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Highway and Railroad Engineering > MODULE 2: Horizontal alignment > Flashcards

MODULE 2: Horizontal alignment Flashcards

1
Q

Or Alignment of road
The center line position of highway on the ground
Guides the good pass of the road through right alignment which is ECONOMICAL and easy to construct

A

HIGHWAY ALIGNMENT

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2
Q

TWO TYPES OF ALIGNMENT

A
  1. HORIZONTAL ALIGNMENT
  2. VERTICAL ALGINMENT
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3
Q
  • includes combination of straight lines and curves
A

HORIZONTAL ALIGNMENT

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4
Q
  • includes vertical curves
A

VERTICAL ALGINMENT

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5
Q

HORIZONTAL ALIGNMENT

A

Describes the location and orientation of highway in plan view (horizontal curves)
Consists of a series of straights (tangents), circular curves (simple, compound and reverse) and transition curves (spirals)

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6
Q

The basic elements for horizontal curves are

A

Radius of Curvature and Superelevation Rate

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7
Q

Proper designs results in high performance regarding

A

Speed
Safety
Efficiency
Comfort
*economy and increased capacity

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8
Q

Designs of horizontal alignment follows that the arc distance is the same as the chord distance

A

HORIZONTAL ALIGNMENT in RAILROADS

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9
Q

Distances along the arc is considered for the design of horizontal alignment

A

HORIZONTAL ALIGNMENT in HIGHWAYS

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10
Q
  • defined by the radius, R and degree of curvature, D
    • a short radius is a sharp curve
      • make the curve risky and dangerous
    • a small degree of curvature is a flat curve
A

SHARPNESS OF HORIZONTAL CURVE

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11
Q

true or false:
the radius of the curve is inversely proportional to the sharpness the degree of curve is directly proportional to the sharpness the radius is inversely proportional to the degree of curve

A

true

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12
Q

true or false:
- a provision of an adequate safe stopping sight distance is important for any change in direction or alignment of road

A

true

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13
Q
  • Usually unacceptable for high-speed roads because of superelevation at reversal point cannot be provided
A

REVERSE CURVES

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14
Q

For the other type of ______________, the approach is the same as for compound curves

A

REVERSE CURVES

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15
Q

Characterized by a short tangent between two curves in the same direction
Should avoided in design since most drivers do not expect succeeding curves to be in the same direction

A

BROKEN BACK CURVE

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16
Q
  • also referred to as Easement curve
  • A curve of varying radius at tangent point to a design circular radius
  • Provided in between straight and circular path in order for the centrifugal force to change gradually
A

TRANSITION CURVES

17
Q

OBJECTIVES of providing transition curve:

A
  • Gradually introduce centrifugal force between tangent and point of curvature to avoid sudden jerk
  • Increase comfort of passengers and ease of maneuver for drivers
  • Introduce designed superelevation at desirable rate
  • Fit road alignment
  • Aesthetic enhancement and introduce extra widening at desirable rate
18
Q

Types of Transition Curves

A
  1. Spiral or Clothoid
  2. Bernoulli’s Lemniscate
  3. Cubic Parabola
19
Q

A curve at which radius of curve is inversely proportional to its length (arc)

A

Spiral or Clothoid

20
Q

A curve at which radius of curve is inversely proportional to the length of the chord

A

Bernoulli’s Lemniscate

21
Q

A curve at which radius of curve varies inversely as its abscissa (x)

A

Cubic Parabola

22
Q
  • a circular curve with two clothoids at each end serving as transition paths

Note: the two clothoids are identical

A

Symmetrical clothoid

23
Q

Standard Length of clothoid based on:

A
  1. Based on travel time (sufficient reaction time)
  2. Based on rate of change of acceleration
  3. Based on aesthetics
    Longitudinal gradient of superelevation runoff should be not exceed 1/200
24
Q

Standard Length of clothoid based on:

A
  1. Based on travel time (sufficient reaction time)
  2. Based on rate of change of acceleration
  3. Based on aesthetics
    Longitudinal gradient of superelevation runoff should be not exceed 1/200
25
Q

If ∆R > ____ m, then spiral curves are necessary.

A

0.2

Highway and Railroad Engineering (10 decks)

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