1. Consideration of Dual Left Turns at 82 nd Street Intersections & at 50 th Street Intersections City of Lubbock Citizens Traffic Commission By: Jere Hart City Traffic Engineer August 24, 2004/September 21, 2004

2. Dual Left Turn Locations Dual left turn lanes (protected/permitted) are currently installed at four intersections along 82 nd Street: –82 nd and Slide –82 nd and Quaker –82 nd and Indiana –82 nd and University Three On 50th Street: –50 th (WB) & Slide –50 th (EB) & Q –Indiana (NB) & 50 th

3. Advantages of Dual Left Turns Congestion Management –Twice as much traffic is serviced compared to a single turn lane. –The saved time helps relieve congestion for the entire intersection.

4. Disadvantages of Dual Left Turns The intersection is less safe –Visibility becomes a problem for drivers using the new left turn lane.

5. Visibility Problems

6. Impact on Traffic Safety Accident reports from 2003 were compared for the Slide, Quaker, Indiana, and University intersections at 82 nd Street. In 2003, only Slide had dual lefts installed – the others had single left turn lanes.

7. Traffic Safety Data 82nd and Slide 2003: 22 of 29 applicable collisions were LT colliding with oncoming ST traffic 82nd and Quaker 2001: 5 of 22 = 23% 82nd and University 2003: 5 of 18 = 28% 82nd and Indiana 2003: 5 of 15 = 33%

8. Graph

9. Collision Diagram

10. Proposed Solution A possible solution to this problem is to prevent left turn traffic from making “permissive” turns (green ball). Traffic in the dual left turn lanes would be serviced only during the “protected” phase - when drivers see the green arrow.

11. Effects on Traffic Flow Intersection performance is measured in terms of a “level of service.” LOS values range from A through F, with A being the best.

12. Level of Service Values Simplified LOS A - Traffic flows freely; very little or no delay. LOS B - Good flow rate; slight delays. LOS C – Fair flow rate; light delays. LOS D – Below average flow rate; moderate delays. LOS E – Poor flow rate; heavy delays. LOS F – Delays are severe. Most motorists consider this to be an unacceptable condition.

13. LOS Impact

14. Extra Stops Required Per Year Intersection Extra vehicle stops required per year in “protected only” mode 82 nd @ Slide2.79 million 82 nd @ Quaker2.76 million 82 nd @ Indiana1.08 million 82 nd @ University1.81 million

15. Recommendation The Traffic Engineering department recommends changing to “protected-only” phasing for improved safety. Will require additional left turn signal heads placed on far left side (2 heads per protected direction) & New overhead sign:

16. Visibility Problems