Layout method for complex angular and curvilinear designs

Angles, bearings, and arcs

Dimension lines are extended from an object at a ___ angle

90 degree

Best pH for most plants

6.0 - 7.5

Diameter of a tree 4” or less measured 6” above the ground

Caliper

Layout Plan: Problem associated with under-dimensioning

Greater interpretation by the contractor / loss of control of the design

Layout Plan: Problem associated with over-dimensioning

Greater potential for error or confusion; implies an inflexibility in accommodating field conditions

Hierarchy of Dimensioning

Fixed dimensions > Semi-fixed dimensions > Flexible dimensions

Dimension type that locates features w/ high level of accuracy; Usually for legal purposes; Typically located by a licensed land surveyor

Also BASELINES; defines features w/ semi-fixed locations

e.g. property lines, ROW, building locations, setbacks, and other aspects governed by code requirements)

Fixed dimensions

Dimension type for points, lines, or planes located by fixed dimensions (baselines)

Used to locate most landscape improvements

Semi-Fixed Dimensions

Dimension type used to locate site elements that do not require precision and / or may be adjusted based on field conditions

May uses ‘+/-‘ or ‘VIF’

Flexible Dimensions

Dimensions that can be determined only after construction has progressed to a point where an actual measurement can be taken

Field Dimensions

Level of precision is usually assumed to be:

½ of the smallest unit indicated

e.g 84’-3” = +/- ½” precision

When dimensions are provided as a decimal (e.g. 84.25ft, eg) assumed precision is ½ of the lowest decimal point (e.g. .005ft)

Degree of precision should reflect realistic tolerances that can achieved in construction of a particular feature / material

Identifies the distance bw two points

Dimension Line

- Should be heavier in weight than dimension lines
- Should not be broken

Extend at a right angle from the dimension line to the object measured

Extension Line

Should be lighter in weight than dimension lines

Convention of locating dimension line labels

- Above the dimension line

- Read from bottom right hand side of sheet

Horz. Layout Method:

Used when a considerable % of side elements are orthogonal to the Fixed Features (PL, new / ex. Building, etc)

Baselines (e.g. building walls) serve as reference points from which objects are measured

String / chain dimensions are closely associated w this method

Perpendicular Offsets

Horz. Layout Method:

Often used w/ curvilinear elements that do not require a high degree of accuracy

Uses offsets at fixed intervals taken from a baseline to the edge or centerline of an element

Accuracy of the shape is limited by the offset interval

Baseline System

Horz. Layout Method:

Distances provided along an X,Y axis to provide unique geographical positions of points from a known POB or PO (point of origin)

Coordinate System

Horz. Layout Method:

Latitude (N-S); departure (E-W)

Either a bearing angle or a length is provided for ea. Point (but not both)

Latitude and Departure

Horz. Layout Method:

Used for the layout of complex curvilinear designs

Bearing: direction of a line specified by a given angle bw the line and an established meridian

Arc: segment of a circle; defined by a center point, a radius and an internal angle; its end points and orientation must be defined

Angles, Bearings, and Arc

Horizontal Curve Type:

Two curves in the same direction connected by a tangent; to be avoided in road design

Broken-back curve

Horizontal Curve Type:

Single radius; most commonly used for low speed roads

Simple curve

Horizontal Curve Type:

Two or more radii in the same direction; difference in the length of the radii should not be more than 50%

Compound

Horizontal Curve Type:

Two arcs in opposite directions; usually requires a tangent between them

Length of tangent depends on road’s design speed

Reverse curve

Horizontal Curve Type:

Typical curves for high speed roads entail a series of curves with a constantly changing radius

Spiral Transitional Curves

More difficult to calculate and lay out; typically not used by LAs since it is primarily for high speed roads

Marks the beginning of the curve at which the road alignment diverges from the tangent line in the direction of stationing

Point of Curvature (PC)

Marks the end of the curve at which the road alignment returns to a tangent line in the direction of stationing

Point of Tangency (PT)

Where two tangent lines intersect

Point of Intersection (PI)

Central angle of the curve; equal to the deflection angle between the tangents

Included Angle (I)

Distant from the PI to either the PC or the PT; always equal for simple circular curves

Tangent Distance (T)

Distance from PC to PT measured along a straight line

Chord (C)

Point about which the included angle (I) is turned

Center of Curve (O)

Used in surveying linear routes (e.g. streets, power lines, stationary storm sewers, etc)

Marked along a centerline from a starting point (0+00)

Full station intervals are indicated along a center line; key areas will also be indicated

Stationing

In stationing, FULL stations are at ___ intervals

100 ft (represented at 1+00)

In stationing, HALF stations are at ___ intervals

50 ft (represented at 0+50)

Forward sight distance should not be ___

Less than the safe stopping distance for the design speed of the curve

Banking / tilting to compensate for centrifugal forces acting on a vehicle as it travels around a curve

Superelevation

BVC

Beginning of vertical curve

PVI

Point of vertical intersection

EVC

End of vertical curve

(2) Types of Vertical Sight Distance

- Safe stopping distance
- Safe passing distance

(LA’s typically only address stopping distances)