What Is a Flat Yield Curve?

The flat curve refers to the general name of the curve where the route turns in the plane alignment. Includes circular and spiral curves. The line connecting two straight lines enables the vehicle to transition from one straight line to another.

(1) The plane line shape should be direct, continuous, compliant, compatible with the terrain and features, and coordinated with the surrounding environment;

(2) The requirements of driving mechanics are basic. The visual and psychological requirements should satisfy the expressways, first-grade highways and highways with a calculated driving speed greater than 60km / h as far as possible. The three-dimensional linear design should be emphasized to achieve The line is continuous, the indicators are balanced, the vision is good, the landscape is coordinated, and it is safe and comfortable. The higher the calculated driving speed, the more comprehensive the factors considered in the linear design.

(3) Maintaining the balance and continuity of the plane linearity In order to make the vehicles on a highway travel as evenly as possible, attention should be paid to maintaining the continuity of each linear element without sudden changes in technical indicators. The following points should be fully paid attention to when designing: 1 The end of a long straight line cannot be followed by a small radius curve. 2. There must be a transition between high and low standards

(4) Lines that are continuously sharply bent should be avoided. This line shape causes inconvenience to the driver and adversely affects passenger comfort. When designing, you can insert a long enough straight line or spiral curve between the curves.

(5) The flat curve should have sufficient length. If the flat curve is too short, the driving time of the car on the curve is too short to make driving adjustment too late. Generally, the minimum of the flat curve (including the circular curve and the relaxation curve at both ends) should be controlled. length. The curve of a road is generally composed of two sections of transition curve (or superelevation, widened section) and a section of circular curve. The length of the transition curve cannot be less than the minimum length specified by the highway of this class, and the length of the middle circular curve. Should have more than 3 strokes. When the conditions are limited, the transition curve can be connected at the same curvature, and the length of the circular curve is zero. Generally, the minimum length of a flat curve is 9s stroke, and the minimum minimum length is 6s stroke.

(1) Basic type

The combination of line-convolute line-circular curve-convolute line-straight line.

Applicable occasions: Unlimited spacing of intersection points. The parameters of the convolute line and the minimum length of the circular curve in the basic type should meet the relevant regulations. The parameters of the two arcs can be equal, or they can be designed as unequal asymmetric curves according to the terrain conditions.

(Two) S type

A combination of two opposite circular curves connected by two segments of convoluted lines

Applicable conditions: (1) The parameters A1 and A2 of two adjacent convolute lines of the S type should be equal. When different parameters are used, the ratio of A1 to A2 should be less than 2.0, and if appropriate, it should be less than 1.5. (2) On the S-shaped curve, there is no straight line between the two reverse convoluted lines, which is desirable in driving mechanics. When you have to insert a straight line, you must keep it as short as possible. The length of the short straight line or the coincident section should conform to the following formula, where l--the length of the short straight line or the coincident section between reverse convoluted lines (m); The formula for calculating the length of the middle short straight line above is derived from super-height reduction. If the middle straight line is much longer than the above length, it is considered to be two basic curves instead of S-shaped curves. (3) The ratio of the radius of the two circular curves of the S type should not be too large.

(Three) oval

Connect a combination of two concentric circular curves with a convolution line

Applicable occasions: the intersection distance is limited (the intersection distance is smaller).

(Four) convex

A combination of diameters that do not insert a circular curve between two concentric lines

The parameters of the convex convolute line and the radius of curvature of their connection points should meet the requirements of the minimum allowable convolute line parameter and the general minimum radius of a circular curve, respectively. Although the curvature of the convex curve is continuous at each joint, because the length of the middle circular curve is 0, it also causes some disadvantages to the driving maneuver. Therefore, the convex shape can be used only when the route is strictly restricted by terrain and features.

(5) Compound type

Forms where two or more concentric lines are connected to each other at the same curvature

Complex roundabouts are rarely used except for places that are restricted by terrain and other special restrictions, and they mostly appear in the ramp linear design of three-dimensional crosses.

(6) Type C

The two convolution lines of the same direction curve are connected at a radius of zero

Applicable occasions: the intersection distance is limited (the intersection distance is smaller). Applicable conditions: same oval curve.