FEASIBILITY STUDY UPDATE State Highway 82 – Maroon Creek Roundabout to Main Street Reversible Lane Aspen, Colorado
Prepared for:
The City of Aspen Pitkin County Aspen, Colorado
Prepared by:
Schmueser Gordon Meyer 118 West 6th, Suite 200 Glenwood Springs, Colorado 81601
Original: January 2008 Update: May 2008
SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
FEASIBILITY STUDY UPDATE STATE HIGHWAY 82 – MAROON CREEK ROUNDABOUT TO MAIN STREET REVERSIBLE LANE Aspen, Colorado
CONTENTS
EXECUTIVE SUMMARY 1
1.0 INTRODUCTION 3
1.1 Project History and Need 3 1.2 Purpose and Scope of Feasibility Study 3
2.0 EXISTING CONDITIONS 6
2.1 Project Corridor Existing Conditions 6 2.2 Castle Creek Bridge Existing Conditions 7
3.0 REVERSE-FLOW ROADWAY CHARACTERISTICS 8
3.1 Reverse-Flow Fundamentals 8 3.2 Reverse-Flow Traffic Control Devices 8 3.3 Reversible Lane Feasibility Conditions 10 3.4 Reversible Lane Evaluation 12
4.0 EXISTING CASTLE CREEK BRIDGE 14
4.1 Site Constraints 14 4.2 Site Opportunities 15 4.3 Utilities, Easements and ROW 15
5.0 BRIDGE MODIFICATIONS AND LIMITATIONS 17
5.1 Caveats to Design Recommendations 17 5.1.1 HS25 Design Live Loading 17 5.1.2 Designing for a New Hydraulic Event 17 5.1.3 Evaluation of Environmental Impacts 18 5.2 Increased Length at Pier Cap to Expand Roadway Width 18 5.3 Bearing Issues at Footings and Abutments 18 5.4 Constructability Review 19 5.5 Summary of Possible Bridge Expansion 20
REFERNCES
APPENDIX
i SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
LIST OF FIGURES AND EXHIBITS
Figure P1. Reversible Lane Alternative – Cemetery Lane Updated Figure P2. Reversible Lane Alternative – 7th St & Hallam St Updated Figure P3. Reversible Lane Alternative – 7th Street & Main St Updated Figure S1. Existing Bridge Sections Figure S2. Proposed Bridge Sections – North Expansion Figure S3. Proposed Bridge Sections – Symmetric Expansion Exhibit A. Preliminary Opinion of Probable Construction Costs
ii SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
FEASIBILITY STUDY UPDATE STATE HIGHWAY 82 – MAROON CREEK ROUNDABOUT TO MAIN STREET REVERSIBLE LANE Aspen, Colorado
EXECUTIVE SUMMARY
Update May 2008: This update to the Feasibility Study (dated January 2008) stems from comments made by members of City Council in the February 19, 2008 work session. Initially, this study assumed that the Castle Creek Bridge widening would occur symmetrically about the existing bridge centerline, in order to minimize Right-of-Way impacts on adjacent properties. Council’s primary direction was to remove the ROW constraint from the study to reduce construction delays and duration. This concept allows the bridge expansion to occur solely on the north side of the existing structure, while maintaining two-way traffic on the current alignment during the majority of a relatively shortened construction period. The savings in the construction timeframes could potentially be offset in additional time necessary for right-of-way acquisitions necessary for this option.
A reversible lane along State Highway 82 from the Maroon Creek roundabout to the intersection of Seventh and Main in Aspen would be the first of its kind in Colorado. Although some contra-flow lanes exist along the Front Range, this would be the first location in Colorado having a reverse-flow lane on a low-speed arterial facility. Reversible lanes have been in operation for years in many areas of the country, typically in suburban and urban environments where there is a substantial peak directional commuter pattern. This feasibility analysis describes the basic fundamentals of reversible lane operations, key components of the reversible lane system, the required structural modifications to the Castle Creek Bridge and a preliminary cost estimate for the bridge widening and traffic signal equipment and associated line items necessary to operate a reversible lane from the Maroon Creek Roundabout to Seventh and Main.
The concept of a reversible lane has been identified in the Entrance to Aspen Final Environmental Impact Statement supporting documentation but its alignment did not meet all of the selection criteria and it was deemed a rejected alternate. This alternative gained revived interest when the City of Aspen created the “S-Curves” Task Force in 2003 to investigate interim solutions until the Entrance to Aspen was fully funded. While this Task Force also deemed this possible solution as an unobtainable interim goal, interest continued in this possible solution.
This study reviewed the SH 82 corridor for the traffic operational feasibility of reversible lanes. Of the eight corridor conditions that should be present when considering a reverse- flow system, the project on the SH 82 corridor generally meets five of the eight conditions. This would imply that that area has merit for consideration; however it does not imply that it is ideal for this traffic solution because of the significance of the conditions not met.
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
A critical component to this application is the expansion of the existing Castle Creek Bridge to allow a third travel lane across it. If CDOT will allow an expansion of this bridge using the original design parameters (traffic loading, hydraulic events, etc) then it would be possible to widen the existing pier to support additional road deck section. If CDOT requires the planned structural modifications to include current bridge design standards, we believe that it would be more feasible to completely remove and replace the existing Castle Creek Bridge. Because this feasibility report would require in depth interaction with CDOT and possible additional work associated with the Reevaluation of the Entrance to Aspen, an exact determination from CDOT on bridge modifications can not be determined without further advancement of this feasibility study.
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
FEASIBILITY STUDY UPDATE STATE HIGHWAY 82 – MAROON CREEK TO MAIN STREET REVERSIBLE LANE Aspen, Colorado
1.0 INTRODUCTION
1.1 Project Description and Need
A reversible lane along State Highway 82 from the Maroon Creek roundabout to the intersection of Seventh and Main in Aspen would be the first of its kind in Colorado. Although some contra-flow lanes exist in the Denver metro area, this would be the first location in Colorado having a reverse-flow lane on a low-speed arterial facility. Reversible lanes have been in operation for years in many areas of the country, typically in suburban and urban environments where there is a substantial peak directional commuter pattern. This feasibility analysis describes the basic fundamentals of reversible lane operations, key components of the reversible lane system, the required structural modifications to the Castle Creek Bridge and a preliminary cost estimate for the bridge widening and traffic signal equipment and associated line items necessary to operate a reversible lane from the roundabout to Main and Seventh.
In 2007 CDOT conducted a Reevaluation of the Entrance to Aspen Final Environmental Impact Statement and Record of Decision initially approved in 1997. The findings for this Reevaluation deemed that the original conclusions were still applicable today, and the preferred alignment remains the primary choice. This feasibility study is being done independent of the Reevaluation and could contain components that do not fully meet the assessment criteria in selecting the preferred alignment. Coordination has been conducted with CDOT staff on an informational basis only for this study and further advancement of this feasibility report would require in depth interaction with CDOT and possible additional work associated with the Reevaluation. This study does not attempt to address any of the discussion in the Reevaluation or previous Entrance to Aspen documents.
1.2 Purpose and Scope of Feasibility Study
The City of Aspen Transportation Department has asked Schmueser Gordon Meyer (SGM) to conduct a feasibility study to assess the implementation of a reversible center lane on State Highway 82 through the “S Curve Area” and an expansion of the bridge over Castle Creek (Castle Creek Bridge). The technical analysis of a bridge expansion feasibility study is being done in conjunction with a feasibility study to assess the potential for the addition of the reversible center lane and associated roadway expansions and improvements in the corridor.
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
The concept of a reversible lane had been identified in the Entrance to Aspen Final Environmental Impact Statement supporting documentation but its alignment did not meet all of the selection criteria and it was subsequently rejected as a potential alternative.
This alternative gained revived interest when the City of Aspen created the “S- Curves” Task Force in 2003 to investigate interim solutions until the Entrance to Aspen was fully funded. While this Task Force also deemed this possible solution as an unobtainable interim goal, interest continued in this possible solution. Listed below are the outcomes listed from the task force pertaining to potential three lane configurations.
Three-Lane, Reversible Lane Alternative
Opportunities
• Improved peak hour capacity during peak hours. • Maximizes the utilization of existing pavement with minimal bridge deck expansion. • Minimal curve softening will not require relocation of structures. • Potential additional landscaping replacement.
Constraints
• Structural modifications to the existing bridge will be required. • Operation may be confusing for visitors and others new to the operation. • Will require restricting Cemetery Lane to right-in/right-out movements during times the reversible lane is in use. If full movements are maintained at Cemetery lane during peak periods, movable barriers or delineators would have to be manually employed on a daily basis. • Traffic movements crossing the reversible lane at the Seventh/Main Street intersection would need to be prohibited during reversible lane operations. This could lead to increased traffic on Seventh Street, Hopkins Avenue, and Sixth Street. • Visual impacts from overhead lane use signals. • Reversible lane striping could be obscured in inclement weather. • Plowing operations could be complicated if barrier system is used instead of striping.
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
Three-Lane Transit Priority Alternative
Opportunities
• Potential for decrease in transit travel times. • Will encourage transit usage. • Operation of the transit lane will be less confusing to the unfamiliar motorist than would the reversible lane alternative. Also have fewer impacts to side street access. • Minimal curve softening will not require relocation of structures. • Potential additional landscaping replacement.
Constraints
• Structural modifications to the existing bridge will be required. • Loss of parking during peak periods on the North side of Main Street. Permanent loss of parking on Main Street due to restriping of all traffic lanes. • Transit lanes would still have to be open to right-turn movements. This could present difficulty enforcing the lane restriction. • Will only negligibly improve capacity for private vehicles. • Visual impacts from overhead lane use signs. However, these signs will create less visual impact than the overhead signals required for the reversible lane alternative.
To expand on the previous discussions, the purpose and scope of this feasibility study is to determine the following:
• Conduct an independent study of the a three lane alignment not intended to supplement any previous documents that govern the Entrance to Aspen such as the Final Environmental Impact Statement, the Record of Decision or the recent Reevaluation.
• Identify the current roadway and bridge layout and acquire what design limitations would be in place if they were to be expanded to accommodate an additional reversible lane of capacity.
• Identify the viability and feasibility of the required traffic control measures associated with a reversible lane through the S Curves
• Determine the viability and feasibility of expanding the current Castle Creek bridge to accommodate additional vehicular & pedestrian loadings
• Provide a conceptual estimate of probable construction costs of a Reversible Lane and Castle Creek Bridge Expansion
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
2.0 EXISTING CONDITIONS
2.1 Project Corridor Existing Conditions
State Highway 82 between the Maroon Creek roundabout and the intersection of Seventh and Main has several roadway cross sections that are described below from the perspective of an eastbound, inbound, or “up valley” oriented traveler:
• At the roundabout, there are two eastbound and two westbound lanes that transition to one lane as they near the Cemetery Lane intersection. • At the signalized intersection of Cemetery Lane, there are two thru lanes (one in each direction), a left turn lane for eastbound vehicles, and a right turn acceleration/deceleration lane for westbound vehicles turning to and from Cemetery Lane. • East of the Cemetery intersection, two travel lanes exist on the Castle Creek Bridge. These lanes are approximately 14’ wide, with attached 5’ sidewalks on both side of the bridge. • East of Castle Creek Bridge, a second eastbound lane develops. This lane becomes the primary inbound lane that continues around the first S-curve, while the other through lane becomes a dedicated left turn lane for vehicles turning onto North Seventh Street. • From Hallam to Main, two inbound lanes and one outbound lane exists. However, there is adequate pavement width (about 45’) through this section for two lanes in each direction. The single outbound lane has a width of approximately 22’. • At Main Street beginning at the second S-curve, there are two inbound lanes and a single outbound lane. Further east on Main Street, the outbound lanes include two general purpose lanes and one PM peak bus lane that serves as a parking lane at all other times of the day. Between Fifth and Seventh Streets, the outbound lane drops occur to transition from three lanes to one.
On-street parking is restricted throughout the corridor, except for a short section on the north side of SH 82 between the Castle Creek bridge and Eighth Street. The parking along the north side of Hallam Street between the bridge and Eighth Street, will likely be lost under this either widening plan.
The traffic signal at Cemetery Lane will play a critical role in the operations of the reverse-flow system and the current intersection signal would be rebuilt to bring up to current standard and allow for the master controller interface to occur from this traffic controller. The timing of the reverse-flow operations should be coordinated with the signal cycle timing at Cemetery Lane.
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
2.2 Castle Creek Bridge Existing Conditions
The Castle Creek Bridge is a five span bridge that runs in an East-West direction on State Highway 82. The bridge’s superstructure is made up of a conventionally reinforced concrete bridge deck resting on four steel plate girders that is 40 feet wide and consists of two 15-foot vehicular lanes with 5-foot wide pedestrian sidewalks on each side. The pedestrian walkways are also made up of conventionally reinforced concrete that rest on wide flange W27x94 steel beams. All of the plate girders and W27x94 beams bear on a 5-foot deep by 2-foot wide pier cap and stepped abutments with 3½-foot difference in seats between the plate girders and sidewalk steel beams. Each pier consists of two tapering columns that rest upon 3 feet thick, 8 feet wide by 12 feet long footings. The roadway and sidewalks are centered on the pier caps/piers. The current sub/superstructure is designed for H20-S16-44 vehicular live loading, and the piers bear on footing pads. See appendix Figure #S1 for the existing bridge section.
The only viable bypass into and out of town is for vehicles to descend into Castle Creek on Power Plant Road which connects Cemetery Lane and Smuggler Street. This option “bypasses” traffic under (through) the work zone on SH 82. From a traffic flow standpoint, this is a poor option because these are restricted roads that are not able to meet the current traffic volumes or oversized vehicle demands of SH 82. This restricted alternate route is currently a detriment to the structural rating of the existing bridge in the PONTIS evaluation system conducted by CDOT.
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
3.0 REVERSE-FLOW ROADWAY CHARACTERISTICS
3.1 Reverse-Flow Fundamentals
The primary intent of reverse-flow operations on an arterial roadway is to maximize capacity in the predominant direction during peak hours. AASHTO states that reverse-flow operation is generally “justified where 65 percent or more of the traffic moves in one direction during peak periods.” Other characteristics that may justify their use include locations where there is continuity in the route and width of the street, where there is no median, and where left turns and parking can be restricted. Factors that can influence the design of reverse-flow facilities include the existing roadway characteristics (volumes, geometry, and number of minor access points), the cost and level of complexity of traffic control, and the agency that will be responsible for maintaining and managing the reverse-flow operations. The capacity benefit in the primary direction should not come at the cost of the secondary direction’s operating capacity.
3.2 Reverse-Flow Traffic Control Devices
On low speed undivided roadways, the traffic equipment necessary for reverse- flow operations is much more simple than the equipment needed to control contra-flow freeway lanes (found on I-25 north of Denver). Given a corridor that can accommodate three through travel lanes (which isn’t exactly the case here with the Castle Creek Bridge), the basic traffic signal equipment necessary for the reversible lane operations includes:
• Ground mounted VMS Signs on both ends of the project corridor • Monotube overhead sign bridges (10 each ) with overhead LED lane control signals • Master controller with communications hookups to Hanging Lake tunnel (CDOT control center) and the City’s traffic control center (to be established) • Closed circuit television cameras connecting to control centers • Signing, striping and wiring
It’s possible to reduce the cost of the items listed above by using span wire poles in place of the costly monotube overhead sign bridges, although these do not look as sleek as the monotube structures. An even simpler system that is essentially created by permanent signage displaying the time of day that the reverse-flow operations are in effect has been used successfully in other areas on low-speed facilities. Under these simpler conditions, the safety of the corridor is often compromised if the driver population consists of non-commuter and tourist traffic (as is the case in Aspen). Additional complications are imposed during adverse weather, such as snow and heavy rain, which also limit the effectiveness of the simpler approach. Overhead changeable lane use signs control traffic flow much more actively than simple permanent signage with times of operation. The traffic
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update turning onto the corridor from side streets creates the primary safety issue when active overhead signing is not employed.
Sign Bridges with Lane Controls on I-70
SGM continues to investigate the operations and maintenance of the reverse-flow lane system with CDOT Region 3 staff. Ideally, the system would be controlled by an upgraded master traffic signal controller proposed at the Cemetery Lane intersection, which would link to a separate controller for the reverse-flow lane control system. Connecting these two systems would allow the reverse-flow lane control system to be ordinated with the Cemetery Lane signal. Typically CDOT would retain operational control over these traffic control devices, similar to the traffic signals on Main Street, and an Intergovernmental Agreement would need to be reached between CDOT and Aspen to address this extra demand on their resources.
Under any system failure conditions, the reverse-flow lane system would be programmed to default back to single lane flow in both directions with a center turn lane (similar to off-peak operations). Communications between the system and the traffic control center would be accomplished through a cellular modem interface, in the event that the system needed to be manually controlled. Closed- circuit cameras would provide images to the control centers for monitoring manual operations. CDOT and/or the City of Aspen would be responsible for the maintenance and operations of the reverse-flow lane system.
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
3.3 Reversible Lane Feasibility Conditions
A study that reviewed the operational feasibility of reversible lanes on US 1 in Miami, Florida lists eight corridor conditions that should be present when considering a reverse-flow system. The eight conditions are as follows:
1. Traffic congestion problem in the peak direction of traffic 2. Traffic congestion should be periodic and predictable 3. No adequate parallel street is available to accommodate peak demand 4. Proportion of traffic is high for through vehicles and low for turning vehicles 5. Peak direction traffic has at least a split of 60/40 two-way traffic demand 6. Transitions and terminal locations should have adequate capacity 7. Off peak direction should have adequate capacity 8. Cost of implementation should be low and/or offset by the improvements
This report identifies corridor-specific criteria for each condition and whether or not the condition is met.
For Conditions 1 and 2, traffic entering and leaving Aspen typically spikes during several peak seasonal months throughout the year. These peak seasonal periods typically occur in February – March and July – August, corresponding with the busy summer and winter seasons. The average daily traffic volume crossing Castle Creek Bridge during the peak seasonal periods of 2007 ranged from 23,000 – 27,200 vehicles per day. The peak periods of the day during the heavy seasonal months can last for four – six hours as a result of the limited capacity of one through lane on the bridge. During other times of the year, the total daily traffic volumes on the SH 82 corridor are lower, and peak periods of the day tend to be shorter. However, the peak hour traffic volumes during these off-season months still reaches the roadway capacity for two – four hours of the day.
Having studied the flow of traffic entering and leaving Aspen over the past 5 – 10 years, SGM has found that the one-way, hourly capacity on SH 82 ranges from 1,000 – 1,200 vehicles per lane of direction. This capacity is typically achieved in the inbound direction in the morning and outbound direction in the afternoon throughout all months of the year. During the peak seasonal periods, especially the summer, the outbound morning demand and inbound afternoon demand typically reach capacity as well. This is ultimately the result of the growth of Snowmass Village and the lower Roaring Fork valley, which have many more opportunities for shopping, recreation, and living than they had just 10 years ago. Conditions 1 and 2 are generally met.
For Condition 3, the only parallel facility into Aspen is Power Plant Road, which actually runs underneath the Castle Creek Bridge. This steep and narrow roadway has been the alternate route for years for locals and commuters trying to avoid the
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
congestion on SH 82 during peak periods. The daily volume on Power Plant was measured during the “S-curve improvements summer demonstration” and was found to range from 2,100 – 2,650 vehicles per day, with a peak hour volume ranging from 500 – 725 in the peak direction during the summer of 2005. The use of Power Plant Road as a parallel reliever is mainly limited to the afternoon rush hour. By no means is this facility adequate to serve all traffic entering or leaving Aspen, so Condition 3 is met.
For Condition 4, since the S-curve improvements have been in place (street closures at Hallam/Seventh, Bleeker/Seventh, and the alleys between), there are only a few opportunities for vehicles to turn to and from SH 82 through the project corridor. These locations include the signal at Cemetery Lane, Eighth Street, Seventh/Hallam (inbound left turns only) and Bleeker, west of Seventh Street. Several private driveways also exist north of the corridor between the Castle Creek Bridge and Eighth Street. Overall, the traffic traveling the corridor is primarily through traffic; condition 4 is met.
For Condition 5, based on counts collected in the summer 2007, there was 68/32 inbound/outbound split in the morning and a 43/57 split in the afternoon. This shows that the PM peak tends to see a more equal directional distribution than the morning. Therefore, the condition is typically met in the AM peak, but not in the PM peak.
For Condition 6, the west end of the project corridor (roundabout) provides two through lanes in each direction entering and leaving the roundabout. The east end of the project corridor (Seventh/Main) provides enough width for two lanes in each direction, although the outbound laneage is reduced to one outbound lane prior to making the turn onto Seventh Street. Seventh Street provides adequate width for four through lanes, but is only striped for one wide outbound lane. Aside from the constraint at the Castle Creek Bridge, Condition 6 is met. The needed bridge expansion is discussed later in this report.
For Condition 7, the off-peak direction will maintain the existing number of through lanes as is provided today. The only difference is this direction will not have a left turn lane provided during off-peak operations. This would only affect the PM inbound capacity, as the outbound direction has no left turn options past Bleeker Street. The inbound direction has allowable left turns at Eighth and Seventh, so a small reduction in capacity would occur during the PM peak. The left turn lane at Cemetery would be maintained throughout the duration of reverse-flow operations. Condition 7 is not met.
For Condition 8, the reversible lane concept will provide a travel-time savings for vehicles entering and leaving Aspen by providing additional capacity in the morning (inbound) and afternoon (outbound). The success of this project is also contingent on providing two bus lanes in each direction from the roundabout to Buttermilk, which is a second bottleneck (the first being the Castle Creek Bridge)
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
in the roadway network leading out of Aspen. The bus lane project from the roundabout to Buttermilk is expected to be completed in the fall of 2008 when the new Maroon Creek Bridge is also opened.
The cost of the reversible lane project is not limited to the traffic signalization equipment needed to control the reverse-flow lane, but also by the cost to upgrade the two-lane Castle Creek bridge to allow a third lane. This additional cost is detailed in the appendix of the report and is substantially higher than originally anticipated. The cost for the traffic equipment for the reversible lane controls is only about 34% of the potential $7.2 million dollar project due to the condition of the aging existing structure. Additional lane control costs include supplying the power to the system, providing peak hour support monitoring at the control center, and maintaining the system on an annual basis. These on going operations and maintenance costs have not been quantified but would need to be once a control system had been established and an intergovernmental agreement finalized with CDOT.
Additional adjacent street closures may be necessary at Eighth, Seventh, Bleeker and the connecting alleys to further restrict traffic to through movements along the corridor to improve the safety of the reversible lane operations. This has been experimented with in a temporary condition with removable barrier and temporary bollards but these measures would need to be more permanent requiring reinforcing signage with the reversible center lane concept.
Update May 2008: The curves of the “S-Curves” would also require softening to gain a 20-25 MPH design speed but this can be accommodated within the existing ROW template. The US Forest Service property is not the appropriate side of the street to improve the curve’s design speed. If improvements were made utilizing the Forest Service property, additional impacts on the property west of the Forest Service property (Poppies) would likely be required. This site has been previously identified in the Entrance to Aspen EIS as a historically significant property and impacts to it have been avoided. Again, the three-lane alignment could be accommodated within the existing ROW template and still allow 25 MPH speeds.
3.4 Reversible Lane Evaluation
Based on the above discussion of corridor conditions, the project corridor generally meets five of the eight conditions. The cost of the project (Condition 8) is the primary condition that may not be met. It is anticipated that this project would contain several substantial soft costs difficult to define because of the departure from the Record of Decision, the Entrance to Aspen Reevaluation, and previous documents for the corridor.
Attached as Figures #P1 – #P3 in the appendix is the improved concept for the corridor that was first considered during the S-Curve Improvements Study that
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update occurred in 2003 – 2005. This shows the need for a 3-lane section on the Castle Creek Bridge and a short 4-lane section through the Cemetery Lane signal to provide a constant left turn lane during all phases of reverse-flow operations.
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
4.0 EXISTING CASTLE CREEK BRIDGE
4.1 Bridge Site Constraints
Since the current bridge lies above a roadway and the City of Aspen’s maintenance facility, any bridge expansion would have to utilize a debris catching system that would prevent any falling objects from hitting the roadway or structures below. Also, because the proposed road alignment would add 20 feet to the north side of the bridge deck, temporary barrier would have to be placed next to existing traffic during the construction process. Below is a similar, but more extensive, debris retention system used in 2004 on the Red Cliff Arch Bridge on SH 24. This was a comparable application with a local roadway underneath the construction zone which served as the only feasible detour route during construction.
SafeSpan retention system at Red Cliff Bridge SH 24
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
4.2 Bridge Site Opportunities
Update May 2008: The purpose of this feasibility study is to examine the possibility in expanding the existing Castle Creek Bridge. In a previous iteration of our feasibility study we looked at an expansion that would add additional road width to each side of the existing bridge (Symmetric Expansion.) In this update to the study we are examining the possibility of adding the additional road width necessary to one side of the existing structure (North Expansion.) This 20-foot expansion would add a third vehicular lane and a 10-foot wide pedestrian/bike path, while maintaining the existing 5-foot wide sidewalk along the south side of the bridge. This addition would include independent piers to support the expanded pier cap bearing the additional bridge girders and road deck width. The new piers would be placed in-line with the existing piers and pier caps to minimize unbalanced structural deflections.
The north side of Castle Creek Bridge has been selected for the expansion because of the impacts that the proposed piers would have on the roadway and structures below. If the expansion were to take place on the south side of the existing bridge at least one pier would fall within the Power Plant Road pavement section and cause the road to be realigned. With the proposed expansion on the north side of the bridge, the only ground impacts would be into the City of Aspen’s maintenance facility’s property, although not directly impacting any existing buildings.
4.3 Utilities, Easements and ROW
There are three buried steel penstock lines that run skewed along the western side of the footings at pier no. 3 (RE: sh. #1/13 of original design plan set). Care should be taken if any structural modifications were to take place to the footings in this area. Also beneath the bridge is Power Plant Road, which passes under the bridge twice. This road is the only means of access to the Aspen Maintenance facility and therefore would have to remain open during the entire expansion process. Additional dry utilities have been attached to the underside of the existing deck that would need to be adjusted or relocated.
The existing corridor of CDOT ROW in the vicinity of project varies from 100’ to 75’ in width, typically centered on the roadway. In the vicinity of the Bridge the existing ROW is only 75’ which would be sufficient for the planned modifications but would need temporary access easements to construct the widenings. There could also be points on the alignment at proposed sign bridge locations that could require additional ROW or easements but these were not individually analyzed.
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
Update May 2008: If the bridge deck expansion occurs exclusively on the north side, additional ROW would be necessary for SH 82 to accommodate the pedestrian connections from the east abutment to Eighth Street. Access and construction easements would also be necessary, as well as in the symmetric expansion, from the City in and around the City Maintenance facility. In most instances the Local Agency, the City in this instance, advancing the improvements would be responsible to follow the FHWA Uniform Acquisitions Process to obtain these new areas for SH 82 and then deed them back to CDOT.
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
5.0 BRIDGE MODIFICATIONS AND LIMITATIONS
5.1 Caveats to Design Recommendations
SGM’s design recommendation involves several assumptions that may require modification by CDOT if a bridge expansion were to take place. The original bridge was designed in 1959 and uses an AASHO design live load of H20-S16-44 and the original hydraulic design information for Castle Creek is not available. These assumptions have been made to help quantify values for modeling purposes, and also to assist in determining planning level costs for the expansion of this bridge.
5.1.1 HS25 Design Live Loading
The first assumption is that the current vehicular rating of H20-S16-44 on the existing structure would remain in effect for any future expansion of this bridge. AASHTO & CDOT’s current design rating is an HS25 Live Load and this change standards has occurred to accommodate heavier vehicles utilizing the highways today opposed to the traffic 50 years ago. We feel that if CDOT were to require modification of the Castle Creek Bridge to conform to the current standard, then the existing bridge substructure and superstructure would not provide sufficient structural capacity, thus requiring a complete replacement. At such point, it would become more cost effective to completely remove and replace the bridge preferably in accordance with the Entrance to Aspen’s preferred alignment. To remove and replace the crossing in the current alignment with live traffic would also greatly exceed the stated costs of the replacement bridge that would align with Main Street by at least 30% to 50%. Furthermore, disruption to existing traffic if the new structure is constructed at the location set forth in the Record of Decision would be minimal when compared to rebuilding or expanding the bridge on the existing alignment.
5.1.2 Designing for a New Hydraulic Event
If substantial structural upgrades are planned for the Castle Creek Bridge, CDOT may also require that the bridge be designed to withstand a hydraulic event greater than used of the original design. This would mean that all of the piers may have to be upgraded (i.e. widened & adding more reinforcement) to resist increased lateral loading and protection against scour. The design standards for hydraulic events have changed drastically since the original construction. For the purposes of this study we have assumed that the bridge’s current design for lateral loading from a design hydraulic event will be sufficient.
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
5.1.3 Evaluation of Environmental Impacts
Due to the limited focus of this feasibility study there has not been a Habitat Suitability Assessment done for the Castle Creek Bridge at this time. If these concepts are advanced with CDOT for further development an assessment should be conducted after their inclusion in this concept.
5.2 Increased Length at Pier Cap to Expand Roadway Width
Update May 2008: Expanding the bridge roadway 20 feet to the north side of the bridge means that the bridge pier caps will have to be extended, and new plate girders added outboard of the existing to support the extra bridge deck. This expansion would also include the addition of a new pier to bear the expanded pier cap and girders. The new girders, pier and pier cap would take the majority of the expanded bridge deck loads, thus providing the existing structure with a minimal increase in both live and dead loads. The main concern in attaching a new section of deck and pier cap to the existing deck is ensuring that each section, new and existing, will react uniformly with one another. Ensuring that our new expansion is designed to have the same deflections and stresses as the existing will be critical in ensuring the long term service of this expanded structure. Figure #S2 in the appendix shows the proposed bridge cross-section for the North Expansion. Figure #S3 showing the Symmetric Expansion (January study) is attached for reference.
The previous symmetric expansion to the bridge roadway 7 feet on each side means that the bridge pier caps will have to be extended and new plate girders added outboard of the existing to support the extra bridge deck. The existing pier cap would have to be widened (attachment one – detail 2) and additional reinforcement added to resist the increased bending moments that would be generated at the Pier-Pier Cap intersection. Preliminary Finite Element Analysis (FEA) modeling shows that there would be a 33% increase in factored loading between the existing and new bridge at this intersection. In order to achieve sufficient strength between the extended & existing pier cap members, a post tensioning system may have to be employed. This would make the new and existing pier cap sections act compositely with one another.
5.3 Bearing Issues at Footings and Abutments
Update May 2008: Because the updated analysis bridge expansion will take place on one side of the bridge and there will be installation of a new pier and footing. The new live and dead loads of the expansion will be taken by the additional footings opposed to loading the existing piers. This proposed expansion, all to one side of the existing structure, will have much less impact on the existing structure than the previous concept of widening symmetrically on the centerline of the existing bridge.
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
Live and dead loads over the existing structure would still be tracked down to the existing piers and footings. The loads over/at the expanded section would be tracked down to the new girders, pier caps, piers, and footings. This would effectively isolate the load paths so that there will be a minimal increase in stresses on the existing structure. This is a major benefit over the previous expansion iteration, where the existing structure was to bear all of the increased loads from the expanded bridge deck.
When expanded symmetrically, the new bridge deck, new girders, and extended pier caps, our FEA model indicates that there would be a 30% increase in reactions at the footings. SGM’s preliminary design recommendation would be to underpin the existing footings with a piling system to resist the increased loads.
Update May 2008: 5.4 Constructability Review
SGM had an independent assessment conducted by a contractor, Kiewit Western, to assess the constructability of the proposed bridge widening to the north side as well as the concentric expansion of State Highway 82. The two superintendents who provided the review have previous valley structural experience on the Snowmass Creek and Shale Bluffs construction projects along SH 82 as well as recent experience on the T-REX project on I-25 in Denver.
Primarily, Kiewit expressed concern that gaining acceptance from CDOT and the FHWA for the prior loading standards (HS20) would be pretty difficult to obtain based on their interactions with CDOT in other portions of the State. In additional to the new loading requirements, Kiewit pointed out that there may also be some seismic issues associated with the newer code that may need to be addressed. If a parallel structure were built to widen the existing structure, the structural design and method of construction will need to account for potential eccentric loadings to the bridge substructure.
Kiewit provided some suggestions for strengthening the existing structure including a carbon-fiber wrap, additional post-tensioning, and adding concrete around the footings to increase the load capacity of the existing structure. Kiewit also echoed concerns about the winter maintenance and how it will affect the visibility of the lanes and the operations of the reverse-flow lane, given the heavy amount of tourists on the roadway.
In summary, they also reaffirmed the volatility of the current construction market and stressed that costs in the Roaring Fork Valley as well as much of the Western Slope are outpacing historic trends.
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
5.5 Summary of Possible Bridge Expansion
In conclusion, we believe that if CDOT will allow an expansion of this bridge using the original design parameters (HS20, hydraulic event) then it would be possible to widen the existing pier caps to support the additional road deck section to the north. However, this expansion/modification project would significantly exceed the initially estimated 2 million dollar budget discussed within the City. The additional cost would mostly be due to the increasing material costs in the Roaring Fork Valley, the extensive debris catching system, and required traffic control and diversion measures during construction. Drastic changes in construction costs could also continue to affect this feasibility estimate in the immediate future.
Update May 2008: There are also indirect impacts to the community like the additional congestion that would be created by this restricted work zone that is difficult define. Under the north expansion concept, the time required to build the separate structure and tie it to existing would be significantly less than the previous symmetric concept. Maintenance of traffic during construction would be better, since two lanes could be maintained during the majority of construction. Overall the construction costs would be reasonably similar for the two concepts, but the duration and cost for traffic control would be less for the single sided expansion concept. The duration of this project is likely to be in the 1 – 2 year range rather than 2 – 3 years.
If CDOT requires the planned structural modifications to include HS25 design standards and to accommodate the current hydraulic standards, we believe that it would be more feasible to completely remove and replace the existing Castle Creek Bridge. The final “hidden” cost and associated timeframe for these improvements is the expense and duration associated with re-opening the Record of Decision to evaluate this alternative (and all the others) again for the Entrance to Aspen’s preferred solution.
References
1. A Policy on Geometric Design of Highways and Streets, (AASHTO 2001) 2. US 1 Reversible Flow Lane Study (Miami-Dade MPO, October 2007) 3. Planning and Operational Practices for Reversible Roadways (ITE Journal, August 2006) 4. CDOT Bridge Design Manual, (August 2002)
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SH 82 – Maroon Creek Roundabout to Main Street Reversible Lane Feasibility Study Update
APPENDIX
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