Roundabouts What is a roundabout? What is a regular traffic light intersection? How are they similar and different? Do you know where any roundabouts are in Lincoln? What purpose do you think a roundabout serves? What safety features might a roundabout have verse a regular traffic signal intersection?

Roundabout at Sheridan Blvd and S 33rd St., Lincoln, NE

Point of Contact A point of contact is when two or more vehicles collide. traffic accidents

Activity I With your group you are going to build a regular 4 way intersection. Supplies: 14 pipe cleaners 4-5 match box cars, trucks, etc.

What to do: Using your pipe cleaners, build a replica of a regular intersection Once you have your intersection built, simulate different kinds of point of contacts Record the “different” point of contacts on a piece of paper (you can draw pictures)

Roundabouts in action Activity II: Seeing a roundabout in action. Show the video: working roundabout

Make a Roundabout Now take 2 more pipe cleaners and make a circle that will fit in the middle of your intersection. Now record the different kinds of point of contacts. Now lets compare the two different intersections

Let’s look at the parts of a roundabout _____________ Departure Width Circular Roadway Width ____________ _____________ Truck Apron Raised Central Island ____________ Entry Radius _____________ ____________ Exit Width _____________ Entry Width Inscribed Circle Diameter _____________ _____________ Central Island Diameter _____________ Exit Radius _____________ Yield Line _____________ Splitter Island _____________ Approach Width

What parts of a Circle do you know?

What parts of a circle do you see? roundabout

Problem Solving  You are designing a roundabout to be built in your neighborhood. 1. The dimensions of the Central Island has a radius of 35’. What is the diameter? What is the circumference?

What would the diameter of the inscribed circle be? 2. The circulating roadway, that portion of the roundabout between the central island and the inscribed circle is the portion of the roadway used by vehicular traffic. The inscribed circle of the roundabout encloses the circulating roadway. The circulating roadway is approximately 15’ wide. What would the diameter of the inscribed circle be? What would the circumference be?

Stopping Sight Distance Stopping Sight Distance (SSD) is the distance between the hazard and the approaching driver, measured along the vehicle path. It is used to assess safety for vehicle to vehicle and vehicle to pedestrian or bicycle hazards. When a vehicle is approaching a roundabout, it needs to have time to see and react safely to enter the roundabout.

Converting mph to ft/sec Let’s look at the equation below

Distance traveled during braking: V = initial vehicle speed in ft/sec a = 11.2 ft/s

Distance traveled during perception-reaction time is: V = initial vehicle speed in ft/sec t = 2.5 sec

Stopping Sight Distance Now combine the two

Now let’s look at a current project at 14th & Superior Show the video: http://www.oasites.com/north14th/videosimulations.aspx