2.57. A circular curve of radius 900 m is to be constructed between two straights of a proposed highway...

A circular curve of radius 900 m is to be constructed between two straights of a proposed highway. The deflection angle between the straights is 14°28'06" and the curve is to be set out by the tangential angles method using a theodolite and a tape.

This setup involves constructing a circular curve, which is essential in connecting two straight segments of a highway smoothly. The curve has a specified radius of 900 m, meaning that all points on the curve are 900 m away from the center of that circle. The deflection angle (14°28'06") represents how sharply the highway will turn at the intersection of the two straight segments. To accurately lay out this curve, surveyors will use tools like a theodolite for measuring angles and a tape for measuring distances, which ensures precision during construction.

Imagine driving a car on a highway where straight paths transition into curved paths as you approach a bend. Just as you would steer at a specific angle to navigate the curve smoothly, the deflection angle outlines how sharp the turn should be designed. This approach ensures that vehicles can proceed safely and comfortably without abrupt changes in direction.

The chainage of the intersection point is 1345.82 m and pegs are inserted at the centre line at 20 m multiples.

The term 'chainage' refers to a linear measurement along a designated path—in this case, the highway. The intersection point’s chainage is specifically noted as 1345.82 m from a reference point along the highway. To facilitate the construction and ensure accuracy in positioning, survey markers (or pegs) are placed at intervals of 20 m along the centerline of the highway. This systematic peg placement allows builders to refer back to these markers throughout the construction process.

Think of a park with a walking trail. If you were to identify your position along the trail, you might say, 'I am 1345.82 m from the entrance.' Now, to ensure everyone can follow the trail easily, small markers are spaced out every 20 m, helping people know how far they've walked or how much further they need to go.

Tabulate the data required to set out the curve and compute the (i) tangent lengths (ii) length of the circular curve (iii) chainages of the two tangent points.

Setting out the curve requires gathering specific measurements, which typically include calculating the tangent lengths (the straight sections leading up to the curve), the total length of the circular curve itself, and determining the locations (chainages) of the tangent points where the straight roads connect to the circular curve. These need to be calculated precisely to ensure the highway behaves as designed and provides a smooth transition from straight to curved sections.

Imagine if you were laying out a new roundabout at a busy intersection. You would first measure how long the roads entering the roundabout should be (the tangents), then determine how big the roundabout itself will be (the circular curve), followed by marking the points where the straight roads meet the roundabout. This thorough planning prevents confusion and ensures the roundabout functions effectively for traffic.

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