الاعتبارات الخاصة بالمسار الافقي والرأسي
204- HORIZONTAL AND VERTICAL
ALIGNMENT CONSIDERATIONS
204.1
General
There are many controls to consider
when designing horizontal and vertical alignments. These controls are separated
into horizontal, vertical and horizontal/vertical coordination. It would be
virtually impossible to meet each of these. Some even tend to conflict, and
compromises will have to be made. The considerations listed in each category
are guidelines and suggestions to assist the designer in obtaining a more
optimal design.
اعتبارات
المسار الأفقي
204.2
Horizontal
Considerations
·
Alignment should be as directional as possible while still being
consistent with topography and the preservation of developed properties and
community values.
·
Use of maximum degree of curvature [minimum curve radius] should be
avoided wherever possible.
·
Consistent
alignment should be sought.
·
Curves should be long enough to avoid the appearance of a sudden or abrupt
change in direction.
·
Tangents
and/or flat curves should be
provided on high, long fills.
·
Compound
curves should only be used with caution.
اعتبارات المسار الرأسي
·
A smooth grade with gradual
changes consistent with the type of facility
and character of terrain
should be strived for.
·
The
"roller-coaster" or the "hidden-dip" type of profile should
be avoided.
·
Undulating grade lines involving substantial lengths of steeper
grades should be appraised for their effect on traffic operation since they may encourage excessive truck speeds.
·
Broken-back grade lines (two crest or sag vertical curves separated
by short tangent grade) generally should be avoided.
·
Special attention should be given on curbed sections to drainage
where vertical curves having a K value in excess of 167 are used.
·
It is preferable to avoid long sustained grades by breaking them into shorter intervals with steeper
grades at the bottom.
تناسق المسار الأفقي والرأسي
204.4 Coordination of Horizontal and Vertical Alignments
Curvature and grades should
be properly balanced.
Normally horizontal curves
will be longer than vertical curves.
·
Vertical curvature superimposed on horizontal curvature
is generally more pleasing. P.I.'s
of both vertical and
horizontal curves should nearly coincide.
·
Sharp horizontal curvature should not be introduced at or near the
top of a pronounced crest vertical curve or at
or near the low point of a pronounced
sag vertical curve.
·
On two-lane roads,
long tangent sections are desirable to provide adequate passing sections.
·
Horizontal
and vertical curves should be as flat as possible at intersections.
·
On divided highways the use of variable median widths and separate
horizontal and vertical alignments should be
considered
·
In urban areas, horizontal and vertical alignments should be
designed to minimize nuisance
factors.
·
These might include
directional adjustment to increase buffer
zones and depressed roadways to decrease
noise.
·
And
vertical alignments may often be adjusted to enhance views of scenic areas.
الاعتبارات الخاصة بالمسار الافقي والرأسي
204- HORIZONTAL AND VERTICAL
ALIGNMENT CONSIDERATIONS
There are many controls to consider
when designing horizontal and vertical alignments. These controls are separated
into horizontal, vertical and horizontal/vertical coordination. It would be
virtually impossible to meet each of these. Some even tend to conflict, and
compromises will have to be made. The considerations listed in each category
are guidelines and suggestions to assist the designer in obtaining a more
optimal design.
اعتبارات
المسار الأفقي
204.2
Horizontal
Considerations
·
Alignment should be as directional as possible while still being
consistent with topography and the preservation of developed properties and
community values.
·
Use of maximum degree of curvature [minimum curve radius] should be
avoided wherever possible.
·
Consistent
alignment should be sought.
·
Curves should be long enough to avoid the appearance of a sudden or abrupt
change in direction.
·
Tangents
and/or flat curves should be
provided on high, long fills.
·
Compound
curves should only be used with caution.
اعتبارات المسار الرأسي
·
A smooth grade with gradual
changes consistent with the type of facility
and character of terrain
should be strived for.
·
The
"roller-coaster" or the "hidden-dip" type of profile should
be avoided.
·
Undulating grade lines involving substantial lengths of steeper
grades should be appraised for their effect on traffic operation since they may encourage excessive truck speeds.
·
Broken-back grade lines (two crest or sag vertical curves separated
by short tangent grade) generally should be avoided.
·
Special attention should be given on curbed sections to drainage
where vertical curves having a K value in excess of 167 are used.
·
It is preferable to avoid long sustained grades by breaking them into shorter intervals with steeper
grades at the bottom.
تناسق المسار الأفقي والرأسي
204.4 Coordination of Horizontal and Vertical Alignments
Curvature and grades should
be properly balanced.
Normally horizontal curves
will be longer than vertical curves.
·
Vertical curvature superimposed on horizontal curvature
is generally more pleasing. P.I.'s
of both vertical and
horizontal curves should nearly coincide.
·
Sharp horizontal curvature should not be introduced at or near the
top of a pronounced crest vertical curve or at
or near the low point of a pronounced
sag vertical curve.
·
On two-lane roads,
long tangent sections are desirable to provide adequate passing sections.
·
Horizontal
and vertical curves should be as flat as possible at intersections.
·
On divided highways the use of variable median widths and separate
horizontal and vertical alignments should be
considered
·
In urban areas, horizontal and vertical alignments should be
designed to minimize nuisance
factors.
·
These might include
directional adjustment to increase buffer
zones and depressed roadways to decrease
noise.
·
And
vertical alignments may often be adjusted to enhance views of scenic areas.