Dennis Eyler, P.E., P.T.O.E. Vice President SRF Consulting Group, Inc. deyler@srfconsulting

1. VISSIM and Mn/DOT’s INTERSECTION CONTROL EVALUATION (ICE)VISSIM USER’S GROUP MEETINGMAY 15-16, 2008Philadelphia Dennis Eyler, P.E., P.T.O.E. Vice President SRF Consulting Group, Inc. deyler@srfconsulting.com Leif Garness, E.I.T. Traffic Engineer SRF Consulting Group, Inc. lgarness@srfconsulting.com

2. Presentation Overview • What is ICE? • Issues with ICE • Two examples of ICE for roundabout projects • Old US 12 at Wayzata Boulevard • Mn Hwy 22 and Blue Earth County 90 • Lessons learned • Using VISSIM for roundabouts • Roundabout Design

3. ICE OVERVIEW

4. ICE – Definition and Goals • Creates standard analysis for Mn/DOT intersections • Select geometry and traffic control early during project development • Encourage considering other forms of intersection geometry and traffic control • However, default is side street STOP control • Anything else must be evaluated and “proven” • Evaluate viable alternatives for: • Safety • Peak hour capacity • Efficiency through all traffic levels • Document selection reasons • To avoid re-visits later in the project

5. ICE Flow Diagram

6. Standard intersections Mn/DOT minimum for signals 3 lanes (L-T-R) in, 1 lane out Roundabouts One way pairs Offset “T’s” Quadrant roadways Michigan U (left) -turns Continuous flow or lefts in advance Jug handle Through-about Super street Reduced conflict Double cross-over Intersection Alternatives

7. CFI Jug handle Continuous flow intersection Patented by F. Mier Through about At-grade Intersection Alternatives Indirect or “Michigan” U (left) turns No left turns No left turns Quadrant intersection

8. SRF – Planning Level Evaluation • Reduce alternatives early • Evaluate alternatives quickly and efficiently by using planning-level analysis • Volume to capacity (V/C) determined by critical lane • Performance impacts from look-up tables • SRF spreadsheet intersection evaluation tool

9. SRF Intersection Evaluation Tool Traffic Volume Input Sheet

10. Intersection Alternatives - Worksheet Results are V/C ratios Right turn bypass? Number of lanes

11. ISSUES WITH ICE AND WARRANTS

12. Intersections - Warrants - Issues • Warrants - guidelines for installing traffic control devices: • All-way stops • Signals • However, what are the warrants for intersection geometry? • Roadway system issues • Hierarchy of intersecting roadways • Corridor consistency • Performance goals • Costs versus needed level of control and capacity • What if? • Warrants for traffic controls are not met for 10 years • But policy requires intersection design for 20 year forecasts?

13. Warrant Status • Are warrants met? • Traffic signal • All-way stop • Roundabouts • Warrants? – (Mn/DOT criteria only if all-way stops or signals are warranted) • If not, will warrants be met by design year? • When will warrants be met? • What is interim solution? • A roundabout is an intersection traffic control device • Roundabouts are built as roadways • What if warrants are not met in year of opening?

14. The BIG Question • What do you build now if a roundabout is the proper solution for the 20 year forecasts, but the roundabout “warrants” are not met? • The answer is to then “justify” the roundabout • Show that there is no safety issue • Show that there are no capacity or efficiency issues during the interim until warrants are met

15. Controls and Travel Time • VISSIM was selected by Mn/DOT as the best tool for alternatives evaluation • Obtain total travel time - from free flow in to free flow out • Queuing • Delay • Stops • Evaluation of geometric features • Capacity versus intersection geometry • Also: • Turn lane lengths • Downstream merge distances • Vehicle tracking • Decision distance • Effects of higher approach speeds and vehicle mix

16. Controls and Travel Time Traffic control impactstotal travel time • Lengthening of path (e.g. downstream u-turn) • Path geometry (e.g. slowing to use a roundabout) • Control device delay (e.g. STOP sign) • Control delay and impacts from sharing intersection with other traffic • Roundabouts – waiting to enter • Signals – waiting for green • All-way stops – waiting for turn • Side street stops – waiting for gap • Congestion delay to other traffic going in the same direction (e.g. queue discharge or following a truck)

17. CARS Stop sign 35 to 0 to 35 = 14.2 secs 65 to 0 to 65 = 24.4 secs Roundabout - 15 mph (2) 35 to 15 to 35 = 9.1 secs 65 to 15 to 65 = 18.6 secs TRUCKS Stop sign 35 to 0 to 35 = 19.7 secs 65 to 0 to 65 = 45.0 secs Roundabout - 15 mph (2) 35 to 15 to 35 = 20.7 secs 65 to 15 to 65 = 46.8 secs Added Travel Time(1) Due to Major Speed Changes (1) Compared to traveling at steady speed (2) Design speed of roundabout (3) Includes added travel time for distance in roundabout, but not delay due to other traffic

18. Travel time “trap” Collect total travel time for all vehicles from approaching at free flow speed to returning to free flow speed free flow

19. Project Examples

20. North Project Location Project Examples • Old US Hwy 12 in Orono, Minnesota • Mn Hwy 22 at Blue Earth Co Rd 90 – south east of Mankato, Minnesota Project Location

21. Old US 12 at Wayzata Boulevard Close access Add frontage roads Construct roundabout New US 12 freeway

22. Alternatives

23. Old Hwy 12 - Project Issues • Prove that a roundabout is “justified” • Prove that it won’t back traffic onto freeway • Document the benefits • Determine the required design for existing conditions and for 20 years of traffic growth

24. Old US 12 – Results – 2008 volumes

25. Old US 12 – Results – 2028 volumes

26. Queue Lengths - pm EB TH 12 WB TH 12 WB TH 12 EB TH 12

27. MN Hwy 22 at Co Rd 90 - alternatives Signal with 3-in, 1 out geometry Single lane roundabout Multi-lane roundabout

28. Hwy 22 at Co Rd 90 - Project Issues • Evaluate roundabout versus traffic signals • Evaluate single lane versus multi-lane roundabout • Evaluate cost effectiveness of design features • Document the overall benefits • VISSIM results recommended the multi-lane design • Will operate as a 1.5 roundabout with added through lane as passing opportunity • Roundabout geometry will work with future divided roadway alignments

29. Lessons Learned

30. Lessons Learned - VISSIM • Use “special" links on approaches and exits to network • Constant locations for traffic inputs, routing decisions, speed limits and beginning of travel time traps, creating alternatives that are consistent is much easier • Consider using only a physical headway rather than time gap for roundabout entry priority rules (matches driver decision making more realistically) • Add a further speed reduction (below curve speed) at Yield line • Run links into the roundabout as 4 through routes, make all turns with connectors, rather than having a circular roadway • Create short links at Yield lines with lane closures • Use separate right turn priority rules under certain conditions

31. Lessons Learned - VISSIM • ICE requirements require “total” travel time evaluations not just VISSIM node evaluations • Don’t try using general speed zones for the roundabout environment, use curve speed areas • The batch run feature works well • Consider the connector decision distance as travel time (rather than feet) and reduce accordingly based on the lower speed environment of a roundabout, particularly if closely spaced multiple roundabouts • Also consider the emergency stop distance (16.4 ft) is way too short for lane drops and some decision points

32. Lessons Learned - VISSIM • Vehicle tracking is useful tool (no need to keep checking in Autoturn) • Easy to: • Measure queues • Assess impacts of nearby intersections • Assess pedestrian impacts • Demonstrate and measure the effects of geometric changes • Visualize results of design decisions • VISSIM is an effective presentation tool for elected officials

33. Checking vehicle tracking in VISSIM

34. Lessons Learned – Roundabout Selection and Design • Planning – Understand roadway system issues, mobility versus access • Roundabouts tend to “equalize” the network and favor access over mobility • A roundabout is both an intersection and a traffic control device, the issue of “warrants” is complex • Consider all hours and volume levels of operation, not just the peaks • Understand the range of variability of the forecasts • Consider all modes and vehicle types that will use the roundabout • Roundabout geometry does affect capacity and efficiency, but in ways not apparent in RODEL • Use wide splitter islands • Better gap selection • Better deflection

35. Roundabout splitter width test 5 % more capacity 5 to 7 seconds reduction in travel times Reduced truck off-tracking

36. However… Roundabouts have a “cult” following in some placesDon’t be pressuredDo the math

37. Traffic engineer Politician, Planner or Landscape Architect

38. X X X X X X X X X X X X X X X X “Standard” Conflict Diagrams Roundabout Intersection

39. X X X X “True” roundabout conflict points

40. The End Questions?