Presentation on theme: "Elements of a Typical Cross-section of Road and Highway drainage"— Presentation transcript:
1 Elements of a Typical Cross-section of Road and Highway drainage Transportation Engineering – IDr. Attaullah Shah
2 RoadA way or path over which cyclists, vehicles and pedestrians can pass lawfully.Roads are normally used for transportation within a country.
3 Advantages of RoadsNearest to the man, as for going to airport, harbor or railway station.Can be used by all types of vehicles from cycles to trailers.Can lead to any remote area and road users have freedom of movement.Vehicle movements are not time bound, roads are open to traffic for 24 hours.
6 Cross-Section Elements The cross section of a road includes some or all of the following elements:Traveled wayRoadwayMedianShoulderKerbTraffic BarriersBicycle and pedestrian facilitiesDrainage channels and side slopes
9 Selection of appropriate cross-section elements In selecting the appropriate cross-section elements and dimensions, designers need to consider a number of factors:Volume and composition (percent trucks, buses, and recreational vehicles) of the vehicular traffic expected to use the facilityThe likelihood that cyclists and pedestrians will use the routeClimatic conditions
10 Selection of appropriate cross-section elements The presence of natural or human made obstructions adjacent to the roadway (e.g., rock cliffs, large trees, wetlands, buildings, power lines)Type and intensity of development along the section of the highway facility that is being designedSafety of the usersThe most appropriate design is the one that balances the mobility needs of the people using the facility (motorists, pedestrians, or cyclists) with the physical constraints of the corridor within which the facility is located.
11 Right of WayThe right of way can be described generally as the publicly owned area of land that encompasses all the various cross-section elements.The right of way is the land set aside for use as a highway corridor.Rights of way are purchased prior to the construction of a new road, and usually enough extra land is purchased.Sometimes, rights of way are left vacant after the initial roadway facility is constructed to allow for future highway expansion.
12 Right of Way Requirements of area for right of way are as follows: For 2 lane road = 150 ft width of areaFor 4 lane road = 250 ft width of areaFor 8 lane road = 300 ft width of area
13 Traveled Way or Carriage Way The portion of the roadway provided for the movement of vehicles, exclusive of shoulders.Number of lanes on a traveled way are decided on the basis of expected traffic volumes and appropriate level of service required for the facility.
14 Traveled Way or Carriage Way Lane width strongly influences traffic safety and comfortLane width ranges from m with 3.6 m lane predominant on high-type highwaysTwo-lane two-way highways with the 3.6 m lane provide safe clearance between large commercial vehicles
15 Dual Carriage WayWhen traffic volumes are quite heavy, carriageway may be divided into two parts by providing a median strip and each portion of the carriage way is reserved for traffic moving in opposite direction.
16 Road Way The portion of a highway provided for vehicular use. It includes both carriageway and shoulders.
17 Formation WidthIt is the sum of widths of carriage way, shoulders and median strips if provided.In case of embankments, it is measured as the top width.In case of cutting, it is the bottom width of the cutting from which side drains are excluded.
18 ShouldersShoulders are the strips provided on both sides of the carriage way.
19 Functions of shoulders accommodation of stopped vehicles (disabled vehicles, bus stops)emergency uselateral support for the pavementspace for roadside facilitiesspace for bicycles and pedestriansdriving comfort (freedom from strain)improvement in sight distanceimprovement in capacity
20 Width of shouldersLow-type roads -- minimum 0.6 m, recommended mShoulder provided for bicycles -- minimum 1.2 m wideHigh-type roads -- minimum 3.0 m, recommended 3.6 mShoulders should be continuous.Shoulders on bridges should have the same width as on the approach sections.
21 Median or Traffic Separators It is the physical or painted separation provided on divided highways between two adjacent roadways.Medians can also be used to isolate slow and fast moving traffic in the same direction.Width of medians ranges from1.2 to 24 m.
32 Bicycle and Parking lane Bicycle lane is a portion of the roadway designated by striping, signing, and/or pavement markings for preferential or exclusive use by bicycles and/or other non-motorized vehicles.Parking lane is an additional lane provided on Urban roads and streets for on-street parking.
33 Bicycle and Parking lane Minimum Width Requirements
35 Traffic BarriersA longitudinal barrier, including bridge rail, or an impact attenuator used toRedirect vehicles from hazards located within an established Design Clear ZoneTo prevent median crossoversTo prevent errant vehicles from going over the side of a bridge structureTo protect workers (occasionally)To protect pedestrians, or bicyclists from vehicular traffic
38 Drainage Channels and Side slopes Drainage channels and side slopes are provided along the length of road for storm water drainage etc.
39 Drainage Channels and Side slopes Drainage channels should:have adequate capacity for the design runoff,minimize damage to the highway caused by unusual storm water,minimize risk for motorists,be resistant to the high speed water flows where expected,prevent sedimentation of the particles carried by water.
40 Drainage Channels and Side slopes Side slopes shouldinsure the stability of the roadwayprovide opportunity for recovery of an out-of-control vehicle
41 Transportation Engineering - I Part 2 Highway DrainageTransportation Engineering - I
42 Highway DrainageA means by which surface water is removed from pavement and ROWRedirects water into appropriately designed channelsEventually discharges into natural water systems
43 Inadequate Drainage Damage to highway structures Loss of capacity Visibility problems with spray and retro-reflectivitySafety problems, reduced friction and hydroplaning
44 Highway Drainage Transverse slopes Longitudinal slopes Removes water from pavement surfaceFacilitated by cross-section elements (cross-slope, shoulder slope)Longitudinal slopesMinimum gradient to maintain adequate slope in longitudinal channelsLongitudinal channelsDitches along side of road to collect surface water after run-off
48 Drainage System Three phases To Estimate the quantity of water to reach the systemHydraulic design of system elementsComparison of different materials to serve the purposeSteep slopes provide good hydraulic capacity and lower ROW costs, but reduces safety and increases erosion and maintenance costs
49 Hydrologic Analysis Q = CIA (english) or Q = 0.0028CIA (metric) Q = runoff (ft3/sec) or (m3/sec)C = coefficient representing ratio or runoff to rainfallI = intensity of rainfall (in/hour or mm/hour)A = drainage area (acres or hectares)
50 Transverse SlopeUndivided traveled ways (two- and multilane) on tangents and flat curves have a crown in the middle and slope downward toward both edges (camber). The downward cross slope may be a plane or rounded section (parabolic), or a combination of the two.One-way traveled ways on divided highways may be crowned separately or may have a unidirectional cross slope/cross fall.
54 Crowns vs. Unidirectional Slopes Type of RoadwayProsConsCrowned separatelyrapid drainage during rainstormsdifference between low and high points is minimalinlets and underground drainage (drainage towards the median)difficult design of at-grade intersection elevationuse of such sections should be limited to regions with high rainfallUnidirectional cross slopesmore comfortable for drivers changing lanesdrainage away from the median saves inlets and drainssimplifies treatment of intersectionsdrainage is slowerdifference between low and high points of the cross section is larger
55 Cross Slopes on Tangents Contradictory design controlsA steep lateral slope reduces water ponding and the width of the water flow along the curb.A flat lateral slope reduces vehicles' drift towards the low edge.Recommended design controlsLateral drift of vehicles at high speed is barely perceptible on cross slopes up to 2%. The slope of % is acceptable on high-speed highways. In the areas of intense rainfall a maximum cross slope is 2.5%.Crown sectionChange in the cross slope of 3-4% causes swaying of high body vehicles. Rounded crowns reduce discomfort.
56 Curbed HighwaysThe minimum slop values of % in areas with intense rainfalls will cause wide sheet of water on the curbed traveled way.Possible improvements:parabolic cross section with increasing cross slope towards the outer edges,gutter along the curb with the cross slope larger than on the traveled way,on multilane traveled way, cross slope broken along traffic lane edges, increasing from the minimum value on the innermost lane up to the maximum value on the outermost lane. This solution is used on uncurbed sections as well.
58 Drainage Channels and Sideslopes Design considerations of highway drainage includessafetygood appearancecontrol of pollutantseconomy in maintenanceThis can be achieved by applyingflat side slopeswide drainage channelsrounding
60 Drainage Channels Drainage channels should: have adequate capacity for the design runoff,minimize damage to the highway caused by unusual storm water,minimize risk for motorists,be resistant to the high speed water flows where expected,prevent sedimentation of the particles carried by water.
61 Side slopes Side slopes should: insure the stability of the roadway provide opportunity for recovery of an out-of-control vehicles
62 Roadside ChannelsSteep sides improve hydraulic efficiency and reduce right of way costsFlatter sides improve slope stability and traffic safety, reduce maintenance costsSide slopes 1:4 or flatter provides a good chance of recovery for errant vehicles and relax drivers' tension (roadside channel is visible to drivers)Side slopes of 1:5 or 1:6 are recommended in the flat areasIntercepting channels have a flat cross section form by a dike made with borrow materialMedian drainage channels are shallow depressed areas with inletsFlumes are open channels or pipes used to connect intercepting channels or shoulder curbs with roadside channelsChannel lining prevents channels erosion caused by fast stream of water.Examples: grass (where possible), concrete, stone etc.
63 Side slopes Safety consideration Rounded hinge point reduces the chance of an errant vehicle becoming airborneFore slopes 1:6 or flatter can be negotiated by errant vehiclesFore slopes 1:3 with liberal rounding provide a good chance for recoverySlopes steeper than 1:3 can be used only where justified by local conditions. The use of roadside barriers should be consideredMaintenance considerationFlat and well-rounded side slopes simplify establishment of turf and its maintenanceSlopes 1:3 or flatter enable the use of motorized equipment
64 Side slopes Other rules Flat, well-rounded side slopes create a streamlined cross section. Advantages for the streamlined cross sections are:natural, pleasant appearance,improved traffic safety,snow drift prevented,easy maintenance.Retaining walls should be considered where slopes would be steeper than 1:2.Standard slope for rock cuts is 2:1. In good-quality rock, slopes ranges from 6:1.