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It deals with visible elements of a highway. It is influenced by: Nature of terrain. Type Composition and hourly volume / capacity of traffic Traffic.

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Presentation on theme: "It deals with visible elements of a highway. It is influenced by: Nature of terrain. Type Composition and hourly volume / capacity of traffic Traffic."— Presentation transcript:

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2 It deals with visible elements of a highway. It is influenced by: Nature of terrain. Type Composition and hourly volume / capacity of traffic Traffic Factors Operating speed (Design Speed) Landuse characteristics (Topography) Environmental Factors (Aesthetics).

3 TERRAIN CLASSIFICATION Terrain type Percentage cross slope of the country Plain0-10 Rolling10-25 Mountainous25-60 Steep>60

4 Maximize the comfort Safety, Economy of facilities Sustainable Transportation Planning.

5 geometric cross section vertical alignment horizontal alignment super elevation intersections various design details.

6 HIGHWAY GEOMETRIC DESIGN Cross sectional elements Sight distance Horizontal curves Vertical curves

7 Comparision of Urban and Rural Roads Section Capacity Peak Hour flow Traffic fluctuations Design Based on ADT Speed

8 Urban Road Classification ARTERIAL ROADS SUB ARTERIAL COLLECTOR LOCAL STREET CUL-DE-SAC PATHWAY DRIVEWAY

9 Urban Road Classification ARTERIAL ROADS SUB ARTERIAL COLECTOR LOCAL STREET CUL-DE-SAC PATHWAY DRIVEWAY

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12 ARTERIAL No frontage access, no standing vehicle, very little cross traffic. Design Speed : 80km/hr Land width : 50 – 60m Spacing 1.5km in CBD & 8km or more in sparsely developed areas. Divided roads with full or partial parking Pedestrian allowed to walk only at intersection

13 SUB ARTERIAL Bus stops but no standing vehicle. Less mobility than arterial. Spacing for CBD : 0.5km Sub-urban fringes : 3.5km Design speed : 60 km/hr Land width : 30 – 40 m

14 Collector Street Collects and distributes traffic from local streets Provides access to arterial roads Located in residential, business and industrial areas. Full access allowed. Parking permitted. Design speed : 50km/hr Land Width : 20-30m

15 Local Street Design Speed : 30km/hr. Land Width : 10 – 20m. Primary access to residence, business or other abutting property Less volume of traffic at slow speed Origin and termination of trips. Unrestricted parking, pedestrian movements. (with frontage access, parked vehicle, bus stops and no waiting restrictions)

16 CUL–DE- SAC Dead End Street with only one entry access for entry and exit. Recommended in Residential areas

17 HIGHWAY CROSS SECTIONAL ELEMENTS 1.Carriage way (Pavement width) 2.Camber 3.Kerb 4.Traffic Separators 5.Width of road way or formation width 6.Right of way (Land Width) 7.Road margins 8.Pavement Surface (Ref: IRC 86 – 1983)

18 The primary consideration in the design of cross sections is drainage. Highway cross sections consist of traveled way, shoulders (or parking lanes), and drainage channels. Shoulders are intended primarily as a safety feature. Shoulders provide: –accommodation of stopped vehicles –emergency use, –and lateral support of the pavement. –Shoulders may be either paved or unpaved. –Drainage channels may consist of ditches (usually grassed swales) or of paved shoulders with berms of curbs and gutters.

19 Two-lane highway cross section, with ditches. Two-lane highway cross section, curbed.

20 Divided highway cross section, depressed median, with ditches.

21 Standard lane widths are 3.6 m (12 ft). Shoulders or parking lanes for heavily traveled roads are 2.4 to 3.6 m (8 to 12 ft) in width. narrower shoulders used on lightly traveled road.

22 CARRIAGE WAY (IRC RECOMMENDATIONS) Single lane without Kerbs = 3.50m Two lane without kerbs= 7m Two lane with kerbs = 7.5m 3 lane with or without kerbs= 10.5 / lane with or without kerbs= 14.0m 6 lane with or without kerbs= 21.0 m Intermediate carriage way = 5.5m Multilane pavement = 3.5m/lane

23 Footpath (Side walk) No of Persons/HrRequired Width of footpath (m) All in one direction In both direction

24 Cycle Track Minimum = 2m Each addln lane= 1m Separate Cycle Track for peak hour cycle traffic more than 400 with motor vehicle of traffic 100 – 200 vehicles/Hr. Motor Vehicles > 200; separate cycle track for cycle traafic of 100 is sufficient.

25 Median Width of Median Depends on: –Available ROW –Terrain –Turn Lanes –Drainage. Mim Width of Median: –Pedestrian Refuge=1.2m –To protect vehicle making Right turn = 4.0m (Recc – 7.0m) –To protect vehicle crossing at grade = 9 – 12m. –For Urban area1.2 to 5m

26 KERBS Road kerbs serve a number of purposes: - retaining the carriageway edge to prevent 'spreading' and loss of structural integrity - acting as a barrier or demarcation between road traffic and pedestrians or verges - providing physical 'check' to prevent vehicles leaving the carriageway - forming a channel along which surface water can be drained

27 KERBS Low or mountable kerbs : height = 10 cm provided at medians and channelization schemes and also helps in longitudinal drainage. Semi-barrier type kerbs : When the pedestrian traffic is high. Height is 15 cm above the pavement edge. Prevents encroachment of parking vehicles, but at acute emergency it is possible to drive over this kerb with some difficulty. Barrier type kerbs : Designed to discourage vehicles from leaving the pavement. They are provided when there is considerable amount of pedestrian traffic. Height of 20 cm above the pavement edge with a steep batter. Submerged kerbs : They are used in rural roads. The kerbs are provided at pavement edges between the pavement edge and shoulders. They provide lateral confinement and stability to the pavement.

28 CAMBER (OR) CROSS FALL S. No Type of Surface % of camber in rainfall range Heavy to light 1 Gravelled or WBM surface2.5 % - 3 % ( 1 in 40 to 1 in 33) 2 Thin bituminous Surface2.0 % % ( 1 in 50 to 1 in 40) 3 Bituminous Surfacing or Cement Concrete surfacing 1.7 % % 4 Earth4 % - 3 %

29 Types of Camber Parabolic or Elliptic Straight Line Straight and Parabolic

30 29 Sight Distances The actual distance along the road surface up to which the driver of a vehicle sitting at a specified height has visibility of any obstacle. The visibility ahead of the driver at any instance.

31 SIGHT DISTANCE THE SIGHT DISTANCE AVAILABLE ON A ROAD TO A DRIVER DEPENDS ON –FEATURE OF ROAD AHEAD –HEIGHT OF THE DRIVERS EYE ABOVE THE ROAD SURFACE

32 31 Sight Distances 1. Stopping Sight distance 2. Over Taking Sight distance 3. Passing 4. Intermediate

33 32 Sight Distance in Design Stopping Sight Distance (SSD) – object in roadway Passing Sight Distance (PSD) – pass slow vehicle

34 Stopping Sight Distance (SSD) THE DISTANCE WITHIN WHICH A MOTOR VEHICLE CAN BE STOPPED DEPENDS ON –Total reaction time of driver –Speed of vehicles –Efficiency of brakes –Gradient of road –Frictional resistance

35 TOTAL REACTION TIME PERCEPTION TIME BRAKE REACTION TIME

36 TOTAL REACTION TIME DEPENDS ON PIEV THEORY PERCEPTION INTELLECTION EMOTION VOLIATION

37 36 Perception-Reaction Process Perception Identification Emotion Reaction (volition) PIEV Used for Signal Design and Braking Distance

38 37 Perception-Reaction Process Perception –Sees or hears situation (sees deer) Identification –Identify situation (realizes deer is in road) Emotion –Decides on course of action (swerve, stop, change lanes, etc) Reaction (volition) –Acts (time to start events in motion but not actually do action) Foot begins to hit brake, not actual deceleration

39 38 Typical Perception-Reaction time range 0.5 to 7 seconds Affected by a number of factors.

40 39 Perception-Reaction Time Factors Environment Urban vs. Rural Night vs. Day Wet vs. Dry Age Physical Condition Fatigue Drugs/Alcohol Distractions

41 40 Age Older drivers –May perceive something as a hazard but not act quickly enough –More difficulty seeing, hearing, reacting –Drive slower –Less flexible

42 41 Age Younger drivers –Quick Response but not have experience to recognize things as a hazard or be able to decide what to do –Drive faster –Are unfamiliar with driving experience –Are less apt to drive safely after a few drinks –Are easily distracted by conversation and others inside the vehicle –May be more likely to operate faulty equipment. –Poorly developed risk perception –Feel invincible, the "Superman Syndrome

43 42 Alcohol Affects each person differently Slows reaction time Increases risk taking Dulls judgment Slows decision-making Presents peripheral vision difficulties

44 43 Stopping Sight Distance (SSD) Required for every point along alignment (horizontal and vertical) – Design for it, or sign for lower, safe speed. Available SSD = f(roadway alignment, objects off the alignment, object on road) SSD = LD + BD Lag distance Braking Distance

45 Lag Distance Speed of the vehicle= v m/sec Reaction Time of Driver= t sec ; (2.5 sec) Lag Distance= v t m If the design speed is V kmph, Lag Distance= V x 1000 x t 60 x 60 = V t m

46 Braking Distance Kinetic Energy at the design speed of v m/sec= ½ m v 2 = W v 2 ; m = W/g 2g W = weight of the Vehicle G = acceleration due to gravity (9.9 m/sec 2 ) Work done in stopping the vehicle= F x l F = Frictional force L = braking distance F = coeff of friction = 0.35 Wv 2 = fWl; l = v 2 2g 2fg

47 46 SSD Equation SSD,m = 0.278V t + _____V 2 _____ 254f SSD in meter V =speed in kmph T =perception/reaction time (in seconds) f =design coefficient of friction

48 STOPPING SIGHT DISTANCE FOR ASCENDING GRADIENT AND DESCENDING GRADIENT SSD = 0.278vt + v 2 2g(f+ (n/100)) (or) SSD = 0.278Vt + V 2 254(f - n/100)

49 Passing Distance Applied to rural two-lane roads The distance required for a vehicle to safely overtake another vehicle on a two lane, two-way roadway and return to the original lane without interference with opposing vehicles Designers assume single vehicle passing Several assumptions are considered (vehicle being passed s traveling at a uniform speed, and others) Normally use car passing car Passing distance increased by type of vehicle Minimum passing distance currently used are conservative

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51 Geometric Design of Highways Highway Alignment is a three-dimensional problem –Design & Construction would be difficult in 3-D so highway alignment is split into two 2-D problems

52 Horizontal Alignment Components of the horizontal alignment. Properties of a simple circular curve.

53 Horizontal Alignment TangentsCurves

54 Tangents & Curves Tangent Curve Tangent to Circular Curve Tangent to Spiral Curve to Circular Curve

55 TWO CURVES HORIZONTAL CURVES VERTICAL CURVES

56 Stationing Horizontal Alignment Vertical Alignment

57 Alignment Design Definition of alignment: Definitions from a dictionary In a highway design manual: a series of straight lines called tangents connected by circular curves or transition or spiral curves in modern practice 1.Definition of alignment design: also geometric design, the configuration of horizontal, vertical and cross-sectional elements (first treated separately and finally coordinated to form a continuous whole facility) Horizontal alignment design 1.Components of horizontal alignment Tangents (segments of straight lines) Circular/simple curves Spiral or transition curves

58 Alignment Design 2.Horizontal curves Simple curves This consists of a single arc of uniform radius connecting two tangents Compound curves A compound curve is formed by joining a series of two or more simple curves of different radius which turn in same direction..

59 Simple curve elements

60 Simple curve in full superelevation

61 Compound curve

62 Alignment Design 2.Horizontal curves TRANSITION CURVE A curve having its radius varying gradually from a radius equal to infinity to a finite value equal to that of a circular curve Reverse curves A circular curve consistings of two simple curves of same or different radii and turn in the opposite direction is called reverse curve 61 Sunday, January 12, 2014

63 Reverse curves

64 The vertical alignment of a transportation facility consists of tangent grades (straight line in the vertical plane) vertical curves. Vertical alignment is documented by the profile.

65 Vertical Alignment

66 Vertical curves

67 Convex and concave curves

68 Vertical Alignment Objective: –Determine elevation to ensure Proper drainage Acceptable level of safety Primary challenge –Transition between two grades –Vertical curves G1G1 G2G2 G1G1 G2G2 Crest Vertical Curve Sag Vertical Curve

69 Coordination of vertical and horizontal alignments

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71 Outline 1.Concepts 2.Vertical Alignment a.Fundamentals b.Crest Vertical Curves c.Sag Vertical Curves d.Examples 3.Horizontal Alignment a.Fundamentals b.Superelevation 4.Other Non-Testable Stuff

72 Concepts Alignment is a 3D problem broken down into two 2D problems –Horizontal Alignment (plan view) –Vertical Alignment (profile view) Stationing –Along horizontal alignment –12+00 = 1,200 ft. Piilani Highway on Maui

73 Stationing Horizontal Alignment Vertical Alignment

74 From Perteet Engineering

75 Vertical Alignment

76 Objective: –Determine elevation to ensure Proper drainage Acceptable level of safety Primary challenge –Transition between two grades –Vertical curves G1G1 G2G2 G1G1 G2G2 Crest Vertical Curve Sag Vertical Curve

77 Vertical Curve Fundamentals Parabolic function –Constant rate of change of slope –Implies equal curve tangents y is the roadway elevation x stations (or feet) from the beginning of the curve

78 Vertical Curve Fundamentals G1G1 G2G2 PVI PVT PVC L L/2 δ x Choose Either: G 1, G 2 in decimal form, L in feet G 1, G 2 in percent, L in stations

79 Relationships Choose Either: G 1, G 2 in decimal form, L in feet G 1, G 2 in percent, L in stations

80 Example A 400 ft. equal tangent crest vertical curve has a PVC station of at 59 ft. elevation. The initial grade is 2.0 percent and the final grade is -4.5 percent. Determine the elevation and stationing of PVI, PVT, and the high point of the curve. G 1 =2.0% G 2 = - 4.5% PVI PVT PVC: STA EL 59 ft.

81 G 1 =2.0% G 2 = -4.5% PVI PVT PVC: STA EL 59 ft.

82 Other Properties G1G1 G2G2 PVI PVT PVC x YmYm YfYf Y G 1, G 2 in percent L in feet

83 Other Properties K-Value (defines vertical curvature) –The number of horizontal feet needed for a 1% change in slope

84 Crest Vertical Curves G1G1 G2G2 PVI PVT PVC h2h2 h1h1 L SSD For SSD < LFor SSD > L Line of Sight

85 Crest Vertical Curves Assumptions for design –h 1 = drivers eye height = 3.5 ft. –h 2 = tail light height = 2.0 ft. Simplified Equations For SSD < LFor SSD > L

86 Crest Vertical Curves Assuming L > SSD…

87 Design Controls for Crest Vertical Curves from AASHTOs A Policy on Geometric Design of Highways and Streets 2001

88 Design Controls for Crest Vertical Curves from AASHTOs A Policy on Geometric Design of Highways and Streets 2001

89 Sag Vertical Curves G1G1 G2G2 PVI PVT PVC h 2 =0 h1h1 L Light Beam Distance (SSD) For SSD < LFor SSD > L headlight beam (diverging from LOS by β degrees)

90 Sag Vertical Curves Assumptions for design –h 1 = headlight height = 2.0 ft. –β = 1 degree Simplified Equations For SSD < L For SSD > L

91 Sag Vertical Curves Assuming L > SSD…

92 Design Controls for Sag Vertical Curves from AASHTOs A Policy on Geometric Design of Highways and Streets 2001

93 Design Controls for Sag Vertical Curves from AASHTOs A Policy on Geometric Design of Highways and Streets 2001

94 Example 1 A car is traveling at 30 mph in the country at night on a wet road through a 150 ft. long sag vertical curve. The entering grade is -2.4 percent and the exiting grade is 4.0 percent. A tree has fallen across the road at approximately the PVT. Assuming the driver cannot see the tree until it is lit by her headlights, is it reasonable to expect the driver to be able to stop before hitting the tree?

95 Example 2 Similar to Example 1 but for a crest curve. A car is traveling at 30 mph in the country at night on a wet road through a 150 ft. long crest vertical curve. The entering grade is 3.0 percent and the exiting grade is -3.4 percent. A tree has fallen across the road at approximately the PVT. Is it reasonable to expect the driver to be able to stop before hitting the tree?

96 Example 3 A roadway is being designed using a 45 mph design speed. One section of the roadway must go up and over a small hill with an entering grade of 3.2 percent and an exiting grade of -2.0 percent. How long must the vertical curve be?

97 Horizontal Alignment

98 Objective: –Geometry of directional transition to ensure: Safety Comfort Primary challenge –Transition between two directions –Horizontal curves Fundamentals –Circular curves –Superelevation Δ

99 Horizontal Curve Fundamentals R T PC PT PI M E R Δ Δ/2 L

100 Horizontal Curve Fundamentals R T PC PT PI M E R Δ Δ/2 L

101 Example 4 A horizontal curve is designed with a 1500 ft. radius. The tangent length is 400 ft. and the PT station is What are the PI and PT stations?

102 Superelevation α α F cp F cn WpWp WnWn FfFf FfFf α FcFc W 1 ft e RvRv

103 Superelevation

104 Selection of e and f s Practical limits on superelevation (e) –Climate –Constructability –Adjacent land use Side friction factor (f s ) variations –Vehicle speed –Pavement texture –Tire condition

105 Side Friction Factor from AASHTOs A Policy on Geometric Design of Highways and Streets 2004 New Graph

106 Minimum Radius Tables New Table

107 WSDOT Design Side Friction Factors from the 2005 WSDOT Design Manual, M New Table For Open Highways and Ramps


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