A line is a direct link between two points, either real or implied. The strongest lines on a highway are created by the pavement edges. Other prominent lines are created by railings, girders, piers, abutments, and the top edges of retaining walls and noise walls.

Our aesthetic reaction to this bridge is strongly influenced by the attractiveness of its parallel curvilinear lines.

When a line closes, it forms a two-dimensional surface with spatial directions of height and width. This two-dimensional surface is the shape.

The haunch gives the girder a more interesting and attractive shape than a girder with parallel edges. It also indicates how the girder works structurally: it makes the girder deepest over the pier where the forces are the highest. I-81, Virginia.

Form reveals objects in three dimensions, adding depth to the height and width of shape. The visual experience of moving under or over a bridge is primarily influenced by the form of the bridge, its geometry, span arrangement, horizontal alignment, vertical profile, and relationship to adjacent structures. The form of a roadway is seen in the context of space or sets of spaces that create its environment.

The three dimensional form of a highway is a result of the interaction of the pavement, the side slopes and the larger landscape of which it is a part. I -5, San Diego, CA.

Color can be applied to define, clarify, modify, accentuate, or subdue the visual effects of structural elements. Warm colors (yellows and browns) tend to emphasize the presence and size of forms, whereas cool colors (blues and greens) diminish the visual importance of the elements to which they are applied. Intensity of color reverses the effects just described.

Colors are perceived differently at different times of the day and at different times of the year because of the changes in light conditions created by changes in sun position and atmospheric conditions.

Seasonal colors screen the noise wall behind. I -295, Trenton, NJ.

Colors are also influenced by the background against which they are seen, and their appropriateness is often judged in terms of their fit with their background. Background is particularly important for most highway color selections because the highway element is almost always a very small part of a much larger scene, the colors of which are outside the designers control.

Intense colors enhance the importance of a highway element. I -81, Scranton,PA.

The science of color.

Texture is found on the surface of all objects and is closely related to form. Texture helps define form through subtle surface variations and shadings. It can be used to soften or reduce imposing scale, add visual interest, and to introduce human scale to large objects such as piers, abutments, and retaining walls. Distance and motion alters the perception of texture. When viewed from a distance or at high speeds, fine textures blend into a single tone and appear flat. As a rule, the greater the distance, the higher the observer's speed or the larger the object to which it is applied, the coarser or larger the texture must be.

	This texture would be more obvious at highway speeds if the relief were greater. I-75, Ohio.