Cross-section elements.

1. Cross Section Elements
• Slope, Shoulder, Median, Curbs
• Lane width
• Parking lane
• Diversity of freeway cross-sections
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2. • two lane rural highway cross-section design
features and terms
Source: Flexibility in highway design, FHWA 2
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3. The element includes:
- right-of way
- Roadside
- Traveled Way A and B
- Right and Left Shoulders for both traveled ways
- Median
- Traffic Lanes
- Fence
- Side Slope (fill)
- Side Slope (cut)
- Curbed Section
- Drainage Channel
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4. Urban highway cross-section design features and terms
The element includes:
- right-of way
- Border
- Roadway
- Sidewalk, residential
- Traffic lanes
- Traveled way
- Sidewalk, commercial
- Median
- Parking lane
- Left-turn lane
- Curb offset
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Considerations for Design of Cross-Section
 Volume and composition (percent trucks, buses, and
recreational vehicles) of the vehicular traffic
 likelihood of bicyclists and pedestrians using the route
 Climatic conditions (storage space for plowed snow,
amount of rain)
 Presence of natural or human-made obstructions
adjacent to the roadway (rock cliffs, etc)
 Type and intensity of development along the facility
 Safety of the users (speed of traffic)
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6. Typical cross-section
- Normal crown
Source: Green Book 6
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7. Typical cross-section
- superelevation
Source: Green Book 7
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8. Slopes
Source: Green Book 8
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9. 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
Shoulders
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10. Shoulder:
Source: Green Book 10
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11. Shoulder can be surfaced by using:
lawn, gravel, crushed rock, mineral or chemical additives, bituminous
treatment, asphalt or concrete pavements.
Functions of shoulders on low-type vs. high-type roads
Width of shoulders
Low-type roads -- minimum 0.6 m, recommended 1.8-2.4 m,
Shoulder usable by bicycles -- minimum 1.2 m,
High-type roads -- minimum 3.0 m, recommended 3.6 m.
Clearance to roadside elements (barriers, walls, signs, etc.)
High-type roads -- 0.6 m to the edge of the usable shoulder,
Low-type roads -- minimum 1.2 m to the edge of the traveled way.
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13. Medians
Medians are used on arterials with four or more lanes.
Function of medians
 separate opposing traffic
 recovery area for out-of-control vehicles
 stopping area
 storage of left-turning and U-turning vehicles
 minimize headlight glare
 provision for future lanes
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14. Medians
Types of medians
 depressed - on freeways with slope 1:6 (1:4), drainage inlets,
safety grates
 raised - relatively narrow on arterial streets
 flush - crowned or slightly depressed on all types of urban
arterials
 convenient to convert into two-way left-turn lanes (3.0-4.8 m wide)
Width of medians ranges from 1.2 to 24 m.
Full separation of traveled ways is achieved when the median is at least
12 m wide.
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15. Road Side Barriers:
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16. Median Barriers:
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18. Median:
Source: Green Book 18
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19. Functions of curbs
• drainage control
• roadway edge delineation
• right-of-way reduction
• delineation of pedestrian walkways
• reduction in maintenance operation
Types of curbs:
Vertical curbs -- discourage vehicles from leaving the roadway, not
desirable on high-speed highways, desirable on urban roads, and
along long walls, tunnels to protect safety walks.
Sloping curbs -- vehicle can cross them readily when required, used
at median edges, to outline channelizing islands, at the outer edge
of the shoulder.
Curbs
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20. Exhibit 4-6
Sloping Curbs
Vertical Curb
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21. • Lane width strongly influences traffic safety and comfort
• Lane width range is 2.7-3.6 m with the 3.6 m lane
predominant on high-type highways
• Two-lane two-way highways with the 3.6 lane provide safe
clearance between large commercial vehicles
Circumstances that justify narrower lanes
• Urban areas with land restrictions -- 3.3 m
• Low speed facilities -- 3.0 m
• Auxiliary lanes at intersections -- 3.0 m
• Low-volume roads in rural and residential areas -- 2.7 m
• Continuous two-way left-turn lanes -- 3.0-4.8 m
Lane Widths
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22. On-Street Parking
 Curb-parking should be prohibited on freeways and
major arterials
 Recommended on minor arterials, collectors and
local roads located in developed areas
 Parallel parking preferred over angle parking
(performance of through lanes and safety)
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23. On-Street Parking Design Rules
Arterials
 Minimum width of parking lane is 2.4 m (recommended width is 3.0-
3.6),
 Minimum width of parking lane with adjacent bicycle route is 3.0-
3.6 m.
Urban collectors
 Minimum width of parking lane is 2.4 m (recommended width is 3.0-
3.6),
 Minimum width of parking lane with adjacent bicycle route is 3.0-
3.6 m,
 In residential areas, 10.8 m two-lane two-way traveled ways are
sufficient (2.1 m parking lanes and 3.3 m through lanes).
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24. Local streets
 In residential areas 7.8 m traveled ways are sufficient for two-way
traffic.
 Parking lanes should end 6.0 m in advance of the intersections.
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25. Parking lane:
Source: Green Book 25
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26. • control access to the
arterial
• serve adjoining property
• maintain circulation of
traffic when the arterial
is blocked
• separate local traffic
from the through traffic
• collects local traffic
Frontage Roads
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27. Source: Green Book 27
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28. Frontage road
Source: Green Book 28
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29. Cross-section with retaining wall
Source: Green Book 29
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30. Depressed freeway
Source: Green Book
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31. Elevated freeway-with ramp
Source: Green Book 31
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32. Elevated freeway on embankment
Source: Green Book 32
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See http://www.dot.state.ia.us/local_systems
Urban Design - New Construction
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Rural Design - New Construction
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