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SR-9-A (89) 9..,4 OCT 2 9 1(;Q1 LUTM:PPD: w/hcmsigms COUNCIL MEETING: October 29, 1991 Santa Monica, California TO: Mayor and City Council FROM: city staff SUBJECT: Recommendation to Select a Definition of Significant Impact When Analyzing Traffic Impacts as Part of the Environmental Review Process INTRODUCTION This report recommends that the City Council select a criterion to determine what constitutes a significant traffic impact under the Highway Capacity Manual (HCM) delay methodology. This report presents four alternative criteria for defining a significant traffic impact for purposes of environmental review, and recommends one as the preferred alternative. BACKGROUND On May 14, 1991 the City Council directed staff to use the HCM delay methodology to assess traffic in the Master Environmental Assessment (MEA) and for use in future traffic studies. The HCM delay methodology was selected after a study session and public hearing on the various ways to prepare traffic impact reports. The existing city significance criterion for traffic impacts is based upon the use of the Critical Movement Analysis (CMA) 9--4 - 1 - OCT ') rI 1M' "-' V I.... v; traffic methodology. The CMA methodology focuses on the volume of traffic that travels through an intersection in relation to the theoretical capacity of the intersection. The HCM delay methodology focuses on the average delay of vehicles at intersections. since these two methodologies are distinctly different, it is necessary to redefine the city's definition of a significant traffic impact for purposes of environmental review. The civic Center specific Plan EIR traffic study is in preparation and will be the first traffic study to use the HCM delay analysis and new significance criterion. The study will be based upon the Master Environmental Assessment data for existing and future base traffic conditions developed using the HCM delay methodology. While a significance criterion is not required for the MEA analysis, it is essential that the Council select a significance criterion for use in future studies. Failure to determine a new definition will delay the release of the civic Center Specific Plan Draft ErR. ANALYSIS DETERMINING LEVEL OF SERVICE Under any method of traffic analysis (the previous CMA, the current HeM, or other accepted methodology), the first step is classifying the level of service, or LOS designation, for each intersection. Intersections are classified as LOS A F, depending upon the severity of traffic conditions. - 2 - As stated in Policy 4.3.1 of the Land Use and Circulation Element for the City of Santa Monica: 11 Safe or acceptable levels of service on city streets shall be a criterion for evaluation of new development proposals. Level of Service shall be 'c' for collector, feeder, and local streets and 'D' for arterials or better where possible." Based on this policy, intersections operating at a level of service A through Dare determined to be acceptable. Intersections operating at E and F are determined to be unacceptable. Under the new proposed significance standard, an impact will be considered "significant" if it causes an intersection operating at LOS A - D to operate at an unacceptable level (LOS E or F). Mitigation will be required to return the intersection to an acceptable level. The balance of the discussion concerning significance criteria only applies to intersections that will operate at a level of service E or F. OTHER JURISDICTION'S USE OF HCM No guidance is found from other jurisdictions concerning a workable definition of Usignificant impactU using the HCM methodology. A number of cities throughout California currently use the HCM delay traff ic methodology for assessing operating conditions of intersections. These cities include Rancho Cucamonga, San Juan Capistrano, Lancaster, San Jose, Berkeley, - 3 - San Francisco and Palo Alto. However, the HCM methodology is not used by these Cities for evaluating project impacts. These jurisdictions use different methodologies or definitions of significance for determining environmental impacts. Some cities use a hybrid approach where HeM is used, but volume/capacity ratios or other methods are the criteria used to determine a significant impact. Many cities that use HCM are located in outlying suburban areas where, even at buildout, intersections are not expected to reach LOS E or F conditions. This is important since, as explained later, the seconds of delay criterion using the HCM delay methodology cannot reliably be used once an intersection has reached LOS F. Some cities in Northern California do not define a significant impact and often do not require mitigation for projects that add traffic to congested intersections. These cities are able to do this since they have an extensive urban transit system available to commuters and prefer to encourage transit use rather than making expensive street improvements to accommodate more vehicles. METHODOLOGY CAPACITY AND LEVEL OF SERVICE The HCM delay methodology determines level of service based on average seconds of delay. Under the city's previous methodology (CMA), level of service was based on capacity. Because delay is a complex measure, its relationship to capacity is also complex. - 4 - The HCM intersection capacity analysis evaluates volume/capacity (v/c) ratios for individual lane movements and then develops a composite v/c ratio for the sum of critical movements or lane groups within the intersection. The v/c ratio is the actual or projected rate of flow on a lane or group of lanes during a peak 15 minute interval divided by the capacity of the lane or group of lanes. Level of service is based on the average delay per stopped vehicle for various movements within the intersection. Delay is a measure of driver discomfort, frustration, fuel consumption and lost travel time. While vlc affects delay, there are other parameters that more strongly affect it, such as the length of green phases, signal timing, and others. Thus, for any given v/c ratio, a range of seconds of delay values may occur, and vice-versa. The HeM LOS criteria are stated in terms of the average delay per stopped vehicle, and can be described as follows: o LOS A describes operations with very low delay, where most vehicles do not stop at all and arrive during the green phase. On average, vehicles wait less than or up to 5 seconds. o LOS B describes where more vehicles stop than at LOS A, causing higher levels of average delay. On average, vehicles wait between 5.1 to 15.0 seconds. - 5 - o LOS C describes operations where the number of vehicles stopping is significant, although many still pass through the intersection without stopping. On average, vehicles wait between 15.1 to 25.0 seconds. o LOS D describes operations where the influence of congestion becomes more noticeable with longer delays, more vehicles stopping and the proportion of vehicles not stopping declining. On average, vehicles wait between 25.1 to 40.0 seconds. o LOS E describes operations that are considered the limit of acceptable delay. On average, vehicles wait between 40.1 to 60.0 seconds. o LOS F describes operations with delay in excess of 60 seconds which is considered unacceptable to most drivers. On average, vehicles wait beyond 60.1 seconds. RELIABILITY OF THE HCM DELAY METHODOLOGY According to the Highway Capacity Manual Special Report 209 (1985) which defines the HCM delay based methodology, once an intersection reaches a v / c of 1.2 or greater, the seconds of delay produced by the model is no longer valid and cannot be used for purposes of determining impacts at an intersection. This situation will likely occur at most intersections in the City with a LOS F. Thus, for determining whether a siqnificant impact - 6 - will occur at a LOS F intersection, the seconds of delay provided by the HCM delay methodology cannot reliably be used. CRITICAL MOVEMENT ANALYSIS Regardless of the methodology used, HeM or CMA, another important factor which the City may wish to use in determining significance is critical movements at intersections. Critical vehicle movements are those movements that use the greatest amount of green time at a particular signal phase. This concept is important because vehicles can be added to non-critical movements without impacting the overall intersection operating conditions. This is because the critical vehicle movements already use up more green signal time, so the extra vehicle can move through on the non-critical movements without needing any extra green time to accommodate it, therefore not causing any increase in delay. Some of the alternatives presented below take critical movements into account when determining significance. ALTERNATIVES This report presents four alternative definitions to determine a significant traffic impact. These alternatives range from the existing definition of significant impact to the most stringent level, which prohibits a net increase in vehicles at a LOS E or F intersection. Defining a significant impact in a strict manner does not prohibit the city from approving development that cannot mitigate a significant impact. Instead, a strict definition will - 7 - require the decision makers to weigh the benefits of the project against the negative impacts and, where appropriate, adopt findings to justify the project approval. Since seconds of delay cannot be accurately quantified for intersections operating at LOS F, a different significance criterion will have to be utilized for those intersections. While the HCM v/c ratio is not used for determining LOS under the HCM methodology, it still represents a tangible, quantifiable criterion for analyzing impacts at an intersection, and is appropriate for determining significant impacts. ALTERNATIVE 1: NO NET INCREASE IN AVERAGE SECONDS OF DELAY This alternative would define a significant traffic impact as any net increase in the average seconds of delay per vehicle for intersections operating at a future base level of service E. For intersections operating with a future base level of service F, this alternative would define as a significant impact any increase of .01 or greater in the HeM v/c ratio. Thus, this alternative uses two methods to measure the impact due to the fact the HCM methodology does not provide reliable seconds of delay after an intersection reaches a v/c of 1.2 or greater. This alternative allows additional vehicles to be added to an intersection if a project adds vehicles to non-critical movements thereby adding vehicles but not increasing the overall vehicle delay. This makes efficient use of the available capacity at an - 8 - intersection and represents a fair significance criteria by emphasizing the overall operation of an intersection. This alternative also responds to the criticism that the city's previous significance definition allowed projects to increase traffic at LOS E and F intersections by an increase in the vjc ratio of .02 before mitigation would be required. Finally, this alternative uses the HCM seconds of delay criterion for determining significant impacts at LOS E, and the HeM v/c ratio for intersections at LOS F. This provides the City with a consistent methodology for determining both levels of service and significant impacts. ALTERNATIVE 2: GREATER THAN .f SECOND INCREASE IN DELAY This alternative would define as a significant impact an increase of greater than four seconds in average vehicle delay due to the addition of project traffic to intersections with future base LOS of E. Intersections with LOS F will have a significance criterion of an increase of .02 or greater of the HCM vjc ratio. Four seconds was chosen because it is roughly equivalent to the City's existing significance criterion under the CMA methodology. Intersections at LOS F will continue to use the .02 allowable increase, but with the HeM vjc ratio. - 9 - This alternative would allow projects to increase average vehicle delay at an LOS E intersection by 4 seconds, and the v/c by .02 at LOS F intersections, regardless of impacts to critical movements. This alternative uses the same significance criterion that the City previously used, but applies it to the HCM methodology. ALTERNATIVE 3: ANY INCREASE IN NUMBER OF VEHICLES This alternative would define as a significant impact the increase of one additional vehicle to any movement at an LOS E or F intersection. This provides a significance criterion that is not dependent upon seconds of delay or the HCM vjc ratios. This is a very strict alternative because it would not allow any increase in vehicles even though vehicles could be added without resulting in a delay to non-cri tical movements at an intersection. This alternative prevents the efficient use of the existing capacity that may exist at an intersection. ALTERNATIVE 4: ANY INCREASE IN VEHICLES TO THE CRITICAL MOVEMENTS This alternative would define as a significant traffic impact any increase in the number of vehicles to a critical movement of an LOS E or F intersection. Like alternative number 3, this alternative relies solely upon the number of vehicles added and is not dependent upon seconds of - 10 - delay or HeM v/c ratios. The theory behind using the number of vehicles added to the critical movements is that those are the movements that are significantly impacting an intersection. Additional vehicles can be added to movements at an intersection where they will not result in any additional delay. BUDGET/FINANCIAL IMPACT The recommendation presented in this report does not have a budget or fiscal impact. NOTIFICATION A notification flyer was mailed to a list of over 500 interested parties notifying them of the October 29, 1991 City Council meeting on the selection of a significant traffic impact for purposes of environmental review. RECOMKENDATION It is recommended that the City Council adopt alternative one as the criterion to determine a significant traffic impact. This alternative defines a significant impact as any net increase in average seconds of delay per vehicle for intersections operating at a future base LOS E. For intersections operating at a future base LOS F, this alternative defines a significant impact as any increase of .01 or greater in the HeM v/c ratio. - 11 - This alternative is recommended because it provides for essentially a no net increase in the HCM seconds of delay and v/c ratio for intersections operating at a future base of LOS E or F. Yet the alternative allows for efficient use of the available capacity at an intersection by allowing vehicles to be added to the non-critical movements as long as there are no significant impacts associated with those additional vehicles. Also, by using the HCM seconds of delay and v/c ratios, this alternative provides the city with a consistent methodology for determining both levels of service and significant impacts. It is recommended that the city council also define as "significant" an impact which causes an intersection operating at LOS A - D to operate at an unacceptable level (LOS E or F). Mitigation will be required to return all impacted intersections to an acceptable level. Where mitigation is not feasible, unavoidable significant adverse impacts will result. The Planning Commission, or City Council on appeal, would be required to adopt a statement of overriding considerations finding that the benefits of a project outweigh the adverse environmental impacts if a project is to be approved. Prepared By: Paul Berlant, Director of LUTM Suzanne Frick, principal Planner Liz Casey, Associate Planner Paul Casey, Transportation Planner Land Use and Transportation Management Department Program and Policy Development Division - 12 -