ROAD PROFILE - 14071_66

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1.  The  symbol  A  (Delta),  or  the  symbol  I, represents  the  intersecting   angle,   which  is  the deflection  angle  made  by  the  tangents  where  they intersect. 2. D is the degree of curvature,  or degree  of curve. It is the angle subtended by a 100-foot arc or chord (to be discussed in chapter 11 of this TRAMAN). 3. R is the radius of the curve, or arc. The radius is always perpendicular to the curve tangents at the point of curvature (PC) and the point of tangency (PT). 4. T is the tangent distance,  which  is  measured from the PI to the PC and the PT. The PC is the beginning of the curve, and the PT is the end of the curve. 5. L is the length of the curve  measured  in  feet along the curve from the PC to the PT. A horizontal curve is generally selected to fit the terrain. Therefore, some of the curve data will be known. The  following  formulas  show  definite  relationships between  elements  and  allow  the  unknown  quantities  to be  computed: 1. To find the radius (R), or degree of curvature (D),  use  the  following  formula: 2. To find the tangent distance (T), compute as follows: 3. To find the length of curve (L), use the following f o r m u l a : The PC and PT are designated on the plan by a partial radius drawn at each point and a small circle on the center line. The station numbers of PC and PT are noted as shown in figure 3-3. The length of the curve (L) is added to the PC station to obtain the station of the PT. The curve data is noted on the inside of the curve it pertains to and is usually between the partial radii. Since  most  horizontal  curves  have  superelevation (that is, the outside edge of the traveled way is higher than the inside edge), there must be a transition distance in which the shape of the road surface changes from a normal crown to a superelevated curve. The transition length is generally 150 feet and starts 75 feet before the PC is reached. The same is true in leaving curves. The transition begins 75 feet before the PT and ends 75 feet beyond.  The  beginning  and  end  of  the  superelevation are noted on the plan. Control Points A control point maybe a PT, PC, PI, or a point on tangent  (POT).  Since  these  control  points  may  be destroyed  during  construction,  you  must  reference  them to other points. In the field, a common practice that you should use is to drive iron pins or other reference stakes at right angles to the control point on each side of the center line, and then measure and record the distance from the pins to the control point. If room allows, these reference points should be drawn on the road plan opposite the control points, as shown in figure 3-3. If not, you should show the control points and references on a separate sheet, called a reference sheet. ROAD PROFILE The procedure used to plot road profiles is discussed in chapter 7 of the EA3 TRAMAN. From your study of that  TRAMAN,  you  know  that  a  profile  is  the representation of something in outline. When applied to roads, this means that a profile is a longitudinal-section view of the earth along the centerline, and it is always viewed perpendicular to the centerline. As  you  know,  profile-leveling  procedures  are  used to determine the ground elevations at each of the station points  along  the  center  line.  These  elevations  are recorded  in  the  surveyor’s  notebook,  which  is  used  by the draftsman to prepare the profile drawing. Generally, the  profile  is  drawn  on  the  bottom  portion  of plan-and-profile  paper,  directly  below  the  road  plan.  An example of a road profile is shown in figure 3-4. A road grade line is also drawn on the lower portion of  the  plan-and-profile  paper  and  is  represented  by  a heavy solid line, as shown in figure 3-4. Like the profile, the grade line is a longitudinal section taken along the center line and shows the elevations to which the road is  built.  The  grade  line  is  normally  the  center-line elevations  of  the  finished  surface  but  may  be  the center-line elevations of the subgrade. If the subgrade was used, make a special note of it. The grade lines are a series of straight lines that are connected,  where  necessary,  by  curves  (called  vertical 3-4

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