Transportation Systems Design Project
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CEE121: University of California, Irvine Introduction to Transportation Systems: Analysis and Design - Highway extension project
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Transportation Systems Design Project
- 1. Centennial Transportation Extension of the SR-241 Toll Road Engineers: Alireza Behbahani Megan Hanrahan Sarah Kevorkian Kevin Kirk Chosita Sribhibhadh 0
- 2. Executive Summary The transportation engineers at Centennial Transportation were charged with the task of designing a two lane highway extension of the toll road SR-241 that would connect it to SR-74, the Ortega Highway. This extension, approximately 4 miles long, would span along the Cota de Caza mountainous terrain. In order to devise the desired design that would allow a converging path joining the 241 and 74 corridors, it was necessary for the specific safety and design standards of Caltrans and AASHTO to be satisfied while producing the project plan. It was also important to take into consideration the environmental impacts of this freeway which would span along untouched nature inhabited by many forms of wildlife. The challenge before us was to meet standards, please nearby residents, environmentalists, and future travelers of the road all while keeping construction cost and time at a minimum to increase efficiency. A more detailed description of the design standards that we went by is given in Chapter One of this report. The five skilled engineers that worked on this project started off by discussing environmental concerns. It would have been easiest just to construct the highway along the path with the most consistent elevation, but we wanted to take into consideration the surroundings of the highway that residents use every day. Once we factored in the surrounding area of the highway, we were then able to choose a path connecting the corridors. This straight path was then connected with horizontal curves. The lengths and radii of these curves was set by safety standards of the design speed of seventy miles per hour. The highway extension has many horizontal curves since it goes out of its way to try and not disturb nature and wildlife habitats as much as possible. Horizontal curves are discussed further in Chapter Two of this report. The next task at hand for the team was designing vertical curves. Since our highway goes through mountainous terrain and changes grade and elevation often, it was necessary to make sure that the ride was as smooth as possible for drivers, as well as safe. In order to ensure this, fifteen vertical curves were put in place along our highway. In placing these vertical curves, it was necessary to ensure that they were all contained within horizontal curves for good design practice and it was necessary to make sure that cut and fill levels of earthwork were relatively even. More about the vertical curves in the highway extension can be found in Chapter Three of this report. Superelevation is an extremely important factor in ensuring the safety of drivers along the highway. Banked roads help make horizontal curves more safe by reducing sliding friction. This is especially important since the highway design speed is relatively high. Because of the need for superelevated roads, much time and care was put into calculating superelevation transition lengths of the important stations along our curves. The full list of superelevation transition calculations can be found in Chapter Four of this report. The last step in the design of our highway was choosing the proper pavement design. Several different combinations of materials were available for selection, but it was important to choose the right combination that had the least cost. All thicknesses were calculated from AASHTO safety standards and all prices were calculated from those given in the project description. A more detailed description of the pavement design chosen for the freeway extension is given in Chapter Five of this report. In the end, through the careful planning of the highway extension, construction time and cost were minimized, while safety and environmental protection were maximized. 1
- 3. Table of Contents Page number Chapter1: Overview of Design Section 1.1: Summary……………………………………………………………. 3 Section 1.2: Alternate Designs…………………………………………………… 4 Section 1.3: Selection of Optimal Design………………………………………... 4 Chapter 2: Horizontal Alignment Section 2.1: Design Criteria…………………………………………………….... 5 Section 2.2: Design Methodology……………………………………………...… 5 Section 2.3: Summary Table………………………………………………...…… 6 Chapter 3: Vertical Alignment Section 3.1: Design Criteria………………………………………………………. 7 Section 3.2: Design Methodology……………………………………………........ 8 Section 3.3: Summary Table……………………………………………………… 8 Chapter 4: Superelevation Runoff Section 4.1: Selection and required lengths…………………………………….…. 9 Section 4.2 Summary Tables………………………………………………….…... 9 Chapter 5: Pavement Design Section 5.1: Optimal Design…………………………………………………....… 14 Section 5.2: Summary Tables…………………………………………………...... 15 Appendices: A1: Plan and Profile Views of Horizontal and Vertical Curves………………….. 16 A2: Sample Calculations………………………………………………………….. 46 2
- 4. Chapter 1: Overview of Design Section 1.1 Summary: In order to produce a proper highway design that would join the CA-241 and SR-74 corridors, many factors were taken into consideration. In order to reach our goal, it was necessary to follow all Caltrans design standards and the AASHTO pavement design method. Here we highlight some key points of the project design including components and characteristics of the project that are vital in many, if not all, areas of the design process. A simple, yet critical factor was the design speed of 70 miles per hour, which determined many design features from the early stages of the project. Also, the project’s region, residing in a rural and mountainous area, constantly changing in elevation, also dictated certain components due to design standards. Another factor taken into consideration was the fact that the highway only consists of two lanes, with lane widths of 12 feet and shoulder widths of 8 feet. These basic, yet crucial, elements of the project gave us the fundamental standard to start with and allowed us to go forth in producing a proper design. The production of the horizontal alignment involved the implementation of tangent paths, with minimum elevation changes using the given topographic map. The starting and ending points match the latitude, longitude, and elevation given as well. Once completing tangent lines, circular curves are used to connect the tangents. These circular curves follow the Caltrans standard radii from its design speed in the Caltrans Design Manual (Table 203). Following the creation of the horizontal alignment, the vertical alignment was created following Caltrans design standards, taking into consideration factors such as maximum and minimum grades for rolling terrain (Table 204.3), the algebraic grade differences (Section 204.4), Sight Distance standards (Table 201.1), and minimum curve lengths (Figure 201.4 and 201.5) depending on tangents created. Also, the design is congruent with the initial and final grade at the BP and EP specified by the project description while crest curves length exceeding more than half a mile were avoided. We also made sure to practice good design form by keeping all vertical curves within horizontal curves. In designing the superelevation runoff of the highway, we made certain to meet AASHTO minimum standards, selecting the appropriate superelevation for the horizontal curves from the Caltrans design manual from Table 202.2. Once the proper superelevation rate was chosen, the proper crown runoff and superelevation runoff lengths were chosen from Figure 202.5A on superelevation transition. Finally, considering the pavement design, we chose an optimal design following AASHTO flexible pavement design methods and AASHTO’s standards for minimum thickness for each layer of pavement found in the project description. We compared the cost estimate for each design option to find the minimal pavement cost in order to efficiently execute this project. 3
- 5. Section 1.2 Alternate Designs: While producing this project, two different sets of alignments were constructed with varying design elements. By comparison, we were able to implement transportation engineering judgment in order to choose between the more superior of the two possible plans. The first of the two possible highway design options, Design A, had a total length of 27,262 feet. It contained 22 horizontal curves and 14 vertical curves. This particular design was comprised mostly of earthwork area which needed to be filled that was much greater than the amount of cut needed. In comparison to the first possible design, the second design option, Design B, features a total design length of 26,883 feet. It consists of 11 horizontal curves and 15 vertical curves. This design provided more evenly distributed areas of cut and fill, which in nature is more efficient in overall project production, as it not only is beneficial to the budget, but also time spent in constructing the highway. Section 1.3 Selection of Optimal Design: The optimal design between the two choices, we felt, was Design B. The cost of construction in Design A would be greater than that of the latter design, due to the fact that its length is greater than that of Design B. Also, the fact that Design A has many horizontal curves contributes to why it is not the primary choice in design, as having a minimal amount of curves provides a more aesthetically pleasing environment for drivers. In addition, the overall grade change of design A was more than the grade change produced in Design B, which contains smoother transitions in the elevation change throughout the alignment. In consideration of the earthwork involved in the project, it costs more to seek out soil from other locations than to use the cut area of soil from the same project to fill the necessary space. Design A requires a significant amount of soil to be filled, which exceeds the amount of area cut out from the design. This would result in more time and money spent displacing soil in order to achieve adequate results. In comparison, Design B allows for cut soil from this project to be transported to areas close by needing to be filled, which in nature is more efficient in earthwork costs and time spent on cut and fill. The final factor in the decision to choose Design B, was that the initial and final grades and elevation of Design A did not correspond to that of the project description. In Design A, the end point elevation is not the specified elevation in the provided project description and the final grade of +3.0% did not agree as well. Though Design A did not meet the required grades and elevation, Design B executes these necessary factors in designing the projected highway. 4
- 6. Chapter 2: Horizontal Alignment Section 2.1 Design Criteria: This section outlines the design standards followed in creating the highway’s horizontal alignment. The focus of the highway was to keep the road on the same contour line, in order to keep the elevation difference to an absolute minimum to keep cost low. As a part of our public outreach, the group decided to avoid building too close to a school, Tesoro High School, located near our starting point. Due to environmental issues, the design also took into account the location of the Thomas F. Riley Wilderness Park, located east of the planned highway. The last restricted area was a power plant near the end point of the highway. All precautions were taken into account and all sensitive sites will not be disturbed by this freeway design. This project followed its own design standards, in accordance with the standards provided by AASHTO and Caltrans. Based off of the geometric design Table 203.2 in the Caltrans Design Manual, with a highway design speed of 70 miles per hour, the horizontal curve’s minimum radius in the alignment is equivalent to 2,100 feet in addition to a minimum horizontal curve length of 750 feet. This planned horizontal alignment does not implement any broken back, reverse, or compound horizontal curves. Section 2.2 Design Methodology: Several factors were considered in designing the highway’s horizontal alignment: Follow the Caltrans design standards: I. II. III. IV. V. VI. A study of the vertical profile of the land before finalizing the design Minimizing cost where applicable without losing any safety factors Avoiding any restricted areas Following the BP and EP latitude/longitude points given by the project guidelines Keeping all vertical curves within horizontal curves Exceeding minimum curve radii The maximum horizontal curve length of 2,100 feet was not exceeded; therefore the earthwork’s cost was minimized. In general, horizontal curves with bigger curve lengths incur a greater cost, compared to shorter horizontal curve lengths. Table 1 represents all the information of the eleven horizontal curves present in our project. It was crucial that our team avoided steep drops and great inclines in the route, as this would incur great costs by requiring large amounts of cut and fill. The highway’s horizontal alignment consisted of curves that followed the design standards for curve radius and length while providing the highest level of safety for the lowest projected cost. 5
- 7. Section 2.3 Summary Table: Table 1: Horizontal Alignment Summary PC [stations] HC 1 25+84.08 HC 2 30+78.70 HC 3 58+37.36 HC 4 84+31.98 HC 5 108+38.21 HC 6 141+56.95 Elevation-PC [ft] 687.25 680.16 699.26 685.98 671.41 596.02 PT [stations] 27+43.45 40+51.78 63+78.08 98+60.81 112+08.74 155+65.26 Elevation-PT [ft] 683.81 679.83 702.45 675.62 668.87 555.49 Curve Length [ft] Radius [ft] Central Angle [degrees] Tangent Length [ft] Superelevation Rate [ft/ft] Superelevation Runoff Length [ft] Crown Runoff Length [ft] Superelevation Transition Length [ft] 159.36 973.08 540.71 1428.83 370.53 1408.32 2100 4.348 2100 26.5491 2100 14.7526 2100 38.9837 2100 10.1094 2100 38.4241 79.7195229 495.4341518 271.8591243 743.3128475 185.7465682 731.7926234 0.06 0.06 0.06 0.06 0.06 0.06 150 150 150 150 150 150 50 50 50 50 50 50 200 200 200 200 200 200 PC [stations] Elevation-PC [ft] PT [stations] Elevation-PT [ft] Curve Length [ft] Radius [ft] Central Angle [degrees] Tangent Length [ft] Superelevation Rate [ft/ft] Superelevation Runoff Length [ft] Crown Runoff Length [ft] Superelevation Transition Length [ft] HC 7 187+83.48 502.12 193+08.37 495.7 524.9 2100 14.3212 HC 8 200+89.38 486.15 203+73.26 481.98 283.89 2100 7.7455 HC 9 223+02.04 441.12 227+97.25 429.11 495.22 2100 13.5114 HC 10 237+94.36 400.8 250+79.05 346.17 1284.68 2100 35.0509 HC 11 250+79.05 346.19 275+05.63 260.32 2426.58 2100 66.2061 263.8246902 142.1602634 248.7632243 663.1531235 1369.132077 0.06 0.06 0.06 0.06 0.06 150 150 150 150 150 50 50 50 50 50 200 200 200 200 200 6
- 8. Chapter 3: Vertical Alignment Section 3.1 Design Criteria: In this project were able to designate vertical curves which coincide with standards of both the given project as well as the corresponding rules and regulations specified in the Caltrans Highway Design Manual. In designing these Vertical curves, grade standards were kept in mind. Referencing to Table 204.3, which provides the maximum grades for various forms of terrain and highways, the corresponding grade for rolling terrain is 5%. This was the maximum grade that was allowable in the project which was not exceeded. Also, the minimum grade of 0.3% was met, also mentioned in Table 204.3. An important factor in geometric design standards is sight distance, consisting of both Stopping Sight Distance and Passing Sight Distance. The Caltrans Highway Design Manual provides Table 201.1: Sight Distance Standards which gives a list of design speeds and their corresponding stopping sight distances and passing sight distances in accordance with AASHTO’s standards. With a design speed of 70 mph, the corresponding stopping sight distance and passing sight distance are 750 ft and 2,500 ft, respectively. The consideration of the passing sight distance is particularly important in this two lane design, for section 201.2 highlights that only in 2-lane roads would there be consideration of a passing sight distance. Various factors are taken into consideration when designing vertical curves, including curve length as well as sight distance which may be considered further. In order to consider the proper curve lengths and stopping sight distance on crest vertical curves, Figure 201.4 was utilized to take the correct precautions. It provides two equations which factor in sight distance, curve length, and algebraic grade difference which provides us with proper curve length. Crest curve lengths exceeding more than half a mile were avoided, following standards. Also, the Figure 201.5 provides proper stopping sight distance on sag vertical curves and also provides a reference for proper curve length based on specified design speeds. There are two unique equations to sag vertical curves relating the curve length, sight distance, and algebraic grade difference for each curve. Sample calculations for both crest and sag curves are provided; however, one must also consider the minimum curve lengths specified in the manual. Due to standards, specified in Section 204.4 of the manual, an algebraic grade difference between initial and final grades of less than 2% has a corresponding minimum vertical curve length of 200 feet. Also, in this section is a reference to minimum curve lengths in situations where the grade difference is greater than 2 percent and with a design speed exceeding 40 miles per hour, stating that in such situations the minimum length of the vertical curve would be 10 times the velocity. With a design speed of 70 miles per hour, the minimum vertical curve length is 700 ft, which would override the sample calculations of curve lengths below this number. This condition was applied to several curves as the grade difference and design speed satisfies the requirements. Overall, the vertical alignment design was created accurately, following standards, and agrees with the beginning and end points, as specified in the project description. 7
- 9. Section 3.2 Design Methodology: Using the proper minimum grades and minimum vertical curve lengths, we were able to produce a design that coincides with the Caltrans safety standards. However, this project enabled us to practice our personal opinions as transportation engineers on design as well, particularly in terms of earthwork. As previously mentioned, we chose a design which resulted in more evenly distributed volume between cut and fill, which would reduce both time and monetary needs to conclude the project. Though we used more Vertical Curves than initially intended with the previous design, we were able to reach our goal of a more efficient project result in earthwork. Also, we hoped to produce a corridor path that would be both aesthetically pleasing and safe for drivers. The given project, in nature, was a challenge in producing a design in such a terrain as the Coto de Caza mountainous area, with large elevation differences. However, we were able to design this project under such conditions while following proper Caltrans standards. Overall, as section 204.4 in Caltrans manual states, correctly designed vertical curves should provide safety, comfortable driving, proper drainage, adequate sight distance, and be aesthetically pleasing. We believe that we have complied with all of the above. Section 3.3: Summary Table Table 2: Vertical Alignment Summary PVC [Stations] PVT [Stations] Curve Length [ft] Initial Grade [%] Final Grade [%] Grade Difference Min. Length of Curve [ft] PVC [Stations] PVT [Stations] Curve Length [ft] Initial Grade [%] Final Grade [%] Grade Difference Min. Length of Curve [ft] VC 1 VC 2 VC 3 VC 4 VC 5 VC 6 VC 7 VC 8 26+81.74 34+91.00 44+76.55 60+00.00 70+10.75 80+85.46 121+50.00 146+64.20 28+81.74 36+91.00 46+76.55 62+00.00 72+10.75 82+85.46 128+50.00 148+64.20 200 200 200 200 200 200 700 200 -2.5 -0.72 0.73 1.24 0.3 -1.25 -0.69 -3.86 -0.72 1.78 0.73 1.45 1.24 0.51 0.3 0.94 -1.25 1.55 -0.39 0.86 -3.86 3.17 -2.13 1.73 200 200 200 200 200 200 700 200 VC 14 273+56.08 280+56.08 700 -3.12 0.06 3.18 700 VC 15 285+52.07 287+52.07 200 0.06 3 2.94 200 VC 9 170+00.00 172+00.00 200 -2.13 -1.22 0.91 200 VC 10 202+21.65 204+21.65 200 -1.22 -2.13 0.91 200 VC 11 VC 12 224+94.09 238+42.62 226+94.09 245+42.62 200 700 -2.13 -2.84 -2.84 -4.88 0.71 2.04 200 700 VC 13 255+85.69 257+85.69 200 -4.88 -3.12 1.76 200 8
- 10. Chapter 4: Superelevation Runoff Section 4.1 Selection and required lengths: For this highway design there are 11 horizontal curves, all with equal radii of 2100 feet. Referencing to the Table 202.2 in the Caltrans Design Manual, for a 2-lane conventional highway with a curve radii between 1900 and 2199 feet, will have a superelevation of 0.06 feet per foot when the curve is in full superelevation. Therefore all of the horizontal curves’ superelevation runoff lengths are the same and have a value of 150 feet. The curves also all have the same crown runoff lengths of 50 feet, as well as a normal crown of 2% and a shoulder cross slope of 5%. Curves were designed with minimum lengths to ensure that the requirements for driver safety and comfort are achieved. Section 4.2 Summary Table Table 3: Superelevation Transition Summary Left Stations Curve 1 North End Shoulder Elevation Centerline Shoulder Offset Pavement Elevation Elevation Offset Shoulder Elevation 1 23+50.75 24+34.08 691.01 -0.24 691.01 -0.24 691.25 -0.24 691.01 -0.64 690.61 24+84.08 690 0 690 0 690 -0.24 689.76 -0.64 689.36 4 25+34.05 688.99 0.24 688.99 0.24 688.75 -0.24 688.51 -0.64 688.11 PC 25+84.08 687.73 0.48 687.73 0.48 687.25 -0.48 686.77 -0.64 686.61 6 26+34.08 686.97 0.72 686.97 0.72 686.25 -0.72 685.53 -0.72 685.53 6' 26+93.45 685.29 0.72 685.29 0.72 684.57 -0.72 683.85 -0.72 683.85 PT 27+43.45 684.01 0.48 684.01 0.48 683.53 -0.48 683.05 -0.64 682.89 4' 27+93.45 682.78 0.24 682.78 0.24 682.54 -0.24 682.3 -0.64 681.9 3' 28+43.45 682.01 0 682.01 0 682.01 -0.24 681.77 -0.64 681.37 2' 28+93.45 681.21 -0.24 681.21 -0.24 681.45 -0.24 681.21 -0.64 680.81 1' 29+46.78 680.43 -0.64 680.83 -0.24 681.07 -0.24 680.83 -0.64 680.43 1 28+45.37 680.94 -0.64 681.34 -0.24 681.58 -0.24 681.34 -0.64 680.94 2 29+28.70 681 -0.24 681 -0.24 681.24 -0.24 681 -0.64 680.6 3 29+78.70 680.87 0 680.87 0 680.87 -0.24 680.63 -0.64 680.23 4 30+28.70 680.76 0.24 680.76 0.24 680.52 -0.24 680.28 -0.64 679.88 PC South End -0.24 Shoulder Offset 3 Curve 2 North End -0.24 Pavement Elevation 2 South End -0.64 Offset Right -0.64 30+78.70 680.64 0.48 680.64 0.48 680.16 -0.48 679.68 -0.64 679.52 6 31+28.7 680.5 0.72 680.5 0.72 679.78 -0.72 679.06 -0.72 679.06 9
- 15. Chapter 5: Pavement Design Section 5.1 Optimal Design: The pavement of the highway extension was designed using the AASHTO Flexible Pavement Design Method. The cross section of the pavement design chosen, design #2, is shown in the picture below. The surface course is made up of 5.7 inches of plant mix asphalt, with a 6 inch, cement treated base course and a 6 inch sandy clay subbase course. The objective was to keep the cost for pavement construction as low as possible. This particular design was chosen as the optimal design because it meets all the standards for safety and is the most affordable of all three alternative designs. About 9,000 vehicles utilize the highway each day per lane, but only about 720 of these vehicles are trucks that cause significant damage to the pavement over time. The thicknesses of each section of the pavement are based on the daily axle loading of the trucks assuming that the structural number was 4 and checking this assumption with the AASHTO Nomograph. Because of the small percentage of trucks on the highway, it was okay to stick with the minimum allowable thickness for the subbase layer when designing the pavement. The cost to construct each layer of the pavement was based on the cost per volume of its individual material. Volumes were computed from the thickness of each layer, the width of the highway (12.2m), and the length of the entire stretch of highway (8,193.6m). Figure 1: Cross Section of Optimal Pavement Design 14
- 16. Section 5.2 Summary: Table 4: Pavement Design Summaries Design #1 Materials Road Mix Sandy Gravel Sandy Clay Thickness 17” 5.5” 6” Cost $6,474,534 $698,234 $837,881 Total Cost: $8,010,649 Design #2 Materials Thickness Cost Plant Mix Cement treatment Sandy Clay 5.7” 6” 6” $2,894,497 $1,371,078 $837,881 Total Cost: $5,103,456 Design #3 Materials Plant Mix Thickness 7.4” Cost $3,757,768 Crushed stone Sandy Clay 4.2” 6” $799,795 $837,881 Total Cost: $5,395,444 15