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A head on crash is very severe when compared to other types of highway crashes. It takes just a few seconds for vehicles moving at highway speed to cross the median and collide with the vehicles from the other side of the lane. Median barriers are effective in separating the opposing traffic streams of a road physically. It also helps to stop vehicles moving into the opposite lane accidentally and to avoid pedestrians crossing the road at risky places. In 2006 there were 821 median cross over accidents that resulted in fatalities on U.S National highway system alone.

The factors that influence the selection of a barrier system are the type of the vehicles involved Luke Falk Rush Jersey , roadway geometry and the potential severity of any head on crash incident. In most locations a standard barrier capable of redirecting the vehicles to the right area would suffice. However, in locations with complex geometry, adverse environmental conditions Kevin Byard Rush Jersey , heavy truck traffic and high traffic volumes and speeds, a barrier with high performance is necessary.

There are basically three categories of median barriers. They are detailed below,

Rigid barriers

The most common type of the median barrier in use today is the concrete barriers.

Pros:

- They are widely used because of their maintenance free characteristics Derrick Henry Rush Jersey , low life cycle cost and safety performance.
- They are very effective in avoiding vehicle crossover collision on accident prone regions with high traffic volumes and speed.
- They can also be used in areas where the required median widths to install other types of barriers is not available.

- Jersey barrier is a modular concrete barrier that allows the vehicles to collide on its lower slopped face, pivoting it back in its original direction.
Cons:

- Comparatively the installation cost of rigid barriers is high.

Semi rigid barriers

It is otherwise called as guardrail or guiderail. These rails are made of metals and they are collected in segments supported by posts or blocks.

Pros:

- Unlike rigid barriers, semi rigid barriers are designed to absorb more energy from the impact and the entire assembly move or deflect during the crash. Hence Jack Conklin Rush Jersey , lesser damage to the vehicle.
- Installation cost is less.

Cons:

- They are only suitable in the areas that are not sloppy and have good soil condition.
- The cost of the repair following an impact is high.

Cable barriers

Typically it consists of multiple cables that are connected to each other in a series of posts.

Pros:

- It is the most versatile and forgiving barrier system in minimizing the median crossover crashes. This absorbs most of the energy of the impact and reduces the forces exerted on the vehicles and its occupants.

Cons:

- Considerable time and cost must be spent maintaining, endangering motorists and workers during each repair.

The other factors that are considered before deciding the barrier type are road alignment, crash history and the number of lanes. Axial flow fans performance ranges from 100 to 500 Jonnu Smith Rush Jersey ,000 cubic feet per minute (3,000 to 15,000 cubic meters per minute). Impellers usually have blades with airfoil cross-sections.

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Selection of a a right fan one should consider such factors like cost optimization Corey Davis Rush Jersey , power rating & noise levels govern the selection of a fan suitable for a given application. Various combinations are possible to meet any given duty or operating requirements for best performance, lesser noise, power and cost characteristics.

Once the volume of airflow and the static pressure of the system are known Harold Landry Rush Jersey , it is possible to specify a fan. The governing principle in fan selection is that any given fan can only deliver one flow at one pressure in a given system. To select a fan one must consider the following parameters:

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Thus the fan efficiency is directly contingent upon selection of fan and the operating point relevant to the system resistance.

The way fan impellers (blades or rotors) are designed, the amount of air they can move decreases as the pressure they are working against increases.

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