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From page 18... ... 16 CHAPTER 4 PRACTITIONER SURVEY RESULTS As part of assessment of practice in the design of sag curves, a survey was administered to the highway agencies in every state and a review of practices by domestic and international agencies was conducted. DOMESTIC STANDARDS The survey was administered to the departments of transportation in all 50 states and Puerto Rico. Read the entire page →
From page 19... ... 17 Table 4. State Survey Responses St at e D oc um en te d D es ig n C ri te ri a C ri te ri a sa m e as A A SH TO Si tu at io ns w he re D iff er en t R ec om m en da tio ns ar e us ed C ri te ri a us ed w he n D es ig ni ng V er tic al C ur ve s Ex em pt io ns K ee p A cc id en t R ec or ds Y es N o Y es N o Y es N o H ea dl ig ht Pa ss en ge r C om fo rt D ra in ag e A pp ea ra nc e U nd er cr os si ng D ec is io n or Pa ss in g SD O th er Y es N o N o Y es N ot S ur e 1 X X X X X X 2 X X 3 X X X X X X X X X X 4 X X X X X X 5 X X X X X X X X 6 X X X X 7 X X X X X X X X 8 X X X X X X X X X 9 X X X X X X X X X X 10 X X X X X X X X X 11 X X X 12 X X X X X X X 13 X X X X X X 14 X X X X X X X X X X X 15 X X X X X X X X X X 16 X X X X X X X X X X 17 X X X X X X X 18 X X X X X X X X X X X 19 20 X X X X X X X X 21 X X X X X 22 X X X X X X 23 X X X X X X 24 X X X X X X 25 X X X X X X X 26 X X X X X X 27 X X X X X X X X X Read the entire page →
From page 20... ... 18 St at e D oc um en te d D es ig n C ri te ri a C ri te ri a sa m e as A A SH TO Si tu at io ns w he re D iff er en t R ec om m en da tio ns ar e us ed C ri te ri a us ed w he n D es ig ni ng V er tic al C ur ve s Ex em pt io ns K ee p A cc id en t R ec or ds Y es N o Y es N o Y es N o H ea dl ig ht Pa ss en ge r C om fo rt D ra in ag e A pp ea ra nc e U nd er cr os si ng D ec is io n or Pa ss in g SD O th er Y es N o N o Y es N ot S ur e 28 X X X X X X 29 X X X X X X X X X 30 X X X X X X 31 X X X X X X X X 32 X X X X X X X X X X 33 X X X X X X 34 X X X X X X X 35 X X X X X X X 36 X X X X X X X X 37 X X X X X X 38 X X X X X X 39 X X X X X X X X X X X 40 41 X X X X X X X X X 42 X X X X X X X X X X 43 X X X X X X 44 X X X X X X X 45 X X X X X X X X X X X X 46 47 X X X X X X X 48 X X X X X X X 49 X X X X X X 50 X X X X X X X X X X X 51 Note: The States are not shown in any particular order and for some cases information was completed by VTTI with available public information from online state information Read the entire page →
From page 21... ... 19 Question 1 Does your Agency have documented design criteria for vertical sag curves (Road Design Manual, Design Specifications, etc.) Read the entire page →
From page 22... ... 20 Table 5. Stopping Sight Distance for California Department of Transportation (DOT) Read the entire page →
From page 23... ... 21 The third difference is that: "For algebraic grade differences of 2 percent and greater, and design speeds equal to or greater than 40 miles per hour, the minimum length of vertical curve in feet should be equal to 10V, where V = design speed. As an example, 65 miles per hour design speed would require a 650-foot minimum vertical curve length. Read the entire page →
From page 24... ... 22 Florida also modified the SSD, but only for Interstates, as is shown in the corresponding question 4. Question 3 Are there any situations where your agency recommends the designer use different specifications than the ones specified in your answer for question 1? Read the entire page →
From page 25... ... 23 average daily traffic] is less than 1,500 VPD [Vehicles per day] Read the entire page →
From page 26... ... 24 Table 8. Criteria used by the States for Vertical Sag Curve Design Criteria Number of Responses Headlight SD 45 Passenger comfort 21 Drainage control 19 General Appearance 19 SD at Undercrossing 16 Decision or Passing SD considerations 13 Other 10 Headlight Sight Distance All the states that used Headlight SD as a criterion specified that they used the AASHTO criteria of 2 ft for headlight height and a 1-degree upward divergence of the light beam from the longitudinal axis. Read the entire page →
From page 27... ... 25 Figure 10. Relation of minimum length of sag vertical curves to stopping sight distance (Source: Roadway Design Guidelines. Read the entire page →
From page 28... ... 26 Table 9. Design Standards – Freeway with Median Barrier Design Standards (For given Design Speed) Read the entire page →
From page 29... ... 27 Table 10. K Values for Sag Vertical Curves Design Speed (mph) Read the entire page →
From page 30... ... 28 Table 11. Design Control for Sag Vertical Curves' Upper and Lower Ranges DESIGN CONTROL FOR VERTICAL SAG CURVES BASED ON STOPPING SIGHT DISTANCE Design Speed Assumed Speed for Condition Coefficient of Friction Stopping Sight Distance For Design Rate of Vertical Curve K (km/h) Read the entire page →
From page 31... ... 29 Figure 11. Design control for sag vertical curves (Source: Nebraska Department of Roads Roadway Design Manual page 3-34) Read the entire page →
From page 32... ... 30 Passenger Comfort Passenger comfort was specified as a criterion by 21 states. For most of the states, SSD or headlight SD is the primary control, with the exception of the North Dakota DOT that uses passenger comfort as the primary criterion for sag vertical curves and passing SD in special situations, In general, the states check for the AASHTO comfort criteria based on the assumption that riding on a sag vertical curve is comfortable when centripetal acceleration does not exceed 0.3 m/s2. Read the entire page →
From page 33... ... 31 Texas standards acknowledge that passenger comfort is one of the criteria recognized to some extent to define sag vertical curves, but the standards specify that: "Because cost and energy conservation considerations are factors in operating continuous lighting systems, headlight sight distance should be generally used in the design of sag vertical curves. Comfort control criteria are about 50 percent of the sag vertical curve lengths required by headlight distance and should be reserved for special use. Read the entire page →
From page 34... ... 32 The Indiana Design Manual states that the minimum length of a sag vertical curve in feet should be 3.2 V (which is slightly longer than the AASHTO criteria) Read the entire page →
From page 35... ... 33 "Interregional System: Decision sight distance should be considered in areas where complex driver decisions are required, such as intersections with major collectors or higher, interchanges, lane drops or additions, etc. Passing areas should be provided at reasonable intervals based on terrain and traffic volumes. Read the entire page →
From page 36... ... 34 In Arizona, sag vertical curve not only shall be long enough that the light beam distance is nearly the same as the SSD, but the SD requirements for vertical curves also needs to satisfy minimum length requirements, as shown in Table 13. Table 13. Read the entire page →
From page 37... ... 35 Question 9 What are the design criteria for vertical sag curves in the case of Continuously Lighted Sections of highway? Most of the states do not have specific design criteria for continuously lighted sections, but lighting can be considered as a mitigation factor in several states, as shown in Table 14. Read the entire page →
From page 38... ... 36 A "comfort" sag may be used with a design exception approved by the State Roadway Engineer None In cases of fully lighted sections of highway, the sag vertical curve may be designed to meet the comfort criteria. Design criteria for vertical sag curves in lighted sections of highway are the same as for sections of highway that are not lighted 50% of the sag vertical curve lengths When K values at or near the lower end of the design range are used, they consider providing fixed street lighting with the UDOT Traffic and Safety Division. Read the entire page →
From page 39... ... 37 The New Hampshire DOT "…endorses minimum desirable lengths of vertical curves, although shorter ones will comply with the "Green Book" criteria." (Highway Design Manual Chapter 4, alignment and typical section, pages 4-38 New Hampshire DOT, March 1999.) The Utah Roadway Design Manual of Instruction states that sag vertical curves may have a length less than that required for SSD when all three of the following are provided: 1. Read the entire page →
From page 40... ... 38 "If the cost of bringing the vertical curve up to the standard exceeds the benefit, the department has a process to provide justification of nonstandard and nonconforming features. This justification includes the computation of advisory speed, accident analysis, cost estimates, and mitigation factors." Question 11 Has your agency identified any issues with the current design criteria for vertical sag curve that need to be addressed? Read the entire page →
From page 41... ... 39 curves in some of the European countries instead of parabolic vertical curves which are used in the United States. For this case the K values represent the radius of the vertical curve. Read the entire page →
From page 42... ... 40 Table 15. Vertical Curve Appearance Criteria Design Speed (km/h) Read the entire page →
From page 43... ... 41 Sight Distance Requirements The length of a sag vertical curve should normally be determined by headlight SD requirements. When these cannot be met, sag vertical curve length must be determined by vehicle occupant ride comfort criteria. Read the entire page →
From page 44... ... 42 Table 16. K Values for Sag Vertical Curve Design Speed (km/h) Read the entire page →
From page 45... ... 43 Figure 16. Vertical curves K values. Read the entire page →
From page 46... ... 44 Figure 17. Length of sag vertical curves L (m) Read the entire page →
From page 47... ... 45 set of graphics for minimum size sag vertical curves, as shown in Figure 18. The graph was developed using the following criteria to determine the lower bounds: 1. Read the entire page →
From page 48... ... 46 Spain In Spain, the Design Normative for sag vertical curves states that the sag vertical curves will be designed using a parabolic curve with the following equation (Ministerio de Fomento, Gobierno de Espana, 2011) Kv=Parabolic parameter Ѳ= algebraic differences in grade percent Sight Distance requirement And And where • h1= height over the pavement (m) Read the entire page →
From page 49... ... 47 Canada The length of the sag vertical curve must be, at a minimum, the SSD (Transportation Association of Canada Geometric Design Guide for Canadian Roads, 1999; NCHRP 15-41 survey) Read the entire page →
From page 50... ... 48 range of High Standards and Low Standards for selecting the minimum K value. Switzerland defines sag vertical curves based upon SD requirements. Read the entire page →
From page 51... ... 49 height and 1-degree upward divergence of the light beam from the longitudinal axis. Some states incorporate additional modifications to the headlight SD (e.g., Connecticut and California) Read the entire page →
From page 52... ... 50 Exceptions from the absolute minimum length are permitted and are computed as using Design Speed Steps (e.g., as in Ireland) or minimum and desirable K values (e.g., as in Spain) Read the entire page →

From page 18...

... 16 CHAPTER 4 PRACTITIONER SURVEY RESULTS As part of assessment of practice in the design of sag curves, a survey was administered to the highway agencies in every state and a review of practices by domestic and international agencies was conducted. DOMESTIC STANDARDS The survey was administered to the departments of transportation in all 50 states and Puerto Rico.