what are road medians and why they are used?types of road medians.transportation engineering 5th semester.

1. ASSIGNMENT TYPES OF MEDIANS IN URBAN ROADS ROLL NO. 2K13-CE-02
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Road median
Road median is the portion in between the dual carriage way which separates the traffic flow in opposite
direction.
Types of road medians
They are of the following types:
 Traversable
 Flush
 Non-Traversable
 Barrier.
 Deterring.
 Traversable median
The medians on which vehicles can move in case of emergency are called as traversable road medians.
The recommended width of traversable median By NHA Pakistan is 7m.
Further explanation:
 A traversable median is a median that by its design does not
physically discourage vehicles from entering or crossing over
it. This may include painted medians.
 A traversable median, whether raised, depressed or flush,
consists of a visible separation without any physical
obstruction and which can be crossed with ease and comfort.
 flush medians
Flush medians can be used to wait to move into a gap in the traffic flow after
you've turned right onto the road, or to slow down and wait before turning right from the road.
There are sometimes right turning bays within flush medians called 'right turn pockets'. They differ from
that of an isolated right turn bay. They will only be marked if the side road has high turning volumes. If
not, then the flush median will be marked all the way through the intersection.
If there is a right turn pocket, the terminal of the pocket is marked with a white line at right angles to the
median where the vehicle should stop, and a single white arrow signals the direction of the turn.
The following diagrams show T-intersections where a flush median can be used to turn into the side road
(the bottom of the T). In the first one the flush median indicates that there's likely to be light traffic flow
turning into the road.
traversablemedian

2. ASSIGNMENT TYPES OF MEDIANS IN URBAN ROADS ROLL NO. 2K13-CE-02
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in this image there is more of a moderate traffic flow into the side road and the median strip and right
turn pocket have more explicit markings.
There are other variations of this for staggered intersections and crossroads.

3. ASSIGNMENT TYPES OF MEDIANS IN URBAN ROADS ROLL NO. 2K13-CE-02
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 Non-Traversable
A non-traversable median is a physical barrier in a roadway or driveway that separates vehicular
traffic traveling in opposite directions. Non-traversable medians include physical barriers (such as
a concrete barrier, a raised concrete curb and/or island, and a grass or a swale median) that
prohibit movement of traffic across the median.
 Barrier median
The median on which vehicles cannot approach is known as barrier median. It is made up of concrete or
steel.
Median barriers are longitudinal barriers most commonly used to separate opposing directions of traffic
on a divided highway. While these systems may not reduce the frequency of crashes due to roadway
departure, they can definitely help prevent a median crash from becoming a median crossover head-on
collision.
Barrier Design and Placement Considerations
Barrier design and placement needs to effectively protect motorists traveling in opposing lanes, while also
considering the safety of the occupants of the errant vehicle. Among the factors involved in selection of a
barrier system are the types of vehicles using the roadway, the roadway geometry, and the potential
severity of a median crossover crash? Standard barriers capable of redirecting passenger cars, light vans
and trucks are considered cost effective for most situations. However, at locations with adverse
geometrics, high traffic volumes and speeds, significant amounts of heavy truck traffic, or special
environmental considerations, a higher performance median barrier may be more appropriate.

4. ASSIGNMENT TYPES OF MEDIANS IN URBAN ROADS ROLL NO. 2K13-CE-02
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Type of barrier medians
There are three basic categories of median barriers: rigid barrier systems, semi-rigid
barrier systems, and flexible barrier systems.
o Rigid Barriers:
Concrete barriers are the most common type of rigid median barrier in use today. While the initial cost of
installation can be relatively high, concrete barriers
are known for their relatively low life-cycle cost,
effective safety performance, and their relatively
maintenance-free characteristics. One drawback is
that crashes associated with rigid barriers may result
in more severe injuries because, relative to other
barrier systems, a rigid system absorbs the least
energy in a crash. Nevertheless, concrete barriers
have proven to be very effective at mitigating median
crossover collisions, especially in locations with high
traffic volumes and high speeds. These barrier
systems have proven to be highly effective in
locations with high traffic volumes and high speeds. Concrete barrier systems are also very effective in
places with heavy truck traffic, and in areas where sufficient median widths to accommodate other barrier
systems are not available.
o Semi-Rigid Barriers:
Commonly referred to as guardrail or guiderail, semi-rigid barriers typically
consist of connected segments of metal railing supported by posts and blocks.
The semi-rigid barrier system is most suitable for use in
traversable medians having no or little change in grade
and cross slope. In comparison to rigid barriers, semi-
rigid barriers can be less costly, but can be more difficult
to install in locations with slope and poor soil conditions.
Additionally, the need for repair following impact can
drive up life-cycle cost. Guardrail systems are designed
to absorb energy during a crash, and the entire
assembly is designed to move or deflect during an
impact.
o Cable Barriers:

5. ASSIGNMENT TYPES OF MEDIANS IN URBAN ROADS ROLL NO. 2K13-CE-02
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A typical cable barrier consists of
multiple steel cables that are connected to a series of posts. These
systems are considered the most versatile and forgiving barrier
systems available for reducing the severity of median crossover
crashes. Cable median barriers minimize the forces on the vehicle
and its occupants and absorb most of the energy of a crash. In
comparison to rigid and semi-rigid barriers systems, cable barrier
systems generally have a lower installation cost. Like guardrails,
however, they typically require maintenance after a crash, and
therefore can have a higher life cycle cost.
Ease of maintenance and repair for these barrier systems is an
important consideration. When several posts are hit during a single crash, the barrier system may
then be vulnerable to subsequent crossovers until the damaged section is repaired. Some high
tension systems are designed to reduce deflection and resist impact forces. These high tension
systems can be easier to repair when posts are hit, and have the added advantage of being
practical for use in narrower spaces.
 Deterring median
Artificial median which may be removed in case of any emergency is known as deterring median. For
example to caught thief or any robber, this median may be removed and police can catch the thief
easily.
Deterring median may be traversable or barrier.
References:
https://definedterm.com/median_traversable

6. ASSIGNMENT TYPES OF MEDIANS IN URBAN ROADS ROLL NO. 2K13-CE-02
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http://www.civilengineeringterms.com/transportation-engineering/road-median-purposes-and-types/
http://safety.fhwa.dot.gov/roadway_dept/policy_guide/road_hardware/ctrmeasures/median_barriers/
https://definedterm.com/median_non_traversable
https://www.google.com.pk (pictures are taken)
http://www.drivingtests.co.nz/roadcode-questions/car/road-position/when-can-flush-medians-be-
used-check-all/