Design Technical Review Checklist
SPECIAL CONDITIONS
BOS Resolution Conditions |
- Site plans
- Rezone
- Developers agreement
- Subdivisions
- General/area plan amendment
- Developers agreement
- Rezone
- Preliminary plat and petition of exceptions
- Abandonment
- Reversion to acreage
TRAFFIC OPERATIONS AND SAFETY ANALYSIS AND DESIGN
Traffic Impact Analysis |
Site development characteristics (i.e., land use and size) may require a traffic impact statement or traffic impact analysis prepared in accordance with the Mohave County Traffic Impact Analysis Standards.
Traffic Control Devices |
Traffic Signing and Marking Plan included with road improvement plans. Plan(s) shows layout of improved roads and streets with location of all proposed traffic control devices (e.g., STOP signs, street name signs, speed limit signs, markings, etc.).
- Plan presents or references standard detail for all types of traffic control devices (signs and markings) proposed for review of materials, design/configuration, and placement.
- Reference MCPW Traffic Signing and Striping Requirements for policies, guidelines, and detail drawings on sign/post/marking materials, STOP signs, speed limit signs, street name signs, permanent roadway termination barricades, longitudinal pavement markings, and transverse pavement markings.
- Other traffic control device types must comply with standards set forth in the Manual on Uniform Traffic Control Devices, latest edition.
ROAD DESIGN
Exterior / Access Road Improvements |
- Right-of-way in accordance with County standards for designated functional class for all interior and exterior roads and access roads providing site ingress and egress from nearest County or other publicly maintained right-of-way.
- Right-of-way requirements per County standards for road functional class.
- Reference Mohave County Standard Detail No. 60 (rural/non-curb), No. 61 (urban/curb), and No. 62 (inverted crown curb).
- Proposed exterior road improvements.
- Widening, paving, etc. in accordance with County standard section and sitegenerated traffic loading on unimproved versus improved road surface.
- Incorporation of traffic impact analysis recommendations.
- Contemplated half-street improvements provide 12 feet of pavement minimum on undeveloped side of centerline for all road functional classes. Stakeholder written concurrence necessary on improvement requirements, design, and construction if State or other local jurisdiction facility proposed for site access.
Cross Section |
- Reference County standard section for road functional class (curb or non-curb). Border area (distance between edge of travel way and right-of-way boundary) width meets or exceeds 8 feet for local roads and 12 feet for collector and arterial roads.
- Physical obstructions (e.g., headwalls, poles, etc.) or steep cut/fill slopes (steeper than 3H:1V) in right-of-way have shielding or adequate clear zone provided. Proposed sidewalks provide minimum 5-foot width.
Geometric Alignment |
- Specification of design speed for all improved roadways.
- Reference County standards for road functional class.
- For any range of design speeds provided in County standards, consider highest value for level terrain, midpoint value for rolling terrain, and lowest value for mountainous terrain as minimum allowable for design.
- Horizontal curves where normal section maintained.
- Reference AASHTO standards for minimum horizontal curve radius (Section 3.3 of the 2018 Policy on Geometric Design of Highways and Streets aka Green Book.
- Vertical curves.
- Reference AASHTO standards for crest curve k-value (Table 3-36, Page 3172 of the 2018 Green Book) and sag curve k-value (Table 3-37, Page 3-176 of the 2018 Green Book).
- Grade breaks (intersection of two grades without curve) no greater than 0.5%.
- Landing grade of road approach to and within 75 feet of intersecting crossroad.
- Maximum 3% (local road), 2% (collector), and 1% (arterial) grade.
- Curbed streets retain minimum grade of +/- 0.3% for drainage.
- Normal crown on road sections except low-water crossings and (superelevated) horizontal curve sections.
Intersection Design |
- Intersection skew and radius return.
- Reference Table 5-1 in Mohave County Land Division Regulations.
- Adjacent intersections offset minimum of 200 feet centerline to centerline.
- L-intersections include knuckle design as per Figure 5-1 of the Mohave County Land Division Regulations.
- Dead-end street termini treatment.
- Permanent barricade on stub streets with no driveways per Mohave County Uniform Standard Detail 130-1.
- Temporary turnaround or permanent cul-de-sac on streets with driveways in accordance with Section 5.2.H of the Mohave County Land Division Regulations.
- Minor street or driveway approach design provides adequate departure sight distance per AASHTO (reference MCPW Intersection Sight Distance Diagram).
- Horizontal and/or vertical curves in the vicinity of any minor street or driveway approach may limit available sight distance for motorists to safely enter a major, uncontrolled roadway.
- Reference traffic impact analysis recommendations for turn lane requirements.
- Lane taper (e.g., lane merge or lane shift) lengths meet MUTCD requirements. Urban street sections include sidewalk ramps and detectable warning plate per MAG standard detail, latest edition.
New Utility Design and Installation in County ROW |
Where public utility easements do not exist, utilities are placed in the public right-ofway in the following order unless otherwise approved:
- Water on one side of the right-of-way.
- Sewer in the center.
- Gas, then electric and communications on other side of the right-of-way.
- Communication, power and other utility poles are placed one (1) foot from the rightof-way boundary unless otherwise approved.
- Minimum depth of cover for all utilities including solid, liquid, dry or slurry transporting or collection utilities and electric utilities of all voltages and sizes whether single or in a bank, shall be forty-two (42) inches unless required to be deeper by code authority.
- All utilities within right-of-way crossing washes have protection against flood scour. Avoid conflict between utility accessories (e.g., valves and covers) and concrete sidewalks and structures.
Specifications and Details |
- Plans present or reference (e.g., MAG standard detail, latest edition) detail drawing. Plans specify pavement structural section for all improved roads and streets. Plans specify or reference (e.g., MAG standard specifications, latest edition) specifications for all construction materials and methods.
- •Plans cite all engineering technical reports (e.g., drainage, traffic, pavement, geotechnical, etc.) supporting design.
PAVEMENT EVALUATION AND DESIGN
Geotechnical Report |
- Pavement structural design method and input data meets Mohave County Pavement Structural Design Standards.
- Traffic load (ESALs) forecast in accordance with County standard procedure.
- Published data or field tests on existing native material support subgrade (roadbed) strength/stiffness input into pavement design (expressed as resilient modulus, MR).
Road Surface Evaluation |
- Site-generated traffic loading determines need for mitigating road surface improvement and surface treatment type.
Road surface improvement considered, on basis of engineering calculations, for any land use generating truck, bus, or significant recreational vehicle traffic as well as any site development requiring a traffic impact analysis.
- Road surface treatment types include:
- Non-structural asphalt surface (chip seal) over stabilized roadbed.
- Asphalt concrete pavement structural section.
- Asphalt concrete overlay to mitigate long-term effects of site-generated traffic loading on existing paved road.
Minimum Pavement Structural Section |
- Reference recommended structural section specified in geotechnical report. Practical minimum pavement structural sections when applying design standards:
- 2” AC over 6” ABC for local or residential collector roadways on average (sandy – SC to SW classification) to good (gravelly – GC to GW classification) subgrade soils.
- 2” AC over 8” ABC for local or residential collector roadways on poor (silty/clayey – CL/ML classification) subgrade soils.
- 2” AC over 6” ABC for collector roadways on good subgrade soils.
- 2” AC over 8” ABC for collector roadways on average subgrade soils.
- 3” AC over 8” ABC for collector roadways on poor subgrade soils.
- 3” AC over 6” ABC for arterial roadways on good subgrade soils.
- 3” AC over 8” ABC for arterial roadways on average subgrade soils.
- 4” AC over 8” ABC for arterial roadways on poor subgrade soils.
Site Access Points |
- Site plan or improvement plan references Mohave County Standard Detail 250A (asphalt) or 250C (concrete) for any driveway construction. Portland cement concrete aprons considered in context of requirements set forth in Mohave County Pavement Structural Design Standards.
DRAINAGE ANALYSIS AND DESIGN
Apply Requirements and Guidelines of the Mohave County Drainage Design Manual (DDM)
Hydrology |
- Drainage report presents clear summary of flows and within existing and proposed rights of way both adjacent and within the project.
Roadway Drainage |
- Reference Chapter 9 of the DDM.
- DDM Section 9.4.2 – engineering calculations demonstrate road/street section capacity to convey design flows (longitudinal drainage).
- Manning’s n-value of 0.015 for paved roadways.
- Normal crown only for County Highway, arterial, and all-weather roads.
- Arterial and all-weather (curbed) streets – one 12-foot dry lane maintained in each direction during 10-year peak discharge.
- Local and collector (curbed) streets – 10-year peak discharge depth does not exceed curb height.
- All streets – 100-year flow depth between curbs no greater than 8 inches.
- All streets – velocity of flow no greater than 8 fps.
- Non-curbed roadways – 100-year peak discharge contained in channel with maximum depth not to exceed outside shoulder hinge point.
- DDM Chapter 12 – engineering calculations demonstrate adequate capacity and stability (lining) of roadside ditches for flow conveyance.
Culverts and Low Water Crossings |
- Reference Chapter 11 of the DDM. Select minimum culvert design parameters:
- 24-inch pipe diameter for all roadway cross drains; 18-inch pipe diameter for driveway culverts in County right-of-way.
- Material consisting of corrugated steel pipe, rubber gasket reinforced concrete pipe, or reinforced concrete box.
- Cover of fill at least 18 inches.
- Engineering calculations demonstrate culvert capacity under design flow conditions:
- Outlet velocity (maximum 15 fps).
- Reference citation and calculations for structures and materials (e.g., riprap) providing outlet protection.
- Design plans specify inlet/outlet elevations, direction of flow, pipe slope, pipe material/gauge and all dimensions labeled, cover depth, materials and structures providing erosion protection and installation details, and headwall/wingwall type, dimensions, and detail reference as applicable
- Inlet and outlet elevation consistent with natural wash/stream bottom.
- Multiple pipes to disperse flow across wide channels but single pipe preferred for concentrated areas of flow.
- Concrete headwalls provided for culverts 48 inches in diameter or greater.
- Flared end sections or headwalls provided for pipe sizes less than 48 inches
- •Drainage system elements (e.g., pipe, headwalls, riprap, etc.) and backwater effects contained wholly within existing right-of-way or existing drainage easement. DDM Section 11.4.3 – design storm for roadway cross drainage.
- 25-year peak discharge for two-lane County Highway and arterial roads.
- 10-year peak discharge for local and collector roads.
- Maximum 12-inch roadway overtopping depth for 100-year peak discharge.
- DDM Section 11.4.7 – low water crossings
- Hardened surface at crossing and extending to flow boundaries for unpaved roadways or engineering calculations supporting unpaved crossing.
- Erosion protection (e.g., concrete cutoff walls, asphalt turndowns, etc.) at upstream and downstream ends of crossing.
- Geometric design of low water crossing approaches in accordance with AASHTO standards for sag vertical curves and grade breaks.
- Design detail or reference (e.g., MAG standard detail) for elements of low water crossing system.