Section 2: Intersections
This section refers to at-grade intersections. Intersections are the most complex transportation elements. Because there is crossing traffic and numerous potential turning movements, intersections account for a majority of all traffic accidents. For this reason landscape and aesthetics development in an intersection requires careful consideration to ensure that safety is not compromised. Issues affecting aesthetics and design of intersections are:
- high concentration of visual information in the form of signage, signals, off-site activities, and advertising
- complex patterns of shade, shadow, and reflection
- placement of design elements
- pedestrian movements (including bicycle)
- future off-site development
- aesthetics of intersections
The visibility of intersections must never be compromised. A sight triangle that allows full view of crossing and oncoming traffic must be provided for all turning movements at an intersection. (Refer to Figure 2-12.) The exact dimensions of the site triangle are a function of highway function and speed. (See the Roadway Design Manual, Chapter 2, Section 5 for specific guidelines.)
Since traffic slows at intersections, development and design detail are more visible and appropriate aesthetic treatment becomes more important.Anchor: #i1002655
Concentration of Visual Information
Intersections have high concentrations of visual information in the form of traffic signs, signals, other commercial signs and icons (see Figures 4-59 through 4-61). This visual confusion can lead to driver disorientation and may increase the potential for mistakes that lead to accidents. Where possible designers should use landscape and aesthetics tools to reduce the visual complexity at intersections. It is not always possible to simply screen out objectionable background elements, particularly in commercial areas. In these areas designers should focus on the use of visual contrasts in material textures and colors to make the functional components of the highway intersection visually prominent.
Figure 5-1. Addition of color to highlight the traffic island enhances visual character of the scene.Anchor: #i1002678
Shade, Shadow, and Reflection
The structures, signs, and other hardware associated with an intersection interact with the quality of light and cast a variety of light, shade, and shadow patterns on an intersection. These patterns of light and dark shift depending on the time of day and the amount and angle of natural or artificial light.Anchor: #i1002688
Placement of Design Elements
Many times the placement of design elements can add to the overall visual complexity and contribute to other types of hazards at intersections. For example, the use of evergreen trees with dense canopies will shade the pavement in winter, resulting in conditions which contribute to icing of the intersection.Anchor: #i1002698
- Use color or texture changes to highlight pedestrian lanes.
- Check that no elements hide pedestrians near cross-walks.
- Provide visible, vertical separation such as curbs between pedestrians and the travel lane.
- Use ample lighting for pedestrian and bicycle areas.
Future Off-Site Development
Design all intersections, including those in undeveloped areas, to include room for future addition of pedestrian access. This may include wider medians or traffic islands. Leave ample space in islands between the curb and any bridge columns and barrier devices.Anchor: #i1002733
Accessibility for maintenance must also be considered. If a development cannot be maintained it will become an aesthetics liability. Likewise the high level of activity at intersections can make maintenance activities very dangerous to crews and highway users. Landscape and aesthetics goals must be balanced against considerations of long term maintenance.
Figure 5-2. Areas that are difficult to maintain may lead to a negative visual character for an entire corridor.Anchor: #i1002753
Aesthetics of Intersections
The aesthetics goal within intersections should focus on ensuring visibility and clarity of traffic-related activities. Several design techniques are available to meet this goal.
- Use contrasting textures and colors to visually mark different zones of activity such as cross-walks and islands.
- Maintain and enhance lines of sight through the intersection.
- Select plant materials that will not obstruct critical views as they mature.
- Maintain appropriate setbacks for plantings or screening structures.
- Provide a neutral visual background to the intersection where possible.
Landscape and aesthetics considerations must be maintainable. Weeds and collected road debris will reduce the aesthetic quality.
- Where turf is used as the primary roadside surface, be sure that there is safe, direct access for mowing machinery.
- Bedded plant materials must be accessible for weed control
Use aesthetic elements to reduce the visual complexity of an intersection. Visual complexity can be reduced by:
- dividing the travel sequence into visual segments with screens set perpendicular to the driving lanes
- providing visual background that helps the structural and operational features of the intersection to be interpreted more easily
- screening distracting views
Select and place plant materials so that they will not interfere with views to the intersection.
- Plants should help focus the view on the intersection.
- Plants should be selected and placed so that they will not block views of the intersection when mature. For example, high branching trees are preferred over trees that tend to branch close to the ground.
- Shrubs should be avoided within the appropriate sight triangle at an intersection.