9.6 Turning Roadways and Channelization, 9.6.1 Types of Turning Roadways p.9-55 ~ 9-92

1. 9.6 Turning Roadways and Channelization, 9.6.1 Types of Turning Roadwaysp.9-55 ~ 9-92 Objectives: • Lean how to determine minimum edge-of-traveled-way radii for the curves at at-grade intersections (no islands) • Become familiar with design guidelines for right-angle turns

2. General, P.9-55 • The width of turning roadways for intersections are governed by the volumes of turning traffic and the types of vehicles to be accommodated. • Three types of right-turning roadways at intersections • A minimum edge-of-traveled-way design • A design with a corner triangular island • A free-flow design using a simple radius or compound radii Fig. 9-23(p.9-65)

3. Minimum Edge-of-Traveled-Way Designs, P.9-55 Rule 1: When the turning speed at an intersection is assumed to be 10 mph or less, the curves for the pavement edges are designed to conform to at least the minimum turning path of the design vehicle. If the speed is greater than this, the design speed is also considered to determine the radius (Remember? R = u2/(g[e + fs]).  This means that you are not supposed to use the values in Table 9-15 and Table 9-16 of the Greenbook for RT speeds faster than 10 mph. Rule 2: The angle of intersection affects the curve design. Typical curve design types: • Simple curve • Simple curve with taper • 3-centered compound curve

4. Minimum edge of pavement designs: Simple curve and simple curve with taper (Table 9-15) R R

5. Minimum edge of pavement designs: 3-Centered Compound (Table 9-16)

6. Designs for Specific Conditions • P Design Vehicle (p.9-80) Fig. 9-23 All these reflect values in Table 9-15 and 9-16.

7. SU Design Vehicle (p.9-81) Fig. 9-24

8. WB-62 Design Vehicle (p.9-82)

9. Effect of Curb Radii on Turning Paths (p.9-83) Fig. 9-31 uses R=15 ft; Fig. 9-32 uses R=40 ft.

10. Cross Street Width Occupied by Turning Vehicle (p.9-83) – no curb parking Table 9-17. Cross St Width Occupied by Turning Vehicle for Various Angles of Intersection and Curb Radii (P design vehicle turns within 12 ft where R=15 ft or more. No parking on either street)

11. Effect of Curb Radii and Parking on RT Paths (p.9-90) Affecting the opposing lane Fig. 9-33

12. Effect of Curb Radii on Pedestrians (p.9-88) Total addition on both ends = Δd Fig. 9-35 Fig. 9-34 and 9-35 (p.9-35) Fig. 9-34 Fig. 9-34 The dimensions presented in Fig. 9-34 and 9-35 demonstrate why curb radii of only 10 to 15 ft have been used in most cities. If the extra walking distance becomes too long for a single-cycle crossing, there needs to be a refuge island. (Note that the tables below the figures were accidentally (?) excluded in the 2011 version…)

13. Pedestrian consideration guidelines (p.9-88) • Radii of 15 to 25 ft are adequate for passenger vehicles. • Radii of 25 ft or more should be provided at minor cross streets, on new construction and on reconstruction projects where space permits. • Radii of 30 ft or more should be provided at minor cross streets where practical so that an occasional truck can turn without too much encroachment to the opposing lane. • Radii of 40 ft or more, or preferably 3-centered curves, or simple curves with tapers should be provided where large truck combinations or buses turn frequently. Where speed reductions would cause problems, longer radii should be considered. • Curb radii should be coordinated with crosswalk distances or special designs should be used to make crosswalks efficient for all pedestrians.

14. Corner Radii into Local Urban Streets (p.9-92) • In local urban streets curve radii for turning movements may be smaller than those normally used in rural areas. • 5 to 30 ft, and most are 10 t 15 ft. • Most passenger cars operating at very low speed on lanes 10 ft or more in width are able to make a RT with a curb radius of about 15 ft with little encroachment on other lanes. • Desirable to provide corner radii of 15 to 25 ft for passenger cars (P) and 30 to 50ft for most trucks and buses • If trucks are routed over local streets to reach their destinations, careful consideration should be given to the network to be used.