InTrans / Oct 02, 2021

Improving safety through vegetation control and maintenance of drainage features

Example of overgrown vegetation at a guard rail

The question is: Why is the maintenance of drainage features needed and how does it affect roadway safety?

In 2018 alone, over 2.7M people were injured in crashes on US roadways, which equals approximately 5 people every minute. At the same time, over 36,000 people were killed in crashes. This results in a huge loss of life and a massive economic impact ($242B as of 2010).

Nicole Oneyear, a safety researcher at the Institute for Transportation’s Center for Transportation Research and Education had this to say:

“A good maintenance program is necessary to have a safe road.”

Vegetation control for safety

Vegetation can be a hazard on the road or in the right-of-way. For example, trees can be fixed object hazards and vegetation can block or limit a driver’s view of traffic control devices, other vehicles, wildlife, and pedestrians and bicyclists.

Oneyear noted that the overarching goals of a good vegetation control program should address or correct these issues by:

  • Keeping signs visible to drivers
  • Keeping road users (e.g., vehicles, bicycles, and pedestrians) visible to drivers and vice versa
  • Keeping sidewalks and pedestrian paths clear and free from overhanging vegetation
  • Improving the visibility of livestock and wildlife near the road

Efforts should be made to eliminate and control vegetation through preventative strategies like mowing, brush cutting, herbicides, livestock grazing, etc.

“When developing a roadside vegetation management program, you should consult with a local weed control specialist,” Oneyear suggested. “That way you can properly identify what weeds are present on your roadside as well as identify the best way to address them. Some weeds should be mowed down while others, if you mow them, will spread and then next year you will have an even bigger problem.”

Three types of mowing used frequently to address vegetation issues are: safety, transition, and contour or selective mowing. The FHWA released in 2008 their Vegetation Control for Safety: A Guide for Local Highway and Street Maintenance Personnel, which describes these types of mowing in detail and when they should be used.

Winter maintenance also plays a role in roadside safety, especially as a preventative strategy. For example, trees and shrubs can cast shadows on pavement, which leads to black ice.

“It is suggested that taller vegetation be cut (known as daylighting) and provide light to the roadway to help keep the pavement temperature up and hopefully not freezing.”

Maintenance of drainage features for safety

Drainage structures are systems that remove stormwater run-off from streets and highways. Examples include curbs, gutters, channels, ditches, pipes, grates, and drop inlets.

According to Oneyear, a good drainage system ensures the safe operating condition of a roadway surface (i.e., it removes storm run-off, provides for snow removal, and reduces the ability for ice to form) and that they do not result in a reduction in crashworthiness.

“A good drainage system is not a hazard itself,” Oneyear said. “Drainage structures are often fixed objects, which can be hazardous to drivers.”

Poor drainage systems often affect travel way pavement surfaces. Water ponding can increase stopping distance, thin layers of standing water can lead to hydroplaning, and vehicles may try to avoid standing water completely by swerving and increasing the likelihood of a roadway departure. Additionally, erosion due to deterioration of the pavement edge is likely.

“Ditches and side slopes can also be hazardous, mainly because of erosion,” Oneyear added. “Ditches need to be cleaned to prevent them from silting and forcing water onto the travel way surfaces.”

Drainage ditches should be traversable (i.e., so an errant vehicle can cross without overturning, being abruptly stopped, or causing the driver to lose control).

It should be noted that pedestrian and bike paths face similar issues as the streets; however, users are more able to avoid or compensate for standing water or ice on the path. Maintenance activities and low-cost drainage improvements can prevent these problems.

The best way to identify drainage problems is through citizen complaints, local police noticing problems during patrols or when responding to crashes, crash data, reading the road, and field reviews.

“Ultimately, the ability to recognize maintenance tasks related to vegetation and drainage and how they impact safety will only benefit agencies as they develop and better their vegetation control programs and routine maintenance efforts,” Oneyear said.

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