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ST9904-CS001107Grapevine SH 121 I SH 114 BIS Alternative Schematic Development AGENDA 1. Introduction - Robert Jenkins 2. Traffic Volumes - Don Szczesny 3. Analyses - Matt Brown A. Level-of-Service B. Simulation 4. Discussion PARSONS TECHNICAL MEMORANDUM To: Jerry Hodge From: Robert W. Jenkins, P.E. Parsons Transportation Group Inc. Date: November 7, 2000 RE; SH 114/121 MIS Alternative Schematic Development DRAFT Introduction and Background The Cities of Grapevine and Coppell expressed concerns about the access afforded by the proposed SH 114/SH 121 MIS schematic that was presented by HDR this past May. Parsons Transportation Group Inc. (PTG) was asked by the Cities to investigate alternatives to provide better access in the corridor between Bus 114 (LP 382) and the Grapevine Mills Parkway (FM 2499)/Grapevine Mills Blvd. North/Sandy Lake Road area. It was agreed that TxDOT would furnish a revised assignment calibrated to reflect the recent growth is this corridor; and that this assignment would be the basis for analyzing alternative configurations. TxDOT staffing availability in Austin precluded upgrading the assignment. As a result, PTG worked with NCTCOG to develop an assignment for the alternative schematic. Peak hour assignments were developed and analyzed in developing and refining alternative geometrics. Although the assignment process appeared to amply address the important connections in this segment of the corridor, some inaccuracies are noted as follows. The addition of an arterial connection between SH 26 at Fairway and Royal Lane did not generate traffic along the frontage road from Bass Pro; in reality we would some traffic to use this connection. Likewise, very Iow peak volumes were assigned to the connection from the Airport to LP 382. With the impending development like the Opryland Hotel, use of this route seems reasonable. This analysis effort supports the use of the alternative-interchanging concept to provide better access in this corridor. We recommend that it be the basis for preliminary design in lieu of the MIS concept for this part of the corridor. Traffic Volumes To determine the traffic volumes expected in Year 2020, PTG requested the assistance of the North Central Texas Council of Governments (NCTCOG). NCTCOG provided PTG a previously coded network of the study section for modification. PTG modified the network to reflect the proposed changes in the freeway section. After the coded network was revised, NCTCOG proceeded to run the model and produced Year 2020 AM and PM peak hour model assignments. These traffic volumes were then checked for reasonableness and adjusted, if necessary. These volumes became the basis for the level-of-service analyses and the CORSIM simulation runs that were performed. To further refine the LOS analyses and CORSIM simulation, PTG determined the weaving movements in the major weaving areas. To determine the weaving movements, the existing traffic counts (traffic counts previously collected by Grapevine and/or TxDOT) were used and the percentages calculated were applied to the projected traffic volumes. Traffic Analyses Planning level traffic analysis was conducted of the proposed alternative using procedures outlined in the 1997 Highway Capacity Manual. The purpose of the analysis was to determine, on a preliminary basis, the number of traffic lanes along each ramp and freeway section needed to accommodate year 2020 traffic volumes. Once the basic number of lanes was determined for the alternative, the geometry was reviewed and preliminary lane designations were made (through and auxiliary lanes). The lane designations were selected to maximize freeway operations for the given cross-section. The following Table summarizes the maximum allowable flow rate for basic freeway segments for each combination of HCM level-of-service and number of lanes. This table was used to determine the basic number of lanes to provide, at a minimum, a level-of- service E during year 2020 peak traffic hours. Table 1 Maximum Flow Rate by Number of Lanes and Level-of-Service Criteria 1997 Highw~ ! Capacity Manual No of Lanes Maximum Flow Rate* (pcph) for stated LOS LOS A LOS B LOS C LOS D LOS E 2 1,190 1,910 2,850 3,660 4,330 3 1,790 2,870 4,280 5,490 6,500 4 2,390 3,830 5,710 7,320 8,670 5 2,990 4,790 7,140 9,150 10,830 6 3,590 5,750 8,560 10,980 13,000 *Assumes level terrain, 6% trucks/buses, 65 mph free-flow speed, 0.95 PHF. Detailed traffic analysis was conducted to evaluate the geometry and lane assignments determined during the planning phase. Based upon the traffic forecasts, the critical time period of analysis was determined to be the AM peak period in the southbound direction. A CORSIM model was developed of the AM peak period that included southbound 121 from the Sandy Lake on-ramp to the mainline split between southbound 121 and Highway 114/DFW airport. Southbound FM 2499 was also included from the on-ramp at Stars and Stripes to its junction with southbound 121. CORSIM is a microscopic simulation tool developed for the Federal Highway Administration that models individual vehicle and driver characteristics. Each vehicle in the traffic stream is assigned a vehicle type having performance characteristics ranging from a high-performance auto to a heavy commercial truck. Based upon the vehicle type, allowable acceleration and deceleration ranges are assigned to the vehicle. Drivers are assigned an aggressiveness rating ranging from passive to aggressive. A driver's aggressiveness affects its tolerance to lane changing and car following under prevailing traffic conditions. Geometry is explicitly modeled, including multiple destination lanes and acceleration/deceleration lanes. The advantage of a simulation model is that it permits a more thorough and therefore accurate analysis of complex traffic operations such as those found within weaving and merge/diverge areas. It also reports detailed measures-of-effectiveness (MOEs) such as density and speed that assist in the evaluation of traffic operations. A number of simulation runs were conducted of the alternative under year 2020 AM and PM peak hour conditions. Where the simulation results indicated that operational problems existed, improvements were made to the alternative's geometry to mitigate the problem. Several iterations of geometry and simulation were needed until an acceptable level-of-service was achieved for all segments. A summary of the AM and PM simulation results is contained in Tables 2 and 3.