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Roundabouts intersections

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Roundabouts are a common type of circular intersection used to regulate the traffic efficiently without the need for traffic signals generally. There are different types of circular intersections:
  • Rotaries: rotaries are a circular intersection with a large diameter exceeding 100 mm, rotaries allowing the vehicles to travel within the circulatory roadway at high speeds exceeding 50 km/hr.
  • Neighborhood traffic circles: this type of circle built for the purpose of aesthetic or calming the traffic at intersections of local streets. The approaches for this type of traffic circles can be uncontrolled or stop-controlled. Neighborhood traffic circles don’t include a raised channelization to guide the into the circulatory roadway.
  • Roundabouts: roundabouts are a circular intersection with specific design and traffic control features. The features will include the yield control of all entering traffic, channelized approach, and specific geometric curvature to ensure maintaining a speed of less than 50KM/HR on the circulatory roadway.
Figure 1

The roundabout has a different component such as:

  • Central island: the central island is the raised circle of the roundabout where the vehicles circulate around it.
  • Splitter island: splitter island is a raised or painted area that separates the entering and exiting traffic. Also, it provides a storage area for the pedestrian crossing the road. 
  •  Circulatory roadway: it is the curved path used by the vehicle to travel counter-clockwise around the central island.
  •  Yield line: it is a pavement marking for the entering traffic, as shown in figure no:2. The entering vehicles should give way for cars crossing from left before crossing the yield line.
  •  Accessible pedestrian crossings: accessible pedestrian crossings are a designated area for the pedestrians. The pedestrian crossings are important, and it should be provided for all roundabouts. Locations of pedestrian crossings should be set back from the yielding line, and it should cross the splitter island.
  •  Bicycle treatments: bicycle treatments provide the bicyclist the options of traveling as vehicles or pedestrian depending on the bicyclist level of comfort.
  • Landscaping buffer: landscaping buffers provided for most of the roundabouts, the landscaping buffers can serve many functions such as separation of pedestrians and vehicles and improving the aesthetic of the roundabout.
Figure 2

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My name is Mohammad Hamdan, and I am a Civil/bridge Engineer with extensive professional background and experience in the field of construction. I have 10+ years of experience in the construction field. During my professional career, my emphasis has been placed on structural projects, mainly bridges, infrastructure and roads. Reading and practicing the design of structures is my passion.i was lucky to be a part of a big team that executed major highway interchanges. I believe in spreading the knowledge, thus, i compose these courses to share my experience and knowledge. My course focuses on the practical side of construction field. On other word, i am sharing some of what new engineers need to know about construction field. Beside working on construction field, i love writing some articles on my website ( curious civil engineer) Moreover, i wrote some engineering papers, you can check them  by searching my name on Google (Mohammad mamon Hamdan)