Based on the AASHTO: PREPARED FOR

Transcription

1 Based on the AASHTO: Ne va da PREPARED FOR Pr oj P R ec t O C Sa E S fety S September 2015

2 Introduction The Nevada Department of Transportation (NDOT) has as its first department goal to optimize safety and has taken on the monumental challenge of attaining zero fatalities related to traffic crashes. Through the focused effort of NDOT staff and other relevant agencies, the number of traffic fatalities and the fatality rate in Nevada has been significantly reduced. Continued efforts and new approaches are necessary to continue this progress towards zero fatalities. NDOT has been applying crash reduction factors (CRFs) developed from historical crash data to estimate the anticipated benefit of certain countermeasures for many years. In 2010, the first edition of the AASHTO Highway Safety Manual (HSM) was published, which provides detailed processes for consistently quantifying the safety impacts of proposed improvements. This document, the Nevada Project Safety Process (PSP), is a guide for the incorporating these processes into the project development process in Nevada. The purpose of the PSP is to establish a consistent process of quantifying the expected crash impacts for transportation improvements based on the HSM to the extent practicable. When projects are proposed, certain improvements are identified. Professionals select improvements based on a number of project specific criteria. The safety performance is measured by annual reduction in crashes. This document specifies two method of analysis to determine the change in crashes: 1. Crash Modification (CMF) Method (HSM Part D) 2. Predictive Method (HSM Part C) One important metric in the decision making process for improvements is cost. After annual change in crashes is determined, the proposed improvements can be further analyzed for economic effectiveness. The PSP references the HSM Chapter 7 Economic Appraisal for performing Benefit- Cost Analysis and verifying if the improvements selected are economically justified according to safety benefit. The HSM is highly dependent on the availability of applicable data. Therefore, application of this PSP will continuously evolve as the HSM and the associated relevant data evolves. Engineering judgment is required to apply PSP and HSM procedures appropriately. Updates to the PSP will be posted on NDOT s Project Safety Process website. 1

3 Nevada Project Safety Process The safety impacts of all project are to be evaluated quantitatively to the extent practicable. All safety evaluations are to be performed by someone that has completed Highway Safety Training. Acceptable Highway Safety Training alternatives are listed on NDOT s PSP website. This PSP is based on applying the principles within the HSM to the extent feasible. All project evaluations are to include the annual reduction in crashes. All safety improvement alternatives are to also include the benefit-cost ratio (BCR) The following graphic indicates the change in crash analysis method according to project type: Project Type Change in Crash Analysis Method PLANNING» Corridor Studies» Highway Safety Improvement Program (HSIP)*» Project Prioritization MAINTENANCE» Roadway Maintenance CRASH MODIFICATION FACTOR (CMF) METHOD (See following procedure) DESIGN ALTERNATIVES» Road Safety Audits» Project Scoping» Construction Drawings» Encroachment Permits CONSTRUCTION» Design Exceptions» Value Engineering PREDICTIVE METHOD (See following procedure) *SafetyAnalyst to be used for HSIP network screening when the required data is available. 2

4 Crash Modification Factor (CMF) Method A crash modification factor (CMF) is a multiplicative factor used to compute the expected number of crashes after implementing a given countermeasure at a specific site. CMF = EXPECTED CRASHES WITH TREATMENT EXPECTED CRASHES WITHOUT TREATMENT CMF = 1.0 CMF < 1.0 CMF > 1.0 Expected to have no impact on safety Expected to reduce crashes Expected to increase crashes A crash reduction factor (CRF) is similar to a CMF but stated in a different way. A crash reduction factor (CRF) is the percentage crash reduction that might be expected after implementing a given countermeasure at a specific site. Caution should be used in selecting an appropriate CMF. The following guidance must be followed: CMFs may be used from the Highway Safety Manual Part D or the FHWA CMF Clearinghouse website ( An approved list of CMFs applicable to Nevada s roadways will be maintained on NDOT s PSP website. Select the most appropriate CMF for the proposed improvement based on four areas: Countermeasure read the abstract and determine if the CMF countermeasure is applicable to the proposed improvement Star Rating CMFs may be used from the Highway Safety Manual Part D or the FHWA CMF Clearinghouse with a star rating of 4 or greater. The star ratings are based on a score (0-14) ( The score is given from an equation of quality assessment of the CMF development: Context CMF selected should match three types of project context: Situational Area type, time of day, etc. Geometrics Slope, number of lanes, width, driveway density, hazard ratings, etc. Operational Traffic related ADT, traffic volumes, etc. Crash Related Crash history and type CRF = (1 - CMF) * 100 SCORE = (2*Study Design) + (2*Sample Size) + Standard Error + Potential Bias + Data Source Judgment Use engineering judgment and be able to justify the use of the selected CMF Be sure the selected CMF is applicable to the particular crashes used in analysis and that the existing condition equals the base condition. Some CMFs are only applicable to particular crashes and not all crash types. For example, a CMF for installing lighting is typically only applicable to night-time crashes and not all crashes. Unless the countermeasure being applied to a site addresses independent crash types, multiplying several CMFs is likely to overestimate the combined effect. Engineering judgment must be used in applying multiple CMFs. Applying multiple CMFs that are not independent of each other is not allowed. No more than three independent CMFs may be applied to a particular site. 3

5 Crash Modification Factor (CMF) Method (continued) The current process is for CMFs to be applied to a minimum of three years of crash data for an urban/suburban site and five years of crash data for a rural site. The following is a sample calculation: 10.1 crashes / year x 0.91 (CMF) x 1.04 (CMF) = 9.6 crashes / year: a reduction of 0.5 total crashes per year and a CRF of 5% 4

6 Predictive Method The Predictive Method is based on the Highway Safety Manual (HSM Part C) and is used to estimate the average crash frequency under both existing conditions and conditions which are not yet present. The predictive method can be used to quantitatively assess safety in future conditions. The first step is to predict future crashes for existing conditions. The initial prediction is based on empirical data including crashes for a particular roadway type under base conditions from across the United States. SAFETY PERFORMANCE FUNCTION (SPF) National Crash Data Predicted Crash Frequency per Mile =Observed Crashes SPF 0 5,000 10,000 10,000 20,000 AADT (veh/day) The crash predictions are calculated based on the particular roadway conditions for a homogenous site/segments specified by a SPF. These SPFs have particular CMFs associated with their development and are included in the HSM for that particular roadway type. All of the CMFs associated with a SPF in the HSM may be applied to the crash reduction calculations, unlike the CMF method, which is limited to three. SPF CRASH MODIFICATION FACTOR CMF = Expected crashes with treatment Expected crashes without treatment CMF = 1.0 = Expected to have no impact on safety CMF < 1.0 = Expected to reduce crashes CMF > 1.0 = Expected to increase crashes A calibration factor (C) is applied to adjust the estimated crashes from national data to local conditions by comparing observed crashes for 30 to 50 local sites and the crashes predicted from the national data. Available calibration factors that are to be used will be listed on NDOT s PSP website and do not need to be calculated on a project basis. If a calibration factor is not available for specific SPF on the NDOT PSP website, a calibration factor of 1 should be used. C= CALIBRATION FACTOR Observed Crashes (sample all sites) Predicted Crashes (sample all sites) 5

7 Predictive Method (continued) EMPIRICAL BAYS WEIGHTING The estimated crashes are further refined through a weighting process using the Empirical Bayes (EB) method. Observed # at a location Crash # Potential for Safety Improvement (PSI) Corrected expected # at this location by EB method Predicted # from SPF SPF AADT The Predictive Method is applied independently to each homogeneous roadway segment and to each intersection. Therefore, a project is typically broken into a large number of independent pieces and although the calculations can be completed by hand, the use of an analysis tool is beneficial. The main tools are the Interactive Highway Safety Design Model (IHSDM), spreadsheets developed as part of NCHRP 17-38, and extended spreadsheets developed by further research for Alabama DOT and Virginia DOT. The IHSDM is the recommended tool for consistent application in Nevada and is considered an acccurate software implementation of the HSM Part C. The following is a sample Predictive Method results table: Annual Crashes Annual Crash Reduction CRF Existing Condition Project Alternative A % Project Alternative B % The HSM section C.7 recommends four application methods of the predictive method for estimating the safety effectiveness of a proposed project listed in order of reliability. A summary is shown below of those methods: 1. Apply the Part C predictive method to estimate the expected average crash frequency of both the existing and proposed condition. 2. Apply Part C predictive method to estimate the expected average crash frequency of the existing condition and apply appropriate CMF from Part D to estimate the safety performance of the proposed condition. 3. If the Part C predictive method is not available, but an SPF applicable to the exiting conditions (developed outside the HSM) is available, use the SPF to estimate the expected average crash frequency of the existing condition. Apply an appropriate project CMF from Part D to estimate the expected average crash frequency for the proposed condition. 4. Use the observed crash frequency to estimate the expected average crash frequency of the existing condition and apply an appropriate project CMF from Part D to estimated expected average crash frequency of the exiting condition to obtain the estimate expected average crash frequency for the proposed condition. (Similar to the Crash Modification Factor (CMF) Method) Effectiveness is estimated by taking the difference in expected average crash frequency between the existing and proposed condition. 6

8 Benefit-Cost Ratio (BCR) A benefit-cost ratio (BCR) is the ratio of the present-value benefits of a project to the cost of project implementation. If the ratio is greater than 1.0, the project is considered to be economically justified. Countermeasures are ranked from highest to lowest BCR. BCR = PV BENEFITS PV COSTS PV BENEFITS = Present value of project benefits PV COSTS = Present value of project costs Apply the following to the calculation: Use a current prime interested rate of 3.25%, an annual benefits growth of 2%, and a capital recovery factor of 6.88%. Use NDOT s Cost Wizard to prepare the estimated project construction costs. The following 2012 societal cost of crashes is to be used for all projects in Nevada: The BCR is calculated slightly differently for the CMF Method versus the Predictive Method. The CMF Method includes benefits based on multiplying the crash reduction factor with observed crashes, whereas the Predictive Method assigns the benefits based on the reduction of estimated future crashes. Calculation forms and a sample calculation for both methods are shown on the following pages. Fatal $5,339,711 Injury A $285,349 Injury B $104,302 Injury C $59,037 PDO $9,638 7

9 ENGINEERING AUTHORIZATION NO. PROJECT NO. COUNTERMEASURE PROJECT LOCATION AADT - Segment or Main St & Cross St NONE NONE Install a Roundabout PROJECT SAFETY PROCESS CMF METHOD BENEFIT-COST RATIO (BCR) (2012 DOLLAR FIGURES) 01/22/13 ROADWAY CHARACTERISTICS DEMOGRAPHIC DESIGNATION FUNCTIONAL CLASSIFICATION IMPLEMENTATION COSTS $1,634, ANNUAL MAINTENENCE COSTS $1, CURRENT PRIME INTEREST RATE 3.25% PERCENTAGE OF GROWTH 2.00% ESTIMATED SERVICE LIFE 20 YEAR(S) LENGTH OF STUDY SR Bragg Rd YEAR(S) CALCULATION OF REDUCTIONS Crash Reduction Factor (CRF) - Clearinghouse, Equate crash types to crash severity for total reductions by severity. PRESENT EXPECTED CRASHES SAVED CRASHES CRF % ANNUALLY 2012 CRASH (A) (B) (C) COSTS FATAL $5,339, % 0.00 INJURY A $285, % 0.26 INJURY B $104, % 1.03 INJURY C $59, % 2.07 PDO $9, % 2.61 CALCULATION OF BENEFITS CRASHES SAVED SOCIETAL SOCIETAL ANNUALLY COST BENEFIT (C) (D) (E) FATAL 0.00 $5,339,711 $0 INJURY A 0.26 $285,349 $73,810 INJURY B 1.03 $104,302 $107,918 INJURY C 2.07 $59,037 $122,167 PDO 2.61 $9,638 $25,123 TOTAL ANNUAL BENEFITS (Summation of Column E) $329,018 TOTAL ANNUAL BENEFITS (Including Growth ) $335,599 CAPITAL RECOVERY FACTOR The costs below are projected and are for informational puposes only ANNUALIZED IMPLEMENTATION COSTS $112,393 COST at 1 to 1 = ($5,000,000.00) TOTAL ANNUALIZED COSTS $113,393 COST at 2 to 1 = ($2,500,000.00) AVERAGE ANNUAL NET RETURN $222,206 COST at 3 to 1 = ($1,670,000.00) BENEFIT/COST

10 ENGINEERING AUTHORIZATION NO. Not Known PROJECT NO PROJECT LOCATION SR MP 7.4 to MP 14.3 ALTERNATIVE NO. COUNTERMEASURE PROJECT SAFETY PROCESS PREDICTIVE METHOD BENEFIT-COST RATIO (BCR) (2012 DOLLAR FIGURES) 01/22/13 Alt 2 Revise single curve at MP 9 per RSA recommendation (1700-foot curve), includes roadside improvements at location. AADT - Segment or Main St & Cross St SEGMENT ROADWAY CHARACTERISTICS 2 LANE UNDIVIDED DEMOGRAPHIC DESIGNATION RURAL FUNCTIONAL CLASSIFICATION IMPLEMENTATION COSTS $1,474, ANNUAL MAINTENENCE COSTS $5, CURRENT PRIME INTEREST RATE 3.25% PERCENTAGE OF GROWTH 2.00% 3 OTHER PRINICPLE ARTERIAL ESTIMATED SERVICE LIFE & NUMBER OF YEARS PREDICTED 20 YEAR(S) NUMBER OF YEARS OF CRASH HISTORY DATA 5 YEAR(S) CALCULATION OF REDUCTIONS USING IHSDM IHSDM (Interactive Highway Safety Design Model) EXSITING CONDITION ALTERNATIVE PRESENT EXPECTED EXPECTED EXPECTED CRASHES SAVED CRASHES CRASHES CRASHES CRF (%) ANNUALLY 2012 CRASH (A) (B) (C) (D) (E) COSTS FATAL $5,339, % 0.04 INJURY A $285, % 0.03 INJURY B $104, % 0.04 INJURY C $59, % 0.04 PDO $9, % 0.09 CALCULATION OF BENEFITS CRASHES SAVED SOCIETAL SOCIETAL ANNUALLY COST BENEFIT (E) (F) (G) FATAL 0.04 $5,339,711 $209,622 INJURY A 0.03 $285,349 $7,468 INJURY B 0.04 $104,302 $4,095 INJURY C 0.04 $59,037 $2,318 PDO 0.09 $9,638 $820 TOTAL ANNUAL BENEFITS (Summation of Column E) $224,322 TOTAL ANNUAL BENEFITS (Including Growth ) $228,808 CAPITAL RECOVERY FACTOR ANNUALIZED IMPLEMENTATION COSTS $101,429 TOTAL ANNUALIZED COSTS $106,429 AVERAGE ANNUAL NET RETURN $122,380 BENEFIT/COST