FHWA State Geotechnical Workshops


Developing Rational Criteria

For rock cut slopes, aesthetic criteria have often been expressed in contract documents and environmental assessments using language such as:

  • “blend with the natural terrain”
  • “reflect the form, line, color, and texture of natural formations”
  • “natural-appearing cut slopes”
  • “roughened cut slopes”
  • “mimic natural land forms”

and so forth. Although this may be meaningful to landscape architects and others who have an intuitive understanding of the desired finished product, road building contractors and engineering designers find such language imprecise and confusing. Others within the highway engineering community may see attempts to “naturalize” the appearance of rock cut slopes as opening the door to slope instability and liability exposure. These individuals express a preference for more economical, steeper cut slopes excavated using techniques that minimize rock disturbance and produce a planar, uniform, and engineered appearance.

Even though the process of constructing “natural appearing” cut slopes does not preserve rock mass integrity and construction economy to the same degree as rigorously controlled cut slopes, there are aesthetic enhancement techniques that acceptably improve the visual characteristics while retaining an acceptable degree of rock slope stability and economy.

The key is to develop a working partnership between the highway development and recreational land management agencies to make the aesthetic criteria deterministic, rational, biddable, and constructible.

The need for aesthetic enhancement is driven by regulatory and management requirements that highway engineers and constructors may view as arbitrary. However, there is practical justification. This justification derives from three main factors. First, for many highway users, travel to the recreational site is an important part of the overall recreation experience. Having a more attractive highway extends the recreational experience. Second, in areas of high scenic quality, an economic as well as social value may be attached to the scenic highway designation. Users are attracted to the area, its campgrounds, and its towns. Third, the view enjoyed by off highway recreationists is an important part of their experience. Hikers and campers who do not have to travel as far to put themselves in a natural setting are more likely to use the area.

Understanding these factors can form the basis of a rational and deterministic process in design and construction. In essence, the design team must define who exactly is to be served by the improved aesthetics and what their visual perspective is, and how much enhancement is appropriate.