Estimating the Life-Cycle Cost of Intersection Designs (2016) / Chapter Skim
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From page 72... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4 – Case Studies Page 66 CHAPTER 4 CASE STUDIES As part of the LCCET validation process, the team prepared illustrative case studies to demonstrate the tool's value to prospective users and to facilitate implementation. Through the agency coordination process during Phase I of the project, the team identified those agencies that had interest in participating and had projects suitable for including as a case study.
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From page 73... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4–Case Studies Page 67 provide perspective on the various transportation alternatives. The following two intersection alternatives were considered for this case study.
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From page 74... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4 – Case Studies Page 68 study, a base year analysis of alternatives was not available from the state agency. Therefore, assumptions were made for this case study evaluation to provide a consistent base scenario from which the signalized and roundabout alternatives could be compared.
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From page 75... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4–Case Studies Page 69 Table 4-2: Case Study Information Summary Alternative: Base Case Roundabout Enhanced Signal Base Analysis Year 2014 Future Analysis Year 2035 Average Annual Daily Traffic (veh/d) Base 38,000 Future 67,000 Total Entering Volume (Base)
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From page 76... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4 – Case Studies Page 70 Figure 4-3: Graphical Output from Intersection Alternative Analysis This life-cycle cost evaluation shows that the roundabout alternative results in the least cost in terms of net present value. Interestingly, the enhanced signalized intersection alternative results in relatively small savings through the horizon year due to an increased likelihood of crashes and modest savings in delay.
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From page 77... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4–Case Studies Page 71 Figure 4-4: Existing Powell Butte Highway/Neff Road Intersection East-west traffic at the intersection is controlled by stop signs, with uncontrolled north-south movements on the Powell Butte Highway. The county has previously implemented low-cost treatments to improve driver visibility at the rural, high-speed intersection, such as an overhead flashing beacon and Intersection Ahead signs with LED lights on the sign border that flash as motorists approach the intersection.
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From page 78... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4 – Case Studies Page 72 Figure 4-5: Alternative 1 - Roundabout Concept Alternative 1, shown in Figure 4-5, illustrates a single-lane roundabout concept that was considered. The roundabout includes an inscribed circle diameter of 160 feet and maintains all turning movements while minimizing the number of conflict points.
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From page 79... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4–Case Studies Page 73 Alternative 2, shown in Figure 4-6, evaluated the intersection as two offset "T" intersections, which separates movements and reduces the number of conflict points from 32 to 22. This concept includes left-turn lanes and a median on Powell Butte Highway between the offset intersections.
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From page 80... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4 – Case Studies Page 74 Figure 4-7: Offset T-Intersection Concept – TEV and Delay Calculations In general, TEV is calculated by adding all volume entering the intersection system, being careful not to double count vehicles. The method shown for calculating delay is a simplified approach that considers only control delay incurred at the intersections.
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From page 81... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4–Case Studies Page 75 Table 4-3: Case Study Information Summary Alternative: Base Case Two Offset Intersections Roundabout Base Analysis Year 2014 Future Analysis Year 2030 Average Annual Daily Traffic (veh/d) Base 6,470 Future 9,980 Total Entering Volume (Base)
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From page 82... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4 – Case Studies Page 76 Figure 4-7: Graphical Output from Intersection Alternative Analysis This life-cycle cost evaluation shows that the roundabout alternative results in a lower cost than the two offset intersections, in terms of net present value. The roundabout alternative is expected to have a higher cost than the existing base alternative by approximately $140,000.
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From page 83... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4–Case Studies Page 77 commuter traffic and Meek Road is expected to experience additional traffic from adjacent industrial developments. Figure 4-8 illustrates a schematic of the existing offset T-intersections.
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From page 84... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4 – Case Studies Page 78 Figure 4-10: Alternative Traffic Control and Lane Configurations Alternative 1 includes a roundabout with two lanes at both the northbound and southbound entries on Jackson School Road. The eastbound approach on Scotch Church Road includes a shared left-turn and through lane and a right-turn lane, while the westbound approach of Meek Road includes a shared left-throughright lane and a dedicated right-turn lane.
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From page 85... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4–Case Studies Page 79 Table 4-4 Case Study Information Summary Alternative: Base Case Roundabout Signal Base Analysis Year 2013 Future Analysis Year 2035 Average Annual Daily Traffic (veh/d) Base 13,750 Future 20,167 Total Entering Volume (Base)
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From page 86... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4 – Case Studies Page 80 Figure 4-11: Graphical Output from Intersection Alternative Analysis As shown above, the life-cycle cost evaluation showed that the roundabout alternative results in a lower cost than the signalized intersection in terms of net present value. This is primarily due to the safety cost parameter that was used in the comparison, as shown graphically in Figure 4-11.
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From page 87... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4–Case Studies Page 81 The proposed traffic signal is expected to address the broadside crashes at this intersection and enhance the safety of pedestrians and bicycles by increasing the right-of-way control at the intersection. Based on this information, Case Study 4 considered the following intersection alternatives for this project location: • Alternative 0: Base case (existing unsignalized intersection)
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From page 88... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4 – Case Studies Page 82 Table 4-5: Case Study Information Summary – Safety Evaluation Alternative: Base Case Signal Base Analysis Year 2014 Future Analysis Year 2029 Base Year Safety Performance PDO Crashes 1.6 1.3 Injury Crashes 2.4 1.9 Fatal Crashes 0 0 Future Year Safety Performance PDO Crashes 1.6 1.31 Injury Crashes 2.4 1.9 Fatal Crashes 0 0 Planning/Engineering Costs n/a n/a Right-of-Way Costs n/a $70,000 Construction Costs n/a $550,000 Net Present Value $6,569,325 $4,762,229 Benefits/Costs n/a 3.91 1Assumed crashes are average per year through the horizon year (i.e., same in base and future years)
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From page 89... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4–Case Studies Page 83 Figure 4-13: Graphical Output from Intersection Alternative Analysis As shown above, the life-cycle cost evaluation showed that the signalized alternative would cost nearly $2 million less than the existing base alternative over the life of the intersection. This is primarily due to the safety cost parameter that was used in the comparison, as shown graphically in Exhibit 4-18.
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From page 90... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4 – Case Studies Page 84 main intersection. Based on this information, Case Study 5 considered the following intersection alternatives for this project location: • Alternative 0: Base case (existing offset T-intersections)
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From page 91... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4–Case Studies Page 85 Traditional northbound left-turn Northbound left-turn at a median U-turn intersection Figure 4-15: Travel Time Schematic for Traditional and Median U-Turn Intersections As shown, three components make up a vehicle's travel time within the cordon line. These are: • Running time • Geometric delay • Control delay To fairly compare travel time between alternatives, vehicles must be tracked between the same entry and exit points on the cordon line for each movement.
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From page 92... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4 – Case Studies Page 86 Equation 4-1: Total Travel Time Equation 𝑇𝑇𝑇𝑇𝑇𝑇 𝑡𝑡𝑡𝑇 = �𝑇𝑟𝑟𝑟𝑡𝑟𝑟 𝑡𝑡𝑡𝑇 + �𝑟𝑇𝑔𝑡𝑇𝑡𝑇𝑡𝑔 𝑑𝑇𝑇𝑇𝑑 + �𝑔𝑔𝑟𝑡𝑇𝑔𝑇 𝑑𝑇𝑇𝑇𝑑 The comparison of travel time conducted for Case Study 5 during existing conditions is shown in Table 4-61. As shown, the median U-turn intersection has a lower weighted travel time even though out of direction travel is introduced.
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From page 93... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4–Case Studies Page 87 Table 4-7: Case Study Information Summary Alternative: Base Case Median U-Turn Base Analysis Year 2008 Future Analysis Year 2035 Average Annual Daily Traffic (veh/d) Base 40,045 Future 48,054 Total Entering Vehicles (Base)
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From page 94... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4 – Case Studies Page 88 Figure 4-16: Graphical Output from Intersection Alternative Analysis The life-cycle cost evaluation showed that the median U-turn intersection alternative would cost nearly $1 million less than the existing base alternative over the life of the intersection. This is primarily due to the auto passenger time cost parameter that was used in the comparison, as shown graphically in Exhibit 4-16.
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From page 95... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4–Case Studies Page 89 • Emissions. This hypothetical example considered the following intersection alternatives: • Alternative 0: Base case (existing all-way stop-controlled intersection)
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From page 96... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4 – Case Studies Page 90 Figure 4-17: Graphical Output from Intersection Alternative Analysis Based on the life-cycle cost evaluation, the following conclusions were identified with the hypothetical example in Case Study 6. • The existing intersection configuration is forecasted to have moderate delays in the future • The benefit-cost ratio of the signalized intersection option shows the least benefit by far • The roundabout option provides slight benefits in delay and safety, but those benefits are offset by the higher initial capital costs • Based on total net present costs, maintaining the existing configuration provides equal costs to a roundabout and less cost than a signalized intersection through the horizon year 4.7.
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From page 97... ...
NCHRP Project 03-110: Estimating the Life-Cycle Cost of Intersection Designs Final Report Chapter 4–Case Studies Page 91 This includes a hypothetical case study that further demonstrates some of the unique attributes of the tool, such as the ability to account for emissions, which were not included in the other project examples.
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