1. The symbol A (Delta), or the symbol I,represents the intersecting angle, which is thedeflection angle made by the tangents where theyintersect.2. D is the degree of curvature, or degree ofcurve. It is the angle subtended by a 100-foot arc orchord (to be discussed in chapter 11 of this TRAMAN).3. R is the radius of the curve, or arc. The radiusis always perpendicular to the curve tangents at thepoint of curvature (PC) and the point of tangency(PT).4. T is the tangent distance, which is measuredfrom the PI to the PC and the PT. The PC is the beginningof the curve, and the PT is the end of the curve.5. L is the length of the curve measured in feetalong the curve from the PC to the PT.A horizontal curve is generally selected to fit theterrain. Therefore, some of the curve data will be known.The following formulas show definite relationshipsbetween elements and allow the unknown quantities tobe computed:1. To find the radius (R), or degree of curvature(D), use the following formula:2. To find the tangent distance (T), compute asfollows:3. To find the length of curve (L), use the followingf o r m u l a :The PC and PT are designated on the plan by apartial radius drawn at each point and a small circle onthe center line. The station numbers of PC and PT arenoted as shown in figure 3-3. The length of the curve(L) is added to the PC station to obtain the station of thePT. The curve data is noted on the inside of the curve itpertains to and is usually between the partial radii.Since most horizontal curves have superelevation(that is, the outside edge of the traveled way is higherthan the inside edge), there must be a transition distancein which the shape of the road surface changes from anormal crown to a superelevated curve. The transitionlength is generally 150 feet and starts 75 feet before thePC is reached. The same is true in leaving curves. Thetransition begins 75 feet before the PT and ends 75 feetbeyond. The beginning and end of the superelevationare noted on the plan.Control PointsA control point maybe a PT, PC, PI, or a point ontangent (POT). Since these control points may bedestroyed during construction, you must reference themto other points. In the field, a common practice that youshould use is to drive iron pins or other reference stakesat right angles to the control point on each side of thecenter line, and then measure and record the distancefrom the pins to the control point. If room allows, thesereference points should be drawn on the road planopposite the control points, as shown in figure 3-3. Ifnot, you should show the control points and referenceson a separate sheet, called a reference sheet.ROAD PROFILEThe procedure used to plot road profiles is discussedin chapter 7 of the EA3 TRAMAN. From your study ofthat TRAMAN, you know that a profile is therepresentation of something in outline. When applied toroads, this means that a profile is a longitudinal-sectionview of the earth along the centerline, and it is alwaysviewed perpendicular to the centerline.As you know, profile-leveling procedures are usedto determine the ground elevations at each of the stationpoints along the center line. These elevations arerecorded in the surveyor’s notebook, which is used bythe draftsman to prepare the profile drawing. Generally,the profile is drawn on the bottom portion ofplan-and-profile paper, directly below the road plan. Anexample of a road profile is shown in figure 3-4.A road grade line is also drawn on the lower portionof the plan-and-profile paper and is represented by aheavy solid line, as shown in figure 3-4. Like the profile,the grade line is a longitudinal section taken along thecenter line and shows the elevations to which the roadis built. The grade line is normally the center-lineelevations of the finished surface but may be thecenter-line elevations of the subgrade. If the subgradewas used, make a special note of it.The grade lines are a series of straight lines that areconnected, where necessary, by curves (called vertical3-4

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