2. The Cross Slope
The cross slope is provided in all tangent sections of
the roadway. Slopes usually fall in both directions
from the centre line of the two lane highway except
where super elevation of curves direct all water
towards the inside.
For a high type pavement, the crown or slope is often
1% to 2%. However, steeper slopes are strongly
recommended because rainwater flow away more
rapidly and thereby reducing the water thickness
on the road pavement. A cross slope in one
direction of a multi-lane highways makes driving
comfortable, but with heavy rainfall, the water
depth increases on the roadway.
3. Highway Median
A median is a portion of a divided highway separating
the traveled way for traffic in the opposing
direction. The median width is the dimension
between the through-lane edges and includes left
shoulders, if any. A median provides freedom from
the interference of opposing traffic, a recovery area
for out-of-control vehicles, a stopping area in case
of emergencies, room for speed changes and
storage of left- and U-turning vehicles and for less
headlight glare, and space for additional future
lanes.
4. Highway Median
Although medians should be as wide as possible,
economic factors often limit this width because of
cost of land and general maintenance. Medians are
classified as traversable, deterring, or barrier.
Traversable medians are merely paint stripes or
buttons and are easily traversable.
When a mountable curb or corrugation is provided,
it is known as deterring median.
Barrier median is usually in the form of a guardrail
or a concrete wall that prevents traffic from
crossing over.
5. The Grade Line
Grade line is a line or slope used as a longitudinal
reference for a railroad or highway. Inclinations with
the horizontal of a road, railroad, etc., usually
expressed by stating the vertical rise or fall as a
percentage of the horizontal distance; slope.
In vehicular engineering, various land-based designs
(cars, SUVs, trucks, trains, etc.) are rated for their
ability to ascend terrain. (Trains typically rate much
lower than cars.) The highest grade a vehicle can
ascend while maintaining a particular speed is
sometimes termed that vehicle's "gradeability" (or,
less often, "grade ability"). The lateral slopes of
highway geometry are sometimes called fills or
cuts where these techniques have been used to
6. The Grade Line
One factor that significantly influences the selection
of a highway location is the terrain the land, which
in turn affects the laying of the grade line. The
primary factor that the designer considers on laying
the grade line is the amount of earthwork that will
be necessary for the selected grade line. The
height of the grade line is usually dictated by
expected floodwater level. Grade lines should also
be set such that the minimum sight distance
requirements are obtained.
Maximum grade - Maximum grade is determined by
a table, with up to 6% allowed in mountainous
areas and hilly urban areas.
7. The Grade Line
Profile grade line (PGL) - This is a single line,
straight or curved, along the length of the highway,
sometimes but not always on the center of the
highway.
Grade separation - is the process of aligning a
junction of two or more transport axes at different
heights (grades) so that they will not disrupt the
traffic flow on other transit routes when they cross
each other. The composition of such transport axes
does not have to be uniform; it can consist of a
mixture of roads, footpaths, railways, canals, or
airport runways. Bridges, tunnels, or a combination
of both can be built at a junction to achieve the
needed grade separation.
8. Right-of-Way
A right-of-way (R/W) is a strip of land that is granted,
through an easement or other mechanism, for
transportation purposes, such as for a trail,
driveway, rail line or highway. A right-of-way is
reserved for the purposes of maintenance or
expansion of existing services with the right-of-way.
In the case of an easement, it may revert to its
original owners if the facility is abandoned.
The right-of-way has three basic categories
distinguished by the degree of separation from
other traffic:
9. Right-of-Way
CATEGORY A: “a grade-separated” or “exclusive”.
It is a fully controlled R/W without grade crossings
or any legal access by other vehicles. In some
ways, this category resembles a freeway system.
CATEGORY B: includes R/W types that are
longitudinally physically separated from other
traffic, but with grade crossing for vehicles and
pedestrians, including regular street intersections.
A light-rail system that crosses a few streets at the
surface falls into this category.
CATEGORY C: surface streets with mixed traffic.
Most bus systems and streetcar systems fall into
this category.
10. Road Alignment
Road alignment should be consistent. An abrupt
change from flat to sharp curve and long tangents
followed by sharp curve should be avoided
because it will only create hazard and invite
accident. Similarly, designing circular curves of
different radius from end to end or compounded
curve is not a good practice, unless suitable
transitions between them are provided.
To have a short tangent between two curves is also
poor practice. Along flat curve is acceptable at all
times. It is pleasuring to look at, with less
probability of future obsolescence. Alignment
should be provided with tangent because there are
drivers who hesitate to pass on curves. A short
