CEPC 118 Road Design Finals PDF

CEPC 118 LESSON 1 - GEOMETRIC DESIGN OF ROADS c) Design Traffic Volume & Ingress/Egress Control SOME MAJOR ELEMENTS OF ROAD GEOMETRY: – the ADT stated in the Table may be taken as an Horizontal alignment,...

CEPC 118 LESSON 1 - GEOMETRIC DESIGN OF ROADS c) Design Traffic Volume & Ingress/Egress Control SOME MAJOR ELEMENTS OF ROAD GEOMETRY: – the ADT stated in the Table may be taken as an Horizontal alignment, estimate of traffic at the end of the design life of the Vertical alignment, road to build. The ingress/egress control depends Sight distances, on the requirements and its suitability with the type Cross-section, etc. of the road to build. - Each element is designed in accordance with d) Design Vehicle – Weight, size, and operational various standard of practices such as AASHTO, characteristics of a vehicle determine the design of DPWH, etc. to meet traffic flow characteristics. the basic elements of a road section, i.e., radius of Why must we follow the standard code of practice in the road bends, pavement width, uphill and downhill design? gradients, etc. To ensure uniformity in the design, e) Capacity – ideal condition, design volume, service To ensure smooth/consistent, safe and reliable volume, and LOS and v/c. traffic movements, and Design of the Highway Elements To assist engineers in designing the engineering A. Sight Distances – is the forward distance measure details of the road sections from vehicle within which all objects are visible by Aspects considered in road design the driver while driving. Function – to serve as inland linkage between The distance is influenced by factors such as: locations for moving people and goods. - Driver’s perception & reaction time, Safety – roadways must be designed with safety - Deceleration & acceleration rates, characteristics. - Friction between tire and road surface, Comfort – road features must be designed and - Height of the driver’s eyes & objects on the built for comfort riding quality. road, etc. Economic – in terms of construction and vehicle’s Braking or Stopping Sight Distance operating costs. Consists of two components: Aesthetic – roadways must be built as an element a) Distance traveled during perception (𝑑1): of the environment; its design must include 𝑑1 = 0. 28𝑉𝑡 𝑚𝑒𝑡𝑒𝑟 aesthetical values to suit the existing environment. Criteria that govern the geometric design 𝑉 = 𝑣𝑒ℎ𝑖𝑐𝑙𝑒'𝑠 𝑠𝑝𝑒𝑒𝑑 (𝑘𝑚/ℎ) a) Terrain – influences the design of both horizontal 𝑡 = 𝑝𝑒𝑟𝑐𝑒𝑝𝑡𝑖𝑜𝑛 − 𝑟𝑒𝑎𝑐𝑡𝑖𝑜𝑛 𝑡𝑖𝑚𝑒 (𝑠𝑒𝑐) and vertical alignments. Earthworks and b) Distance traveled during braking (𝑑2): construction costs usually depend on the vertical 2 𝑉 −𝑈 2 𝑑2 = 𝑚𝑒𝑡𝑒𝑟𝑠 alignment and terrain. 254(𝑓+𝐺) Road terrain is divided into 3 types: 𝑉 = 𝑖𝑛𝑖𝑐𝑖𝑎𝑙 𝑠𝑝𝑒𝑒𝑑 (𝑘𝑚/ℎ) - Level – if the average slope of the contour 𝑈 = 𝑓𝑖𝑛𝑎𝑙 𝑠𝑝𝑒𝑒𝑑 (𝑘𝑚/ℎ) = 0 is less than 3%. 𝑖𝑓 𝑣𝑒ℎ𝑖𝑐𝑙𝑒 𝑠𝑡𝑜𝑝𝑠 - Rolling – if slope is in the range of 3 – 𝐺 = 𝑔𝑟𝑎𝑑𝑖𝑒𝑛𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑟𝑜𝑎𝑑 25% 𝑓 = 𝑠𝑖𝑑𝑒 𝑓𝑟𝑖𝑐𝑡𝑖𝑜𝑛 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑟𝑜𝑎𝑑 𝑠𝑢𝑟𝑓𝑎𝑐𝑒 - Mountainous – if slope greater than 25%. 𝑎𝑛𝑑 𝑡𝑦𝑝𝑒 b) Design Speed Stopping Sight Distance: 2 2 𝑉 −𝑈 𝑆𝑆𝐷 = 0. 28𝑉𝑡 + 254(𝑓+𝐺) 𝑚𝑒𝑡𝑒𝑟𝑠 Passing or Overtaking Sight Distance  CEPC 118 Minimum Passing Sight Distances B. Alignments - Horizontal & vertical alignments concern with the design of the turning radius and road gradients. To meet the safety requirements, road physical design is balanced with the characteristics that influence drivers such as sight distance. Horizontal Alignment - It concerns with the design of the road section as it is seen from bird’s eye view – Minimum Radius of Circular Curve a straight section or a road bend. 𝑉 2 𝑅= 𝑚𝑒𝑡𝑒𝑟 - If a road bend is required, what is shape 127(𝑒+𝑓) and what is the radius of the bend? 𝑉 = 𝑑𝑒𝑠𝑖𝑔𝑛 𝑠𝑝𝑒𝑒𝑑 𝑖𝑛 𝑘𝑚/ℎ - Base on a simple circular curve 𝑒 = 𝑠𝑢𝑝𝑒𝑟𝑒𝑙𝑒𝑣𝑎𝑡𝑖𝑜𝑛 - Base on a spiral curve (i.e. a 𝑓 = 𝑟𝑜𝑎𝑑 𝑠𝑢𝑟𝑓𝑎𝑐𝑒 𝑓𝑟𝑖𝑐𝑡𝑖𝑜𝑛 combination of a circular curve and transition curves)  CEPC 118 Degree of Curvature Once the length of the tangent and the length of the curve are known, the stations for the PC and PT can be determined: 𝑃. 𝐶. = 𝑃. 𝐼. − 𝑇 𝑃. 𝑇. = 𝑃.. 𝐶 + 𝐿 Stopping SIght Distance and Horizontal Curve Design  CEPC 118 Minimum Radius Using Limiting Values of 𝑒 𝑎𝑛𝑑 𝑓𝑠  CEPC 118 Vertical Alignment - Concerns with the design of the longitudinal cross–section of a roadway - Vertical curves are in the shape of a parabola. Types of vertical curves: - Uphill or downhill slopes – gradient or slope must be selected in such a way that the performance of vehicles are not affected especially the uphill gradient. Two aspects considered are: - Maximum Gradient - Length of Critical Gradient Transition or Spiral Curve - When vehicles enter or leave a circular - Crest vertical curves – the entry tangent horizontal curve, the gain or loss of grade is greater than the exit tangent centrifugal force cannot be effected grade. instantaneously, considering safety and - Sag vertical curves - the entry tangent comfort. grade is lower than the exit tangent grade. - In such cases, the insertion of transition curves between tangents and circular curves warrants consideration. A properly designed transition curve provides the following advantages - A properly designed transition curve provides the following advantages - A natural, easy to follow path for drivers such that the centrifugal force increases and decreases gradually as a vehicle enters and leaves a circular curve. - A convenient desirable arrangement for superelevation runoff. - Flexibility in the widening of sharp curves. - Enhancement in the appearance of the highway. A basic formula used for computing the minimum length of a spiral 3 𝑅×𝑔×𝑒 𝑉 (1− 2 ) 𝑉 𝐿𝑝 = 𝑐×𝑅 𝑚𝑒𝑡𝑒𝑟 Where: 𝐿𝑝 = 𝑚𝑖𝑛𝑖𝑚𝑢𝑚 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑠𝑝𝑖𝑟𝑎𝑙, 𝑚 𝑉 = 𝑑𝑒𝑠𝑖𝑔𝑛 𝑠𝑝𝑒𝑒𝑑, 𝑚/𝑠 𝑅 = 𝑟𝑎𝑑𝑖𝑢𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑐𝑖𝑟𝑐𝑢𝑙𝑎𝑟 𝑐𝑢𝑟𝑣𝑒, 𝑚 2 𝑔 = 𝑎𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛 𝑑𝑢𝑒 𝑜 𝑔𝑟𝑎𝑣𝑖𝑡𝑦 = 9. 81𝑚/𝑠 𝑒 = 𝑠𝑢𝑝𝑒𝑟𝑒𝑙𝑒𝑣𝑎𝑡𝑖𝑜𝑛 (𝑝𝑒𝑟𝑐𝑒𝑛𝑡 𝑝𝑒𝑟 ℎ𝑢𝑛𝑑𝑟𝑒𝑑) 𝑐 = 𝑟𝑎𝑡𝑒 𝑜𝑓 𝑖𝑛𝑐𝑟𝑒𝑎𝑠𝑒 𝑜𝑓 𝑐𝑒𝑛𝑡𝑟𝑖𝑓𝑢𝑔𝑎𝑙 2 𝑎𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛 (𝑏𝑒𝑡𝑤𝑒𝑒𝑛 0. 30 𝑎𝑛𝑑 0. 91𝑚/𝑠  CEPC 118 LESSON 2 - VERTICAL ALIGNMENT The vertical alignment of a roadway consists of straight sections known as grades or tangents connected by vertical curves. The basic tasks involved in the design of the vertical alignment therefore consist of the selection of appropriate grades for the tangents and the design of appropriate vertical curves to connect these grades. The selection of the appropriate grade depends on the topography on which the travelway is to be located and the standards given for the specific For crest vertical curves, the minimum length depends on mode. the sight distance, the height of the driver’s eye, and the The shape of the vertical curve for each of these height of the object to be seen over the crest of the curve, as modes is the parabola. illustrated in the figure. There are two types of vertical curves: crest vertical curves and sag vertical curves. TYPES OF VERTICAL CURVE Uphill or downhill slopes Crest vertical curves – the entry tangent grade is greater than the exit tangent grade. Sag vertical curves - the entry tangent grade is lower than the exit tangent grade. The minimum length is given by the formula DEIGN OF HIGHWAY VERTICAL CURVES The main criterion used for designing highway vertical curves is the provision of the minimum stopping sight distance. Two conditions exist for the minimum length of highway vertical curves: - when the sight distance is greater than the length of the curve; and - when the sight distance is less than the length of the curve. For stopping sight distance, the height of object is Considering the Properties of the Parabola normally taken to be 0.150 m. For passing sight distance, the height of object used by AASHTO is 1.300 m. Height of eye is assumed to be 1.070 m. Inserting these standard values for h1 and h2, Equation (4.4) may be reduced to  CEPC 118 For sag vertical curves, stopping sight distance is breaks are less than 2 percent or design speeds based on the distance illuminated by the headlights are less than 60 km/h. at night. Design standards are based on an ➔ Where the grade break is greater than 2 percent assumed headlight height of 0.600 m and an and the design speed is greater than 60 km/h, the upward divergence of the headlight beam of 1°. minimum vertical curve is given by L=2V where L in the vertical curve length in meters and V is the design speed in km/h. Vertical curve lengths may be limited by the need to provide clearances over or under objects such as For sag vertical curves, the formula is overpasses or drainage structures. In the case of sag vertical curves passing over objects or crest vertical curves passing under them, the required clearances establish minimum lengths; in the case of crest vertical curves passing over objects or sags passing under them, the clearances establish maximum lengths. In some cases, sag vertical curves with a small total grade change can be sharp enough to cause In the figure, C represents the critical clearance, z discomfort without violating sight distance the horizontal distance from the P.I. to the critical standards. In this case, it is necessary to establish point, and y’ the offset between the critical point and a comfort criterion of the form. the tangent passing through the BVC. - where r is the rate of change of grade, a is the maximum radial acceleration permitted, and y is speed. There is no general agreement as to the maximum value of radial acceleration that can be tolerated without producing discomfort. AASHTO suggests a The equation for the offset is value of 0.3 m/s², and suggests the standard where L = length of vertical curve, m; A = g2 - g1, percent; V = design speed, km/h ➔ Minimum vertical curve standards for highways may also be based on appearance. ➔ Appearance standards vary from agency to agency. ➔ Current California standards, for instance, require a minimum vertical curve length of 60 m where grade  CEPC 118 Vertical tangents with different grades are joined by vertical curves such as the one shown in the figure. Vertical curves are thus of the form where g2 is the grade just beyond the end of the vertical curve (EVC) and L is the length of the curve.