22 Cross Sections
Download
Report
Transcript 22 Cross Sections
Cross Sections
CE 453 Lecture 22
Iowa DOT Design Manual Chapter 3
1
See also Iowa DOT Standard Plans
2
Objectives
1.
Identify cross section components and design
criteria
See:
http://www.fhwa.dot.gov/environment/flex/ch06.htm
(Chapter 6 from FHWA’s Flexibility in Highway
Design)
3
Cross Section Elements
1.
Roadway
2.
Median
3.
Roadside
Roadway Components
1.
Travel Lanes
2.
Shoulders
4
Source:http://www.fhwa.dot.gov/environment/flex/ch06.htm
Cross Section Elements
1.
Roadway
2.
Median
3.
Border
Roadway Components
1.
Travel Lanes
2.
Auxiliary Lanes
5
Source:http://www.fhwa.dot.gov/environment/flex/ch06.htm
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
Flexibility in Highway Design Chapter 6
6
Considerations for Design of
Cross-Section
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)
7
Travel Lanes
Function: guidance to drivers and vehicle support
Pavement types:
high (modern standards),
intermediate (surface treatments), and
low (unpaved)
8
Travel Lanes
Selection Criteria:
Traffic volume and composition
Soil characteristics
Past performance in area
Availability of materials
Energy conservation
Initial cost
Maintenance cost
Overall life-cycle cost
9
Cross Slope
Slope perpendicular to flow of traffic on tangent
section
Rural – normal crown – uniform slope from
center to edge of pavement (cross slope break
typically at centerline)
Urban – parabolic shape (gutter capacity)
10
Cross Slope
•
•
•
Rate of Cross Slope = f(drainage, steering,
and rollover or cross slope break)
Drivers cross the crown line during passing
maneuvers
•
Difficult to negotiate steep slopes
AASHTO Recommends
•
High 1.5 to 2% (0.015 ft/ft m/m)
•
Intermediate 1.5 to 3%
•
Low 2 to 6%
11
12
Urban Cross-Sections
13
Urban Cross-Sections
14
HMA Cross-Sections
15
Drainage Considerations
16
Drainage Considerations
17
Roadway Component – Travel
Lane
Lane Width Considerations
•
•
•
•
•
•
What is the impact of weather on
cross slope design?
Safety: Allow steering adjustment
and lateral clearance
Pavement edge crumbling
(deterioration) less with wide lane
Cost/Benefit (depends on traffic)
Bicycle Use
18
Lane Width
Limited by physical
dimension of vehicles
12 ft desirable
11 ft acceptable in urban
areas with restrictions
10 ft okay for low
speed/urban roadways
9 ft – okay low volume rural
and residential roadways
14 ft – shared outside lane
with bike
TWLTL 10 – 16 ft (3.0 –
4.8m)
Auxiliary 10 ft. (3.0 m) or
more
19
Shoulders
•
•
•
•
•
•
•
Functions:
Lateral Support
Avoidance Space
Emergency Stop
Ped/Bike Use
Turning/Passing at
Intersections
Mail Delivery, Buses,
etc.
Flexibility in Highway Design Chapter 6
20
Shoulders
Should be flush with roadway surface
Sloped to drain away from traveled
way
Should be stable enough to support
vehicles in all kinds of weather w/out
rutting
Should be visibly different from
traveled way
21
Shoulder geometry
Paved/Unpaved (earth, turf, gravel)
Graded and usable width depends on
foreslope and rounding
Consider function, safety, and capacity
impacts
Slope
2 to 6% (paved)
4 to 6% (gravel)
8% (turf)
Min. 2% + lane slope
Max crossover 8%]
Width 0.6 – 3.6 m (2 – 12 ft)
22
Source: A Policy on Geometric
Design of Highways and
Streets (The Green Book).
Washington, DC. American
Association of State23
Highway
and Transportation Officials,
2001 4th Ed.
Curbs
Control access
Control drainage
Type used varies with location and
design speed
24
Curbs
25
Curbs
26
Iowa’s Roadway-Related
Fatal Crashes
52% of Iowa’s fatalities are
related to Lane Departure
39% of Iowa’s fatal crashes
are single-vehicle
Run-Off-the-Road (ROR)
crashes
27
Safety Investment Strategy
Candidate Safety Projects
Paved shoulders
Milled-in shoulder rumble strips
2-lane shoulder widening
High severity crash intersections
High severity crash 2-lane roads
High crash curves
Expressway intersections
Centerline rumble strips
Cross-median head-on crashes
28
4 Foot Paved Shoulder
US 63
29
Milled Shoulder Rumble Strips
30
Median Function
►
►
►
►
►
►
►
Separate
opposing traffic
Drainage
Aesthetics
Space for future
lanes
Recovery
Access control
Minimize
headlight glare
Flexibility in Highway Design Chapter 6
31
Median Types/Geometry
Depressed (rural arterials,
6:1 preferred, 4:1 min)
Raised (urban arterials)
Flush (urban/sub. some
rural)
Double yellow to limit
access
TWLTL
Width is determined by
Function
Safety
Need for independent
design
Flexibility in Highway Design Chapter 6
32
Iowa DOT Urban Design Aids
See http://www.dot.state.ia.us/local_systems
New Construction
33
Iowa DOT Urban 3R* Guidelines
See http://www.dot.state.ia.us/local_systems
34
*Resurfacing, Restoration, Rehabilitation
Rural Design - New Construction
35