MEMORANDUM. Open Section Background. I-66 Open Section Study Area. VDOT Northern Virginia District. I-66 Project Team. Date: November 5, 2015

Transcription

1 MEMORANDUM To: VDOT Northern Virginia District From: I-66 Project Team Date: November 5, 2015 Subject: Open Section Background The purpose of this technical memorandum is to provide narrative and technical context for analysis results of an additional alternative that was analyzed as part of the I-66 project; graphics and results enclosed in this document were made available at the October Public Information Meetings for the Transform I-66 Outside the Beltway project. This memo presents the findings of a sensitivity analysis conducted to test the operations of an open section (non-barrier separated lanes with no restrictions) along I-66 eastbound and westbound, between the Virginia Route 243 (Nutley Street) interchange and I- 495 interchange. This means that there would be no direct ramp connections from the Express lanes on I- 495 to the proposed Express lanes on I-66. The I-495 interchange would remain as it is under existing conditions, and the proposed I-66 Express lanes outside the Beltway would begin / terminate just east of the Nutley Street interchange. The lanes would continue into an open section of approximately 1.2 miles, during which the vehicles would weave across lanes to access their respective destination lanes. In some cases vehicles may have to make up to five (5) lane change maneuvers in this section (for example, vehicles from the right-lane of the I-495 southbound general purpose ramp destined to I-66 westbound express lanes). An independent traffic microsimulation study was conducted to test the operations for this section using the VISSIM microsimulation modeling approach that was used for the NEPA and IJR traffic operations study. The demand volumes were based on the I-495 interchange movements provided in the Alternative 2A scenario that was developed for the NEPA study, since an open section would allow all movements to occur via weaving [Alternative 2B restricted some movements due to elimination of high-impact ramps]. Alternative 2A assumed direct access ramps for all movements to and from I-66 west and I-495 (General Purpose lanes and Express lanes). These volumes were then assigned to the network as weaving movements in the open section scenario. I-66 Open Section Study Area Figure 1 shows the study limits of the open section along I-66 between the Nutley Street interchange and I-495 interchange.

2 I-66 Corridor Improvements Project November 5, 2015 Figure 1: Study area OPEN SECTION 2 HOT + 4 GP (3 THRU + 1 AUX) Description of the Open Section Alternative In the eastbound direction, the express lanes would terminate west of the Cedar Lane overpass just east of the Nutley Street interchange and add two lanes to the four-lane general purpose segment (3 through lanes plus 1 auxiliary lane). The eastbound segment would continue as a six lane segment until the twolane exit ramp to I-495 southbound general purpose lanes. Five lanes would continue on eastbound I-66 until the two-lane exit ramp to I-495 northbound general purpose lanes. Four lanes would then continue east until the left-exit to the I-495 northbound/southbound Express lanes. Three lanes would continue further on I-66 inside the Beltway, as under existing conditions. In the westbound direction along I-66, the two-lane segment from inside the beltway would become a three lane segment after the merge from I-495 northbound general purpose ramp. The ramp from I-495 southbound express lanes would add another lane and continue as a four lane segment. One more lane Transform 66 Outside the Beltway 2 MEMORANDUM

3 is added from the I-495 southbound general purpose ramp followed by another add-lane on the left-side from the I-495 northbound express lanes on-ramp making it a six-lane section on I-66 westbound. This six-lane segment continues up to the Cedar Lane overpass, beyond which the left two lanes transition into the barrier separated I-66 westbound express lanes east of the Nutley Street interchange. Open Section Traffic Demand and Analysis Results Weaving and No-weaving Volumes To develop the demand volumes for the Open Section VISSIM models the Alternative 2A scenario that was developed for the NEPA study was considered. This alternative includes direct access ramps for all movements to and from I-66 and I-495, which provides demand for all possible movements. These volumes from the ramps that were eliminated under the Open Section scenario were moved over to the corresponding destination ramps under the existing configuration. For example, the vehicles from I-66 eastbound express lanes going to I-495 southbound general purpose lanes would add on the left-side of the six lane segment of I-66 eastbound and weave across 5 lanes to exit on the right-exit ramp to I-495 southbound general purpose lanes. Figure 2 on the following shows the 2040 AM peak hour volumes in the eastbound direction from east of Nutley Street interchange to destinations on I-495 interchange for the Open Section scenario. It also shows the weaving maneuvers that would take place for the volumes destined to each ramp. Similarly Figure 3 shows the 2040 PM peak hour volumes for the westbound direction from the I-495 interchange to the Nutley Street interchange and I-66 westbound destinations for the Open Section scenario. Transform 66 Outside the Beltway 3 MEMORANDUM

4 Figure 2: 2040 AM Peak Hour Eastbound I-66 weaving volumes Transform 66 Outside the Beltway 4 MEMORANDUM

5 Figure 3: 2040 PM Peak Hour Westbound I-66 weaving volumes Transform 66 Outside the Beltway 5 MEMORANDUM

6 I-66 Open Section Traffic and Sensitivity Analysis Draft Memo Traffic Simulation Results - AM Peak The VISSIM microsimulation models were used to conduct the analysis for the 2040 base scenario for AM and PM peak networks to compare with the results of the Preferred Alternative. Figure 4 shows the speed congestion comparison of the Open Section scenario with the Preferred Alternative scenario between the I-495 interchange and Nutley Street for the AM peak period. It shows that with the base conditions for weaving volumes and driver behavior, this segment performs poorly in this segment. The additional lane changes required for vehicles to position themselves to access the existing ramps would result in traffic operations breakdown in the segment between Nutley Street and I-495 interchange. Note the speed graphics on the following pages compare the mini-model developed for this sensitivity analysis against the Preferred Alternative model. In order to optimize the number of model runs and scenarios assessed for this effort, the focus of the mini-model was centered around the study area between Nutley Street and I-495 interchange, so the speeds for the remaining portions of the corridor were not extracted/calculated, and show up as grey in the speed graphics. Transform 66 Outside the Beltway 6 MEMORANDUM

7 I-66 Open Section Traffic and Sensitivity Analysis Draft Memo Figure 4: I-66 Eastbound AM Peak Period - Speed Congestion Results Transform 66 Outside the Beltway 7 MEMORANDUM

8 Figure 5 shows the detailed results by segment for the speeds and densities in the Open Section, using the standard templates developed by VDOT for reporting density and speeds, as provided in the Traffic Operations and Simulation Analysis Manual. It shows all segments along I-66 eastbound between the Nutley Street on-ramp and the I-495 off-ramps operating at a Level of Service (LOS) F equivalent (shown in red note that LOS is based on vehicular density). Figure 5: I-66 Eastbound AM Peak Hour Freeway Simulation Results Transform 66 Outside the Beltway 8 MEMORANDUM

9 Traffic Simulation Results - PM Peak The speed congestion comparisons shown in Figure 6 compare the results of the Open Section base scenario with the Preferred Alternative scenario between the Nutley Street and the I-495 interchange for the PM peak period. It shows that with the base conditions for weaving volumes and driver behavior, this segment performs poorly in this segment. The additional lane changes required for vehicles to position themselves to access the I-66 express lanes entrance and the Nutley Street ramps would result in traffic operations breakdown in the segment between I-495 and the Nutley Street interchange. Transform 66 Outside the Beltway 9 MEMORANDUM

10 Figure 6: I-66 Westbound PM Peak Period - Speed Congestion Results Transform 66 Outside the Beltway 10 MEMORANDUM

11 Figure 7 shows the detailed results by segment for the speeds and densities in the Open Section. It shows all segments along I-66 westbound between the I-495 on-ramps and the off-ramps to Nutley Street operating at a LOS F equivalent. Figure 7: I-66 Westbound PM Peak Hour Freeway Simulation Results Sensitivity Analysis Scenarios Apart from the base conditions described in the previous section, sensitivity testing was conducted, especially for the westbound PM peak hour conditions for the Open Section scenario, to assess the impact of incremental increases in predicted weaving volumes. Changes in weaving could happen for Transform 66 Outside the Beltway 11 MEMORANDUM

12 several reasons, such as an increase in Express lanes demand due to downstream incidents, etc. Also, this segment does not exist under current conditions and it is not possible to predict the aggressiveness of drivers, hence different levels of driver aggressiveness were tested. Table 1 below shows the different scenarios that were tested for the sensitivity analysis based on the weaving volumes and driver aggressiveness. Weaving Volumes Table 1: Sensitivity Analysis Scenarios Lower Aggressive (LA) Driver Aggressiveness Medium-Higher Aggressive (MA) Low Weave Base Conditions (LW) LW-LA LW-MA Medium Weave 15% increase (MW) MW-LA MW-MA High Weave 30% increase (HW) HW-LA HW-MA Weaving demand for different scenarios Figures 4 6 show the different weaving volumes that were tested for the westbound PM peak hour scenario with the Low being the base scenario weaving volumes and the medium representing a 15% increase in weaving volumes and high representing 30% increase in weaving volumes. The total demand was kept constant, only the proportion of weaving volume was increased for the medium and higher demand scenarios (representing the dynamic nature and variability of traffic flow during congested conditions). For each of these weaving volume scenarios, different levels of driver behavior with respect to aggressiveness to make lane changes were tested in this open section between the I-495 interchange and the Nutley Street interchange. Transform 66 Outside the Beltway 12 MEMORANDUM

13 Figure 8: Demand volumes for Low Weaving scenarios Transform 66 Outside the Beltway 13 MEMORANDUM

14 Figure 9: Demand volumes for Medium Weaving scenarios Transform 66 Outside the Beltway 14 MEMORANDUM

15 Figure 10: Demand volumes for High Weaving scenarios Transform 66 Outside the Beltway 15 MEMORANDUM

16 Traffic Simulation Results Table 2 describes the results of the sensitivity analysis. It shows that except for the High Aggressive Base Weaving Volumes (HA-LW) and High Aggressive Medium Weaving Volumes (HA-MW) scenarios, all others operate under Severe Congestion conditions with only the High Aggressive-High Weaving Volumes (HA-HW) working under a Mild Congestion level. Detailed traffic operations results are shows in the Appendix for all the scenarios. Table 2: Traffic Simulation Results (Westbound PM peak hour) Driver Aggressiveness Weaving Volumes Lower Aggressive (LA) Medium-Higher Aggressive (MA) Low Base Conditions (LW) Medium 15% increase (MW) High 30% increase (HW) - No congestion - Moderate congestion - Severe congestion It can be seen from these results that under most of the scenarios that were tested for the Open Section, the operating conditions are poor and would result in congestion and potential safety concerns. Transform 66 Outside the Beltway 16 MEMORANDUM

17 Safety Analysis The Open Section would create more weaving and merging than would otherwise occur under the Preferred Alternative where the Express Lanes have direct access through dedicated ramps and the section is separated by bollards from the general purpose lanes. As shown in Table 3, the minimum number of lane changes to satisfy any given movement in the I-66 eastbound Open Section is 15, compared to 9 for the Preferred Alternative. The minimum number of lane changes required to satisfy all movements in the I-66 westbound Open Section is 23, compared to 14 in the Preferred Alternative. Table 3: Minimum Number of Lane Changes for I-66 Eastbound Section Minimum Number of lane Changes Origin Destination Open Section Preferred Alternative I-495 SB 0 0 Route 243 (Nutley St) On-Ramp I-495 NB 1 1 I-495 Express 5 2 I-66 EB 2 2 I-495 SB 0 1 I-66 GP lanes I-495 NB 0 0 I-495 Express 2 3 I-66 EB 0 0 I-495 SB 3 0 I-66 Express Lanes I-495 NB 2 N/A I-495 Express 0 0 I-66 EB 0 0 Total 15 9 Transform 66 Outside the Beltway 17 MEMORANDUM

18 Table 4: Minimum Number of Lane Changes for I-66 Westbound Section Minimum Number of Lane Changes Origin Destination Open Section Preferred Alternative Route I-495 NB Express I-66 GP 2 2 I-66 Express 0 1 Route I-495 NB GP I-66 GP 0 2 I-66 Express 2 1 Route I-495 SB Express I-66 GP 0 0 I-66 Express 3 0 Route I-495 SB GP I-66 GP 1 0 I-66 Express 4 N/A Route I-66 I-66 GP 0 0 I-66 Express 0 1 Total These operational conditions would present safety challenges for drivers as they need to maneuver their way from general purpose lanes to the Express lanes and vice versa. Any increase in the number of lane changes by itself has the potential to proportionally impact safety conditions in this section. In addition, the open section would present noticeable speed differentials between the tolled lanes and the general purpose lanes. The simulation modeling shows that vehicles traveling on the Express Lanes on an average would travel between 10 to 15 miles per hour higher speed than those on the general purpose lanes. The speed differential would present a safety challenge for those vehicles merging from right to left when trying to access the Express Lanes. It has been proved that right to left merges require additional sight distance in order to accomplish a safe lane change as well as that drivers tend to be more conservative when determining the safe distance (time gap in the adjacent traffic flow) to attempt a lane change. The analysis clearly shows that the open section would fail operationally in those scenarios where a more conservative lane change behavior is assumed. Based on these safety considerations, a more conservative driver behavior is warranted in this section. Transform 66 Outside the Beltway 18 MEMORANDUM

19 APPENDIX RESULTS OF TRAFFIC OPERATIONS ANALYSIS Appendix A: Eastbound AM Open Section Results The section provides detailed results obtained from the eastbound AM open section analysis. These results demonstrate that an open section between Nutley Street and I-495 in the eastbound direction would be unable to adequately handle forecasted AM peak period demand. Transform 66 Outside the Beltway 19 MEMORANDUM

20 Figure A1: Freeway Schematic EB AM Transform 66 Outside the Beltway 20 MEMORANDUM

21 Figure A2: Freeway Schematic EB AM - Increased Weaving Transform 66 Outside the Beltway 21 MEMORANDUM

22 Figure A3: EB AM Peak Period - Speed Comparison Transform 66 Outside the Beltway 22 MEMORANDUM

23 Appendix B: Westbound PM Open Section Results The section provides detailed results obtained from the westbound PM open section analysis. These results demonstrate that, while the westbound open section may be capable of handling forecasted PM peak period demand volumes as straight through volumes (if weaving is not considered), it would be especially sensitive to sudden breakdowns in operations. Transform 66 Outside the Beltway 23 MEMORANDUM

24 Figure B1: PM Lower Aggressive - 15 Percent Weaving Transform 66 Outside the Beltway 24 MEMORANDUM

25 Figure B2: PM Lower Aggressive - 30 Percent Weaving Transform 66 Outside the Beltway 25 MEMORANDUM

26 Figure B3: PM Lower Aggressive - Base Weaving Transform 66 Outside the Beltway 26 MEMORANDUM

27 Figure B4: PM Lower Aggressive - Speed Comparison Transform 66 Outside the Beltway 27 MEMORANDUM

28 Figure B5: PM Medium-Higher Aggressive - 15 Percent Weaving Transform 66 Outside the Beltway 28 MEMORANDUM

29 Figure B6: PM Medium-Higher Aggressive - 30 Percent Weaving Transform 66 Outside the Beltway 29 MEMORANDUM

30 Figure B7: PM Medium-Higher Aggressive Base Weaving Transform 66 Outside the Beltway 30 MEMORANDUM

31 Figure B8: PM Medium-Higher Aggressive - Speed Comparison Transform 66 Outside the Beltway 31 MEMORANDUM