1. From 9. 6. 2 Channelization, Islands and Turning Roadways (p. 9-92 ~ p
Goals:
Know the functions and types of islands
Be familiar with minimum sizes of islands and island edge treatments
Learn how to determine minimum pavement widths of turning roadways
Know how to find dimensions of turning roadways at intersections (slow speed turns)

2. 9.6.2 Channelization: objectives (p.9-94)
Direct the paths of vehicles
Control the merging, diverging, and crossing angle of vehicles
Reduce the amount of paved area (unclear usage)
Provide a clear indication of the proper path for different movements
Give priority to the predominant movements
Provide pedestrian refuge
Provide separate storage lanes for turning vehicles
Provide space for traffic control devices for visibility
Control prohibited turns
Separate different traffic movements at signalized intersections with multiple-phase signals
Restrict the speeds of vehicles
State St & Bulldog Ave, Provo

3. 9.6.3 Island Delineation: 3 Groups (p.9-94)
1. Raised curb islands
3. Islands Formed by Pavement Edges and possibly supplemented by delineators on post or other guide posts – like a grassy area formed by shoulder edges
2. Islands delineated by pavement markings and markers (flush islands)
Just south of the mouth of the Provo Canyon: University Ave. and Canyon Rod merge

4. Functions of traffic islands (1) (p.9-95 ~ 9-98)
(1) Channelizing islands: Control and direct traffic
(2) Divisional islands: Divide opposing or same-directional traffic streams and alert the drivers about the intersection downstream. Usually on undivided highways.
Look carefully. Divisional islands do NOT direct turning movements.

5. Functions of traffic islands (2) p.9-98)
(3) Refuge islands: Provide refuge for pedestrian
These islands must be wide enough to protect pedestrians. At minimum 2 ft but 4 ft recommended for peds, but 6 ft min for bikes.
Univ. Pkwy at 2300 N, Provo

6. Islands used for traffic calming
“Center Island Narrowing”
The motorist feels squeezed in a narrow lane and, feeling unsafe, slows down the speed. Slowing down reduces noise, also.

7. Island Size and Designation (p.9-99)
Need to be large enough to “command attention” or be clearly visible and warn the driver
Need to be large enough to protect pedestrians
Min. 12 ft., but 15 ft. recommended for corner islands
AASHTO GB recommends:
Min. about 50 sq. ft for urban intersections.
Min. about 75 sq. ft for rural intersections.
Min. about 100 sq. ft recommended for both cases.
Islands may be curbed or uncurbed. Curbs can be a barrier type or mountable type.

8. Minimum sizes of islands (2) (p.9-99)
Elongated islands or divisional islands:
Min. 20 to 25 ft
(100 ft min. for curbed divisional islands at isolated intersections on high-speed roads and preferably longer)
4 ft min. (absolute min. is 2 ft)
Avoid placing curbed divisional islands at isolated intersections on high-speed roads unless it is made clearly visible to the motorists.  Hazardous when the vehicle hits the curb. Need signs and markers to warn the drivers. Basically you want to guide the vehicle gradually to the intersection. Use sloping type (mountable) curbs in rural areas.

9. Island delineation and approach treatment (p.9-100)
Without shoulders
Just take a look at examples in Figure 9-38 and 9-39 to get general ideas about location and treatments of the curbed islands
This little space functions like a shoulder. Also it provides space for dirt and water.
For safety purpose
Fig With curb & gutter
Jiggle bars = rumble strips

10. Island delineation and approach treatment (2) (p.9-101)
Fig With curb & gutter
Fig With shoulders

11. 9.6.5 Turning Roadways with Corner Islands (P.9-106)
WB-62
Fig. 9-43
Good for up to 15 mph. (p.9-111)
Read the “Right-Angle Turns with Corner Islands” section starting in page

12. Table 9-18 Typical Designs for Turning Roadways
Typo… Needs to be in feet
Table 3-29 in page can be used to determine turning roadway lane width.

13. Checking the values in Table 9-18 (continued)

14. 9.6.6 Superelevation for Turning Roadways at Intersections, p.9-114
Superelevation runoff: See Section
Then, use the relative gradient values in Table 9-19.

15. Development of superelevation at turning roadway terminals

16. Development of superelevation at turning roadway terminals (2)

17. Maximum algebraic difference in cross slope at turning roadway terminals, p.121