|
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 shouldstudy 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 "flowing"
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.
 |
The alinement of Rt.8 gracefully follows the Naugatuck River.
(Naugatuck, CT)
|
|
Figure 5.1
Inappropriate road design does not integrate with the
natural surroundings. 1 Aesthetics in Transportation, U.S.
DOT, November 1980, p. 89.
|
 |
 |
Figure 5.2
The alinement of a new facility plays an important role in minimizing
impacts on the surroundings. In this example, the character of the landscape
was disrupted.
|
|
In this alternative, the valley is undisturbed and the
road is partially shielded from view.
|
 |
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 newlocation facility. The designs of such facilities have the most dramatic
effects on the natural and human environments through which they pass.
|
Preservation of unique rock formations enhances the
view along this highway. (State Route 313, Moab, UT)
|
 |
The more typical design problem faced by today'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's roadways.
Equally important as the consideration of the horizontal alinement is that
of the facility'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 crosssection; i.e., two lanes versus multiple lanes
- Natural environmental factors, such as wetlands and historic, cultural,
and community resources
COMBINATION OF HORIZONTAL AND VERTICAL ALINEMENT
The interrelationship of horizontal and vertical alinement is best addressed
in the route location and preliminary design phases of a project. At this stage,
appropriate tradeoffs and balances between design speed and the character of
the roadtraffic volume, topography, and existing developmentcan be made. A mistake
often made by inexperienced engineers is designing the horizontal alinement
first and then trying to superimpose the design onto a vertical profile. Because
they must be complementary, horizontal and vertical geometries must be designed
concurrently. Uncoordinated horizontal and vertical geometries can ruin the
best parts and accentuate the weak points of each element. Excellence in the
combination of their designs increases efficiency, and safety, encourages uniform
speed, and improves appearancealmost always without additional cost.
One tool to assist in coordinating horizontal and vertical geometries is the
use of computeraided design (CAD). CAD enables highway designers to quickly
assess the interrelationships between horizontal and vertical alinement, particularly
in areas of difficult terrain.
Proper consideration of these basic design considerations will help to ensure
that both newlocation facilities and improvements to existing highways fit harmoniously
into their surroundings.
|
Good integration of horizontal andvertical
alinement on a reconstructed twolane rural highway.
(State Route 89 near Lake Tahoe, CA)
|
 |
ISSUES
There are numerous examples around this country of excellence in integration
of the horizontal and vertical alinements of highways into their surroundings.
Unfortunately, there are also examples of new or widened highways that have
scarred a rural landscape or disrupted an established community. While these
past actions cannot easily or inexpensively be rectified, future problems can
be avoided by applying the principles outlined above and the creative approaches
detailed below.
Avoiding Impact on Adjacent Natural and Human Environments
Particularly during the era of Interstate construction from the 1950's to the
1980's, a number of instances of new highway construction had a devastating
impact on communities and areas of environmental sensitivity. It is readily
acknowledged that there will be some degree of physical impact on the surroundings
associated with the construction of any new location highway or major reconstruction
or widening of an existing highway facility. However, from the perspective of
horizontal and vertical alinement, much of this impact can and should be alleviated.
Solution
Impact on the surrounding environment can be minimized by careful attention
to detail during the route location and preliminary design phases and a willingness
of all concerned parties to work together toward a common goal. For example,
minor adjustments to the originally proposed horizontal and vertical alinements
(combined with the use of short sections of retaining wall) along the Lincoln
Beach Parkway (U.S. Route 101) in Oregon eliminated the need to acquire any
of the adjacent homes and businesses.
|
Minor alinement changes can avoid impacts on adjacent
properties. (U.S. Route 101, Lincoln Co., OR)
|
 |
Similarly, a minor horizontal alinement shift at the beginning of the project
allowed for the Hollister Bypass (SR 156) in San Benito County, CA, to avoid
affecting a number of historic properties.
 |
Impact on the historic Mitchell Fruit Farm was avoided as a result
of a minor shift in the horizontal alinement of the Hollister Bypass.
(San Benito, CA)
|
The use of a "cutandcover" design, whereby the roadway is placed
below the existing ground level and covered over with a park, building, or other
public space can help to avoid negative impact. Lake Place Park in Duluth, MN
and other public parks were the result of cutandcover tunnels that not only
saved historic properties but also gave pedestrians improved access to Lake
Superior.
|
Designers employed several cutandcover tunnels along
I35 to avoid impacting an historic district and to reconnect the downtown
to the waterfront.
(Duluth, MN)
|
 |
In many cases, there is a potential for designing a divided highway with independent
horizontal and vertical alinements for each direction of traffic.
 |
Separate profiles and varied median widths on divided roadways are
options for designers to minimize impact on the environment.
(Rt 395, Inyo National Forest, CA)
|
|
Each side of the highway can have a different alinement
to better integrate the roadway into its surroundings.
(I15, MT)
|
 |
Coordination Between Horizontal and Vertical Alinement
When horizontal and vertical alinements are designed separately from one another,
unnecessarily large cuts and fills may be required, resulting in very dramatic
and often visually undesirable changes to the natural landscape.
Solution
One of the ways to ensure the most effective coordination of horizontal and
vertical alinement is through the use of a multidisciplinary design team during
the planning and engineering phases of a project. On such projects as 166 in
Fairfax and Arlington Counties in Virginia, the combined expertise of landscape
architects, urban designers, structural engineers, and historic preservationists,
in addition to civil engineers and highway designers, has resulted in superior
highway improvement projects.
The concept of using a multidisciplinary design team is not new; it was pioneered
in the early 1900's during the planning and design of the Bronx River Parkway
in Westchester County, NY After a period of use primarily on largescale or controversial
projects, this approach has come back into more general application as a way
to achieve community consensus.
|
A multidisciplinary design team can help minimize the
impact an urban freeway has on a community.
(I66, VA)
|
 |
|
