King Fahad University of Petroleum and Minerals Civil Engineering Department

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King Fahad University of Petroleum and
MineralsCivil Engineering Department

• CE-576-Geometric Highway Design
• Chapter IV
• Instructor Dr. Nedal T. Ratrout

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Chapter IV
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Objective

• General (Roadway Traveled Way)
• Pavement
• Lane Widths
• Shoulders

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AASHTO Definition for Roadway Traveled Way

• Roadway The portion of highway, includes
  shoulders, for vehicular use. A divided highway
  has two or more roadway.

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• Traveled way The portion of the roadway for the
  movements of vehicles, exclusive of shoulders.

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PavementSurface Type

• Pavement characteristics related to geometric
  design are affecting driver behavior and the
  ability of a surface to retain its shape
  dimensions, to drain, and to retain skid
  resistance.

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• High-type surfaces provide higher operating
  speeds vice versa. Therefore, surface type
  should be consistent with the selected design
  speed.

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PavementCross Slope

• On undivided highways downward cross slope may be
  a plane or rounded section or a combination
  there is a cross slope break at the crown line
  a uniform slope on each side.

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• Rounded cross sections usually are parabolic,
  this section is described by the vertical drop
  from the center crown line to the edge of the
  traveled way (crown height).
• Advantages good for drainage because the cross
  slope steepens toward the edge of the traveled
  way.

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• Disadvantages difficult to construct, cross
  slope of outer lanes may be excessive, and
  warping of pavement areas at intersections may be
  difficult to construct or awkward.

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• On divided highways each traveled way may be
  crowned separately as shown

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• Advantages rapid draining, the difference
  between high low points in the cross section is
  minimal.

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• Disadvantages more inlets underground drainage
  are needed, treatment of intersections is
  difficult because of number of high low points
  on the cross section.
• This section is good for regions of high rainfall
  or where a snow ice are major factors. Sections
  having no curbs wide depressed median are
  well-suited for these conditions.

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PavementCross Slope

• The following figure shows roadways with
  unidirectional cross slopes

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• It provides more comfort to drivers when they
  change lanes to drain away from or toward the
  median.
• Drainage toward median keeps outer lanes surface
  free of water. The runoff is collected into a
  single conduit under median.

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• In case of curbed median drainage will be next to
  or on higher speed lanes.

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• Two contradictory controls affecting the rate of
  cross-slope on tangent flat curves
• 1- Steep lateral slope is desirable to
• minimize ponding of water on
• pavements with flat profile grades.
• Its also desirable on curbed
• pavements.

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• 2- Steep cross slopes are not
• desirable because of vehicles
• drift toward the low edge of
• traveled way, especially when snow ice are
  common.

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• Because of these controls cross-slopes up to
  include 2 are recommended in terms of vehicle
  steering.
• In areas that the effect of wind on vehicle
  steering is significant, high rates of cross
  slopes should be avoided.

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PavementCross Slope

• On high-type two-lane roadways, crowned at the
  center, cross-slope ranges from 1.5 to 2.

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• In case of 3 or more lanes the two lanes adjacent
  to the crown line should have min. slope on
  each successive pair of lanes the rate increased
  by 0.5 to 1 (see Exhibit 4-3G).

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• On high-type high-speed highways, with cross
  slopes steeper than 2 , drivers in passing
  maneuvers will cross recross the crown line
  negotiate cross slope change over than 4 . The
  reverse curve path of traveled vehicle will
  reverse the direction of centrifugal force, then
  it will increase by the effect of reversing cross
  slopes.

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• In areas of intense rainfall, the cross slope of
  high-type pavements increased to 2.5 with
  corresponding crown line crossover of 5. In case
  of 3 or more lanes in each direction, max. cross
  slope should not exceed 4.

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• For the previous situation, consideration should
  be given to the use of grooving or open graded
  mixers.

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The folowing table shows average of values of
cross slope rate applicable for type of surface
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• Low values of ranges of cross-slopes shown are
  not recommended with roadway designed with outer
  curbs.because of water sheet over traveled way
  near the curbs.

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• The rate of width of of traveled way inundated
  with water varies with the rate of cross slope.
  Cross slope greater than 1 is desirable and in
  some cases more than 1.5 needed to limit
  inundation to about half of the outer traffic
  lane.

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PavementSkid Resistance

• Highway geometric affect skidding. Therefore, for
  new construction reconstruction projects
  vertical horizontal alignments can be designed
  in a way to reduce skidding.

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• Pavement type textures affect skid resistance.
  Four causes of poor skid resistance on wet
  pavements are rutting, polishing, bleeding,
  dirty pavements.

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• Measures taken to correct or improve skid
  resistance should result in the following
  characteristics high initial skid resistance
  durability, the ability of retain skid resistance
  with time traffic and min. decrease in skid
  resistance when increasing speed.

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Lane Width

• Lane width affect level of service and capacity.
• Where unequal-width lanes used, locating wider
  lane on the right provide space for large
  vehicles, bicycles to keep vehicles at greater
  distance to right edge.

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• Lane width of 3.6m 12ft is desirable on rural
  urban facilities, in urban areas where the
  pedestrians existing development is the control
  3.3m 11 ft is acceptable.

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• 3.0m 10 ft wide acceptable on low speed
  facilities, and lanes 2.7m 9ft wide are
  appropriate on low-volume roads in rural
  residential areas.
• On multi lane facilities in urban areas sometimes
  narrower inside lanes used to provide wider
  outside lanes for bicycles. 3.0m to 3.3m 10 to
  11ft are common for inside lanes 3.6m to 3.9m
  12 to 13ft for outside lanes.

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• Widths of auxiliary lanes at intersections
  interchanges not less than 3.0m 10ft. Where
  continues two-way left-turn lanes are provided,
  width of 3.0m to 4.8m 10 to 16ft provide
  optimum design.
• Lane shoulder widths on local collector roads
  that carry less than 400 VPD can be designed on
  the same criteria of higher volume roads.

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ShouldersGeneral Characteristics

• A shoulder is the portion of the roadway
  continues with the traveled way that accommodate
  stopped vehicles, emergency use, and lateral
  support of subbase, base and surface course.

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• Width varies from 0.6m 2ft on minor rural roads
  to 3.6m 12ft on major roads.

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• The graded width of shoulder is that measured
  from the edge of the traveled way to intersection
  of the shoulder slope the foreslope planes as
  shown

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• The usable width of shoulder is the actual
  width that can be used when driver makes an
  emergency or parking stop. Where the side slope
  is 1V4H or flatter, the usable width is the
  same as the graded width since the usual
  rounding 1.2 to 1.8m 4 to 6ft wide at the
  shoulder break will not lessen its useful width
  appreciable. See the following figure.

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• Shoulders surfaced either full or partial width.
  Material used in surfacing include gravel, shell,
  crushed rock, mineral or chemical additives,
  bituminous surface treatments, and various forms
  of asphaltic or concrete pavements.

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ShouldersGeneral Characteristics

• The shoulder on minor rural roads with low
  traffic volume serves as structural lateral
  support for the surfacing as an additional
  width for the traveled way.

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Advantages of well-designed shoulders on rural
highways, freeways some types of urban highways
include

• Space is provided away from the traveled way for
  vehicles to stop for emergencies.

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• Space is provided away for occasional stop to
  consult maps or for other reasons.
• Space is provided for maneuvers to avoid
  potential crashes or reduce their severity.

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• Gives a feel of adequate width which contributes
  to driving ease reduced stress.
• Sight distance is improved in cut sections, which
  improving safety.
• Some types of shoulders enhance highway
  aesthetics.

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• Highway capacity is improved because uniform
  speed is encouraged.
• Space is provided for maintenance operations.

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• Lateral clearance is provided for signs
  guardrails.
• Storm water can be discharged farther from the
  traveled way, and seepage adjacent to traveled
  way can be minimized, this may be reduce pavement
  breakup.

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• Structural support is given to the pavement
• Space is provided for pedestrians bicycle use,
  for bus stops, for occasional encroachment of
  vehicles, for mail delivery vehicles, and for
  detouring of traffic during construction

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Width of Shoulders

• A stopped vehicle on shoulder should clear the
  edge of traveled way by at least 0.3m 1ft
  better by 0.6m 2ft. Based on that 3m 10ft
  shoulder width is provided along high-type
  facilities.

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• For lowest-type highway shoulder width will be
  0.6m 2ft, and 1.8 to 2.4m 6 to 8ft width is
  preferable.

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• High-speed highway highways carrying large
  number of trucks have shoulder width at least 3m
  10ft 3.6m 12ft is preferable.
• A min. 1.2m 4ft width used on shoulders
  accommodate pedestrians bicyclists.

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• In case of roadside barriers, walls, or other
  vertical elements are present, graded shoulder
  width should be enough for vertical elements to
  have min. offset of 0.6m 2ft from outer edge of
  the usable shoulder.

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• On low-volume roads, a min. clearance of 1.2m
  4ft should be provided from the traveled way to
  the barrier.
• A shoulder should be continuous and shoulders on
  structures should normally have the same width as
  usable shoulders.

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Shoulder Cross Section

• All shoulders should be sloped to drain away from
  the traveled way on divided highways with a
  depressed median. With raised narrow median, the
  median shoulders may slope in the same direction
  as the traveled way.

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• Bituminous concrete-surfaced shoulders should
  be sloped from 2 to 6, gravel or crushed-rock
  shoulders from 4 to 6 and turf shoulders from 6
  to 8.
• On tangent or long radius curved alignment with
  normal crown turf shoulders, max. algebraic
  difference in the traveled way shoulder grades
  should be from 6 to 7 .

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• Shoulders slopes that drain away from the paved
  surface on outside of well-superelevated sections
  should be designed to avoid too great a
  cross-slope break (see Exhibit 4-2A).

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• In case of great break the shoulder should be
  sloped upward at about the same rate or at lesser
  rate than the superelevated traveled way (see
  dashed line labeled Alternate in Exhibit 4-2A).

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• Where that is not desirable because of drainage
  problems on the paved surface, the grade break at
  the edge of paved surface is limited to
  approximately 8 by flatting the shoulder on the
  outside of the curve (see Exhibit 4-2B).

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• Avoiding too sever grade break can be done by
  using of a continuously rounded shoulder cross
  section on the outside of the superelevated
  traveled way. The shoulder in this case is a
  convex section. (See Exhibit 4-2C).

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• Convex shoulders present more difficulty in
  construction than do planar sections. An
  alternate method to the convex shoulder section
  is multiple breaks in the cross slope.

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• Shoulders designed with a curb or gutter at the
  outer edge of shoulder, this portion of shoulder
  serves as the longitudinal gutter. Cross slope
  should be the same as without curb or gutter
  except the outer portion of shoulder where the
  slope may be increased. Proper delineation should
  distinguish the shoulder from traveled way.

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Shoulder Stability

• Shoulders should be sufficiently stable to
  support occasional vehicle loads in all kinds of
  weather without rutting or skidding.
• All types of shoulders should be constructed
  maintained flush with the traveled way pavement.

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• Unstabilized shoulders generally undergo
  consolidation with time, the elevation of the
  shoulder at the traveled way edge became lower
  than traveled way which adversely affect driver
  controls when driving on shoulder.

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• Advantages of stabilized shoulders include
• 1- Provision of refuge for vehicle
  in
• emergency cases.
• 2- Elimination of rutting drop-off
• adjacent to the edge of the
  traveled way.
• 3- Provision of adequate cross slope
  for
• drainage.
• 4- Reduction of maintenance. and
• 5- Provide lateral support for roadway
  base
• surface course.

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• In some areas, rural highways treated with
  surfacing to the entire width, the surfacing from
  8.4m to 13.2m 28 to 44ft wide for two-lane
  roads. This treatment protect shoulders from
  erosion, and subgrade from moisture penetration
  and enhancing the strength of the pavement

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Shoulder Contrast

• It is desirable that color texture of shoulders
  be different from those of the traveled way.
• Bituminous, crushed stone, gravel, and turf
  shoulders all offer excellent contrast with
  concrete. Satisfactory contrast with bituminous
  pavement is more difficult to achieve.

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• The use of edge lines described in MUTCD(8)
  reduces the need for shoulder contrast. Care
  should be used if the shoulders are to be used by
  bicyclists.

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Turnouts

• It is not always economically practical to
  provide wide shoulders continuously along the
  highways.
• In such cases intermittent sections of shoulders
  or turnouts along the highway can be used.

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• Proper design of turnouts should be consider
  turnout length, including entry exit tapers,
  turnout width, and the location of the turnout
  with respect to horizontal vertical curves
  where sight distance is limited.

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• The entire turnout should be clear to the drivers
  in order to determine whether the turnout is
  available for use.
• If traffic bicycle is expected, turnout should be
  paved so bicyclists may move aside to allow
  faster traffic to pass.

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Thank you