MEMORANDUM. Figure 1. Roundabout Interchange under Alternative D

Transcription

1 MEMORANDUM Date: To: Liz Diamond, Dokken Engineering From: Subject: Dave Stanek, Fehr & Peers Western Placerville Interchanges 2045 Analysis RS Fehr & Peers has completed a transportation analysis of the revised Alternative D (Roundabout Alternative) under the design year of 2045 for the Western Placerville Interchanges project. Compared to the Project Report, Alternative D has a revised design at the proposed roundabout for the Placerville Drive / Fair Lane / US-50 Westbound Ramps intersection and a new roundabout at the Forni Road / Lo-Hi Way / US-50 Eastbound Ramps intersection. Other changes include providing only one southbound lane on the US-50 overcrossing and revising the Placerville Drive / Forni Road intersection to side-street stop control with the eastbound left-turn movement prohibited. Figure 1 shows the proposed roundabout interchange design. Figure 1. Roundabout Interchange under Alternative D 2990 Lava Ridge Court, Suite 200 Roseville, CA (916) Fax (916)

2 Page 2 of 14 Fehr & Peers has prepared the following memoranda for this project. Analysis Methodology and Traffic Forecasts (December 22, 2008) describes the data collection Phase 1A Analysis (March 12, 2009) documents the calibration/validation of the Vissim model 2045 Alternative B Traffic Volume Forecasts (March 30, 2012) presents the 2045 travel demand forecasts Alternative B Analysis (April 18, 2012) analyzes operations for the No Build Alternative and Alternative B This memorandum summarizes the 2045 design year analysis results for the No Build Alternative, Alternative B (signals), and Alternative D (roundabouts). These results have some differences compared to the previously published results due to differences in software build version, pedestrian crosswalk locations, and signal timing optimization. Additionally, roundabout operations analysis results from the Sidra software (prepared by Reid Middleton) are provided for comparison with the Vissim analysis results. Sidra is a deterministic analysis method that analyzes intersections in isolation. Using Sidra for roundabout capacity analysis provides a check of Vissim s microsimulation results. Tables 1 and 2 below provide the thresholds used to assign level of service (LOS) to intersections and freeway segments according to the Highway Capacity Manual (Transportation Research Board, 2011). The HCM provides thresholds based on the intersection and freeway segment types. In particular, unsignalized intersections including roundabouts have lower delay thresholds than signalized intersections. TABLE 1: INTERSECTION LOS THRESHOLDS Average Delay (sec/veh) LOS Control and Roundabout Signal Control Description A < 10 < 10 Very low delay occurs due to little or no conflicting traffic. B > 10 to 15 > 10 to 20 Low delay occurs although conflicting traffic becomes noticeable. C > 15 to 25 > 20 to 35 Average delays result from increased conflicting traffic. D > 25 to 35 > 35 to 55 E > 35 to 50 > 55 to 80 Longer delays occur due to a reduction in available gaps. At signals, individual cycle failures are noticeable. High delays and extensive queues occur. This value indicates volume-to-capacity ratios. This is considered to be the limit of acceptable delay. F > 50 > 80 Delays are unacceptable to most drivers due to over-saturation. Note: sec/veh = seconds per vehicle Highway Capacity Manual, Transportation Research Board, 2011

3 Page 3 of 14 TABLE 2: FREEWAY LOS THRESHOLDS Average Density (vplpm 1 ) LOS Basic Ramp Junction & Weave Description A < 11 < 10 B > 11 to 18 > 10 to 20 C > 18 to 26 > 20 to 28 D > 26 to 35 > 28 to 35 Free-flow speeds prevail. Vehicles are almost completely unimpeded in their ability to maneuver. Free-flow speeds are maintained. The ability to maneuver with the traffic stream is only slightly restricted. Flow with speeds at or near free-flow speeds. Freedom to maneuver within the traffic stream is noticeably restricted, and lane changes require more care and vigilance on the part of the driver. Speeds decline slightly with increasing flows. Freedom to maneuver with the traffic stream is more noticeably limited, and the driver experiences reduced physical and psychological comfort. E > 35 to 45 > 35 to 43 2 traffic stream, leaving little room to maneuver. Any disruption can be Operation at capacity. There are virtually no usable gaps within the expected to produce a breakdown with queuing. F > 45 > 43 2 Represents a breakdown in flow. Notes: 1. vplpm = vehicles per lane per mile 2. The LOS E/F threshold of 43 vplpm comes from HCM The HCM 2010 threshold is volume to capacity ratio (v/c) greater than 1. Since capacity is an output and not an input for simulation analysis, v/c cannot be calculated. Highway Capacity Manual, Transportation Research Board, 2011 The traffic forecasts for the 2045 design year conditions, along with lane configurations and traffic control, are shown in Figures 2, 3, and 4. INTERSECTION OPERATIONS Table 3 lists the AM and PM peak hour study intersection level of service and average delay for the project alternatives under 2045 conditions. Under the No Build Alternative, three of the study intersections would operate at LOS F during both peak hours. The VISSIM model showed queues at theses intersections would spill back into adjacent intersections and onto the freeway mainline. The Alternative B improvements include traffic signals at all study intersections, additional capacity on Placerville Drive and Forni Road, and the construction of the US 50 / Ray Lawyer Drive interchange. With these improvements, all study intersections would operate at LOS C or better during both peak hours. Alternative D, which has roundabouts at the Placerville Drive interchange instead of signals, would also provide LOS C or better conditions at all study intersections during both peak hours.

4

5

6

7 Page 7 of 14 TABLE 3: INTERSECTION OPERATIONS 2045 CONDITIONS No Build Alternative Alt. B (Signals) Alt. D (Roundabouts) Intersection Control AM PM Control AM PM Control AM PM 1/2. Placerville Dr / Fair Ln / US 50 WB Signal F / 269 F / 244 Signal C / 28 C / 26 Roundabout A / 8 C / Placerville Dr / Forni Rd Sidestreet F / >180 F / > 180 Signal A / 9 B / 15 Sidestreet B / 13 C / Forni Rd / Lo-Hi Way / US 50 EB All-way F / 190 F / 244 Signal B / 16 C / 21 Roundabout A / 3 A / 8 5. Ray Lawyer Dr / Fair Ln All-way A / 8 C / 16 Signal B / 13 C / 21 Signal B / 13 B / Ray Lawyer Dr / US 50 WB Does not exist Signal A / 8 B / 14 Signal A / 7 B / Ray Lawyer Dr / Forni Rd / US 50 EB 1 All-way C / 20 E / 45 Signal C / 31 C / 29 Signal C / 31 C / Forni Rd / Courts Drwy Sidestreet A / 9 B / 12 Sidestreet A / 9 B / 13 Sidestreet A / 10 B / 14 Notes: Bold and underline font indicate LOS F conditions. LOS is assigned using the overall average delay, except for side-street stop control and uncontrolled intersections, which use the highest movement delay. 1. The US 50 eastbound connection does not exist in the No Build Alternative. Fehr & Peers The Vissim results for the roundabouts in Alternative D were confirmed using the Sidra software. Table 4 shows that the Sidra results are similar to those predicted by Vissim. The largest difference occurs for the Placerville Drive / Fair Lane / US 50 Westbound ramps. The higher delay in Vissim is due in part to ramp meter queues on the westbound on-ramp that cause vehicles exiting the roundabout to go slower than otherwise. Table 5 shows queue lengths for key movements at the study intersections. The storage listed under each alternative is the length of the turn pocket or the distance to the upstream intersection. Both Alternatives B and D would construct only a portion of a second southbound lane on Placerville Drive approaching Fair Lane. By the 2045 design year, a separate project is assumed to have been built that would widen Placerville Drive to four lanes with a center turn lane from Fair Lane to Ray Lawyer Drive (as shown in the project list for the Sacramento Area Council of Governments 2035 Metropolitan Transportation Plan / Sustainable Communities Strategy).

8 Page 8 of 14 TABLE 4: ROUNDABOUT OPERATIONS COMPARISON 2045 CONDITIONS Vissim Sidra ntersection 1/2. Placerville Dr / Fair Lane / US 50 WB AM PM AM PM A / 8 C / 23 A / 7 B / Forni Rd / Lo-Hi Way / US 50 EB A / 3 A / 8 A / 10 B / 12 Fehr & Peers and Reid Middleton In Table 5, the reported queue length is the maximum queue measured for the movement averaged across the ten iterations using different random number seeds. This value should be higher than the 95th percentile queue, which is typically used for design, since the maximum queue corresponds to the 100th percentile queue. Each iteration represents one day, so the average of the results provides an estimate for a typical day. During both AM and PM peak hours, the queue lengths for the No Build Alternative would exceed the available storage at the Placerville Drive/Forni Road interchange. These results are consistent with the poor intersection operations shown in Table 3. Under Alternative B, the AM peak hour average maximum queue lengths would be shorter than the available storage for the key locations. During the PM peak hour, two locations would have queues that exceed the available storage. The queue on the northbound approach to the Placerville Drive / Fair Lane / US 50 Westbound Ramps will occasionally extend back into the upstream intersection at Placerville Drive / Forni Road. This causes additional delay at the upstream intersection, but the additional congestion is not enough to result in an unacceptable LOS. The second location where the queue would exceed the available storage is the southbound left turn movement at the Ray Lawyer Drive/US 50 Eastbound Ramps. This queue would block southbound through and right-turn movements. To minimize delay to the through and right-turns, the southbound left-turn phase should be a leading phase so that the queue can be cleared. Lengthening the turn pocket is not feasible because an adjacent back-to-back northbound left-turn pocket needs to be maintained. Widening of the roadway to provide side-by-side turn pocket lanes would require an expensive expansion of the freeway overcrossing. Since the upstream intersection at the westbound ramps would operate acceptably, widening the overcrossing would not be cost effective. Under Alternative D, only one location has a queue that exceeds the storage. The PM peak hour queue for the southbound left turn at Ray Lawyer Drive / US 50 Eastbound Ramps would also exceed the storage because the Ray Lawyer Drive interchange has the same configuration in both Alternatives B and D.

9 Page 9 of 14 TABLE 5: AVERAGE MAXIMUM QUEUE LENGTHS 2045 CONDITIONS Intersection Approach/Movement No Build Alternative Alternative B Alternative D Storage AM PM Storage AM PM Storage AM PM 1/2. Placerville Dr / Fair Ln / US 50 WB Northbound Southbound 100 >1,000 >1,000 >1, >1, Westbound Fair Ln >2,000 1,000 1,100 >1, >1, Westbound Off-ramp 850 >1,000 >1, Forni Rd / Lo-Hi Way / US 50 EB Southbound Left/Through 720 >1, Southbound Right 340 >1,000 >1, Eastbound Left Eastbound Through/Right Ray Lawyer Dr / US 50 WB 1 Northbound Left Westbound Left , , Westbound Right Ray Lawyer Dr / Forni Rd / US 50 EB 1 Southbound Left Eastbound Left , , Eastbound Through/Right Notes: Queues are reported in feet. Bold and underline font indicate queues that exceed the storage. 1. The Ray Lawyer Drive interchange does not exist under the No Build Alternative. Fehr & Peers

10 Page 10 of 14 Table 6 compares the average maximum queue predicted by the Vissim model with the 95th percentile back of queue estimated by the Sidra software. At Placerville Drive / Fair Lane, Sidra predicts shorter queues for three of the four approaches but longer queues for the northbound approach. At Forni Road / Lo-Hi Way, the queues are similar for both softwares. TABLE 6: ROUNDABOUT QUEUE LENGTHS COMPARISON 2045 CONDITIONS Vissim Sidra Intersection Storage AM PM AM PM 1/2. Placerville Dr / Fair Lane / US 50 WB Northbound Southbound >1, Westbound Fair Ln >1, Westbound Off-ramp Forni Rd / Lo-Hi Way / US 50 EB Southbound Eastbound Note: Queues are reported in feet. Bold and underline font indicate queues that exceed the storage. Values are rounded up to the nearest 25 feet (the assumed length of an average queued vehicle). Fehr & Peers and Reid Middleton FREEWAY OPERATIONS Figures 5 and 6 list the AM and PM peak hour level of service and average density under 2045 conditions. The freeway operations results are shown on a freeway lane configuration schematic diagram. Detailed analysis results are provided in the appendix. Under the No Build Alternative, the eastbound weaving section between Missouri Flat Road and Forni Road would operate at LOS F during both peak hours. The congestion would be caused by a queue extending from the northbound approach at the Placerville Drive / Fair Lane / US 50 Westbound Ramps intersection, across the freeway overcrossing, and onto the Forni Road off-ramp. Congestion at the westbound US 50 ramp terminal intersection would also cause LOS F conditions in the westbound direction. This congestion would prevent some vehicles from reaching the downstream facilities during the peak hour.

11 Page 11 of 14 FIGURE 5: EASTBOUND FREEWAY OPERATIONS 2045 CONDITIONS Notes: Bold and underline font indicate LOS F conditions. Average density is reported in vehicles per lane per mile. Fehr & Peers Both the Alternative B and D improvements to the Placerville Drive / Forni Road interchange would eliminate congestion under 2045 conditions. Under the build alternatives, all freeway facilities would operate at LOS D or better during the AM peak hour. During the PM peak hour, the worst locations eastbound at the Ray Lawyer Drive on-ramp and westbound between Placerville Drive and Missouri Flat Road would operate at an acceptable LOS E.

12 Page 12 of 14 FIGURE 6: WESTBOUND FREEWAY OPERATIONS 2045 CONDITIONS Notes: Bold and underline font indicate LOS F conditions. Average density is reported in vehicles per lane per mile. Fehr & Peers RAMP METERING The Alternative B and D designs include a ramp meter for the westbound on-ramp at Placerville Drive. The ramp meter storage length depends on the westbound US-50 weaving length between Placerville Drive and Missouri Flat Road. Based on the existing Weber Creek bridge abutments, the minimum weaving length was 845 feet. Using this as a starting point, several values for the weaving length were analyzed under the 2045 PM peak hour to determine freeway operations as shown in Table 7. Based on these results, the weaving length of 1,100 feet was selected, which in turn provided a ramp meter storage length of 567 feet.

13 Page 13 of 14 TABLE 7: WEAVING ANALYSIS RESULTS 2045 PM PEAK HOUR CONDITIONS Location Weaving Length LOS / Density (vphpl) 845 ft F / 49 Westbound US-50: Placerville Dr to Missouri Flat Rd 1,000 ft E / 42 1,100 ft E / 39 1,200 ft E / 38 Note: The analysis assumed no ramp metering on the on-ramp. 1. vphpl vehicles per hour per lane Fehr & Peers To determine the ramp meter configuration, the AM and PM peak hour demand volume was tested within the limits of ramp meter operational parameters: a minimum metering rate of 240 vehicles per hour per lane (vphpl) and a maximum metering rate of 900 vphpl. The resulting queue was checked against the available storage (567 feet) provided by the design. Caltrans policy is to provide an HOV bypass lane at all ramp meters so that HOVs have a travel time advantage. For the calculations, HOVs were assumed to be 15 percent of the on-ramp traffic. Table 8 summarizes the results of the ramp meter storage analysis. The calculations are provided in the technical appendix. TABLE 8: MAXIMUM METERING RATE WITHOUT QUEUES EXCEEDING STORAGE 2045 CONDITIONS Configuration AM Peak Period PM Peak Period 1 metered lane / 1 HOV bypass lane 620 vphpl 1 >900 vphpl 2 metered lanes 358 vphpl 838 vphpl 2 metered lanes / 1 HOV bypass lane 305 vphpl 713 vphpl Note: 1. vphpl vehicles per hour per lane Fehr & Peers The initial design with one metered lane and one HOV bypass lane did not provide enough storage on the ramp under design year conditions during the PM peak period. At the maximum practical metering rate of 900 vphpl, the estimated queue would be more than two miles. With two metered lanes, the PM peak period ramp meter queue can be accommodated on the ramp although an exception to the Caltrans HOV bypass lane policy would be needed. The ramp configuration with two metered lanes and a HOV bypass lane would also work acceptably. However, this design would be more costly to construct, would shorten

14 Page 14 of 14 the weaving length between the Placerville Drive and Missouri Flat Road interchanges, and require shorter tapers to merge the three lanes at the ramp meter down to one lane at the ramp gore. SUMMARY AND CONCLUSION Traffic operations for the project alternatives were analyzed under 2045 conditions during the AM and PM peak hours. The No Build Alternative would have significant congestion (LOS F) at the Placerville Drive / Forni Road ramp terminal intersections. The subsequent queues would extend onto the US-50 mainline and cause LOS F conditions. In contrast, Alternatives B and D would provide LOS C or better at the study intersections and LOS E or better at the freeway study segments. Where the build alternatives differ (at the Placerville Drive / Forni Road interchange), the roundabout alternative (Alternative D) would have the same or lower overall intersection delay compared to the signal alternative (Alternative B). For Alternative B, the maximum queue on the northbound approach to the Placerville Drive / Fair Lane / US 50 Westbound Ramps intersection would extend into the upstream intersection at Placerville Drive / Forni Road during a portion of the peak hour. From the traffic operations analysis, the build alternatives perform similarly. The differences between the build alternatives for traffic operations and other traffic considerations are listed below in Table 9. TABLE 9: ALTERNATIVES COMPARISON Consideration Alternative B (Signals) Alternative D (Roundabouts) Vehicle Delay Higher on average; higher during off-peak hours Higher for some movements; lower during off-peak hours Vehicle Safety More severe crashes Less severe crashes; fewer crashes for single-lane approaches Vehicle Access Some U-turns prohibited All U-turns allowed at roundabouts; no left out at Placerville Dr/Forni Rd Bicycle/Pedestrian Safety Signal-controlled crossings; longer crossing distance Low-speed crossings; shorter crossing distance Bicycle/Pedestrian Convenience Higher delay Lower delay Emergency Response Signal preemption Lower off-peak delay Fehr & Peers