Transportation Engineering

440.1 Pipes and Culverts

440.1.1 Pipe Material

1. The pipe material permitted for use within the public right-of-way is as follows:
   1. Concrete, non-reinforced, ASTM C-14, Class 3 (maximum size: 18" inside diameter).
   2. Concrete, reinforced, ASTM C-76, Class III (minimum).
   3. Ductile Iron, cement lined, class 50 wall thickness for pipes sizes up to 12-inch; class 51 wall thickness for 14-inch pipe sizes and larger.
   4. High Density Polyethylene Pipe (HDPE) smooth interior, corrugated exterior HDPE sewer pipe and associated HDPE fittings shall conform to AASHTO M294, AASHTO 252, ASTM 405 or ASTM 667.
   5. High Performance Polypropylene (HP3) smooth interior, corrugated exterior HP3 sewer pipe (12" to 30") as per ASTM F2736 and smooth interior and smooth exterior HP3 sewer pipe encasing a corrugated layer (30" to 60") as per ASTM 2764. Associated HP3 fittings shall conform to ASTM D3212.
   6. PVC C900 or PVC 3034 with a minimum 3' of cover can be used for storm runs between manholes or between catch basins.  No PVC pipe is allowed as culvert pipe.
2. The minimum life span of pipe used within the right-of-way shall be 70 years.
3. The Engineer shall provide to the County certification with respect to alternative pipe materials, if allowed by the County.  Certification shall state that upon inspection the installation, cover, and backfill compaction are in conformance with the manufacturer's recommendations for installation and the product and installation procedures are sufficient for HS 20 loading.
4. The specific strength and depth of cover for pipe shall be based on the manufacturer's recommendations for the loading requirements.  Private storm drainage materials shall conform to the Oregon State Plumbing Specialty Code and requirements of the local plumbing official.  If private storm drainage materials and applications are not listed in the plumbing code, Engineering will determine the requirements. 

440.1.2 Pipe Size

1. Publicly maintained storm drains shall be a minimum of 12-inch inside diameter. 
2. Pipes shall be sized to convey the 25 year design storm flow within the County right-of-way to accommodate the existing and subject development at a minimum velocity of 3 ft/sec when flowing full.
3. The method of analysis shall be based on Manning's equation as follows:

Q = 1.49/n x A x R0.67 x S0.5
Where: Q = discharge (cfs)
n = Manning's roughness coefficient (see Table 4-2)
A = pipe area (ft2)
R = hydraulic radius (ft)
S = slope of the energy grade line (ft/ft)

Table 4-2

440.1.3 Pipe Slope

All pipes and culverts shall be designed to operate under gravity flow and be sloped to provide a minimum velocity of 3 ft/sec when flowing full.  This may be reduced to 2.5 ft/sec with approval of Engineering.

440.1.4 Pipe Cover

1. Pipe trenching, bedding, and backfill shall conform to Standard Drawings U200 through U270B.
2. The required minimum cover for pipe for all public storm drains shall be 36 inches or shall be as specified by the manufacturer, whichever is greater, as measured from the top of pipe to the finished roadway or ground grade.
3. Reduced depth of cover may be considered by the County due to topographical constraints.  Appropriate pipe material shall be used to ensure the pipe's capacity to withstand HS 20 loading.
4. Fill heights over pipes shall meet manufacturer's recommendations and are subject to the approval of Engineering.

440.1.5 Pipe Alignment and Connections

1. Pipes shall be laid to a straight line and grade with no curves, bends, or deflections in any direction.
2. All changes in pipe slope, material or alignment shall require a manhole or catch basin. 
3. Catch basin locations shall have a maximum spacing of 500 feet from the high point in the road provided that the catch basins drain in opposite directions and there is not a pipe connected for that distance.  Typical in line spacing shall be 250 feet.
4. Extensions of pipes and culverts shall be in the same line, grade, and inside diameter as the existing pipe.  Extensions shall be of like material and with a connection approved by Engineering.

440.1.6 Pipe Inspection Including Televiewing

1. All pipes shall be lamped, mandreled and video recorded. 
2. Upon completion of all storm drain construction, the storm line shall be inspected by televiewing.  The applicant shall coordinate the video recording inspection with Engineering.
3. If deficiencies are revealed by the inspection, the corrections shall be made and the televiewing shall be repeated until all work is accepted.  The cost of the televiewing shall be borne by the Applicant.

440.2 Catch Basins and Inlets

440.2.1 Catch Basin Type

Standard GB-2 catch basins shall be used in locations where vertical curb is used.  Standard catch basins shall conform to WES Standard Drawings.  Substandard catch basins shall be upgraded when connections are proposed.

440.2.2 Catch Basin and Inlet Spacing and Location

1. The spacing of catch basins or curb inlets shall be as required to limit gutter flow to less than 4 inches depth and limit water depth in a travel lane to less than 1 inch during the 10 year storm event.  The maximum length of pipe between catch basins and inlets shall be 250 feet.
2. Catch basins or inlets shall be provided just prior to curb returns where the centerline gradient is greater than 5% or where the next upstream inlet is 100 feet away or farther.  Catch basins also are required within 500 feet of the high point of the roadway profile.

440.2.3 Catch Basin and Inlet Connections

All catch basin laterals shall be a minimum 12 inches inside diameter.  Catch basin laterals shall connect to the receiving main with a manhole or another catch basin or curb inlet.  Blind tee connections are not allowed. 

440.2.4 Lateral Connections

Lateral Connections to newly installed mainlines shall be factory fittings.  "Inserta-Tee" fittings are only allowed on existing pipe when the lateral diameter is at least two nominal sizes smaller than the mainline pipe or the mainline is at least 12".    The lateral shall be installed above the spring line of the mainline.  The lateral shall have a clean out at the property line.  Connections will not be allowed if the lateral is connected to an inlet or area drain. 

440.3 Manhole Sizing and Alignment

1. The diameter of manhole required shall ensure a minimum dimension, of solid concrete manhole wall, between pipe openings of 12 inches.  The standard and minimum manhole size shall be 48 inches in diameter.  Maximum spacing of manholes shall be 250 feet.
2. Access locations shall be required at a change in vertical or horizontal alignment or a change in pipe size or material.
3. Manhole rims shall be flush with top of asphalt.  If only one lift is placed, or a portion of the overall depth of asphalt, the rim shall still be flush with the top of the asphalt constructed.  As additional asphalt thickness is added later, the rim shall be adjusted to be level with the new top of asphalt.

440.4 Open Channels and Ditches

440.4.1 Natural Channels

1. Natural channels are those which occur naturally due to the flow of water or, following construction, those manmade channels that have become vegetated and stable.
2. Natural channels shall remain in their existing, or natural, condition wherever feasible.  The preservation of natural drainage-ways shall conform to the requirements of the ZDO.  Alteration of natural drainage-ways shall not occur without approval of all agencies having jurisdiction.

440.4.2 Constructed Channels & Ditches

1. Constructed channels include those constructed and maintained by human activity and include bank stabilization at existing channels.
2. Roadside ditches shall conform to the requirements and sections for County rural roadways.  Roadside ditches shall not be constructed within the urban growth boundary. 
3. The County may consider a constructed channel along the roadside when pedestrian and vehicle safety are not compromised and sufficient road right-of-way is available.

440.4.3 Design Criteria

1. Roadway grading shall conform to clear zone requirements of Section 245 and cross section requirements of Standard Drawings C110 to C140.
2. Constructed channels and ditches shall be trapezoidal or parabolic in cross section with side slopes no steeper than 3H:1V, or 4H:1V within the clear zone, for vegetation-lined channels and 2H:1V for rock-lined channels.  Constructed channels and ditches shall be designed for a 25 year storm event.  Constructed channels and ditches within the required recoverable slopes shall meet recoverable slope requirements:  4H:1V on the fore slope (down slope) and 3H:1V on the back slope (up slope).
3. Vegetation-lined channels shall maintain a maximum velocity of 5.0 ft/sec at the 25 year event.   Rock-lined channels or bank stabilization shall be required when design velocities exceed 5.0 ft/sec.
4. Access and utility easements shall be provided for all publicly maintained open channels and ditches as required by the County.

430.1 Acceptable Hydrology Methods (Detention Hydraulics)

Engineering accepts the Rational Method, and TR-55, in addition to WES approved methodology. Other methods will require prior approval from Engineering.

Detention pond routing shall be by the Storage Indication (Modified Pulse) method: 

{2S²/ Δt + O² = I² + I¹ +2S¹/ Δt + O¹} or approved equal.

430.2 Rational Method

The Rational Method (Q=ciA) may be used to estimate peak discharge from drainage basins of less than 300 acres. 

The Soil Conservation Service ("SCS") TR55 method may be used for drainage areas less than 25 square miles.  

Refer to the ODOT Hydraulics Manual for additional information. Some of the figures contained herein have been reproduced from the above manual.

430.2.1 Rational Method Basic Methodology

The Rational Method is a simplified model for estimating the discharge of a drainage basin based on the area of the basin, type of ground cover, and intensity of rainfall.

Q = ciA
Q = peak discharge (cfs)
c = runoff coefficient
i = rainfall intensity (in/hr)
A = drainage area (acres)

The Rational Method can result in a wide range of discharge values based on assumptions made by the Engineer. The following sections establish parameters for the variables in the Rational Method and should be used in the design of drainage systems within Clackamas County.

430.2.2 Runoff Coefficient

The runoff coefficient (C) is a dimensionless parameter based on the type of ground cover and slope of the terrain. Table 4-1 lists runoff coefficients for various conditions of ground cover and slope.
           
Where ground conditions vary throughout a drainage basin, a composite runoff coefficient can be calculated as follows:

Cavg = (C1A1 + C2A2 + C3A3 + . . . CnAn)
(A1 + A2 + A3 + . . . An)

430.2.3 Rainfall Intensity

The rainfall intensity indicates the "quantity" of rainfall and is related to the rainfall duration and the design storm. Rainfall intensity is usually represented by an Intensity-Duration-Frequency (I-D-F) curve. The IDF curves for drainage design in Clackamas County are taken from the Hydraulics Manual (see Figures 4-1 to 4-5).

430.2.4 Time of Concentration

1. The duration of rainfall is equal to the time of concentration (Tc), in minutes, where the time of concentration is defined as "that amount of time from beginning of a storm event, that it takes water from the most remote time location in the basin to reach the point being considered."
2. Determination of the time of concentration, Tc, shall be in accordance with the Hydraulics Manual as follows: Most drainage basins will consist of overland flow segments as well as channel flow segments. Overland flow can be further divided into a sheet flow component and a shallow concentrated flow component. Urban drainage basins may be further complicated by having significant pipe flow segments. The travel time is computed for each flow segment and the time of concentration is equal to the sum of the segment travel times.

3. The best method of determining overland sheet flow time is the kinematic wave equation. The equation is only applicable for travel distances less than 300 feet.

   Tc = KL0.6n0.6 / I0.4S0.3

   Where: Tc = overland flow time in minutes
   L = overland flow length in feet
   n = Manning's roughness coefficient (see Table 4-2)
   I = rainfall intensity, in/hr
   S = the average slope of the overland area
   K = 0.93

4. Figure 4-6 is a nomograph for the solution of the kinematic wave equation for overland sheet flow. In using the nomograph, the time of concentration and rainfall intensity are unknown. The solution is one of iteration or trial and error.
5. After a maximum of 300 feet, sheet flow usually becomes shallow concentrated flow. The average velocity for this flow can be determined from Figure 4-7 in which average velocity is a function of watercourse slope and type of channel. This figure was reprinted from the 1972 SCS Handbook.
6. For open channels, Manning's equation can be used to estimate average flow velocity, which is usually determined for bank-full flow.

430.2.5 Design Storm

1. A design storm defines the statistical recurrence interval of a storm event. The probability of a 25-year storm occurring in a given year is 4%. Conversely, a 25-year storm will statistically occur once every 25 years. The selection of a design storm is dependent on the balance between the cost of the drainage facility and the flood risks associated with the storm event. The design storm required for public drainage facilities within the County, but outside an existing stormwater district, shall be based on a 25-year storm event. Design storms within existing surface water management districts, shall be based on the districts requirements, but in no case shall public drainage facilities within the County's right-of-way be designed for less than the 25-year storm at basin buildout with 85% impervious. 
2. The effects of the 100 year storm event on storm drainage structures and bridges shall be evaluated as required.  
3. The effects of the 100 year storm event on developments within a flood plain shall be evaluated as required. 
4. The effect of the 100 year storm shall be evaluated when the path of the drainage could place persons or property in jeopardy.

430.2.6 Drainage Area

The discharge of a storm system is dependent on the size of the basin contributing to the flow. The design of a drainage facility should account for the entire drainage basin surrounding the affected area. The Engineer shall submit a topographic map of the entire drainage basin with the drainage calculations. This map should identify the existing and proposed drainage facilities and sub-basins considered in the design. This overall design shall anticipate and accommodate the acceptance and conveyance of surface water on or crossing the roadway or roadway system considered in the design area.

Figure 4-1. Clackamas County Rainfall Zones
Reference: ODOT Hydraulics Manual

Figure 4-2. ZONE 3 Rainfall Intensity, Duration, Frequency Curves
Reference: ODOT Hydraulics Manual

Figure 4-3. ZONE 5 Rainfall Intensity, Duration, Frequency Curves
Reference: ODOT Hydraulics Manual

Figure 4-4. ZONE 7 Rainfall Intensity, Duration, Frequency Curves
Reference: ODOT Hydraulics Manual

Figure 4-5. ZONE 8 Rainfall Intensity, Duration, Frequency Curves
Reference: ODOT Hydraulics Manual

Figure 4-6. Time of Concentration
Reference: ODOT Hydraulics Manual

Figure 4-7 – Shallow Concentrated Flow Velocity
Reference: ODOT Hydraulics Manual

The following standards are exceptions to WES stormwater standards.  These standards are directed towards the design and construction of public storm drainage facilities and for the coordination of stormwater runoff from private drainage systems into public systems.  The intent is to ensure a comprehensive engineering review and sufficient design to identify and mitigate existing deficiencies, protect the environmental health of our watersheds, and identify the capacity requirement of new system improvements, resulting in an overall benefit of reduced flooding.

If any conflicts arise between these standards and WES standards, the following shall govern.

420.1 Best Management Practices (BMP) & Low Impact Development Approaches (LIDA)

Engineering acknowledges the need for Best Management Practices (BMP) or Low Impact Development Approaches (LIDA) with development.  In addition to any LIDA standards adopted by WES, Engineering encourages designers to submit LIDA designs for review to meet the water quality and infiltration requirements outlined in WES stormwater standards.  Calculations will be required to illustrate to Engineering how a given LIDA provides water quality benefit. Private improvements in rural areas may work with DTD to provide a simplified approach to stormwater management that utilizes vegetation and infiltration if the site conditions warrant it. City of Portland's Simplified Approach for infiltration testing and typical details for stormwater management may be used in the rural area.

420.2 Acreage as a BMP

Development outside WES service districts is predominated by larger lot sizes.  A reasonable BMP outside the UGB may be the utilization of undeveloped acreage.  The applicant shall demonstrate to Engineering that water quality, detention, and/or infiltration requirements are met using the acreage BMP.

420.3 Surface Water Management Applicability

Surface water management plans in conformance with this chapter will be required for any of following:

1. When 5,000 square feet or more of new or reconstructed impervious surface is proposed within the UGB.
2. When 10,000 square feet or more of new or reconstructed impervious surface is proposed outside the UGB.
3. When grading or any new or reconstructed impervious surface is proposed or replaced within 50 feet of a perennial stream, creek, wetland, or lake, or within 10 feet of a property line.

420.4 Underground Injection Control (UIC) Devices

UICs are only permitted in Clackamas County right-of-way when registered with DEQ and maintained by an established stormwater district, unless otherwise approved by DTD Transportation Maintenance.  When UIC are proposed in County right-of-way, an approved IGA and maintenance agreement with an established stormwater district shall be in place prior to Development Permit issuance.

Chapter 4 establishes the technical requirements associated with storm water management.  

410.1 Regulatory Authority

The Engineering Division of DTD is responsible for ensuring the adequate drainage of public roadways and developed properties in unincorporated areas outside of established stormwater districts within the County.  Engineering regulates the construction of public and private roads and other site improvements to ensure adequate drainage of storm/surface water to an appropriate discharge point.

Clackamas County has multiple surface water districts: Water Environment Services (WES) encompasses the Clackamas County Service District #1 (CCSD#1) and the Surface Water Management Agency of Clackamas County (SWMACC) and Hoodland Service District. The other districts are Clean Water Services (CWS) and the Oak Lodge Sanitary District (OLSD).   

Engineering manages storm water drainage and surface water regulations for all development outside of the County's established storm water districts or outside city limits located within the County's boundary.  For the regulations in these other areas, please refer to the respective jurisdiction.

410.2 Engineering Regulations

Engineering has adopted WES stormwater standards, with the exceptions noted within this chapter. 

410.3 Erosion Control Contractor Certification Not Required

WES Erosion Control Certification shall not apply to Engineering regulations.

410.4 Fees

Fees listed in the WES rules and regulations, or their Stormwater Standards, only apply to areas within their surface water management districts.  For information on Engineering stormwater and erosion control fees outside of existing surface water management districts, see County Code, Appendix A: Fees. For surface water management fees, within another district or municipality, contact the district or municipality directly.

Grades may not exceed +/- 3% in the service area.

1. All driveways shall meet ADA accessibility requirements if the driveway intersects with a planned or existing sidewalk or other pedestrian facility.
2. Driveways should be designed with a minimum 28-foot wide approach except where the Comprehensive Plan requires narrower driveways.
3. If the design vehicle for the site requires it per Section 250.1.3 or if traffic operations necessitate additional travel lanes, driveways wider than 28 feet may be required to reduce the pedestrian crossing length or implement additional measures to reduce conflicts with pedestrians.
4. Driveways on streets with curb tight sidewalk should be constructed per Standard Drawing D600. 
5. Driveways on streets with curb and sidewalk with a landscape strip should be constructed per Standard Drawing D650. 
6. In rare cases where a development's trip generation is such that higher speed egress maneuvers from the adjacent roadway are desired or is used for a large number of truck deliveries, the County may allow or require driveways to be constructed per Standard Drawing D675.
7. Driveways constructed without curbs should be constructed per Standard Drawing D500.
8. Driveway throats (measured from the back of the public sidewalk in the UGB and from the edge of pavement outside the UGB to the nearest perpendicular drive aisle) shall have a minimum length of 20 feet but should be designed to accommodate the 95th percentile queue.  Driveway throat depths may be required to be based upon a traffic study per Section 295.
9. Driveways accessed by trucks with trailers, should require a minimum throat length of 50 feet.
10. Parking, intersecting drive aisles and designated pedestrian crossings are prohibited within the minimum throat depth.
11. If a gate is proposed on a driveway serving the public, the gate shall be placed a minimum of 20 feet from back of sidewalk or edge of pavement, whichever is greater.  If queues are likely to extend into the travel lane of the nearest roadway, then a queuing analysis shall be provided per Section 295.  Gates may require the approval of the fire district. 
12. Gates are required to have a minimum of a 20' wide unobstructed opening.  The opening width will be required to increase when the length of the anticipated vehicle increases unless the gate is set back far enough for the vehicle to be perpendicular to the gate.

320.1 Maximum Slopes and Grades

1. The plan review, permit and inspections for ADA improvements will be covered under a Development Permit when they are not related to a building permit under review.
2. The ADA facilities should be designed with a 0.5% tolerance from maximum slopes and grades.
3. General parking areas and adjacent drive aisle slopes should not exceed +/-5%.
4. Drive aisles not adjacent to parking spaces should not exceed a longitudinal slope of 10%.  Cross slopes shall not exceed 5%.

320.2 Pedestrian Walkways

1. Walkway connections to the public sidewalk shall meet ADA landing area requirements per PROWAG and be reviewed and permitted by Engineering.
2. Onsite accessible routes, when permitted through a Development Permit, shall meet the requirements of the latest version of the Oregon Structural Specialty Code (OSSC) Chapter 11 and the International Code Council (ICC) A117.1.

320.3 Vehicular Circulation and Maneuvering

All vehicle maneuvering shall be provided on site and should limit backing maneuvers in locations where pedestrians are expected.

1. For dimensions of parking spaces and drive aisles refer to Standard Drawings P100 and P200.
2. To be considered a parking space, adequate maneuvering area shall be provided for each vehicle to enter and exit said parking space.
3. All garbage and recycling facilities shall have adequate access, with onsite maneuvering and circulation for the service provider's vehicle.
4. All movements for non-passenger design vehicles should be shown on an exhibit, showing paths traced by the extremities of the vehicles, including off-tracking.  Adequate turning radii shall be provided for all loading spaces and the largest anticipated vehicles maneuvering on site and at driveway approaches.  At a minimum, the circulation of a fire truck and garbage truck shall be illustrated.

320.4 Parking and Maneuvering Area Surface & Structural Section

1. The parking and maneuvering surface (gravel or paving) shall comply with ZDO Section 1015 or with Standard Drawing R100 if not related to development. 
2. The structural section of parking and drive aisle areas shall meet or exceed Standard Drawing R100.
    

320.5 Parking Stalls

1. All automobile off-street parking quantity and dimensions shall meet the ZDO and Roadway Standard Drawing P100 or P200
2. Dimensions for on-street parking spaces shall meet or exceed the requirements of Roadway Standard Drawing P100 or P200.  The on-street parking shall utilize the street for the drive aisle.  The parking spaces shall not diminish or obstruct the required travel lanes or bike lanes.
3. All compact, carpool, disabled, and loading berth spaces shall be labeled on the plans. 
4. Accessible parking spaces shall meet the requirements of the Oregon Transportation Commission's Standards for Accessible Parking Places, latest edition.

320.6 Curbs and Wheel Stops

1. If parking lot curbs carry, direct or channel surface water, the curb should be structural curb. 
2. Alternative curbs will be considered when it is determined by Engineering that structural curb is not the most appropriate.
3. Extruded curbs shall not be used for carrying, directing or channeling surface water, or as a vehicle wheel stop.

320.7 Signage and Pavement Markings

1. All traffic control devices on private property shall be installed and maintained by the property owner.  Traffic control devices that are located where private driveways intersect a road right-of-way shall be kept in good condition. 
2. The applicant shall provide a signing and pavement marking plan to Engineering for onsite parking and circulation.  This plan shall be reviewed and approved by Engineering and the local fire service provider prior to the applicant being issued a Development Permit.
3. All compact, carpool, disabled parking spaces shall be clearly marked on the site.

320.8 Reciprocal Access Easements

Comply with Section 220.

Chapter 3 establishes the technical requirements associated with on site design of commercial, industrial and multifamily developments  

Site improvements for commercial, industrial, and multifamily developments are reviewed through the land use approval process, described and administered pursuant to the ZDO. 

This chapter supplements the requirements of the ZDO, which contain greater detail in relation to onsite design of commercial, industrial and multifamily developments.

295.1 General

The objective of a transportation impact study (TIS) is to assess the impacts of a proposed project or land use action on the transportation system and identify mitigation for any capacity or safety deficiencies.  These requirements are intended to provide standards for generation of a TIS for land development applications that are consistent with land use regulations and guidelines for traffic analysis that is prepared for County capital projects.   

295.2 Requirement for a Traffic Impact Study

1. A TIS shall be required based upon an assessment of Engineering regarding the anticipated relative impact of a proposed development on the existing or planned transportation system. 
2. A TIS to address traffic capacity is not required where the proposed development will generate less than twenty vehicles trips in any peak hour unless to address specific safety issues identified by the County.  The need for a TIS is at the discretion of the Road Official.

295.3 Traffic Study Scope and Coordination

1. Engineering and the applicant should coordinate to develop a written TIS scope that will guide the work of the TIS and define the study requirements based upon the anticipated influence area of the proposed development.
2. The influence area of a proposed development establishes the requirements of analysis for the TIS and is defined on a case by case basis, but is typically based upon the trip generation of the proposed development in relation to the proximity of congested roadways and intersections or the proposed development's potential impact on safety issues.

295.4 Traffic Engineering Expertise

All traffic impact studies shall be conducted under the direction of and stamped by an Engineer with expertise in traffic engineering. 

295.5 Coordination with Other Agencies

As applicable, the applicant is expected to coordinate with ODOT and affected local jurisdictions in the scoping, development, and review of a TIS regarding intersections or roadways that are not under the County's jurisdiction.  In some cases, the County has adopted adjacent agency standards as part of the ZDO.

295.6 Zone Changes and Comprehensive Plan Amendments

Zone changes and Comprehensive Plan amendments require analysis compliant with OAR 660-012-0060, the Transportation Planning Rule.  

295.7 Clackamas Regional Center (CRC) Area Analysis Period

1. The ZDO and Comprehensive Plan Chapter 10 require special analysis periods within the Clackamas Regional Center Area. 
2. Within the CRC area, a weekday PM peak two hour analysis is required.  The first hour of analysis shall be based upon the peak hour of the subject intersections.  If the mobility standard is met for the first hour, no further analysis is required.  If the mobility standard is not met in the first hour, a second hour of analysis is required.  The second hour of analysis shall be based upon the "shoulder" ½ hours before and after the peak hour, which may require additional traffic counts.
3. Within the CRC area, a weekday midday hour analysis is required.

295.8 Analysis Methodology

1. All analyses shall be conducted in compliance with the most recent versions of the following:
2. Highway Capacity Manual (HCM) with the exception of signalized intersections, which shall be based upon the HCM 2000
3. ITE Trip Generation Manual
4. ITE Trip Generation Handbook
5. MUTCD
6. AASHTO - A Policy on the Geometric Design of Highways and Streets
7. AASHTO - Guidelines for Geometric Design of Very Low-Volume Local Roads
8. AASHTO - Highway Safety Manual
9. It is recognized that in many instances, the HCM's methodology is limited especially in highly congested conditions.  In instances where the HCM is incapable of providing accurate analysis, the County and applicant shall coordinate on an appropriate analysis method.
10. The following establish the County's LOS and v/c determination method and other analysis parameters required to evaluate the requirements of the Comprehensive Plan and ZDO. 

295.8.1 Two-Way Stop Controlled (TWSC) Intersections

At two-way stop controlled intersections, including driveways, the weighted average methodology of the critical approach of the HCM shall determine the LOS and v/c of the intersection. 

295.8.2 All-Way Stop Controlled (AWSC) Intersections

At all-way stop controlled intersections, the intersection average methodology of the HCM shall determine the LOS and v/c of the intersection. 

295.8.3 Signalized Intersections

At signalized intersections, the intersection average methodology of the HCM shall determine the LOS and v/c of the intersection.

295.8.4 Roundabout Intersections

At roundabouts, the critical approach shall determine the LOS and v/c of the intersection.

295.9 Signalized Intersection Analysis Parameters

1. The TIS shall analyze traffic signals in the following manner with regard to traffic signal timing:
2. The existing, background and total traffic analysis shall be consistent with the existing signal timing. 
3. Analysis of isolated intersections shall optimize the existing splits within the maximum cycle length.
4. Signals that operate in a coordinated timing plan shall be analyzed without adjustments.
5. If modifications to the signal timing are proposed or shown in the analysis, the total traffic analysis shall contain two scenarios:  total traffic with existing signal timing and total traffic with proposed signal timing.  However, signal timing modifications are typically not acceptable as mitigation to a project's impacts.
6. Additional analysis requirements may apply in the case of coordinated signal systems as changes at one intersection may affect other intersections not included in the study area of the project.
7. The Engineer shall request County, ODOT and local jurisdiction signal timing for use in their analysis.  The Engineer is responsible for ensuring that the appropriate signal timing is used in the analysis.
8. If signal timing changes are recommended by the applicant and approved by Engineering as acceptable mitigation to a project's impacts, funds will be required to design and implement new signal timing plans suggested as mitigation by the applicant.
9. Where adaptive signal timing exists, the applicant and County will work together to determine the appropriate signal timing parameters.

295.10 Peak Hour Factor ("PHF")

1. The peak 15 minutes of the peak hour shall be the basis for determining intersection operations except as noted in the ZDO and Comprehensive Plan, which allows a one hour peak period in some situations.  In those instances, the peak hour factor shall be set to 1.0 and the entire peak hour traffic volume shall be evaluated. 
2. The PHF shall be derived from the existing raw manual turning movement counts and be applied uniformly over each scenario except as provided below in 3).
3. In the case of zone change or comprehensive plan amendment analysis, the peak hour factors presented in ODOT's Development Review Guidelines or existing PHF shall be used in analysis.  

295.11 Microsimulation Models

1. Congested conditions will require the use of microsimulation models.
2. The use of microsimulation shall require compliance with the ODOT Analysis Procedures Manual (APM)

295.12 Growth Rates and In Process Traffic

1. For short term analysis of five years or less, linear growth rates shall not be less than 2% per year unless verifiable evidence is submitted or known which indicates that the local growth rate is less than 2% per year.
2. For long term analysis of six years or more, linear growth rates should not be used if regional travel demand volumes are available.  In that case, the analysis should rely upon regional travel demand volumes and post process those volumes per the APM.  If no regional travel demand volumes are available, the historical trends methodology of the APM or other approved methodology may be acceptable.
3. In process traffic, or developments that have been approved and have current land use approval yet are not occupied or fully built-out, shall be included in addition to growth projections.  That information may be omitted for zone changes and comprehensive plan amendments.

295.13 Turning Movement Counts

Turning movement counts shall be conducted as follows:

295.13.1 Count Hours

The count hours stated in Table 2-19 shall be collected in analysis unless the TIS scope specifies otherwise.

295.13.2 Day of Week

Turning movement counts shall be conducted on Tuesdays, Wednesdays and Thursdays unless otherwise directed.

295.13.3 Holidays

Turning movement counts shall not be conducted within one week of a federal holiday.

295.13.4 Current Counts

Traffic counts should be based upon counts collected within 24 months of the completed land use application.  Counts older than 24 months may not be accepted or may require adjustment to current traffic conditions with Engineering approval.

295.13.5 Vehicle Classification, Bicycles and Pedestrian Data

Turning movement counts shall separately include vehicular (truck vs. non-truck), bicycle and pedestrian traffic volumes.

295.14 Trip Generation

1. Trip generation shall be based upon the latest edition of ITE's Trip Generation Manual and Trip Generation Handbook. 
2. The traffic impact study shall include an estimate of site generated trips, pass-by trips, diverted linked trips, and internal capture trips during each study period.
3. If a trip generation rate similar to the proposed use is not available within Trip Generation Manual, then the procedures of the Trip Generation Handbook regarding obtaining local trip rates should be used unless otherwise approved by Engineering.  Engineering may require evidence that the use's trip generation is similar to the use described in the Trip Generation Manual.
4. Trip generation shall be based upon an average weekday unless otherwise specified by Engineering.

295.15 Trip Distribution

Trip distribution shall be approved by Engineering.

295.16 Queuing Analysis

1. All development may be required to provide a queuing analysis that evaluates the impact of queues onto public roadways.  Developments that are anticipated to back traffic onto public roadways are considered to be a safety issue. 
2. Development that proposes a drive-thru service shall provide a queuing analysis that evaluates the impact of drive-thru queues onto public roadways.
3. As required by Engineering, the TIS shall provide 95th percentile queue estimates for each movement at each study intersection.  The TIS shall identify the existing available queue storage, anticipated 95th percentile queue and indicate if that storage is or will be exceeded.
4. In cases where the anticipated 95th percentile queue exceeds the available storage and the queuing is considered to be a safety issue, the development will be required to mitigate a queue back to the background traffic condition.
5. Microsimulation utilized to substantiate queuing shall comply with Section 295.11.

295.17 Traffic Safety

If required, the TIS shall analyze the safety of the transportation network by addressing the following.  If any of these conditions cannot be met and mitigation does not sufficiently address the deficiencies, Engineering may recommend that a proposed development does not meet safety standards:

1. Sight distance is adequate subject to the standards of Section 240.
2. Crash history is adequate per Section 295.17.1.
3. Queuing is adequate per Section 295.16.
4. Access requirements are adequate per Section 220.
5. A turn lane, if warranted and recommended by Engineering per Section 295.18.1, is provided. 
6. Truck circulation is adequate per Section 295.17.2.
7. Off-site access is adequate per Sections 225.4 and 225.5.

295.17.1 Crash History

1. Crash history shall be analyzed for all study intersections and sections of roadway to which access is proposed.  Crash rates, frequency and severity shall be evaluated.
2. The applicant shall evaluate the existing crash history to determine crash patterns, severity and frequency and make recommendations for safety improvements. 
3. Intersection crash rates in excess of typical crash rates require further safety analysis based upon the Highway Safety Manual the APM to determine the development's impact on safety and may require proportional mitigation. 
4. As required, segment crash rates in excess of typical crash rates require further safety analysis based upon the Highway Safety Manual and the APM to determine the development's impact on safety and may require proportional mitigation. 

295.17.2 Truck Circulation

1. For developments that will generate greater than 50 daily vehicles of a size greater than or equal to WB-50, an analysis of truck turning movements at the intersection of the following will be required:
   1. The nearest collector or arterial roadway (whichever is closer) if within the UGB.
   2. With the nearest arterial roadway if outside the UGB.
2. Mitigation will be required if a safety issue would result.

295.18 Mitigation

1. The traffic study shall include suggested mitigation to comply with ZDO and Comprehensive Plan mobility requirements, to provide a minimum level of safety to support the proposed development and to address other requirements of these Standards as required. 
2. Proposed mitigation may require a safety analysis based upon the Highway Safety Manual and APM.
3. Mitigation that shall be considered in the analysis is described below, as applicable:

295.18.1 Turn Lane Warrants

1. The applicant shall analyze the need for right and left turn lane warrants as required by Engineering. 
2. The County utilizes the current ODOT left turn and right turn siting criteria of the Highway Design Manual when establishing the possible need for left and right turn lanes. 
3. The affirmation of a warrant being met for a turn lane does not dictate its installation.  County staff will make a determination regarding the need for turn lanes.
4. Signalized intersections shall be accompanied by channelized left turn lanes on the major street and minor street and designed per Section 250.8.8 except as approved per Section 170.
5. Signalized intersections may require channelized right turn lanes as warranted above and designed per Section 250.8.8.

295.18.2 Traffic Signal Approval

A traffic signal proposed to address safety or capacity issues shall meet the requirements of Section 260 including evidence to indicate that other alternatives have been considered. 

295.18.3 Analysis of Impacts on Local, Residential Streets

1. Some developments may have a detrimental effect upon existing residential uses.  As applicable, the TIS shall evaluate impacts such as traffic volume increases, potential speed increases, safety impacts and other livability issues on local, residential streets. 
2. Based upon the relative impact of the development upon local, residential streets,  improvements to mitigate a development's impact may be required. 
3. Elements to be considered as potential mitigation include the traffic calming measures of Section 265.

295.18.4 Other Mitigation

Other mitigation, such as the installation of stop signs, warning signs, signal timing modifications, additional lanes, roundabouts, traffic circles, pedestrian and bicycle improvements and other potential improvements, will be evaluated on a case by case basis.  Suggested mitigation shall be accompanied by appropriate engineering analysis to allow for the review of such proposals including a review of the mobility and safety impacts of the proposed mitigation. 

295.19 Traffic Study Components

The following elements typically make up a TIS.

295.19.1 Executive Summary

An executive summary that discusses the proposal and the results of the study and any necessary traffic related mitigation to meet the requirements of the land use application.

295.19.2 Project and Study Area Description

A description of the existing and proposed land uses, site characteristics, surrounding land uses, roadway system characteristics, transit service, pedestrian and bicycle facilities, and any pending transportation system improvements as identified in the Clackamas County Capital Improvement Program, Comprehensive Plan, and ODOT or local jurisdiction plans.

295.19.3 Analysis Periods and Scope

1. Analysis of intersection capacity and/or roadway segment capacity, as required by the Scope, meeting the requirements of these Standards, ZDO and Comprehensive Plan. 
2. The analysis shall include the following study scenarios at a minimum or as directed by staff:
3. Existing Traffic (Analysis based upon "current" traffic counts)
4. Background Traffic at a reasonable full build-out year (Existing Traffic + Growth + In Process Traffic)
5. Total Traffic at a reasonable full build-out year (Background Traffic + Site Generated Traffic)

295.20 Submittal Requirements

1. Completed traffic studies and revisions shall be submitted as a pdf document.
2. All electronic files used in support of a traffic analysis shall be submitted upon request.

290.1 General

1. Traffic control in the public right-of-way is subject to a permit.
2. All traffic control shall comply with the requirements of the MUTCD, Oregon MUTCD supplement, the ODOT Sign Policy and Guidelines, FHWA's Standard Highway Signs, Oregon Standard Specifications for Construction, Oregon Temporary Traffic Control Handbook for Operations of Three Days or Less, and Oregon Traffic Control Plans Design Manual. Oregon Standard Drawings TM800 series should be used with particular reference to TM844 for temporary pedestrian access routes.
3. Traffic control plans need not generally bear the stamp of an Engineer, except as required by Engineering.  If required due to complexity, plans shall be prepared under the direction of and stamped by an Engineer with expertise in traffic engineering.

290.2 Control of Site

1. At no time shall flagging operations delay traffic for a period greater than twenty (20) minutes.
2. Work and activity zones (construction, restoration, erosion control) shall extend no more than 2500 lineal feet at any one time unless otherwise approved.
3. Open trenches shall extend no more than 250 lineal feet at any one time, unless otherwise approved. 
4. No trenches are to be left unprotected between dusk and dawn.
5. Trenches shall conform to the technical requirements of Section 00405 of the Oregon Standard Specifications for Construction.
6. Trench plating shall be positively secured from movement and shall be ramped with anti-skid coated plate ramps.

290.3 Temporary Pedestrian Accessible Route

If existing pedestrian access will be obstructed by construction, alteration, maintenance or other temporary conditions, a continuous temporary pedestrian accessible route (TPAR) shall be provided consistent with the requirements of this section. Temporary pedestrian accessible routes shall conform to the requirements of Part 6 of the MUTCD, and the most recent update of the Oregon Standard Specifications for Construction, Section 00220.02(b). The temporary pedestrian accessible route plan shall be included in the traffic control plans. County inspectors will inspect the TPAR. If deficiencies are identified the inspector will stop work until such deficiencies are corrected.  TPAR requirements include:

1. In work zones pedestrian access shall not be blocked by parking of vehicles or equipment, materials storage or for any other reason except for construction.
2. The TPAR shall parallel the disrupted pedestrian access route, on the same side of the street where possible.
3. Bicyclists should not routed into the TPAR. If it is necessary to divert bicyclists around the work, provision should be made for a separate route for bicyclists.
4. If the work impacts the accessibility of pedestrian routes through or around the work zone, limit impacts to one corner of an intersection at a time.
5. Close sidewalk at a point where there is an alternate way to proceed and provide signing and other traffic control devices directing pedestrians to an alternate pedestrian route. 
6. The TPAR shall be inspected by the applicant on a regular basis to ensure that it is safe and does not have gaps or surface displacements creating a hazard. 
7. The TPAR shall meet the standards of a pedestrian access route as defined in PROWAG:
   1. Minimum width shall be 48 inches. Provide a 60 by-60 inch passing space every 200 feet along the route.
   2. Surface shall be smooth and nonslip.
   3. Vertical clearance shall be at least 8 feet.
   4. Cross slope shall be no more than 2.0% perpendicular to the direction of pedestrian travel.
   5. Grade shall be less than or equal to the grade of the adjacent road.
   6. Minimum turning space of 4 feet by 4 feet shall be provided wherever it is necessary for pedestrians to turn.
   7. If it is necessary to cross a curb, the TPAR shall include a temporary ramp meeting standards for a curb ramp.
   8. If it is necessary for the TPAR to cross a driveway or construction access truncated dome warning shall be provided. If it is not possible to provide truncated dome warning construction staff shall be provided at all times when construction vehicles are crossing the pedestrian access route.
   9. Night time lighting shall be provided.
8. Provide and maintain Pedestrian Channelizing Devices (PCD) through the period in which the permanent pedestrian access route is disrupted. Pedestrian channelizing devices are intended to prevent those with disabilities from straying into the vehicular way or an active construction area. Caution tape is not sufficient to guide those who are blind or low vision. Use only PCDs that are on the approved ODOT Qualified Products List, that are designed to be ADA compliant. Provide pedestrian channelizing devices:
9. Between the TPAR and any adjacent construction site.
10. Between the TPAR and the vehicular way, if the temporary pedestrian access route is diverted into the street.
11. Between the TPAR and any protruding objects, drop-offs, or other hazards to pedestrians.
12. At a curb ramp if the opposite curb ramp is temporarily and completely blocked, and no adjacent alternate circulation path is provided.
13. When work briefly or intermittently blocks or restricts the use of a pedestrian route, and a temporary detour route is not practicable due to the short duration of the restriction, provide a temporary means of allowing pedestrian access through or around the work area. Means of providing temporary pedestrian accessibility may include, but are not limited to temporarily suspending the work and making the pathway passable, or use of construction staff to guide pedestrians through or around the area.  When a TPAR is created in the public right-of-way, both visual and audible warning shall be provided at both ends of the temporary pedestrian access.
14. When direction signage or warnings are provided they should be located to minimize backtracking. Audible warnings shall be provided for those who are blind or low vision and should include specific directions allowing them to find the desired path.

290.4 Impacts to Traffic Signals

1. In no case may flagging operations take place in conflict with the indications of an operating traffic signal.
2. No flagging operations may take place within 200 feet of an operating traffic signal without a custom traffic control plan subject to a permit.
3. Should traffic control requirements dictate the "turn-off" and/or "turn-on" of a traffic signal, the applicant shall coordinate with the County Traffic Signal Shop at least two business days prior to turn-off and/or turn-on.

290.5 Temporary Road Closures

Temporary road closures are not for the purpose of convenience or cost reduction for an applicant.  Proposed closures shall establish that a clear public safety and convenience benefit would result from a closure.

1. The detour route shall be capable of safely and legally accommodating the detoured traffic.
2. With increasing ADT, functional classification and closure duration, the applicant's burden becomes greater in establishing the benefit of a proposed closure.
3. If a road closure is proposed, the following may be required:
4. Evidence that other methods of traffic control and/or that temporary improvements are not feasible in order to keep the road open. 
5. Time of day restrictions or extension of normal working hours and days.
6. Contract requirements of incentives/disincentives for completing/not completing closure on time.
7. A public engagement plan.
8. Off-site improvements to meet minimum safety of the detour route and/or to return the detour route to its original condition prior to the detour per Section 225.6.