(1) 
A traffic impact analysis (TIA) is a specialized study of the impacts a certain type and size of development will have on the surrounding transportation system. The traffic impact analysis is an integral part of the development impact review process. It is specifically concerned with the generation, distribution, and assignment of traffic to and from the proposed development. The purpose of a TIA is to determine what impact development traffic will have on the existing and proposed street network and what impact the existing and projected traffic on the street system will have on the proposed development.
(2) 
These guidelines have been prepared to establish the requirements for a traffic impact analysis. The traffic engineer will be the person responsible under SEPA as well as county ordinances for determining the need for a traffic impact analysis. The community development department and public works staff will also have a significant role during the TIA process.
(Ord. 1194 Exh. B, 2007)
(1) 
To adequately assess a proposed development traffic impact on the transportation system and level of traffic service, the public works department may require a traffic impact analysis (TIA). The requirement for a TIA will be based on the size of the development proposed, existing street and intersection conditions, traffic volumes, traffic safety considerations, community concerns, and other pertinent factors relating to traffic impacts attributable to proposed developments. The proponent of a proposed development or redevelopment has the responsibility of preparing, for county review, a traffic impact analysis (TIA) as required below:[1]
(a) 
Level I TIA. Trip Generation and Distribution Study. (Refer to Exhibit 3, Example 1, at the end of this section for Level I TIA sample outline.)
(b) 
Level II TIA. Traffic impact analysis. (Refer to Exhibit 3, Example 2, at the end of this section for Level II TIA sample outline.)
[1]
Editor's Note: Exhibit 3 Examples for Levels I and II TIA is included as an attachment to this title.
(Ord. 1194 Exh. B, 2007)
(1) 
A complete Level I TIA shall be required if any one of the following warrants is met:
(a) 
The project generates 50 or more p.m. peak hour (two-hour peak average) trips; or
(b) 
At the county's discretion, if the project requires a SEPA review.
(c) 
At the county's discretion, if there are existing and projected traffic volumes, accident history, and other operational considerations.
(2) 
A trip generation/waiver request may be submitted by a licensed engineer if the project doesn't trigger county requirements for a traffic impact analysis.
(3) 
A Level I TIA may be required by the county to determine the need and scope of a Level II TIA. A Level I TIA may be expanded to a Level II TIA if any of the warrants in LCC § 12.60.420 are met.
(Ord. 1194 Exh. B, 2007)
(1) 
The following is a list of specific conditions that may dictate the requirement for preparing a Level II TIA. The traffic engineer may require the preparation of a TIA if one or more of the following conditions are satisfied:
(a) 
The development is within the urban area as defined by the Urban Growth Management Boundary and is required by the city.
(b) 
The development will generate 50 or more a.m. or p.m. peak hour trips within the rural areas as defined by the Urban Growth Management Act.
(c) 
The county has required that an environmental assessment or environmental impact statement be prepared.
(d) 
A rezone of the subject property is being proposed.
(e) 
Current traffic or road system problems exist in the local area as identified by the county or a previous traffic study, such as a high-accident location, poor roadway alignment, or capacity deficiency.
(f) 
Adjacent neighborhoods or other areas are perceived to be impacted.
(g) 
The current or projected level of service of the roadway system as a result of the proposed development is perceived to be significantly affected, or is expected to exceed county adopted level of service standards.
(h) 
The proposed development may potentially affect the implementation of street system improvements outlined in the transportation element of the comprehensive plan, the transportation improvement program, or any other documented transportation project.
(i) 
At the time of environmental review, the original TIA is more than two years old or the proposed land use intensity increased by more than 10 percent.
(j) 
The proposed development is within an existing or proposed transportation benefit area. This may include latecomer agreements, road improvement districts (RID), or local/state transportation improvement areas programmed for development reimbursements.
(k) 
The proposed development generates more than 25 percent of p.m. peak hour traffic through a signalized intersection or the "critical" movement at an un-signalized intersection.
(Ord. 1194 Exh. B, 2007)
The Institute of Transportation Engineers (ITE) Trip Generation Manual provides trip generation rates for a variety of land uses, consisting of average rates or fitted curve equations. Appropriate land use code or codes shall be utilized for the traffic study. A sample format to present common land uses and their equivalent development units is shown below in Table 1:
Table 1
LAND USE CODE (LU and Code#)
P.M. PEAK HOUR TRIPS
BASIC TRIP RATE
ENTER
EXIT
Single Family Detached Housing (LU 210)
1.01 per dwelling unit
64%
36%
Apartment (LU 220)
0.62 per dwelling unit
67%
33%
Industrial Park (LU 130)
0.92 per 1,000 sq. ft. gross floor area
21%
79%
Movie Theater with Matinee (LU 444)
44.53 per movie screen
52%
48%
Day Care Center (LU565)
13.20 per 1,000 sq. ft. gross floor area
47%
53%
General Office Building (LU 710)
0.46 per employee
17%
83%
Shopping Center (LU 820)
3.74 per 1,000 sq. ft. gross leasable area
48%
52%
Fast Food Restaurant with Drive-Through Window (LU 834)
0.94 per seat
53%
47%
Drive-in Bank (LU 912)
54.77 per 1,000 sq. ft. gross floor area
50%
50%
(Ord. 1194 Exh. B, 2007)
Traffic impact analyses (TIAs) shall be conducted under the direction of a responsible individual or firm acceptable to the traffic engineer. The TIA shall be prepared by an engineer licensed to practice in the state of Washington with special training and experience in traffic engineering and who is a member of the Institute of Transportation Engineers (ITE). The developer shall provide the traffic engineer the credentials of the individual(s) selected to perform the TIA.
(Ord. 1194 Exh. B, 2007)
The study area shall include all site access drives, adjacent roadways, and major roadways and intersections in all directions from the site that are impacted by 50 or more inbound and outbound p.m. peak hour trips, or less as required by the county. Once the trip distribution for the proposed development has been approved by the traffic engineer, a formal "scoping" meeting may be conducted at the request of the project proponent and at the county's discretion to clearly identify study area and contents expected in the TIA.
(Ord. 1194 Exh. B, 2007)
The county will cooperate with cities within the county and with WSDOT to expeditiously review the transportation impacts of developments within the respective jurisdictions.
(Ord. 1194 Exh. B, 2007)
The horizon year shall be the anticipated build-out/full occupancy year for the development. Development with several stages of construction activity shall select a number of horizon years corresponding with the opening of each phase.
(Ord. 1194 Exh. B, 2007)
(1) 
The level of detail and scope of work of a TIA may vary with the size, complexity, and location of the proposed development. A TIA shall be a thorough review of the immediate and long-range effects of the proposed development on the transportation system.
(a) 
Proposed Development Prospectus.
(i) 
Provide a reproducible copy of the site plan showing the type of development, street system, right-of-way limits, access points, and other features of significance in the proposed development. The site plan shall also include pertinent off-site information, such as locations of adjacent intersections, driveways, land use descriptions, street right-of-way limits with respect to the existing roadway, and other features of significance.
(ii) 
Provide a vicinity map of the project area showing the transportation system to be impacted by the development.
(iii) 
Discuss specific development characteristics such as type of development proposed (single-family, retail, industrial, etc.), internal street network, proposed access locations, parking requirements, zoning, and other pertinent factors attributable to the proposed development.
(iv) 
Discuss project completion and occupancy schedule for the proposed development. Identify horizon years for traffic analysis purposes.
(b) 
Existing Conditions.
(i) 
Discuss street characteristics including functional classification, number of travel lanes, lane width, shoulder treatment, bicycle path corridors, and traffic control at study intersections. A figure may be used to illustrate existing transportation facilities.
(ii) 
Identify safety and access problems including discussions on accident history, sight distance restrictions, roadway geometry deficiencies, traffic control, and pedestrian conflicts.
(iii) 
Obtain all available traffic data from Lewis County and cities within the county. If current or applicable data is unavailable, the individual or firm preparing the TIA shall collect the necessary data to supplement the discussions and analysis in the TIA.
(iv) 
Conduct new manual peak hour turning movement counts at study intersections if traffic volume data is more than two years old at the time of environmental review or if required by the county.
(v) 
A figure shall be prepared showing existing average daily traffic (ADT) and peak hour traffic volumes on the adjacent streets and intersections in the study area. Complete turning movement volumes shall be illustrated. This figure shall represent the base line traffic volumes for analysis purposes.
(c) 
Development Traffic. This element of the TIA shall be conducted initially to identify the limits of the study area. The threshold requirement of development traffic exceeding 50 p.m. peak hour trips (two-hour average) shall apply. The individual or firm preparing the TIA shall submit to the county engineer a figure illustrating the proposed trip distribution for the proposed development. The trip generation shall be included in a table form on the figure with the peak hour traffic volumes assigned to the study area in accordance with the trip distribution.
(d) 
Future Traffic.
(i) 
Future Traffic Conditions Not Including Site Traffic.
(A) 
Future traffic volumes shall be estimated using information from transportation models or applying an annual growth rate to the base line traffic volumes. The future traffic volumes shall be representative of the horizon year for project development.
(B) 
In addition, proposed "on-line" pipeline development projects shall be taken into consideration when forecasting future traffic volumes. The increase in traffic from proposed pipeline projects shall be compared to the increase in traffic by applying the appropriate growth rate.
(ii) 
Future Traffic Conditions Including Site Traffic.
(A) 
The site-generated traffic shall be assigned to the street network in the study area based on the trip distribution model. The site traffic shall be combined with the forecasted traffic volumes to show the total traffic conditions estimated at development completion. A figure will be required showing daily and peak period turning movement volumes for each traffic study intersection.
(e) 
Traffic Operations.
(i) 
The level of service (LOS) and capacity analysis shall be conducted for each pertinent intersection in the study area as determined by the public works department. The methodology and procedures for conducting the capacity analysis shall follow the guidelines specified in the most recent edition of the highway capacity manual. The individual or firm preparing the TIA shall calculate the intersection LOS for each of the following conditions:
(A) 
Existing p.m. peak hour traffic volumes (Figure required).
(B) 
Future p.m. peak hour traffic volumes not including site traffic (Figure required).
(C) 
P.M. peak hour traffic volumes for project completion horizon year, including site traffic (Figure required).
(D) 
Level of service results for each traffic volume scenario (Table required).
(ii) 
The level of service table shall include LOS results for p.m. peak periods. The table shall show LOS conditions with corresponding vehicle delays for signalized intersections.
(iii) 
The capacity analyses for existing signalized intersections shall include existing phasing, timing, splits, and cycle lengths in the analysis as observed and measured during the peak hour traffic periods.
(iv) 
If the proposed development is scheduled to be completed in phases, the TIA shall conduct a LOS analysis for each separate development phase. The incremental increases in site traffic from each phase shall be included in the LOS analysis for each proceeding year of development completion. A figure will be required for each horizon year of phased development.
(v) 
If the proposed development impacts a traffic signal coordination system currently in operation, the traffic engineer may require the TIA to include operational analysis of the system. Timing plans and proposed modifications to the coordination system may be required.
(vi) 
The capacity analysis shall be conducted using computer software. The individual or firm preparing the TIA shall use SIGNAL2000, or an approved equivalent, for capacity analysis of signalized intersections. The computer worksheets shall be submitted concurrently with the TIA document to the public works department. For un-signalized intersections, the highway capacity manual methodology shall be used. SIDRA software or an approved equivalent shall be used for analyzing modern roundabout intersections. A copy of the capacity analysis worksheets shall be submitted concurrently with the TIA document.
(f) 
Mitigation.
(i) 
The TIA shall include a proposed mitigation plan. The mitigation may be either the construction of necessary transportation system improvements and/or contributions to the county for the proposed development's fair share cost of identified future transportation improvements. Mitigation measures shall be required to the extent that the transportation facilities operate at or above the county's adopted level of service (LOS) standards.
(ii) 
The following guidelines shall be used to determine appropriate mitigating measures of traffic impacts generated by proposed developments:
(A) 
On transportation facilities where there is a need to construct improvements by the horizon year of the proposed development, the cost for the mitigation will be entirely borne by the proposed development. However, in the event the public works department and the community development department identify more than one development under simultaneous review, cumulative impacts and distribution of mitigation costs may be considered.
(B) 
On transportation facilities programmed for new improvements as part of a county project, the adverse traffic impacts of the proposed development will be considered mitigated by providing a proportionate share contribution of the costs for the proposed improvements. The proportionate share costs for the improvements shall be based on the percentage of proposed development traffic generated through the intersection. The percentage shall be based on the total projected peak hour volumes for the horizon year of the transportation study.
(C) 
On transportation facilities where the existing level of service is less than the adopted concurrency standard, and where no improvements are programmed to improve capacity and traffic operations, the proposed development shall mitigate the intersection to an acceptable level of service condition or wait until the improvements are implemented by the county, state, or other developments. Improvements made by the county prior to the development of the subject project shall be reimbursed by the proposed development based on a proportionate fair share cost of the facility improvements.
(D) 
Un-signalized intersections that currently operate at less than a level of service "D" condition shall be analyzed for traffic signal and intersection improvements. If two or more traffic signal warrants are satisfied, signal and intersection improvements will be required as a mitigating measure for the proposed development. If at least two traffic signal warrants are not satisfied by the proposed development's horizon year, the TIA shall determine if traffic signal warrants and intersection improvements would be needed within a five-year period after the proposed development's horizon year. The proposed development would be required to provide a proportionate share cost towards future traffic signal and intersection improvements if warranted within the five-year period.
However, if traffic signal warrants are not satisfied after a five-year period from the proposed development's horizon year, mitigating impacts would not be required from the proposed development for traffic signal and intersection improvements.
(E) 
For signalized intersections in the county where the projected level of service condition is at "D" but where one or more of the level of service conditions on the approaches falls below level of service "D," mitigating measures may be required to improve the capacity and traffic operations at the intersection. The county reserves the right to review all adverse traffic impacts at these intersections and to determine appropriate mitigating measures.
(Ord. 1194 Exh. B, 2007)
For traffic analysis, the p.m. peak hour conditions shall be used. The p.m. peak hour is defined as the average of the 60-minute period between 4:00 p.m. and 6:00 p.m. with the greatest sum of traffic volumes on a roadway segment or passing through the area of the project and the next highest hour adjacent to the peak commute hour. Reversed flow at intersections from morning to afternoon, and other unusual conditions, shall require analysis for both a.m. and p.m. peak hour conditions, as required by the county.
(Ord. 1194 Exh. B, 2007)
(1) 
Site-generated traffic of proposed developments shall be estimated using the latest edition of the trip generation manual as published by the Institute of Transportation Engineers (ITE). The land use code or codes appropriate for the development shall be used. Variations of trip rates will require the approval of the traffic engineer. Average trip rates as described in LCC § 12.60.440 shall be used for all land-use categories where applicable. Trip rate equations will be allowed for those land uses without average rates.
(2) 
Site traffic shall be generated for daily and p.m. peak hour periods. For certain types of developments, the traffic engineer or his/her designee may also require site traffic estimates for the a.m. peak period.
(3) 
For multi-use and or phased projects, a trip generation table shall be prepared showing proposed land use, trip rates, and vehicle trips for daily and peak hour periods and appropriate traffic volume discounts if applicable.
(Ord. 1194 Exh. B, 2007)
Adjustments to trip generation made for "pass-by" or "mixed-use" traffic volumes shall follow the methodology outlined in the latest edition of the ITE Trip Generation Manual.
(Ord. 1194 Exh. B, 2007)
The directional distribution of traffic to and from the project shall be estimated using local traffic volume data provided by Lewis County, the cities within Lewis County, and the Washington State Department of Transportation Traffic Data Office. At the county's discretion, the Lewis County transportation model may be used for directional distribution estimates.
(Ord. 1194 Exh. B, 2007)
The minimum level of service (LOS) for roads within Lewis County shall be as shown in the transportation element of the county's comprehensive plan. The level of service for state routes and major county roadways is calculated on a corridor basis. A corridor is defined as a transportation route, or portion of that route, that connects major land use designations. Logical termini, such as major intersection points, land use changes or land use barriers, define the corridor boundaries. An affected corridor is defined as a road link or intersection on which a project may generate 50 new peak hour trips or turning movements.
(Ord. 1194 Exh. B, 2007)
(1) 
The State Growth Management Act and Chapter 17.130 LCC require that a proposed development undergo a concurrency review and determination. Concurrency describes the situation in which road facilities are available when the impacts of development occur. For road facilities, this time period is statutorily established as within six years from the time of development. To satisfy concurrency:
(a) 
That part of the existing transportation system within the significant influence area of the development, functioning at the county's adopted minimum level of service, must have adequate capacity for the additional trips generated by the project at the time of preliminary plat or project approval, or
(b) 
The development must have, at the time of final project approval, a financial guarantee for transportation improvements required to achieve county adopted minimum levels of service with the additional trips generated by the project to be in place within six years of final project approval, or
(c) 
The applicant shall construct the transportation improvements required to achieve county adopted minimum levels of service with the additional trips generated by the project to be in place at the time of final project approval.
(2) 
For purposes of evaluating concurrency on transportation facilities in Lewis County, corridor-wide levels of service are used, rather than single movement or intersection measures. An affected corridor will be defined as any road link or intersection on which a project may generate 50 new peak hour trips or turning movements. The corridor area ends when less than 10 of the new peak hour trips remain on the segment of roadway or if these trips extend beyond the logical termini of the corridor. Typically, the length of corridor in rural areas will not exceed two to three miles and up to five miles in urban environments. The length and termini of an affected corridor will be evaluated on a case-by-case basis as determined by the traffic engineer. The level of service deficiency shall be when the overall average for the entire corridor falls below LOS "D."
(Ord. 1194 Exh. B, 2007)
(1) 
Intersections and roadway segments within the influence area shall be evaluated to determine if the probability of accidents will increase with the addition of project traffic. Accident record research, conflict analysis, and potential for increased accidents shall be evaluated.
(a) 
Accident records for the current three-year period will be analyzed to determine whether patterns of accidents are forming within the influence zone and what alternative treatments should be considered to correct the problem. Examples of recurring accidents include:
(i) 
Right-angle collisions at an intersection.
(ii) 
Rear-end collisions at an intersection.
(iii) 
High frequency of vehicles leaving the roadway.
(b) 
Conflict analysis is applicable to specific locations where accident data is not available or insufficient for analysis. This analysis is used to predict or measure accident potential at a location. A conflict analysis should determine the number of conflict points, frequency of conflicts, and severity of conflicts based on expected traffic volumes and mix of traffic. Similar to the manner in which accidents are grouped by type of collision, traffic conflicts are arranged by type of maneuver. Examples of intersection conflicts are:
(i) 
Cross traffic;
(ii) 
Opposing left-turn cross traffic;
(iii) 
Pedestrian.
A field study shall be completed and the results evaluated to identify the types of conflicts, roadway/intersection characteristics that contribute to the conflicts, and what alternative treatment should be considered to correct the problem.
(c) 
Horizontal and vertical geometry of applicable roadway segments shall be reviewed for consistency with adopted standards and nationally recognized guidelines. Deficiencies for current use and horizon year use shall be identified. The general potential for increased accidents shall be evaluated in the context of projected traffic volume and roadway characteristics.
Impacts to substandard roadway segments shall be evaluated as required by the county.
(Ord. 1194 Exh. B, 2007)
The number of vehicle access points should be minimized by sharing driveways and linking parking lots between adjacent uses. Commercial developments shall provide coordinated internal circulation and connected parking facilities. Well-defined walkways must be designed into all parking lots, with interconnections between walkways to create safe walking conditions[1].
(Ord. 1194 Exh. B, 2007)
[1]
Editor's Note: Exhibit 3 Examples for Levels I and II TIA is included as an attachment to this title.