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Road median and their types

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

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Road median and their types

  1. 1. ASSIGNMENT TYPES OF MEDIANS IN URBAN ROADS ROLL NO. 2K13-CE-02 Do Not Copy Page1 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. 2. ASSIGNMENT TYPES OF MEDIANS IN URBAN ROADS ROLL NO. 2K13-CE-02 Do Not Copy Page2 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. 3. ASSIGNMENT TYPES OF MEDIANS IN URBAN ROADS ROLL NO. 2K13-CE-02 Do Not Copy Page3  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. 4. ASSIGNMENT TYPES OF MEDIANS IN URBAN ROADS ROLL NO. 2K13-CE-02 Do Not Copy Page4 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. 5. ASSIGNMENT TYPES OF MEDIANS IN URBAN ROADS ROLL NO. 2K13-CE-02 Do Not Copy Page5 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. 6. ASSIGNMENT TYPES OF MEDIANS IN URBAN ROADS ROLL NO. 2K13-CE-02 Do Not Copy Page6 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/

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