Low Cost Treatments for Horizontal Curve Safety
CHAPTER 8. MAINTENANCE TREATMENTS
The preceding chapters present specific treatments that road
agencies can apply to a horizontal curve or series of curves to improve safety.
The final word on this publication, however, relates to the importance of
maintaining the roadway and the various traffic control devices installed.
Regardless of the treatments used, road agencies should plan and carry out the
following six maintenance activities to ensure continued safe travel.
Restripe pavement markings as they lose their visibility.
Pavement markings using paint-based materials have a
relatively short service life—1 to 2 years. How long an agency’s pavement
markings last depends on material type, climate, and traffic volume. Markings
of thermoplastic material have a substantially longer service life. To maintain
their effectiveness, pavement markings must be visible, especially at nighttime
and during conditions of limited visibility. An agency’s regular inspection and restriping programs are critical to ensuring pavement
markings provide needed visibility for motorists. For additional information on
pavement marking visibility, visit http://safety.fhwa.dot.gov/roadway_dept/night_visib/pavement_visib/.
Replace faded signs and those with low
levels of retroreflectivity.
The various signs
discussed in this report are visible at night because they are made with retroreflective sheeting material. Few, if any, are
illuminated by external lighting. Even though the retroreflectivity of the sheeting material has improved to provide brighter and longer lasting
signs, all signs deteriorate over time. Signs lose their color and retroreflectivity and eventually they are no longer visible
to motorists from a distance. Therefore, it is good agency practice to schedule
an annual inspection of all signs within its jurisdiction to ensure they are at
or above the appropriate retroreflective level. For
alternative methods for conducting this inspection, see Maintaining Traffic Sign Retroreflectivity (2005 Edition)
(http://tcd.tamu.edu/Documents/MinRetro/MinRetro.htm). Replace any signs found
to be ineffective as soon as possible. For additional information on sign retroreflectivity, visit http://safety.fhwa.dot.gov/roadway_dept/night_visib/.
Cut back foliage to improve the sight
distance through the curve and increase visibility of traffic control devices.
Agencies can improve safety at a horizontal curve by
maintaining the longest possible sight distance through the curve and to the various
traffic signs. During the growing season, grass, weeds, brush, and tree limbs
can limit a driver’s view of the road and signs. This is why agencies should
make an annual inspection of the roadway to identify and correct these
practical tips for controlling vegetation overgrowth are found in the FHWA
report Vegetation Control for Safety (http://www.fhwa.dot.gov/publications/research/safety/90003/).
Maintain the shoulders and smooth
transitions between pavement and shoulder.
Clearing undergrowth on the right side would significantly
improve sight distance through the curve and allow motorists to judge more
accurately the length and sharpness of the curve—and more importantly see oncoming
Unpaved or unstabilized shoulders
can erode over time, especially on the inside curve shoulder. The result is
pavement drop-offs. Chapter 4 focused on ways to correct this situation.
Periodic maintenance of shoulders can prevent this situation.
Eliminate roadside obstacles, such as
culvert headwalls, or provide adequate shielding.
occur more frequently along horizontal curve sections. While implementing the treatments
discussed in this publication should reduce the frequency of these type
crashes, they will unfortunately still occur. It is important, therefore, to
minimize roadside obstacles and shield them with an appropriate traffic
barrier. Once a barrier is in place, road agencies must be ready to repair
damage to it, as necessary. More complete information on treatment of roadside
hazards is available in AASHTO’s Roadside Design Guide and in the FHWA publication Road Safety Fundamentals.
Improve drainage around the curve.
Improper and poor
drainage is particularly troublesome on horizontal curves because of water
flows caused by the pavement superelevation. When
water cannot drain properly, shoulder deterioration can cause pavement drop off
and shoulder loss. Agencies should install curbing and improve drain
maintenance. For tips on road drainage features important to safety, see the
FHWA publication Maintenance of Drainage
Features for Safety.
FHWA Resource Charts, July 2013
FHWA Roadway Lighting Handbook, August 2012
RwD Strategic Plan, April 2013
Updated Guidance on Sign Retroreflectivity, April 2013
Clarifying Guidance on Daytime Luminance, January 2013
Guidance for the Selection , Use and Maintenance of Cable Barrier Systems, November 2012