Tower Bridge, London, 1998, NWG
I. Sight Distance
Describe the concept behind SSD, PSD and DSD, respectively. What is the minimum sight distance for a given roadway? Where should we provide SSD, PSD and DSD, respectively? What are the components of SSD? Know the basis for deriving the formula for breaking distance? What pavement condition is represented by the ‘f ‘ value used for SSD? Know the object and eye heights that are used to determine SSD, DSD and PSD, respectively. Know how to determine the available sight distance from the plan and profile.
II. Horizontal Alignment
Circular Curve
What are the elements of the horizontal alignment? Know the definition of degree of curvature (D). Know how to derive the relationship between R and D. Know how to derive the relationship between L and R. Explain the physical basis for determining minimum radius. List the parameters that are in the equation of minimum radius. Know how the equation for minimum radius is derived: What is ‘f’ in this equation and how does it vary with speed? What are the factors that limit emax? What is the basis for selecting a emax for a design project? What range of emax is applicable to Connecticut?
Superelevation Runoff
Know the definition for superelevation runoff and tangent runout. Know the criteria for determining the length of the superelevation runoff. Know how to determine the relative profile of the edges and centerline during superelevation runoff. Know the location on the alignment where the superelevation runoff occurs with and without a spiral.
Esthetic Aspects
Why is a continuous alignment recommended? Explain the term "continuity of form" (give examples). Explain the term "continuity of scale" (give examples). Give specific factors required to achieve continuity of form and scale: What is a broken back curve.
III. Vertical Alignment
Parabolic Curve
Know how to sketch a parabolic curve and to label the key locations. Know the difference between sag and crest curve. Know the definition for the rate of change of curvature parameter (K). Know how to calculate A. Know how to determine station and elevation of the turning point. Know how to determine elevation at all locations on a vertical curve.
Vertical Curve Design
Describe the criteria for determining minimum length of crest vertical curves. Describe the criteria for determining minimum length of sag vertical curves. Know how to use the equations for determining minimum length of crest curve (S<L or S>L). Know how to use the equations for determining length of crest curve for passing sight distance (S<L or S>L). Know the values of h1 and h2 for this equation. What is the value of S that is used for crest and sag equations, respectively. Explain what types of adjustments are needed if the maximum K for drainage is exceeded
Esthetic Aspects
Why is a continuous alignment recommended? Explain the term "continuity of form" and why continuity of form is not a problem in vertical alignment design. Explain the term "continuity of scale". Give specific factors needed to achieve continuity of scale. Describe the following design flaws – board effect and break. Explain why it is important to coordinate H and V alignments for design. Discuss the main guidelines for coordinating H and V alignments. Know how to make and interpret 1/R and 1/100k plots.
III. Cross-sections
List the main cross-sectional elements of the roadway. Describe, in general terms, the function of each element. Describe the pros and cons of wide travel lanes. Discuss the factors that affect the optimum cross-slope of the roadway. Discuss the pros and cons of a rounded crown. Describe the function of shoulders. Explain the advantages of using contrasting shoulders. Why are walkways needed? Where should walkways be provided? Describe the function of side-slopes and their design features that most affect vehicular safety.
Photographic credit - Norman Garrick (March 98, London)
