Chapter 6 Mobility Standards Appendix 6E Guidelines for Traffic Impact Studies and Air Quality Analysis Page3 of 6

Trip Generation: Average trip generation rates or regression equations for the peak hour of the adjacent street will be obtained from the current edition of the Institute of Transportation Engineer's Trip Generation Manual or Local Trip Generation Study published in October 1993. Other local data may be acceptable provided it was collected using recommended methodology and can be properly documented.
Peak Hour Percent: A peak hour percentage of 10 percent of the daily trips will be assumed for existing traffic unless hourly counts are available.
Peak Hour: The petitioner shall use the peak one hour period which occurs during either 7-9 A.M. or 4-6 P.M. periods or both, as agreed to by the staff and petitioner. In some cases, however, the PW&T staff may require additional hours, for example, Friday nights or Saturday afternoon, to also be analyzed.
Directional Split: The directional split of the entering and exiting traffic associated with the development will be derived from the ITE Trip Generation manual unless other acceptable locally generated data is available.

Pass-by Trips: The percent of pass-by-trips shall be applied to the trips generated by the proposed development and assigned to the adjacent street network. This rate does not affect the proposed project's driveway volumes but rather reassigns existing trips to movements entering and existing the proposed development. The pass-by trip rates will be agreed upon during the preliminary meeting. The following pass-by trip rates have been determined for some land uses in Jefferson County:

Retail		30-35%
Quality and Sit Down Restaurants		25%
Fast-Food Restaurants		30-50%
Banks		55%
Convenience/Gas Stations		55-60%

These rates were determined as Part of a Local Trip Generation Study. The use of these rates are recommended, however, the developer may supply additional information for review and consideration.

Diverted Linked Trips: A reassignment for diverted trips will generally occur outside the impacted study area; therefore, for the purpose of these traffic impact studies, diverted trips would be considered "new trips" within the study area and can be ignored in most cases. This factor, if applicable, will be decided during the preliminary meeting.
Internal Circulation Trips: Reductions for internal circulation trips are applicable for projects such as shopping centers with out-lots and represents a reduction in projected driveway trips. The internal circulation trip rate will be agreed upon during the preliminary meeting and shall not exceed 10 percent.
Trip Distribution: The directional distribution of the generated trips entering and exiting the proposed development via all access points must be justified by the relative locations of other traffic generators (e.g., employment centers, transportation terminals, etc.) and/or trip table information. These factors, or other factors agreed upon by the staff, shall be applied to the traffic generated by the proposed development as well as the traffic generated by nearby approved projects.
Trip Assignment: The distribution factors shall be applied to the trips generated by the proposed development and nearby approved projects and assigned to the existing traffic on the road network providing access to the proposed development.
Capacity Analysis: At the identified critical intersection(s), the existing and generated traffic is to be related to the adequacy of the intersection by using the techniques described in Chapters 9 and 10 of the 1985 Highway Capacity Manual. Special Report 209. The PW&T staff has the necessary computer program to review and verify this analysis. Link volume analysis shall also be related to the Highway Capacity Manual standards. The analysis should be carried out for the A.M. and/or P.M. peaks, as agreed to by the staff and petitioner. This analysis should use traffic data for non- holiday weekdays, unless specifically requested by PW&T staff to analyses other periods. It is also recommended that the operational methodology be used in the analysis of signalized intersections. If so desired, alternative capacity and level of service analysis techniques may be used, provided data is presented in such a form that the results may be duplicated using the latest version of the Highway Capacity Software and Signal Software sponsored by FHWA and McTrans, respectively.
Traffic Data:
1. Traffic volume data IS NOT available from PW&T at this time. Average Daily Traffic volumes, turning movement counts and traffic control signals data on roadways maintained by the Commonwealth of Kentucky MAY BE available from the Department of Highways or KIPDA. The above sources should be contacted concerning the availability of traffic data. If, however, acceptable data is not available, the petitioner is responsible for obtaining such data.
2. Traffic count data should be adjusted to the current year, or new counts should be made by the applicant if, in the opinion of the PW&T staff, traffic volumes have significantly increased due to some change(s) in the traffic pattern, such as the completion of a development project after the count was made.
3. If turning movement data is outdated or if there are locations for which data is non-existent, data must be acquired at the applicant's expense.
4. Intersection traffic counts conducted by the petitioner should be comprised of manual turning movement counts covering the period of 7-9 A.M. and 4-6 P.M. in order to allow for the selection of the peak hour within the nearest fifteen minutes (e.g., 4:00-5:00, 4:15-5:15, etc). The inclusion of all 7-9 A.M. and 4-6 P.M. turning movement data is requested as Part of the petitioner traffic impact analysis., Summaries of each fifteen minute period should be submitted, under separate cover, to PW&T. (A typical turning movement count summary form is present in Appendix D.)
5. Ideally the traffic analysis should be performed for the design hour which represents the 30th highest hourly traffic volume on an annual basis. However most peak hour traffic volumes counts in urban areas closely approximately the 30th highest hour. Exception to this generalization are when special events occur, holidays (and holiday periods), and the month of December. Although these periods should be avoided for traffic counting, on occasions because of scheduling considerations counts are made. Such counts should be adjusted to approximate the 30th highest hourly traffic volumes. Historical counts and staff knowledge of the area will be used to judge the adequacy of counts used by the applicant.
6. If the proposed development includes plans for the installation of a new traffic control signal, the petitioner must conduct a Traffic Signal Warrant Analysis. This analysis would produce documentation that indicates the conditions at the proposed location warrant a traffic signal by meeting the recommended minimum warrants presented in the Manual for Uniform Traffic Control Devices. (MUTCD). Documentation of this analysis should be included in the Appendix of the final report and should include, but not be limited to, the methodology used, daily traffic count data used in the analysis, and the resulting capacity analysis results at this location. A simple analysis form is presented in Appendix D.
Adequate Accommodation of Traffic: The ability of a highway system to carry traffic is expressed in terms of volume-to- capacity (V/C) ratios and level of service at the critical locations, usually intersections. The V/C ratios clearly define the degree of saturation at an intersection. A V/C ratio of 1.0 indicates that the intersection is operating at its theoretical capacity, that is, the traffic volume demand equals the estimated number of vehicle that may pass through the intersection in a given period of time. A value of over 1.0 depicts a situation where the demand exceeds the intersection's capacity and operational problems exist, either in geometries or signalization. As the V/C ratio approaches 0.9, breakdowns in the operational efficiency of the intersection tend to develop. When the V/C increases above 0.9, operational breakdowns also increase in frequency and may result in a high level of delay to motorists.

In considering mitigation measures, the change in V/C ratio and level of service must be taken into account as well as the actual V/C values for individual approaches and the overall intersection. If no mitigation exists or if the improvements required are beyond what could reasonably be expected from the petitioner, then negotiations between the petitioner and PW&T staff members will be conducted to determine the level of petitioner responsibility for improvements at the intersection.

Level of service for signalized intersections is defined by the Transportation Research Board's Special Report 209,1985 Highway Capacity Manual, in terms of delay. Generally, delay is considered a measure of driver discomfort, frustration, lost time and fuel consumption. Delay at signalized intersections is a result of a number of factors, including the signal's cycle length, phasing, progression in relation to other signals, traffic volumes and the intersection's lane configuration and geometries. Although they are an important consideration in intersection analysis, delay and level of service results should not be used in determining mitigation measures. The PW&T staff will rely primarily on the V/C ratio in determining the effectiveness of proposed mitigation measures.

"Levels of service" as defined by the 1985 Highway Capacity Manual are presented in Table A-1.
Air Quality Analysis Model: The recommended model for roadway and signalized intersections is CAL3QHC. A copy of the computer program and user's guide prepared by the U.S. Environmental Protection Agency may be purchased from Pollution Control District. CAL3QHC is a microcomputer-based modeling methodology developed to predict the level of carbon monoxide (CO) emitted from motor vehicles traveling near roadway intersections.
Mapping: The application of the CAL3QHC model requires a scale drawing of each critical intersection. It is recommended that the scale be 1" = 50'. Alternative scales may be considered at the initial review meeting. When a grid system is placed on the scale drawing the spatial relationship between the driving lanes and receptors may be replicated within the computer model. A transparent grid has been successfully used on recent projects. The drawings should provide existing lane configuration, lane widths, and location of all-rights-of-way. Contour lines and spot elevations also must be presented on each drawing. Separate drawings showing existing and proposed conditions should be provided. Copies of these drawing should be submitted along with the impact analysis report.
Receptor Location: The receptors should be located where the maximum total projected concentration is likely to occur (not on the roadway itself). As a rule a receptor should be located outside the "mixing zone" of the travel lanes. The distance from the travel lanes should be 10 feet (3 meters) or at the right-of-way line (if no people generating activity occurs within the right-of-way), whichever is the greatest distance.

All space outside the right-of-way is considered to be available to the general public whether or not it is presently used. A dedicated buffer zone boundary legally identified for landscaping purposes on which routine public access is not intended may be used to locate receptor locations rather than the right-of-way line.

Free Flow Speeds: At an intersection, vehicles are considered to be idling when the traffic signal is red, all other times the vehicles are considered to be in a free flow mode. The speed for a free flow link represents the speed experienced by drivers traveling along the link during the time the traffic signal is not red. A free flow speed must be assigned to each link.

Based on the posted speed limit the following speeds should be used as default values:

Posted Speed (mph)		Free Flow Speed (mph)
55		40
45		35
40		30
35		25
25		20

Actual free flow speeds may be substituted for the above default values based on an acceptable documented study. The techniques in Chapter 9 of the Highway Capacity Manual (TRB 1985) to estimate adjusted vehicle speed may be used.

Emissions - MOBILE 5 a: Separate emission rates are used as input data to CAL3QHC for each free flow and queue link. The U.S. EPA mobile source emission factor model (MOBILE 5 a) has been applied by APCD to generate both free flow and idling emission rates. Appendix E contains approved emission rates for the years 1991 through 2000. No other emission rates may be used without prior approval, in writing, of APCD.
National Ambient Air Quality Standards: The ambient air quality standards for carbon monoxide applicable in Jefferson County are the following Federal Standards

One Hour - 35 ppm or 40 mg/m3
Eight Hour - 9 ppm or 10 mg/m3

These values may not be exceeded more than once per year. Any modeled concentrations above 35 ppm or 9 ppm is considered a violation.
Persistence Factor: The CAL3QHC model is to be used to predict the one-hour worst-case concentrations. A persistence factor is used to convert the one-hour worst-case modeling results to a predicted 8-hour average concentration. The persistence factor primarily accounts for the variation in traffic over the eight hour period and can be estimated by using traffic counts made over the eight hour period on each leg of the intersection. These counts may be made with an automatic traffic counting machine, manual counts are not necessary. The persistence factor is determined by dividing the average of the eight highest hours by the peak hour. The calculated factor shall be used if it is greater then 0.60 or less then 0.80. if lower then 0.60 use 0.60 and if greater than 0.80 use 0.80. The eight highest hours must be continuous and must contain the peak hour.

The counts on the legs of the intersection should be summed for this calculation to determine one overall persistence factor for each intersection. The calculations used to determine the persistence factor shall be documented in the impact study report.

Background Concentrations: All concentrations of carbon monoxide that are not emitted by the sources being modeled are background concentrations. They can be wind blown from far away or from nearby sources such as parking lots and adjacent intersections. The following background concentrations (one hour) should be used for the conditions described:

	Condition	Background Concentration (ppm)
1)	CBD or intersection with congested adjacent 3.0 intersection(s) and nearby parking facilities.	3.0
2)	Intersection with nearby parking facilities	2.0
3)	Isolated intersection (no nearby congested intersection or nearby parking facilities).	1.5

The use of background concentrations other than the above must receive prior approval, in writing, of the APCD.

Meteorological Conditions: The CAL3QHC User's Guide discusses various meteorological parameters that are input to the model. The following values or responses shall be used for air quality analysis in Jefferson County.

Wind Speed		1 Meter/Second
Wind Angle		0°
Multiple Wind Angles		Yes
Increment Angle		10°
First Increment Multiplier		0
Last Increment Multiplier		36
Mixing Height		1000M
Stability Class		D
Surface Roughness		321 cm
CBD		175 cm
Office Area		175 cm
Suburban Area		108 cm

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