PAT 303 HIGHWAY AND TRAFFIC TECHNOLOGY GEOMETRIC DESIGN

PAT 303 HIGHWAY AND TRAFFIC TECHNOLOGY GEOMETRIC DESIGN OF ROADS Prepared By : Madam Liyana Ahmad Sofri

SOME MAJOR ELEMENTS OF ROAD GEOMETRY: • Horizontal alignment • Vertical alignment • Sight distances • Cross-section Each element is designed in accordance with various standard of practices such as JKR, LLM, AASHTO, etc. to meet traffic flow characteristics.

WHY MUST WE FOLLOW THE STANDARD CODE OF PRACTICE IN THE DESIGN? : To ensure uniformity in the design To ensure smooth/consistent, safe and reliable traffic movements To assist engineers in designing the engineering details of the road sections

Aspects considered in road design Function • to serve as inland linkage between locations for moving people and goods. Safety • roadways must be designed with safety characteristics. Comfort • road features must be designed and built for comfort riding quality. Economic • in terms of construction and vehicle’s operating costs. Aesthetic • roadways must be built as an element of the environment; its design must include aethetical values to suit the existing environment.

Road Classifications for Planning & Design Four (4) Categories of Urban Roads: 1. Expressway – divided highway for through traffic & all junctions are grade separated. 2. Arterial – continuous road within partial access control for through traffic within urban areas. . 3. Collector – road to serve as a collector or distributor of traffic between arterial and local road systems. 4. Local street – basic road network within a neighbourhood and serves primarily to offer direct access to collectors, short destination trips

Five (5) Categories of Rural Roads: 1. Expressway – divided highway for through traffic & all junctions are grade separated. 2. Highway – interstate national network & to serve long to intermediate trip lengths. 3. Primary road – major road network within a state. 4. Secondary road – major road network within a district or regional development area. 5. Minor road – local roads.

Design Standard Classifications: • R 6/U 6 – highest geometric design standards; traveling speed ≥ 90 km/h; divided highway with full access control (F). • R 5/U 5 – high geometric standards with speed ≥ 80 km/h; combination of divided & undivided sections; partial access control (P). • R 4/U 4 – medium geometric standards with speed ≥ 70 km/h; usually with partial access control (P). • R 3/U 3 – low geometric standard to serve local traffic; partial (P) or no access control (N); speed 60 km/h. • R 2/U 2 – low geometric standards for low volume of local traffic; speed 50 km/h; no access control (N). • R 1/U 1 – lowest geometric standards; speed ≤ 40 km/h

Criteria that govern the geometric design Design Speed Terrain Capacity Design vehicle Design traffic volume & Ingress/Egress control

Terrain • influences the design of both horizontal and vertical alignments. Earthworks and construction costs usually depend on the vertical alignment and terrain. • Road terrain is divided into 3 types, i. e: • (i) Level – if the average slope of the contour is less than 3%. • (ii) Rolling – if slope in the range of 3 – 25% • (iii) Mountainous – if slope greater than 25%.

Design Speed

Design traffic volume & Ingress/Egress control • the ADT stated in Table may be taken as an estimate of traffic at the end of the design life of the road to build. • The ingress/egress control depends on the requirements and its suitability with the type of the road to build. Design vehicle • Weight, size, and operational characteristics of a vehicle determine the design of the basic elements of a road section, i. e. , radius of road bends, pavement width, uphill and downhill gradients, etc. • Standards for design vehicle are stipulated in REAM-GL 2/2002. or Arahan Teknik Jalan 8/86 Capacity • ideal condition, design volume, service volume, and LOS and v/c

Design of the highway elements Sight distances Alignments

Sight Distances • Sight distance is the forward distance measure from vehicle within which all objects are visible by the driver while driving. The distance is influenced by factors such as: • Driver’s perception & reaction time, • Deceleration & acceleration rates, • Friction between tyre and road surface, • Height of the driver’s eyes & objects on the road

Braking or Stopping Sight Distance

Application Of Sight Distance Design

EXAMPLE 1 • A driver takes 3. 2 s to react to a complex situation while traveling at a speed of 55 km/h. How far does the vehicle travel before the driver initiates a physical response to the situation?

EXAMPLE 2 • What is the safe stopping distance for a section of rural freeway with a design speed of 80 km/h on a 4% uphill grade ? . Use perception-reaction time of 2. 5 s and coefficient of friction of 0. 25.

EXAMPLE 3 • Drivers must slow down from 110 km/h to 70 km/h to negotiate a severe curve on a rural highway. A warning sign for the curve is clearly visible for a distance of 50 m. How far in advance of the curves must the sign be located in order to ensure that vehicles have sufficient distance to safely decelerate? Use the perception-reaction time of 1. 5 s and coefficient of friction of 0. 30.

Passing or Overtaking Sight Distance The overtaking sight distance is the minimum distance open to the vision of the driver of a vehicle intending to overtake the slow vehicle ahead safely against the traffic in the opposite direction.

üd 1 -- The distance the passing vehicle travels while contemplating the passing manoeuvre, and while accelerating to the point of encroachment on the left lane. üd 2 -- The length of roadway that is traversed by the passing vehicle while it occupies the left lane. üd 3 -- The clearance distance between the passing vehicle and the opposing vehicle when the passing vehicle returns to the right lane. üd 4 -- The distance that the opposing vehicle travels during the final 2/3 of the period when the passing vehicle is in the left lane.

Minimum Passing Sight Distances

Design Of The Highway Elements • 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– a straight section or a road bend. • circular curve • transition curves)

Minimum Radius of Circular Curve

Spiral Curve • When vehicles enter or leave a circular horizontal curve, the gain or loss of centrifugal force cannot be effected instantaneously, considering safety and comfort. • 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 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.

Minimum Length Of A Spiral

Vertical Alignment Concerns with the design of the longitudinal cross–section of a roadway Vertical curves are in the shape of a parabola. Components of vertical curves: • Uphill or downhill slopes • Crest vertical curves – the entry tangent grade is greater than the exit tangent grade.

Uphill and 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