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17 Typical concrete barriers are simple in shape, featureless, Surface coatings can be cementitious coatings or pigmented repetitive, and utilitarian in appearance. For most viewers, an coatings (i.e., paints and stains). aesthetically treated barrier will be different in some or all of Deforming a surface can be accomplished by sandblasting these categories. The selection of one alternative aesthetic to change the color and reflectivity of a surface, or parts of a treatment over another will still be a subjective process. How- surface can be recessed or be made to protrude from the pri- ever, an objective set of aesthetic criteria can consist of line, mary surface. Receding or protruding surfaces are perceived profile, surface, and color. by the shadow contrast created by their edges. Surface reflec- tivity and shadow contrast are the ways in which patterns are CHANGING THE AESTHETICS OF A perceived. It may be possible to communicate patterns through LONGITUDINAL CONCRETE TRAFFIC BARRIER the contrast in reflectivity brought about by small changes in surface angles. Concrete traffic barriers are linear elements by design, and Adding aesthetic treatments to the interior of concrete bar- this linear character cannot be fundamentally altered. Improv- riers will entail the addition of vertical edges (i.e., lines per- ing the aesthetic character means that methodologies must be pendicular to the line of the barrier) into the face of the bar- found to add interest to the structure without compromising rier. Research and experience clearly confirm that almost any the functionality of the structure. Interest may be achieved edge that is part of a surface perpendicular to the direction of by modulating the linear character of the barrier. Modula- traffic can negatively influence vehicle impact. The size of tion may be defined as a change in rhythmical measure. In the relative change in the surface determines whether or not terms of a linear structure we may take this to mean the it may snag some part of an impacting vehicle. The issue, change in the amplitude, frequency, or intensity of the line, then, is the degree to which surface reflectivity and patterns color, pattern, or form. can be introduced into a rail surface without negatively affect- The combination of these aspects will do one of two things: ing impact performance. The key question is "how can vertical edges and other sur- Reinforce the linear character of the structure. Intro- face discontinuities be safely introduced into a rail surface duce linear lines that parallel the edge of the structure or design?" use a short, consistent sequence or repeating pattern. Lessen the linear character of the structure. Segment FACTORS AFFECTING DESIGN the rail by varying the height, introducing vertical lines, or using long, discontinuous patterns. Parameters have already been established that greatly influ- ence the search for alternative barrier and rail designs. Three Because barriers are experienced while the viewer is in of the most critical parameters are (1) adequate rail height; motion, the structure is experienced as a thing with a begin- (2) the need for a continuous solid surface (either rounded or ning and end, perceived over a period of time. This temporal flat) of adequate contact surface area at the point of impact; aspect means that the structure is experienced as a pattern of and (3) the absence or protection of any vertical edge that will both rhythm and sequence. The common concrete rail has an snag a vehicle. aesthetic character composed of a singular, boring rhythm The dimensions may vary, but a representative example is and a lack of any sense of sequence. Therefore, creating an shown in Figure 10. Of critical note is the 356-mm impact sur- aesthetic barrier rail means creating a pleasing rhythm and face (and its 330-mm vertical location) and the 115-mm set- sequence to the time in which a rail is experienced. back of the post. The post is set back from the face of the rail to prevent snagging of the vehicle tire/wheel. Snagging can DESIGN TECHNIQUES lead to excessive occupant compartment deformation, high longitudinal deceleration, and/or vehicle instability. Rhythm (i.e., the frequency of a repeated pattern) and This example reflects the minimum considerations for a new sequence (i.e., the segmenting of distance and/or time) can be barrier design for either concrete or steel materials. Aesthetic achieved through the following techniques: elements such as pipes and decorative forms can be added to Create contrasting surface reflectivity by varying the this form as long as these basic parameters are respected. amount of light reflected from a surface. Vertical openings in a concrete rail present serious prob- Create a balanced discontinuity by introducing random- lems. The Texas T411 railing is frequently mentioned as hav- ness into a line, rhythm, sequence, or pattern. ing a very desirable aesthetic. A cross section of the T411 in Create an interesting pattern by using contrasting sur- plan view is shown in Figure 11. The T411 is rated for face reliefs, textures, or colors to create vertical, hori- NCHRP Report 350 TL-2 and is not crashworthy for high- zontal, curvilinear, or angular shapes. speed applications. Using this as a model for performance enhancement, the width of the openings may be narrowed. Modifying the surface of a barrier wall entails introducing However, at some point this approach results in a series of a different surface coating or deforming the surface itself. "slits" rather than "windows" and, in effect, becomes a more