ODOT Roadway Engineers and Certified Traffic

1. ODOT Roadway Engineers and Certified Traffic Office of Roadway Engineering Services March 20, 2008

2. What do designers do with certified traffic? • Capacity of Freeways, Interchanges, Highways, and Intersections • Geometric Design (Cross Section) • Pavement Design • Bridge Design (ADT)

3. What does Roadway Engineering do with certified traffic? • Studies • Planning Level design • Intersections (Turn Lanes, Through Lanes, Etc.) • Interchange Configurations (Diamonds, Par-Clo’s, SPUI’s, etc.) • Geometrics • Cross Sections (Lane Width, Shoulders, etc.)

4. Planning Level Traffic • Differences between planning level, refined planning level, and certified • What does/can this mean to the designer? • What does this mean at certain points in the Plan Development Process (PDP)? • Conceptual Alternative Solutions (CAS) - Step 5 • Alternative Feasible Assessment (AFA) - Step 6 • Preferred Alternative Verification– between Step 6 and Step 7

5. Certified Traffic • Validity for design • Duration of Project can outdate traffic? • How long is certified traffic good for? • Rule of Thumb • 3 years from study approval year • 1 year difference between opening year • Need concurrence from approving office/agencies

6. Design Traffic • Existing Year (Counts) • Opening Year (Identified by Project Manager) • Design Year (20 year from Opening) • Location and Design Manual – All improvements on ODOT’s system will be designed using certified traffic.

7. Design Hour Volume • AM, PM, or DHV • Which is preferred? • It depends on the location • AM / PM peaks – Allows design to be tailor to peak demands • DHV – Design could be conservative with peak demands occurring simultaneously. • OTS supplies AM/PM as default

8. Nuances with Certified Traffic • Traffic Impact Studies (TIS) • Interchange Justification Studies (IJS)/ Interchange Modification Studies (IMS) • TIS’s which turn into IMS’s • No Build / Build for TIS / IMS • Build TIS = No Build IMS (development traffic inc.) • Economic Development Scaling to not to degrade facility.

9. Study Area for TIS Site Minimum intersections to be studied Additional Intersections – determined by PM

10. Study Area for IMS/IJS Potential Intersection Depending on LA R/W Interchange being studied Potential Intersection Depending on LA R/W Analysis Points

11. Intersection Design • Rules of Thumb for Signals (4 leg) • Left Turn Lane • Need a left turn lane at 100 vph (vehicles per hour) • Need a double left at 300 vph • Right Turn Lane • Need a turn lane around 400-500 vph • Try to avoid double right turn lanes • Through Lane • A single lane handles around 400-500 vph

12. Design Software used within ODOT Required • HCS (L&D manual and FHWA policy) Optional • Synchro (closely spaced intersections) • Sidra (multilane roundabouts) • CORSIM (complex freeway analyses) • VISSIM (complex intersection/interchange analyses)

13. Questions