Name: horizontal curve parts and road alignment
Uploaded: 2025-03-26T15:36:25.000Z
Duration: 1 min 19 s
Channel: JoVE

تتكون الخطوط المركزية للطرق السريعة والسكك الحديدية من أجزاء مستقيمة ، أو مماسات ، مرتبطة بمنحنيات أفقية. تسمح هذه المنحنيات للمركبات بالانتقال بسلاسة بين الظلال ، مما يقلل من تقليل السرعة ويقلل من مخاطر الحوادث. يربط منحنى دائري بين مماسين ، بدءا من نقطة الانحناء (PC) وينتهي عند نقطة الظل (PT) ، تلتقي الظلال عند نقطة التقاطع (PI). الظل الأول هو الظل الخلفي ، والثاني هو الظل الأمامي. الزاوية بينهما، I، هي زاوية التقاطع. نصف قطر المنحنى هو R ، ومسافة الظل هي T. المسافة الخارجية ، E ، هي أقصر مسافة من PI إلى نقطة منتصف المنحنى. يمثل L طول المنحنى الفعلي. يجمع المنحنى المركب بين قوسين أو أكثر بنصف قطر مختلف، بينما يتكون المنحنى العكسي من قوسين ينحنيان في اتجاهين متعاكسين.  المنحنى الحلزوني أو الانتقالي له نصف قطر يتغير باستمرار، ويبدأ بشكل مسطح ويزداد تدريجيا في الانحناء أثناء انتقاله إلى قوس دائري.

مقدمة في المنحنيات الأفقية

Introduction to Horizontal Curves

تعتبر المنحنيات الأفقية ضرورية في تصميم الطرق السريعة والسكك الحديدية ، مما يضمن انتقالات سلسة وآمنة بين أجزاء المسار المستقيم أو الظل. تسمح هذه المنحنيات للمركبات بالحفاظ على السرعة دون تغييرات مفاجئة ، مما يقلل من الحوادث ويحسن كفاءة السفر. عادة ما يتم تعريف المنحنى الأفقي من خلال علاقته الهندسية بظلال تلتقي عند نقطة تقاطع (PI) ، حيث يتم إدخال منحنى بسيط لربطهما. يشير الظل الخلفي إلى الظل الأولي المؤدي إلى PI ، بينما يمثل الظل الأمامي الجزء المستقيم الذي يربط PI ونهاية المنحنى. تؤثر الزاوية بين هذه الظلال ، والمعروفة باسم زاوية التقاطع (I) ، على تصميم المنحنى ونعومته. تشمل المكونات الرئيسية للمنحنى الأفقي نصف القطر (R) ، الذي يحدد حجمه وحدته ، ومسافة الظل (T) ، التي تقيس الطول من PI إلى بداية المنحنى أو نهايته. المسافة الخارجية (E) هي المقياس العمودي من PI إلى نقطة منتصف المنحنى ، بينما يمثل طول المنحنى (L) الجزء المنحني بأكمله. بالإضافة إلى المنحنيات البسيطة ، تشتمل التصميمات المتقدمة على منحنيات مركبة ، تتميز بأقواس متعددة بأقطار متفاوتة للمرونة ، ومنحنيات عكسية ، حيث تنحني الأقواس المتتالية في اتجاهين متعاكسين. تعمل المنحنيات الحلزونية أو الانتقالية على تغيير الانحناء تدريجيا ، مما يعزز الراحة والاستقرار أثناء الدخول والخروج ، مما يجعلها حاسمة في هندسة الطرق والسكك الحديدية الحديثة.

Horizontal curves are essential in highway and railroad design, ensuring smooth and safe transitions between straight path segments, or tangents. These ...

Education

JoVE Core

Civil Engineering

الهندسة المدنية

Unit 1

الوحدة الأولى

Horizontal and Vertical Curves

المنحنيات الأفقية والرأسية

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الرئيسية

horizontal curve parts and road alignment

Horizontal curves connect straight road or railroad segments and help vehicles move safely through a change in direction. They are used in highway and railroad design to create smooth transitions between tangents, which are the straight path sections before and after the curve. By reducing abrupt changes, these curves can support steadier travel speed and help lower the chance of accidents.

A simple horizontal curve is defined by its geometry around the intersection point, or P.I., where two tangents meet. The back tangent is the first straight segment that leads into the P.I. The forward tangent is the straight segment that continues from the P.I. to the end of the curve. The angle between them is the intersection angle, often written as I, and it affects how the curve is designed.

Several measurements describe the shape of a horizontal curve. The radius, or R, shows how large or sharp the curve is. The tangent distance, or T, is the length from the P.I. to the start or end of the curve. The external distance, or E, is the perpendicular distance from the P.I. to the midpoint of the curve. The curve length, or L, is the full length of the curved section.

More complex alignments can include compound curves, reverse curves, and spiral curves. Compound curves use multiple arcs with different radii, which gives designers more flexibility. Reverse curves bend in opposite directions one after another. Spiral, or transition, curves gradually change curvature at the entry and exit, which improves comfort and stability in modern road and rail design.

Horizontal Curve Parts and Road Alignment

horizontal-curve-parts-and-road-alignment

introduction to horizontal curves

Horizontal curves connect straight road or railroad segments and help vehicles move safely through a change in direction. They are used in highway and railroad design to create smooth transitions between tangents, which are the straight path sections before and after the curve. By reducing abrupt changes, these curves can support steadier travel speed and help lower the chance of accidents. A simple horizontal curve is defined by its geometry around the intersection point, or P.I., where two...

degree of curvature and radius of curvature

degree-of-curvature-and-radius-of-curvature

Curvature Measures in Civil Engineering Curves

Degree of curvature and radius of curvature help describe how sharply a curve bends in civil engineering. The degree of curvature measures the steepness of the bend. The radius of curvature shows how tight or smooth the curve is. The degree of curvature can be found by the chord basis or the arc basis. In the chord basis method, the degree is the central angle subtended by a chord of 30.48 meters. In the arc basis method, it is the central angle subtended by an arc of length 30.48 meters. <br...

curve equations

Curve Measurements and Arc Length

Curve measurements describe the key parts of a curved line. The main values are tangent distance, chord length, middle ordinate, and total arc length. These measurements help explain a curve’s shape and size using its radius and central angle. Tangent distance, or T, is the straight-line distance from the point where two tangents meet to the start or end of the curve. It depends on the curve radius, R, and the central angle, I. These two values work together to set the curve’s layout. Chord...

horizontal curve: problem solving

Setting Out a Horizontal Curve

A horizontal curve is set out by using its radius, intersection angle, and stationing of key points. In this example, the radius is 400 meters, the intersection angle is 30 degrees, and the station of the point of curvature, or P.C., is 0 + 150 meters. The goal is to find the station values for the point of intersection, or P.I., the point of tangency, or P.T., and the midpoint of the curve. The length of the long chord is also needed. The first step is to calculate the tangent distance, T,...

field procedure for staking out curves

Surveying Curve Layout with Deflection Angles

Surveying curve layout with deflection angles turns a designed curve into stakes placed in the field. In construction, this step helps keep structures aligned along a curved path. Surveyors use calculated positions so the physical markers match the plan. The process starts by finding the curve’s geometric values. These include the radius, central angle, and tangent distances. Surveyors also identify the Point of Curvature (PC), the Point of Tangency (PT), and the midpoint of the curve. These...

introduction to vertical curves

Designing Smooth Road Grade Transitions

Vertical curves are parabolic transitions that connect different grades on highways and railroads. They help create a smooth alignment between the back tangent and the forward tangent. The back tangent is the first grade, and the forward tangent is the next grade. These curves may be symmetrical or nonsymmetrical. In a symmetrical vertical curve, the tangent lengths are equal. In a nonsymmetrical curve, the tangent lengths are different. The main points used to describe the curve are the Point...

vertical curve: problem solving

Calculating Elevations on a Vertical Curve

Vertical curves connect two roadway grades and help make the road safer, smoother, and more functional. To find the elevation at specific stations on the curve, engineers follow a set of steps based on the curve length, the grades, the Point of Vertical Intersection, or P.V.I., and the P.V.I. elevation. The first step is to locate the Point of Vertical Curvature, or P.V.C., and the Point of Vertical Tangency, or P.V.T. The P.V.C. marks the start of the curve, and the P.V.T. marks the end.

elevation of intermediate points on vertical curves

elevation-of-intermediate-points-on-vertical-curves

Finding High and Low Points on Vertical Curves

Vertical curves help roadways move smoothly from one grade to another. Engineers use them to connect changing slopes and keep the road profile safe and even. To design these curves, they calculate intermediate elevations and find the highest or lowest point on the curve. Intermediate elevations on a vertical curve are found with the tangent offset method. This method uses the starting elevation, the grades at each end, and the curve shape. It gives the elevation of any point along the curve by...

sight distance in a vertical curve

Road Safety on Crest and Sag Curves

Road safety on crest and sag curves depends on how far drivers can see ahead. In roadway design, vertical curves must give drivers enough sight distance to notice hazards and react in time. This affects safety, driver comfort, and how efficiently the transportation network works. Vertical curves are grouped into two main types: crest curves and sag curves. A crest curve is shaped like a hilltop, so the road can block the view of what is beyond it. For these curves, sight distance is based on...

design example: setting a curve using design data

design-example-setting-a-curve-using-design-data

Plotting a Horizontal Curve from Field Data

Plotting a horizontal curve from field data starts with careful geometric design. The curve in this example has a radius of 200 meters and an intersection angle of 20 degrees. Engineers use the method of perpendicular offsets from the long chord to place the curve on the ground. The long chord is the straight line between the two ends of the curve. Here, its length is calculated as 69.46 meters. To improve accuracy, 3-meter intervals are marked along the chord. Offset distances at each point...

key terms and concepts

Learn how horizontal curves connect tangents in highway and railroad design, including the P.I., radius, tangent distance, curve length, and curve types.

Horizontal Curve Parts and Road Alignment | JoVE K12

JoVE Core Civil Engineering provides a foundational exploration of essential construction materials in civil engineering, focusing on bricks, stones, steel, wood, and concrete through easy-to-understand animated videos. This collection covers the properties, manufacturing processes, and practical applications of these materials. Additionally, the accompanied science-in-action videos demonstrate the research experiments performed in laboratories.

civil engineering

Horizontal Curve Parts and Road Alignment

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