Traffic and Safety Analysis Compendium for the North Meadows Extension to US 85 and Interstate 25
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Traffic and Safety Analysis Compendium for the North Meadows Extension to US 85 and Interstate 25 March 2010 Prepared for: Town of Castle Rock Douglas County Colorado Department of Transportation Federal Highway Administration Prepared by: Felsburg Holt & Ullevig 6300 S. Syracuse Way, Suite 600 Centennial, CO 80111 CDOT Project CC 0852-095 Douglas County Project CI 05-024 FHU Project No. 07-113 This Page Left Intentionally Blank North Meadows Extension to US 85 & I-25 Environmental Assessment Traffic & Safety Analysis Compendium CONTENTS OF THIS COMPENDIUM This compendium of technical reports includes six traffic and safety analysis reports (listed below) that were performed during the environmental assessment process. The different analyses were prepared to provide technical support for various stages of the alternatives development, screening and evaluation processes. Alternative configurations and their assessment have been refined throughout the environmental assessment process; however, the reports included in this compendium have been incorporated in their original form. Thus, some of the specific traffic forecasts and alternative configurations have been refined in later stages of the environmental assessment process. List of Traffic and Safety Reports in this Compendium Completion Title Subject Author Date Felsburg Holt & Refined Traffic operations analysis of Ullevig and Parsons August 2007 Alignments Study Alternatives 6, 7, 8, and 9. Brinckerhoff (PB) Highway Capacity Software / level of service analysis of I-25 operations with alternative I-25 Alternatives configurations between the North Felsburg Holt & January 2008 Traffic Analysis Meadows and Founders/Meadows Ullevig interchanges, including a standard mainline weaving section and a collector-distributor road system. Traffic analysis of North Meadows / US 85 Interchange Felsburg Holt & US 85 interchange configuration April 2008 Traffic Analysis Ullevig options with Alternatives 6 and 7. CORSIM micro-simulation analysis I-25 Alternatives of I-25 operations with alternative configurations between the North Traffic Analysis – Felsburg Holt & Meadows and Founders/Meadows November 2008 CORSIM Analysis Ullevig Results interchanges, including a standard mainline weaving section and a collector-distributor road system. Colorado Safety Accident history and projections for Department of Assessment for I-25, US 85, and SH 86 with No Transportation, HQ January 2009 North Meadows Build, Refined Alternative 6, and Safety and Traffic Interchange Refined Alternative 7. Engineering Branch Introduced and evaluated a modified North Meadows/I-25 Original Town of Castle Rock I-25 Interchange interchange configuration for May 2009 and Felsburg Holt & Configuration Refined Alternative 7 with a Updated Ullevig roundabout west ramp terminal March 2010 intersection. Town of Castle Rock • Douglas County • CDOT • FHWA Page 1 North Meadows Extension to US 85 & I-25 Environmental Assessment Traffic & Safety Analysis Compendium This Page Left Intentionally Blank Town of Castle Rock • Douglas County • CDOT • FHWA Page 2 North Meadows Extension to US 85 & I-25 Environmental Assessment Traffic & Safety Analysis Compendium SUMMARY OF REPORT CONCLUSIONS Following are summaries of the conclusions of the six reports included in this compendium. Refined Alignments Study The North Meadows Extension to US 85 and I-25 System Level Study (SLS) (PB and Felsburg Holt & Ullevig, December 2006) recommended advancing two sets of build alternatives. Alternative 6 consisted of the North Meadows extension on a Castlegate alignment. Alternative 7 consisted of the North Meadows extension using an Atrium alignment. Both Alternatives 6 and 7 showed the North Meadows extension connecting from the Meadows neighborhood on North Meadows Drive, passing west and north of Castle View High School. During the public scoping process for the environmental assessment (EA), conducted after the completion of the SLS, the option of using an alignment south and east of Castleview High School, connecting with Elegant Street, was suggested as an alternative to the North Meadows alignment due to safety concerns for pedestrians, specifically students, crossing North Meadows Drive to reach the Castle View High School and the Castle Rock Middle School. Two new alternatives, Alternatives 8 and 9, were developed using the Elegant Street alignment, with Alternative 8 using the Castlegate alignment to US 85 and I-25 and Alternative 9 using the Atrium alignment to US 85 and I-25. The Refined Alignments Study is a technical report prepared to assess the traffic operational characteristics of the Elegant Street connection in Alternatives 8 and 9 with the North Meadows Drive connection in Alternative 6 and 7. The report shows that many of the traffic operational and planning characteristics of the North Meadows Drive Alternatives (6 and 7) and the Elegant Street Alternatives (8 and 9) would be very similar. However, some discernable differences were noted: Elegant Street Alternatives (8 and 9) would result in reduced conflicts for pedestrians crossing North Meadows Drive to reach the high school and middle school. Conversely, Elegant Street alternatives would result in some operational concerns along Meadows Drive associated with the proximity of the Elegant Street/Meadows Drive intersection with the student drop-off area for the Castle Rock Middle School. Also, the Elegant Street alternatives would provide lesser vehicle miles of travel and vehicle hours of travel savings than the North Meadows Drive alternatives, primarily because the Elegant Street alignment does not provide as direct a connection between the northern parts of The Meadows and the North Meadows connection. These conclusions fed into the EA screening decision to eliminate Alternatives 8 and 9. I-25 Alternatives Traffic Analysis With Refined Alternative 6 and Refined Alternative 7, the North Meadows Extension would cross I-25 approximately 0.9 miles north of the existing Founders/Meadows interchange with I-25. Since this is slightly closer than the standard one-mile spacing between freeway interchanges, two alternative lane concepts were considered on I-25: A standard ramp section, where on- and off-movements at the proposed North Meadows interchange and the existing Founders/Meadows interchange would connect directly with the I-25 mainline. This concept is also referred to as the standard ramp/mainline weaving concept. Town of Castle Rock • Douglas County • CDOT • FHWA Page 3 North Meadows Extension to US 85 & I-25 Environmental Assessment Traffic & Safety Analysis Compendium A collector-distributor road concept, with parallel two-lane collector-distributor roads provided in both directions between North Meadows and Founders/Meadows interchanges. This concept would allow on-, off-, and weaving movements at the two interchanges to take place off of the I-25 mainline. The I-25 Alternatives Traffic Analysis provides year 2030 forecasts on I-25 and evaluates operations on I-25 with the standard ramp/mainline weaving and collector-distributor concepts. The report used Highway Capacity Software methodology to evaluate level of service for the two concepts. The analysis shows that 2030 traffic forecasts northbound in the AM peak period and southbound in the PM peak period would be greater than the capacity of I-25 with either the standard ramp/mainline weaving and collector-distributor concepts, resulting in poor levels of service. Federal Highway Administration (FHWA) guidance calls for use of micro-simulation to evaluate operations on highly congested, over-capacity systems, because of the limitations of isolated analysis tools like Highway Capacity Software to evaluate the system effects of high congestion locations. The over-capacity findings of the I-25 Alternatives Traffic Analysis resulted in the need to perform a micro-simulation analysis using CORSIM software to further evaluate the standard ramp/mainline weaving and collector-distributor concepts on I-25. US 85 Interchange Traffic Analysis With Refined Alternative 6, the North Meadows Extension would connect with US 85 at a grade- separated interchange at the Castlegate alignment and Refined Alternative 7 would include a grade-separated interchange with US 85 at the Atrium alignment. Two different interchange concepts were developed at US 85 for both Refined Alternative 6 and 7 and evaluated in this traffic analysis. One configuration would be a Diamond Interchange, with signalized ramp terminal intersections on North Meadows Drive spaced approximately 325 feet apart. The second configuration would be a Roundabout Interchange, with eastbound and westbound North Meadows Drive and the northbound and southbound US 85 off-ramps all connecting into a roundabout intersection constructed above US 85. Key conclusions of the analysis included: Both Diamond and Roundabout Interchange configurations are viable options at both the Castlegate and Atrium locations. The Roundabout Interchange configurations were determined to result in the best overall operations at both the Castlegate and Atrium locations. Because there are only approximately 300 feet between US 85 and East Plum Creek at the Castlegate alignment and approximately 1,000 feet at the Atrium alignment, access opportunities west of US 85 are more constrained with Refined Alternative 6 than with Refined Alternative 7. At the Atrium location, the US 85 interchange ramps would merge and diverge from US 85 approximately 1,500 feet from Meadows Parkway. This proximity