	Initial Implementation Cost	NCHRP 500 Performance Rating
Install Advanced Intersection Warning Signs	$0 to $5,000	Tried

Top Recommended Resources:

1. FHWA, Example Intersection Safety Implementation Plan, 2009.

2. FHWA, Stop-Controlled Intersection Safety: Through Route Activated Warning Systems, February 2011.

Install Dynamic Advanced Intersection Warning System

Infrastructure-based Intelligent Transportation System (ITS) technologies can be used to significantly improve the safety at stop-controlled intersections. These systems provide enhanced safety warning information for approaching drivers compared to passive warning systems. A dynamic advanced intersection warning system can provide:

Enhanced warning to the through driver that there is a vehicle on a cross road stop approach that may enter the intersection.
Enhanced warning to drivers on a stop approach that their trajectory speed is high and that they may run the Stop sign.
Enhanced warning to through drivers that they are traveling at too high an intersection entry speed and advising them to slow down.
Enhanced warning to drivers on the stop approach of entering vehicles on the through approach, inferring potential unsafe gaps.

Dynamic warning sign with flashers that activate to warn approaching through traffic that there is a vehicle on a cross road stop approach that may enter the intersection.

Where to Use: This treatment may be provided at intersections that experience severe intersection-related crashes due to speed, low visibility, or insufficient gaps.

Safety Treatment	Initial Implementation Cost	NCHRP 500 Performance Rating	Crash Modification Factor (CMF)
Install Dynamic Advanced Intersection Warning System	$5,001 to $20,000	Proven	0.10-0.76

Top Recommended Resource:

1. FHWA, Stop-Controlled Intersection Safety: Through Route Activated Warning Systems, February 2011. Available at: http://safety.fhwa.dot.gov/intersection/resources/fhwasa11015/traws.pdf.

Modify Horizontal/Vertical Geometry

Horizontal and vertical geometry may be reconstructed in a variety of ways. For example, horizontal and vertical curves may benefit from increased radii, thereby increasing sight distance. Modifying road geometry may also include eliminating horizontal or vertical curves and providing a more direct alignment.

Where to Use: This treatment may be used at locations where improved sight distance is needed and at locations that experience head-on collisions and run-off-road crashes. This treatment can also be used at unsignalized intersections with restricted sight distance due to horizontal or vertical geometry and those with patterns of crashes related to that lack of sight distance that cannot be ameliorated by less expensive methods.

Safety Treatment	Initial Implementation Cost	NCHRP 500 Performance Rating
Modify Horizontal/Vertical Geometry	$100,001 and up	Proven

Relocate Driveways, Entrances, and Intersections

Relocating or removing private and public driveways, commercial entrances, and road or street intersections just beyond the crest of vertical curves in the direction of travel isn't always feasible but does ensure that conflicts at locations with limited sight distances are removed or remediated.

A rural two-lane road with two driveways opposite each other.

Where to use: This treatment may be used near vertical curve crests where sight distance to driveways, entrances, or intersections is limited or obstructed.

Safety Treatment	Initial Implementation Cost	NCHRP 500 Performance Rating
Relocate Driveways, Entrances, and Intersections	$100,001 and up	Tried

4.10. Other Treatments

Treatments in this section may be applied at specific locations to improvement safety and do not fit into any of the previous categories.

Safety Treatment	For more information, visit page	Cost		Frequency of Maintenance (years)	Safety Benefit		Benefit Cost Ratio⁴⁰
Safety Treatment	For more information, visit page	Initial Implementation	Ongoing Maintenance	Frequency of Maintenance (years)	NCHRP 500 Performance Rating	Crash Modification Factor (CMF)	Lower Volume, Optimal Conditions**	Higher Volume, Optimal Conditions*	Lower Volume, Narrower Conditions***	Higher Volume, Narrower Conditions**
Mitigate Ground Water to Prevent Ponding and/or Icing	148	$$$-$$$$			E
Widen Functionally Obsolete Bridges	149	$$$$$
Cost: $ = $0 to $5,000 $$ = $5,001 to $20,000 $$$ = $20,001 to $50,000 $$$$ = $50,001 to $100,000 $$$$$ = $100,001 and up NCHRP 500 Performance rating⁴¹ P – Proven T – Tried E – Experimental U – Unknown Lower Volume ≤ 1000 vpd Higher Volume = Between 1,001 and 8000 vpd Optimal Conditions = 12-foot lanes, 6-foot paved shoulders **Narrower Conditions = 10-foot lanes and no shoulders

Mitigate Ground Water to Prevent Ponding and/or Icing

Good site drainage is needed to keep ponding and icing from occurring. This can be accomplished through a change in runoff conditions, whether by increasing the storm drainage capacity, re-grading ditches for better flow, or making changes to the roadway superelevation.

A roadway drops off into a drainage ditch that runs under a cross-street that serves as the entrance to a residential neighborhood.

Where to Use: This treatment is applicable at locations where roadway ponding occurs.

Safety Treatment	Initial Implementation Cost	NCHRP 500 Performance Rating
Mitigate Ground Water to Prevent Ponding and/or Icing	$20,001 to $100,000	Experimental

Widen Functionally Obsolete Bridges

Widening narrow bridges on HRRR that are unable to accommodate traffic, either as a one-lane two-way operation or lanes too narrow to accommodate two-way traffic, may help to prevent head-on and sideswipe collisions.

Where to Use: This treatment can be used at locations that experience a high frequency of head-on or sideswipe collisions due to narrow lane width or one-lane two-way operations.

Safety Treatment	Initial Implementation Cost
Widen Functionally Obsolete Bridges	$100,001 and up

³⁸ As discussed in Section 1.2, a BCR is only shown where data were available to calculate the ratio. Where data were unavailable, the BCR has been left blank. [ Return to note 38. ]

³⁹ As stated in NCHRP Series 500 Reports (http://safety.transportation.org/guides.aspx). Proven: The safety effect for other similar applications has shown a proven benefit. Tried: The treatment has indications that it can be expected to reduce crashes, but has some conflicting reports as to its associated safety effects or has been deployed and observed to be effective. Experimental: New treatments that still need to be tested and for which the safety effect is unknown. Unknown: Not enough is known about an associated safety performance. [ Return to note 39. ]

⁴⁰ As discussed in Section 1.2, a BCR is only shown where data were available to calculate the ratio. Where data were unavailable, the BCR has been left blank. [ Return to note 40. ]

⁴¹ As stated in NCHRP Series 500 Reports (http://safety.transportation.org/guides.aspx). Proven: The safety effect for other similar applications has shown a proven benefit. Tried: The treatment has indications that it can be expected to reduce crashes, but has some conflicting reports as to its associated safety effects or has been deployed and observed to be effective. Experimental: New treatments that still need to be tested and for which the safety effect is unknown. Unknown: Not enough is known about an associated safety performance. [ Return to note 41. ]

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Page last modified on June 2, 2016