Attachment_0006_-_Highway_Design_Memo.pdf
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- Attached to
- CONANT BANK STABILIZATION
- Solicitation number
- 140L0626R0011
About this file
This is a Highway Design Memorandum dated May 9, 2021, establishing parking area design standards for a Conant access road/parking lot off Conant Valley Loop Road.
The memorandum specifies proposed design standards for the parking area, including a design vehicle of car and boat trailer (P/B) with an estimated Average Daily Traffic (ADT) of 100, though the adjacent Conant Valley Loop Road is estimated at 400 ADT. Design specifications include a 10 mph design speed, 10-foot minimum travel way width to accommodate one lane of traffic, 0-foot shoulder width, 23.8-foot minimum horizontal radius based on AASHTO Green Book standards, 2% crown and superelevation for drainage, and a K Value of 3 for minimum vertical curves. A 6-10 foot minimum clear zone is specified per Roadside Design Guide standards for low volume and low speed barriers. The memorandum addresses proposed design features including enhancement of the kayak parking lot area, wooden fencing, ABA/ADA accommodations to maintain restroom access, and seeding and revegetation requirements. Safety considerations include potential minor pedestrian warning signage within crosswalks, minor parking lot markings (typically 4 inches), potential No Parking and parking signage, and minor crossing treatments within parking lots. The temporary traffic control section indicates the kayak parking lot will be closed during construction with minor flagging and channelizing devices needed, while the main parking lot remains open. A constructability concern is noted regarding extreme Snake River water fluctuations beyond normal levels. Overall risk is assessed as very low with minimal cost impacts anticipated for parking lot signage and markings.
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Text version
MAY 9, 2021
Highway Design Memorandum
Parking Area Design Standards
Description Response Comment Road Name and Route ID Number:
PROPOSED DESIGN STANDARDS
Design Vehicle Car and Boat Trailer (P/B)
Design ADT
Estimated ADT for Conant access road/parking lot off Conant Valley
Loop Rd. (which is estimated at 400 ADT). See attached assumptions/calculations.
Design Speed 10 mph
Travel Way Width 10’ min. To accommodate one lane of traffic
Shoulder Width 0’ Limit width impact Shoulder Type N/A
Min. Horiz. Radius
23.8’
Minimum turning radius for an AASHTO Green Book Passenger
Car and Boat trailer (P/B) Crown 2% For drainage
Superelevation 2% For drainage Min. Vertical Curve (K Value) 3 AASHTO Green Book
Maximum Grade N/A
Min. Stopping Sight Distance N/A Horiz. Clearance to Structure N/A No structures within area
Min. Clear Zone 6-10’ Roadside Design Guide, FLH Low Volume and Low Speed Barrier
Guide. Guidance is to get what’s practical. Likely N/A for parking lot.
Foreslope -- Refer to Geotech recommendations
Backslope -- Refer to Geotech recommendations
Ditch Type (V-ditch or trapezoidal) and Width -- Refer to Hydraulic recommendations
Ditch Depth -- Refer to Hydraulic recommendations
Safety Edge
No
Likely N/A for parking lot and no roadway departure crash concerns there. If any scope is added to adjacent road, Safety Edge is standard practice there.
PROPOSED DESIGN FEATURES
Realignment or grade change required? No Existing parking to remain;
additional will require full design
Will there be any widening off the existing bench? No
Will profile be raised due to proposed pavement structural section?
Additional work required at intersections or driveways?
No known safety/operational concerns or reasons to modify existing access if final scope includes this access point for any reason.
Exist/Proposed Parking/
Pullouts/Vistas? Yes Enhancing the Kayak parking lot area
Exist/Proposed Pedestrian and/or
Bicycle Facilities?
No known special pedestrian/bicyclist facility needs within parking lot or Conant Valley
Loop Rd.
Exist/Proposed Roadside Features
(gates, shelters, etc.) Yes Follow MUTCD requirements for gates if they are included.
Exist/Proposed Fencing? Yes Wooden fence ABA/ADA Accommodations? Yes Maintain access to Restrooms
Seeding and Revegetation Yes Refer to Environment for seeding requirements
Special Features (Railroad Crossings, etc.) No
Architectural or decorative aspects to be incorporated (stone masonry, stone curb, rock facing, etc.)
HIGHWAY SAFETY CONSIDERATIONS
Overall Proven Safety
Countermeasures
Yes
Basic pedestrian accommodations (e.g. crosswalks, signage) will be considered within any parking lot modifications. No other major countermeasures expected.
Typical Section Optimization? No Basic parking lot/access design sufficient.
Roadway Edge Drop-off Concerns?
As discussed above, no existing concerns and SafetyEdge would be used if there is any work on adjacent roads.
Superelevation corrections? No N/A Additional work required to address Sight Distance Issues? No No known concerns at access point w/ Conant Valley Loop Rd.
Clear Zone and Roadside Hazards
No known concerns within parking lot or access location.
Unlikely to be in scope.
NPS – Traffic Barrier Inventory recommended improvements? No N/A
Existing/Proposed Barrier?
No known existing barrier.
It is unlikely to need or be cost effective.
Barrier Type/Typical Section No N/A Aesthetic barrier preference? No Unlikely to need barrier.
Proposed signing (regulatory, warning) and supports?
Potential for some minor warning signage for pedestrians within crosswalk. Likely some No Parking/Parking signage if parking lot modifications are needed.
Proposed signing (guide, special sign needs, etc.)
Unknown at this time if there are any existing guide signs near the site or along adjacent roads/highways. Unlikely to add unless advised by BLM.
Proposed Pavement Markings
(Longitudinal) Yes Potential for minor parking lot markings, typically 4”.
Existing Passing Zone Concerns? No N/A Proposed Pavement Markings
(Others) Yes Typical parking lot markings may be in scope.
Existing/Proposed permanent traffic control (special signs, markings, rumble strips, etc.) Roadside
Delineators
Likely N/A per scope.
Centerline, edge line/shoulder, transverse rumble strips? No N/A
Multimodal Crossing Treatments Yes Minor crossing treatments within parking lots may be in scope.
Speed Concerns? No No known concerns.
TEMPORARY TRAFFIC CONTROL
Anticipated Method(s) of Temporary Traffic Control
Kayak parking lot will be closed.
The need for minor flagging & channelizing devices will be needed to help assist in getting trucks out of the area.
Will alternate routes
(detours/diversions) be provided for during construction?
Temporary traffic control/traffic restrictions during construction? Yes Kayak parking lot will be closed.
Can the road be closed for construction?
Kayak parking lot is anticipated to be closed for the duration of
Construction for staging and work.
The main/large parking lot will remain open for public use.
Risks for this function Comment
Potential Major Impacts to Cost or Schedule
No known safety or operational concerns, very low risk. Minor cost for any parking lot signage/markings that may be proposed.
Constructability Concerns Extreme Snake River water fluctuations beyond normal
File details come from the government source that posted it. Updated .