June 24, 2013 Presented to SigSub Shared Permitted Left-Turn Lane Operations Results from Comparative Testing June 24, 2013 Presented to SigSub

The Issue A follow up evaluation of the HCM procedure for evaluating left-turn operation when opposed by a shared permitted left-turn lane at a signalized intersection revealed the following: “The HCM 2010 and HCM 2000 procedures tend to predict notably different capacity and delay at higher volumes for the one-lane SPLT and the two-lane SPLT. A detailed examination of the two models indicates that the HCM 2010 procedure predicts a higher delay and lower capacity than the HCM 2000.” - Bonneson, J. Working Paper 2: Supplement to Working Paper 1 on Shared Permitted Left-Turn Lane Operation. November 19, 2012.

A Proposed Solution (4.4 Beta) As described in Working Paper 2: Supplement to Working Paper 1 on Shared Permitted Left-Turn Lane Operation, and as presented during the January 2013 SigSub Subcommittee Meeting, the Through Car Equivalent Factor (EL2), is proposed to be modified to include the proportion of right-turn vehicles on the opposing approach, when it is determined that the presence of a right-turn vehicle on the opposing approach creates a gap for left turns on the subject approach. Approach Configuration Proposed Modification to EL2 One-Lane SPLT Approach One-Lane Approach Plus a Left-Turn Bay Two-Lane SPLT Approach In addition: nq is proposed to be modified to reflect a sat flow rate in the opposing lane equal to 1200 veh/h/ln for one lane SPLT configurations and 1800 veh/hr/ln for through or through/right lane configurations

A Charge for Additional Analysis During the January 2013 Annual meeting, SigSub decided not to adopt the “beta” fix and requested additional analysis and scenario testing against a wider range of right-turn proportions and geometric configurations, and by using a wider range of simulation software. A group of volunteers agreed to meet and develop a testing plan, execute the testing plan, and report back to SigSub with results.

Test Configurations Single Lane Configurations Multi-Lane Configurations Geometry A Geometry D Geometry B Geometry E Geometry C Geometry F Performance Measure = Subject Approach Control Delay

Testbed Assumptions Base Saturation Flow Rate 1900 pc/h/ln Left Turns 10% of total volume Right Turns 0, 10, 20 % of total volume Pedestrian Volumes 0 ped/h per crosswalk Peak Hour Factor 1.0 Lane Width 12 feet Percent Heavy Vehicles 0% Number of Parking Movements 0 maneuvers/h Signal Timing Parameters G = 39 seconds Y 4 seconds R 2 seconds e Arrival Type 3 Area Type Non-CBD Other Control is Pretimed All approaches have same geometry Subject Approach = EB

Test Software HCM 2000 (Scott Reinbacher) HCM 2010 (Christopher Kinzel and Daniel Morgan) Comp Engine 4.4 (w/o proposed fix) Comp Engine Beta 6 (w/ proposed fix) TransModeler (Daniel Morgan) Vissim (Bill Cisco)

Test Results: HCS 2000, 2010 & Beta Beta 6 version more closely matches HCS 2000 compared to 2010 v4.4 for A, B, and D All results similar for C Major differences in delay under E and F occur in the “protected” regime RT proportion factor in Beta 6 influences approach delay most heavily for A & D RT pattern “flips” under different configurations (2010)

Test Results: TransModeler TransModeler predicts higher delays than 2000 and 2010 under A, C, and F TransModeler closely resembles HCM 2010 under D TransModeler predicts lower delay than HCM 2000 and 2010 under E (at high LT vols) Results highly unstable at high congestion levels

Test Results: Vissim Vissim results fall in between HCM 2000 and 2010 approaching congestion under D Vissim predicts lower delays than 2000 and 2010 under E

Summary of Findings from Task Force Members Beta version more closely matches HCS 2000 Particularly when “protected” regime is ignored But is HCS2000 the right “truth” set? Is PRT an appropriate factor to introduce into EL2? Could test alternative fixes to EL2 that ONLY consider the opposing lane saturation flow, not the right-turn percentage For Configurations D and E, could adjust ssl3 rather than stretching the EL2 concept to include multi-lane opposing approaches Redefine EL2 based only on gdiff? Future testing should: Test other EL2 models Incorporate field data (ideally) Include CORSIM results Test different volume regimes in which all approaches are not equal New research is needed to fully address left-turn modeling issues