Transcript 2008 Cote - AASHTO - Subcommittee on Design

AASHTO Subcommittee on Design
Reducing Engineering Standards:
Good or Bad?
July 14, 2008
Marc Cote, P.E.
(302) 760-2266
E-Mail: [email protected]
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Reducing Engineering Standards: Good or Bad?
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Delaware is probably somewhat unique in that
91% of the roads in Delaware are state
maintained.
Access to individual homes and streets in small
subdivisions all have to be approved by my
office in addition to the large subdivisions and
commercial developments.
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Reducing Engineering Standards: Good or Bad?
Dedicating Streets to
Public Use and State
Maintenance
Dedicating Streets to
Public Use without
State Maintenance
Private Streets
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Built in accordance with DelDOT’s
Subdivision Manual, Standard
Construction Details, and Standards and
Specifications.
Built in accordance with DelDOT’s
Subdivision Manual, Standard
Construction Details, and Standards and
Specifications.
but privately maintained.
Not subject to our regulations, But
DelDOT still suggests developers
build to our standard.
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Reducing Engineering Standards: Good or Bad?
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Subdivision Manual requires that subdivisions
generating more than 400 vpd or 50 vph in the
peak hour conduct a traffic impact study.
In addition to offsite improvements outlined in
the TIS, the developer is required to improve his
road frontage to meet the standards for the
functional classification of the road.
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Reducing Engineering Standards: Good or Bad?
Department of Transportation
Functional Classification Map
Minimum Road Section
Freeway or Expressway
Principal Arterial
12’ Lanes
10’ Shoulders
Minor Arterial
Major or Minor Collector
12’ Lanes
8’ Shoulders
Local Road or Street (All roads other than
Subdivision Streets not shown)
11’ Lanes
5’ Shoulders
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Reducing Engineering Standards: Good or Bad?
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A completed design checklist must be filled out noting
that all of the required information has been included on
the plans, the design criteria is met, and is in accordance
with DelDOT’s Standard Construction Details and Standards
and Specifications.
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Preliminary entrance plans shall include but are not
limited to the following: traffic generation diagram,
adjacent entrances, functional classification of adjacent
roadway, layout of required auxiliary lanes, sight distance
calculations.
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Reducing Engineering Standards: Good or Bad?
Developers are making substantial improvements to our
road system and there are factors to consider:
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Right of way impacts – local opposition
Cost of improvements vs. the cost of housing
Improved roads over existing conditions
If improvements are too extensive, development
doesn’t happen, improvement doesn’t happen
Support for economic development if it is planned
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Reducing Engineering Standards: Good or Bad?
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Want the best product for our citizens at the
best cost
Need solution that works, doesn’t have to be the
perfect solution
Improve the existing condition
Don’t compromise on safety
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Reducing Engineering Standards: Good or Bad?
Thomas Jefferson once said that:
“The first obligation of government is to
provide for the safety of the people.”
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Reducing Engineering Standards: Good or Bad?
Areas for consideration
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Design speed
Lane width
Shoulder width
Stopping sight distance on vertical and horizontal curves
Vertical alignment
Minimum and maximum grades
Cross slopes
Superelevation rate
Horizontal clearance
Vertical clearance
Bridge width
Structural capacity
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Reducing Engineering Standards: Good or Bad?
Standards to be maintained:
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Design speed
Stopping sight distance on vertical and horizontal curves
Vertical alignment
Minimum and maximum grades
Vertical clearance
Bridge width
Structural capacity
Lane width
Standards considered for reduction:
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Shoulder width
Cross slopes
Superelevation rate
Horizontal clearance
Bridge width
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Reducing Engineering Standards: Good or Bad?
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Development Related Improvements Requiring
New Rights-of-Way
Gives DelDOT ability to acquire right-of-way for projects done
by others (developers) to make improvements for the public’s
benefit in the interest of safety.
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Reducing Engineering Standards: Good or Bad?
Design Element
DelDOT Std.
Subdivision
DelDOT Mobility Friendly Design
Guideline
Right-of –Way
Width
60 feet
53-60’, Includes two 10’ lanes, 1’ curb
offset, 6”curb on each side, one 7’
parking lane, and 10’ planting strip and
5’ sidewalk on each side
Pavement Width
32 feet
22’-29’, max. is two 10’ lanes, 1’ curb
offset and 7’ parking lane
Travel Lane Width
11 feet
10 feet
Parking Lane Width None specified
7 feet
Horz. Curve Radius 300 feet
167’ for unsigned curve, 90’ for signed
curve used for traffic calming
Design Speed
25 mph
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30 mph
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Reducing Engineering Standards: Good or Bad?
Design Element
DelDOT Std.
Subdivision
DelDOT Mobility Friendly
Design Guideline
Sidewalk warrants
Not required
Required on both sides of
street
Sidewalk widths
None specified
5 feet minimum
Planting Buffer/Utility None specified
Strip
10 feet minimum
Alleys
Alleys when lot width is <50’.
20’ r/w for 12’ lane
Corner radius
None specified
Local to local 25’
Maximum Cul-de-sac
Length
500-100 feet
depending on density
of development
300 feet
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Reducing Engineering Standards: Good or Bad?
Design Element
DelDOT Std.
Subdivision
DelDOT Mobility Friendly
Design Guideline
Block Length
None specified
Between 200-500’. >500
requires a midblock crossing
Intersection Design
T-Intersection at 90
degrees
Roundabouts and two-way
stops are preferred to signals
Minimum Driveway 200 feet, narrower lots
Spacing
call for shared driveways
50’, narrower lots require alleys
or shared driveways
Minimum Driveway 12 feet standard,
Width
8’-16’ depending on setback of
garage
Tree/Obstacle
Clearance
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Clear zone of 2’ where a Minimum of 3’ from back of
barrier curb is provided curb to tree
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Background:
International Fire Code (IFC) states “fire access road shall have an
unobstructed width of at least 20 feet.”
DelDOT Standards and Regulations for Subdivision Streets and Highway Access
Issue:
“Are existing 22’ wide streets too narrow
to accommodate emergency vehicles?”
“Should a 24’ section be adopted by DelDOT?”
Wide Streets
• Can encourage speeding
• Increase impervious area
• May reduce the livability of a residential street
• Undermine perceived pedestrian/cyclist safety
• Inconsistent with residential traffic patterns
• Higher maintenance costs
• Community requests for traffic calming measures
“Encourages High Speeds”
Narrow Streets
• May inhibit emergency response
• Can constrain snow plowing operations
• May discourage free flowing traffic
• Reduce vehicular speed
• Can improve pedestrian and cyclist safety
• Reduce maintenance
• Less impervious area
“What Fire Departments Fear”
Source: Arlington County, VA residential streets presentation
Subdivision Street
Type 1-With Curb
(Emergency Vehicle and Standard Vehicle)
Sidewalk
5’
Grass Strip
3’
Curb
2’
Gutter Pan 11”
Fire Engine
Lane
11’
9.5’ (mirror to mirror)
Pickup Truck
Lane
11’
6.6’
Gutter Pan 11”
Curb
2’
Grass Strip 3’
Sidewalk
5’
Existing DelDOT Standards
Graphics by DelDOT Division of Planning
Source: DelDOT Standards and Regulations for Subdivision Streets and State Highway Access
Subdivision Street
Type 1-With Curb w/ 11’ Lanes
Subdivision Street
Type 1-With Curb w/ 12’ Lanes
(Emergency Vehicle and Standard Vehicle)
(Emergency Vehicle and Standard Vehicle)
Top View
Top View
Existing DelDOT Standards
w/parking both sides of street
Graphics by DelDOT Division of Planning
Top View
Proposed DelDOT Standards
w/parking both sides of street
Subdivision Street
Type 1-With Curb w/ 11’ Lanes
Subdivision Street
Type 1-With Curb w/ 12’ Lanes
(Emergency Vehicle and Standard Vehicle)
(Emergency Vehicle and Standard Vehicle)
Front View
Existing DelDOT Standards
w/parking both sides of street
Graphics by DelDOT Division of Planning
Front View
Proposed DelDOT Standards
w/parking both sides of street
Conclusion:
The adoption of new 12’ lane requirements for subdivision streets that fall under the guidelines of the DelDOT Standards and
Regulations for Subdivision Streets and Highway Access would enhance the ability of emergency vehicles to safely reach their intended
destinations
Sidewalk
5’
Grass Strip
3’
Curb
2’
Gutter Pan 11”
Lane
12’
Lane
12’
Gutter Pan 11”
Curb
2’
Grass Strip 3’
Sidewalk
5’
Proposed DelDOT Standards
Graphics by DelDOT Division of Planning
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