Road Alinements need to be consistent with topography, preserve developments along the road and incorporate community values. The horizontal and vertical alinements are best addressed in the preliminary design phases of the project. BACKGROUND

One definition of a visually attractive and unobtrusive highway is the degree to which the horizontal and vertical alinements of the route have been integrated into its surrounding natural and human environments. This takes careful planning and design, as noted in the AASHTO Green Book: Coordination of horizontal alinement and profile should not be left to chance but should begin with preliminary design, during which adjustments can readily be made ...The designer should-study long, continuous stretches of highway in both plan and profile and visualize the whole in three dimensions.

This application of a holistic approach to highway design, where the road is integrated into its surroundings, separates the outstanding project from one that merely satisfies basic engineering design criteria (see Figures 5.1 and 5.2). An excellent description of this holistic design process is contained in the publication Aesthetics in Transportation, from which the following is excerpted:A general rule for designers is to achieve a ﾓflowingﾔ line, with a smooth and natural appearance in the land, and a sensuous, rhythmic continuity for the driver. This effect results from following the natural contours of the land, using graceful and gradual horizontal and vertical transitions, and relating the alinement to permanent features such as rivers or mountains.

HORIZONTAL AND VERTICAL ALINEMENT CONSIDERATIONS

The greatest opportunities for influencing the horizontal and vertical alinements of a highway occur during the planning and preliminary engineering phases associated with a new-location facility. The designs of such facilities have the most dramatic effects on the natural and human environments through which they pass.

The more typical design problem faced by todayﾒs highway engineers is the improvement of an existing highway or street. In many instances, the basic alinements may have been established well over 100 years ago. Regardless, the same basic design principles with respect to horizontal and vertical alinements can, however, be applied to both new and existing facilities. Important points to consider regarding horizontal and vertical alinements are that they should be consistent with the topography, preserve developed properties along the road, and incorporate community values. The superior alinements are ones that follow the natural contours of the land and do not affect aesthetic, scenic, historic, and cultural resources along the way. Construction costs may be reduced in many instances when less earthwork is needed, and resources and development are preserved. It is not always possible, however, to avoid having an impact on both the natural and human environments. That is why the superior alinements incorporate input received by the community through a participatory design process. When possible, the alinement should be designed to enhance attractive scenic views, such as rivers, rock formations, parks, historic sites, and outstanding buildings. The designation of certain highways as scenic byways recognizes the importance of preserving such features along our Nationﾒs roadways.

Equally important as the consideration of the horizontal alinement is that of the facilityﾒs vertical alinement. A number of factors influence the vertical alinement of a highway, including the following:

• Natural terrain
• Minimum stopping sight distance for the selected design speed
• The number of trucks and other heavy vehicles in the traffic stream
• The basic roadway cross-section; i.e., two lanes versus multiple lanes
• Natural environmental factors, such as wetlands and historic, cultural, and community resources