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.

1. 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/.

2. 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/.

3. 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 situations.

   More practical tips for controlling vegetation overgrowth are found in the FHWA report Vegetation Control for Safety (https://www.fhwa.dot.gov/publications/research/safety/90003/).

4. 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 traffic.

   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.

5. Eliminate roadside obstacles, such as culvert headwalls, or provide adequate shielding.

   Run-off-road crashes 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.

6. 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.