Elements of a Typical Cross-section of Road and Highway drainage

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Elements of a Typical Cross-section of Road and
Highway drainage

• Transportation Engineering I
• Dr. Attaullah Shah

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Road

• A way or path over which cyclists, vehicles and
  pedestrians can pass lawfully.
• Roads are normally used for transportation within
  a country.

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Advantages of Roads

• Nearest 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.

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Typical Road Cross-Section
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Typical Road Cross-Section
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Cross-Section Elements

• The cross section of a road includes some or all
  of the following elements
• Traveled way
• Roadway
• Median
• Shoulder
• Kerb
• Traffic Barriers
• Bicycle and pedestrian facilities
• Drainage channels and side slopes

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Two Lane Rural Highway Cross-Section
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Urban Highway Cross-Section
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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 facility
• The likelihood that cyclists and pedestrians will
  use the route
• Climatic conditions

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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
  designed
• Safety of the users
• The 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.

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Right of Way

• The 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.

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Right of Way

• Requirements of area for right of way are as
  follows
• For 2 lane road 150 ft width of area
• For 4 lane road 250 ft width of area
• For 8 lane road 300 ft width of area

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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.

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Traveled Way or Carriage Way

• Lane width strongly influences traffic safety and
  comfort
• Lane width ranges from 2.7-3.6 m with 3.6 m lane
  predominant on high-type highways
• Two-lane two-way highways with the 3.6 m lane
  provide safe clearance between large commercial
  vehicles

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Dual Carriage Way

• When 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.

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Road Way

• The portion of a highway provided for vehicular
  use.
• It includes both carriageway and shoulders.

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Formation Width

• It 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.

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Shoulders

• Shoulders are the strips provided on both sides
  of the carriage way.

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Functions of shoulders

• accommodation of stopped vehicles (disabled
  vehicles, bus stops)
• emergency use
• lateral support for the pavement
• space for roadside facilities
• space for bicycles and pedestrians
• driving comfort (freedom from strain)
• improvement in sight distance
• improvement in capacity

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Width of shoulders

• Low-type roads -- minimum 0.6 m, recommended
  1.8-2.4 m
• Shoulder provided for bicycles -- minimum 1.2 m
  wide
• High-type roads -- minimum 3.0 m, recommended 3.6
  m
• Shoulders should be continuous.
• Shoulders on bridges should have the same width
  as on the approach sections.

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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 from
• 1.2 to 24 m.

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Median
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Function of medians

• separate opposing traffic
• recovery area for out-of-control vehicles
• stopping area
• storage of right-turning and U-turning vehicles
• minimize headlight glare
• provision for future lanes

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Kerb

• It is the dividing line between carriageway and
  footpath.

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Functions of Kerbs

• drainage control
• roadway edge delineation
• right-of-way reduction
• delineation of pedestrian walkways
• reduction in maintenance operation
• Assistance in roadside development

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Types of Kerbs

• Class I Kerb Height 7-9 cms
• Class II Kerb Height 15-20 cms
• Barrier 23-45 cms
• Submerged provide lateral stability

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Foot Path or side Walk

• Foot paths are provided in Urban roads
• These are raised strips constructed along both
  the edges of roads.
• Their minimum recommended width is 1.3 m.

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Foot Path or side Walk
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Foot Path or side Walk
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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.

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Bicycle and Parking lane

• Minimum Width Requirements

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Bicycle and Parking lane
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Traffic Barriers

• A longitudinal barrier, including bridge rail,
  or an impact attenuator used to
• Redirect vehicles from hazards located within an
  established Design Clear Zone
• To prevent median crossovers
• To prevent errant vehicles from going over the
  side of a bridge structure
• To protect workers (occasionally)
• To protect pedestrians, or bicyclists from
  vehicular traffic

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Traffic Barriers
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Traffic Barriers
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Drainage Channels and Side slopes

• Drainage channels and side slopes are provided
  along the length of road for storm water drainage
  etc.

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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.

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Drainage Channels and Side slopes

• Side slopes should
• insure the stability of the roadway
• provide opportunity for recovery of an
  out-of-control vehicle

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Part 2 Highway Drainage

• Transportation Engineering - I

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Highway Drainage

• A means by which surface water is removed from
  pavement and ROW
• Redirects water into appropriately designed
  channels
• Eventually discharges into natural water systems

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Inadequate Drainage

• Damage to highway structures
• Loss of capacity
• Visibility problems with spray and
  retro-reflectivity
• Safety problems, reduced friction and hydroplaning

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Highway Drainage

• Transverse slopes
• Removes water from pavement surface
• Facilitated by cross-section elements
  (cross-slope, shoulder slope)
• Longitudinal slopes
• Minimum gradient to maintain adequate slope in
  longitudinal channels
• Longitudinal channels
• Ditches along side of road to collect surface
  water after run-off

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Transverse slope
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Longitudinal slope
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Longitudinal channel
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Drainage System

• Three phases
• To Estimate the quantity of water to reach the
  system
• Hydraulic design of system elements
• Comparison of different materials to serve the
  purpose
• Steep slopes provide good hydraulic capacity and
  lower ROW costs, but reduces safety and increases
  erosion and maintenance costs

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Hydrologic Analysis

• Q CIA (english) or Q 0.0028CIA (metric)
• Q runoff (ft3/sec) or (m3/sec)
• C coefficient representing ratio or runoff to
  rainfall
• I intensity of rainfall (in/hour or mm/hour)
• A drainage area (acres or hectares)

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Transverse Slope
Undivided 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.
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Transverse Slope
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Transverse Slope
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Transverse Slope
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Crowns vs. Unidirectional Slopes
Type of Roadway Pros Cons
Crowned separately rapid drainage during rainstorms difference between low and high points is minimal inlets and underground drainage (drainage towards the median) difficult design of at-grade intersection elevation use of such sections should be limited to regions with high rainfall
Unidirectional cross slopes more comfortable for drivers changing lanes drainage away from the median saves inlets and drains simplifies treatment of intersections drainage is slower difference between low and high points of the cross section is larger
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Cross Slopes on Tangents
Contradictory design controls A 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 controls Lateral drift
of vehicles at high speed is barely perceptible
on cross slopes up to 2. The slope of 1.5-2.0
is acceptable on high-speed highways. In the
areas of intense rainfall a maximum cross slope
is 2.5. Crown section Change in the cross slope
of 3-4 causes swaying of high body vehicles.
Rounded crowns reduce discomfort.
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Curbed Highways

• The minimum slop values of 1.5-2 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.

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Drainage Channels and Sideslopes

• Design considerations of highway drainage
  includes
• safety
• good appearance
• control of pollutants
• economy in maintenance
• This can be achieved by applying
• flat side slopes
• wide drainage channels
• rounding

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Drainage Channels Types of Drainage Channels
800
802
804
814
806
812
794
810
808
798
800
802
804
806
808
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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.

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Side slopes

• Side slopes should
• insure the stability of the roadway
• provide opportunity for recovery of an
  out-of-control vehicles

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Roadside Channels

• Steep sides improve hydraulic efficiency and
  reduce right of way costs
• Flatter sides improve slope stability and traffic
  safety, reduce maintenance costs
• Side slopes 14 or flatter provides a good chance
  of recovery for errant vehicles and relax
  drivers' tension (roadside channel is visible to
  drivers)
• Side slopes of 15 or 16 are recommended in the
  flat areas
• Intercepting channels have a flat cross section
  form by a dike made with borrow material
• Median drainage channels are shallow depressed
  areas with inlets
• Flumes are open channels or pipes used to connect
  intercepting channels or shoulder curbs with
  roadside channels
• Channel lining prevents channels erosion caused
  by fast stream of water.
• Examples grass (where possible), concrete,
  stone etc.

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Side slopes

• Safety consideration
• Rounded hinge point reduces the chance of an
  errant vehicle becoming airborne
• Fore slopes 16 or flatter can be negotiated by
  errant vehicles
• Fore slopes 13 with liberal rounding provide a
  good chance for recovery
• Slopes steeper than 13 can be used only where
  justified by local conditions. The use of
  roadside barriers should be considered
• Maintenance consideration
• Flat and well-rounded side slopes simplify
  establishment of turf and its maintenance
• Slopes 13 or flatter enable the use of motorized
  equipment

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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 12.
• Standard slope for rock cuts is 21. In
  good-quality rock, slopes ranges from 61.

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Sideslopes
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