Ministry of hiegher educationTikrit universityEngineering colege Civil departmentThird yearClass "A"

Traffic Laboratory

"Islands" Report

Prepared by students:1.Ali Hussein Dalaf 2.Abd Al-Hakeem Amer

Supervisor:

Hana Khaleel

Introduction

Median (Island): The median is defined as : the portion of highway separating the traveled ways for traffic in opposing direction.

Functions of medians:1- Minimizing interference of opposing traffic 2- Providing a recovery area for out-of-control vehicles3- Providing a stopping area in case of emergencies4- Providing open green space5- Minimizing headlight glare from opposing vehicles6- Providing space for speed-change lanes and storage areas for left-and U-

turn vehicles7- Restricting left-turns except at those locations where median openings

are provided

Types of Median:1- Curb A curb, by definition, is something that restrains; an enclosing border or

edging; a raised edge or margin; a wall; or as a verb, to strengthen or confine something. As most people think of curbs, they are raised strips of concrete along the edges of streets or parking lots. The benefits of curbs have been recognized since ancient times, and stone curbs were placed along the edges of traveled ways by early civilizations. Today's concrete curbs still provide many of the same benefits, and more.Concrete curbs or combined curbs and gutters serve several important functions. Curbs collect water from crowned pavements and convey it to points of collection, thus reducing the amount of water that gets under the pavement. They outline the edges of pavements and provide easily definable borders between traveled and untraveled surfaces. They confine pavement structures, especially if the pavements are composed of layers of materials that must be compacted in-place. Curbs help contain low speed traffic within the edges of pavements.

Curb and storm drain Curb

2- Refuge islandAlso known as a pedestrian refuge or pedestrian island, is a small section of

pavement or sidewalk, completely surrounded by asphalt or other road materials, where pedestrians can stop before finishing crossing a road. It is typically used when a street is very wide, as the pedestrian crossing can be too long for some individuals to cross in one traffic light cycle.

3- Flush mediansFlush medians are white diagonal lines, painted down the centre of some

urban and semi-urban roads, marking an area about one-car-width wide.They're called 'flush' because they are not raised, just painted on the surface of the road. Sometimes, however, there will be raised islands on the median to provide extra protection for pedestrians.Flush medians are there to: provide a wider separation between traffic streams on either side of the road provide pedestrians with a place to pause while crossing two traffic streams provide a refuge for vehicles turning into and out of side roads or driveways.

Median WidthThe general range of median width is from [1.2 m to 22.8 m], with

design width dependent on the type and location of the highway or street facility. In rural areas, median sections are normally wider than in urban areas.

For multi-lane rural highways without access control, a median width of [22.8 m] is desirable to provide complete shelter for trucks at median openings (crossovers). These wide, depressed medians are also effective in reducing headlight glare and providing a horizontal clearance for run-off-the-road vehicle encroachments.

Where economically feasible, freeways in rural areas should also desirably include a [22.8 m] median. Since freeways by design do not allow at-grade crossings, median widths need not be sufficient to shelter crossing trucks. In this regard, where right-of-way costs are prohibitive, reduced median widths (less than [22.8 m]) may be appropriate for certain rural freeways. Statistical studies have shown that over 90 percent of median encroachments involve lateral distances traveled of [14.4 m] or less. In this regard, depressed medians on rural freeways sections should be [14.4 m] or more in width.

Urban freeways generally include narrower, flush medians with continuous longitudinal barriers. For urban freeways with flush median and six or more travel lanes, full ( [3.0 m]) inside shoulders should be provided to provide space for emergency parking. Median widths vary up to [9.0 m], with [7.2 m] commonly used. For projects involving the rehabilitation and expansion of existing urban freeways, the provision of wide inside shoulders may not be feasible. Under these circumstances documentation for narrower shoulders should be submitted and a design exception requested. For low-speed urban arterial streets, flush or curbed medians are used. A width of [4.8 m] will effectively accommodate left-turning traffic for either raised or flush medians. Where the need for dual left turns are anticipated at cross streets, the median width should be [8.4 m]. The two-way (continuous) left-turn lane design is appropriate where there exists (or is expected to exist) a high frequency of mid-block left turns.

When flush median designs are selected, it should be expected that some crossing and turning movements can occur in and around these medians. Full

pavement structure designs will usually be carried across flush medians to allow for traffic movements.

The Study Location & Study ConditionWe choose the medians to make the study inside the Tikrit university, on

two sections:The first median that lies on the main road which come through the

university from the express way of (Baghdad – Mousel) ( see picture 1)The second median that lies on the road just beside the (3-arms rotary)

that lies in front of the central library (see picture 2)

Picture (1): the first median

Picture (2): the second medianDiscussion المناقشة غير موجودة في التقرير اآلن