I-26 / Naval Base Terminal Access Road Interchange INTERCHANGE MODIFICATION REPORT CHARLESTON COUNTY, SOUTH CAROLINA Prepared for: South Carolina Department of Transportation Prepared by: Parsons Brinckerhoff, Inc. May 2012 I-26ȀPortAccessRoadInterchangeModificationReport TABLEOFCONTENTS EXECUTIVE SUMMARY ............................................................................................................................................ 1 1. INTRODUCTION .............................................................................................................................................. 3 Project Location.................................................................................................................................................. 3 Project History.................................................................................................................................................... 3 Project Description ............................................................................................................................................. 7 Project Purpose and Need .................................................................................................................................. 9 Project Conceptual Design ................................................................................................................................ 11 Interchange Modification Report (IMR) Scope................................................................................................... 13 IMR Applicant Information................................................................................................................................ 13 2. STUDY AREA ................................................................................................................................................. 15 Demographics .................................................................................................................................................. 15 Land Use .......................................................................................................................................................... 16 Transportation System...................................................................................................................................... 20 I-26 ............................................................................................................................................................... 20 3. METHODOLOGY ............................................................................................................................................ 23 Scenarios Analyzed ........................................................................................................................................... 23 Port EIS Study ............................................................................................................................................... 23 IMR Study ..................................................................................................................................................... 23 No-Build Traffic Forecasts ................................................................................................................................. 24 Port EIS Study ............................................................................................................................................... 24 IMR Study ..................................................................................................................................................... 24 Build Traffic Forecasts....................................................................................................................................... 27 Port EIS Study ............................................................................................................................................... 27 IMR Study ..................................................................................................................................................... 27 Traffic Analysis ................................................................................................................................................. 28 Port EIS Study ............................................................................................................................................... 28 IMR Study ..................................................................................................................................................... 29 4. TRAFFIC VOLUMES ........................................................................................................................................ 30 Existing (2009) Traffic Volumes ......................................................................................................................... 30 Future No-Build (2035) Traffic Volumes ............................................................................................................ 30 Future Build (2035) Traffic Volumes .................................................................................................................. 30 5. TRAFFIC OPERATIONS ................................................................................................................................... 41 HCS(2010) Traffic Level of Service ..................................................................................................................... 41 I-26 Between Dorchester Road and Montague Avenue.................................................................................. 41 I-26 At Dorchester Road Ramps To/From Columbia ....................................................................................... 43 I-26 Between Dorchester Road Ramps .......................................................................................................... 44 I-26 At Dorchester Road Ramps To/From Charleston ..................................................................................... 45 Page i I-26ȀPortAccessRoadInterchangeModificationReport I-26 At Cosgrove Avenue Ramps To/From Columbia ...................................................................................... 46 I-26 Between Cosgrove Avenue Loop Ramps ................................................................................................. 47 I-26 At Cosgrove Avenue Ramps To/From Charleston .................................................................................... 48 I-26 Between Cosgrove Avenue and Meeting Street/Port Access Road .......................................................... 49 I-26 At Meeting Street/Port Access Road Ramps To/From Columbia.............................................................. 50 I-26 Between Meeting Street/Port Access Road and Spruill Avenue/Port Access Road Ramps........................ 51 I-26 At Spruill Avenue/Port Access Road Ramps To/From Charleston............................................................. 52 I-26 Between Spruill Avenue/Port Access Road and Rutledge Avenue............................................................ 53 I-26 At Rutledge Avenue Ramps To/From Charleston .................................................................................... 54 I-26 At Mt. Pleasant Street Ramps To/From Charleston ................................................................................. 55 I-26 south of Mt. Pleasant Street................................................................................................................... 56 CORSIM Simulation of Freeway Operations ....................................................................................................... 57 Commuter AM Peak Hour (7-8 am) ............................................................................................................... 57 Commuter PM Peak Hour (5-6 pm) ............................................................................................................... 57 6. INTERCHANGE JUSTIFICATION....................................................................................................................... 63 Policy Point 1 – Existing Network Capacity is Inadequate................................................................................... 63 Existing Roadway Network ............................................................................................................................ 63 Policy Point 2 – Reasonable Alternatives Have Been Evaluated.......................................................................... 65 Alternatives Evaluated .................................................................................................................................. 65 TSM Improvements ...................................................................................................................................... 68 HOV, Transit & Multi-Modal Improvements .................................................................................................. 68 Policy Point 3 –No Significant Adverse Impacts to Interstate Safety & Operation ............................................... 69 Interstate Operation and Safety .................................................................................................................... 69 Policy Point 4 – Connects to a Public Road and Provide All Movements ............................................................. 70 Interchange Movements ..............................................................................................................................