CE562 Lecture 22 Rural Arterials

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CE562 Lecture 22Rural Arterials
Text A Policy on Geometric Design, Rural
Arterials, pp. 443-468
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Rural Arterials

• An important part of the rural highway system.
• Principal rural arterials include the Interstate
  System, other multilane rural highways, and
  two-lane rural highways that connect most urban
  centers.
• Minor rural arterials link the urban centers to
  larger towns.
• Design speed
• Level terrain - 100-120 km/h
• Rolling terrain - 80-100 km/h
• Mountainous terrain - 60-80 km/h
• Sight distance in Exhibit 7-1

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• Rural principal and minor arterial system has the
  following characteristics
• linkage of cities, larger towns, and other major
  traffic generators
• integrated interstate and inter-county system
• internal spacing consistent with population
  intensity
• trip lengths and volumes greater than those
  served by rural collectors and local system

6 - 12 of rural roads
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Volume and LOS

• Design traffic volume
• Traffic volumes are counted or estimated (ADT),
  and then projected to the design year, normally
  20 years.
• The projected ADT are converted to the design
  hourly volume (DHV) which is the estimated 30th
  highest hourly volume.
• The DHV is used to determine the design features.
• Levels of service
• Refer to the Highway Capacity Manual.
• Rural arterial roads should be designed for
  level-of-service B.
• In mountainous areas level-of-service C is
  acceptable.

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Alignments

• A smooth flowing alignment and coordination
  between horizontal and vertical curves are
  desirable.

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Cross Section

• The number of lanes is determined by the volume,
  the capacity, and the desirable level of service.
• Superelevation is governed by the general rules.
  Maximum superelevation is 12, and value 8 is
  recommended if snow or ice is expected.
• Cross slopes range between 1.5-2. Undivided
  roadways are crowned at the center line. Divided
  roadways are crowned at the center lines of
  traveled ways or each traveled way is sloped one
  way.
• Vertical clearance
• New or reconstructed structures - 4.9 m clearance
  over the entire roadway width,
• The clearance of 4.3 m on the existing structure
  may retain.
• An additional allowance for future resurfacing
  should be provided.

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Cross Section
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Cross Section

• Horizontal clearance to obstruction Refer to
  AASHTO Roadside Design Guide.
• Cross section and right-of-way
• Should be wide enough to include all the
  cross-sectional elements
• A uniform right-of-way is convenient
• An additional right-of-way may be needed
• where the side slopes are considerable
• at intersections and junctions
• at at-grade railroad crossings
• for environmental consideration

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Two-Lane Arterials

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Two-Lane ArterialsProvision for Passing

• Safe passing at frequent intervals
• Climbing lanes should be 3.6 m wide with somewhat
  reduced shoulder width (min. 1.2 m).
• Intersections and railway crossings should be
  provided with sufficient sight distance.
• Rules to be followed in providing passing
  sections
• Horizontal and vertical alignment should provide
  as much visibility for passing maneuver as
  possible.
• Passing sections should be considered where
  volume approaches capacity.
• Climbing lane should be considered if trucks on a
  steep grade are the major source of capacity
  reduction.
• If the above measures are not sufficient, then a
  four-lane highway should be considered.

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Two-lane ArterialsUltimate Development to a
Four-Lane Arterial

• In the areas where traffic volumes are expected
  to grow substantially over years the
  construction of the highway is carried in two
  phases
• in the first phase, a two-way two-lane highway is
  constructed as one of the two roadways, then
• in the second phase, when traffic warrants four
  lanes, the second roadway is constructed.
• No two-way highway should be built with the
  intention of widening its traveled way to
  convert into a four-lane highway.
• Alignment, structures, and right-of-way are
  designed appropriately

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Two-lane ArterialsUltimate Development to a
Four-Lane Arterial
Exhibit 7-5
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Undivided Multilane Arterials

• A undivided multilane arterial is allowed where
  the existing highway is reconstructed and severe
  restrictions on the width of the right of way
  apply.
• All design rules presented in the preceding
  sections are applicable to this type of highway,
  except that passing sight distance is not
  essential.

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Divided Multilane Arterials

• All multilane arterials on new locations should
  be divided with at least 1.2 m median
• Advantages over undivided multilane highways
• increased safety,
• driving comfort, and
• highway operation.
• Lane width - 3.6 m is the rule, 3.3 m can be used
  on reconstructed arterials with local
  restrictions and satisfactory safety record.
• Cross slope 1.5-2 for through lanes, up to 3
  on auxiliary lanes.

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Divided Multilane Arterials

• Shoulders
• Outside shoulders should be at least 2.4 m.
  Paving is preferred.
• Inside shoulders should be at least 1.2 m and
  paved.
• 2.4 m inside shoulder is recommended where more
  than two traffic lanes carry traffic in one
  direction.
• Where the median has steep, downhill cross slope,
  a full-width inside shoulder is recommended.

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Divided Multilane Arterials

• Medians
• The narrowest median is 1.2-1.8 m wide. It is
  used in very restricted conditions. It does not
  provide protection for turning vehicles.
• 3.6-9 meter wide medians provided protection for
  left turning vehicles, less than 7.5 m does not
  give protection for crossing cars.
• 9-15 m wide medians require careful analysis.
  They do not provide sufficient storage space for
  long vehicles crossing the arterial, 15 m for
  school buses.
• 15-25 m wide medians are confusing for drivers at
  intersections.
• 18 m and wider medians reduce efficiency of
  traffic signals

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Divided Multilane Arterials

• Superelevated cross sections
• Three methods of attaining superelevated cross
  sections
• The entire traveled way including median is
  superelevated as one plane. Suitable for narrow
  medians.
• The median is held in a horizontal plane, and the
  two roadways are rotated about the median edges.
  Suitable for intermediate-width medians.
• The two roadway are treated separately. Suitable
  for wide medians.

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Divided Multilane ArterialsSuperelevated
Cross-sections
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Divided Multilane ArterialsSuperelevated
Cross-sections
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Divided Multilane ArterialsSuperelevated
Cross-sections
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Divided Multilane ArterialsTypes of Medians
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Divided Multilane ArterialsTypes of Medians
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Divided Multilane Arterials
Exhibit 7-8
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Divided Multilane Arterials
Exhibit 7-9
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Rural Arterials

• Intersections
• High-type intersections and interchanges are
  highly desirable.
• Traffic signals are not recommended in rural
  areas.
• Barrier curbs at island and median edges should
  not be used.

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Rural Arterials

• Access management
• The degree of access control is an important
  consideration. The following rules should be
  observed
• Access points should be situated on the arterial
  both sides directly opposite to reduce the
  crossing time of slow-moving machinery.
• Dual access points serving two properties reduce
  the number of access locations.
• Adequate and uniform spacing of the access points
  eliminates hiding one entering vehicles by
  another on the nearby entry.
• Short sections of rural frontage roads may be
  sometimes needed to provide optimum intersection
  locations.