The National Academies Press

Currently Skimming:

Pages 693-726

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.

From page 693... ... 693 APPENDIX E PROPOSED HSM APPENDIX B FOR PART C APPENDIX B―SPECIALIZED PROCEDURES COMMON TO CHAPTERS 18 AND 19 TABLE OF CONTENTS List of Figures ................................................................................................................................ 694 List of Tables .................................................................................................................................. Read the entire page →
From page 694... ... 694 LIST OF FIGURES Figure B-1. Determination of the Appropriate Variation of the EB Method .................................... Read the entire page →
From page 695... ... 695 Appendix B -- Specialized Procedures Common to Chapters 18 and 19 This appendix describes two specialized procedures intended for use with the predictive method presented in Chapters 18 and 19. The first procedure is used to calibrate the predictive models in Chapters 18 and 19 to local conditions. Read the entire page →
From page 696... ... 696 for the most recent available period is to be used for all assessment of proposed future projects. If available, calibration factors for the specific time periods included in the evaluation period are to be used in effectiveness evaluations that use the procedures presented in Chapter 9. Read the entire page →
From page 697... ... 697 Table B-1. Predictive Models in Chapters 18 and 19 that Need Calibration Site Type and Cross Section or Control Type Calibration Factor Symbol Equation Number ROADWAY SEGMENTS Freeways Multiple-vehicle fatal-and-injury crashes, all cross sections Cfs, ac, mv, fi 18-3 Multiple-vehicle property-damage-only crashes, all cross sections Cfs, ac, mv, pdo 18-5 Single-vehicle fatal-and-injury crashes, all cross sections Cfs, ac, sv, fi 18-4 Single-vehicle property-damage-only crashes, all cross sections Cfs, ac, sv, pdo 18-6 Ramps Entrance ramp, multiple-vehicle fatal-and-injury crashes, all lanes Crps, EN, mv, fi 19-3 Entrance ramp, multiple-vehicle property-damage-only crashes, all lanes Crps, EN, mv, pdo 19-5 Entrance ramp, single-vehicle fatal-and-injury crashes, all lanes Crps, EN, sv, fi 19-4 Entrance ramp, single-vehicle property-damage-only crashes, all lanes Crps, EN, sv, pdo 19-6 Exit ramp, multiple-vehicle fatal-and-injury crashes, all lanes Crps, EX, mv, fi not shown Exit ramp, multiple-vehicle property-damage-only crashes, all lanes Crps, EX, mv, pdo not shown Exit ramp, single-vehicle fatal-and-injury crashes, all lanes Crps, EX, sv, fi not shown Exit ramp, single-vehicle property-damage-only crashes, all lanes Crps, EX, sv, pdo not shown C-D road, multiple-vehicle fatal-and-injury crashes, all cross sections Ccds, ac, mv, fi 19-8 C-D road, multiple-vehicle property-damage-only crashes, all cross sections Ccds, ac, mv, pdo 19-10 C-D road, single-vehicle fatal-and-injury crashes, all cross sections Ccds, ac, sv, fi 19-9 C-D road, single-vehicle property-damage-only crashes, all cross sections Ccds, ac, sv, pdo 19-11 INTERSECTIONS Freeway Speed-Change Lanes Ramp entrance speed-change lane, fatal-and-injury crashes of all types Csc, EN, at, fi 18-8 Ramp entrance speed-change lane, property-damage-only crashes of all types Csc, EN, at, pdo 18-9 Ramp exit speed-change lane, fatal-and-injury crashes of all types Csc, EX, at, fi 18-11 Ramp exit speed-change lane, property-damage-only crashes of all types Csc, EX, at, pdo 18-12 Crossroad Ramp Terminals One-way stop control, fatal-and-injury crashes of all types CaS, ST, at, fi 19-13 One-way stop control, property-damage-only crashes of all types CaS, ST, at, pdo 19-14 Signal control, fatal-and-injury crashes of all types CaS, SG, at, fi 19-16 Signal control, property-damage-only crashes of all types CaS, SG, at, pdo 19-17 Read the entire page →
From page 698... ... 698 Also established in this step is the calibration period. A calibration period longer than three years is not recommended because the expected average crash frequency is likely to change over time. Read the entire page →
From page 699... ... 699 The crash data used for calibration should include all crashes related to each site selected for the calibration database. Crashes should be assigned to specific sites based on the guidelines presented in Section B.2.3. Read the entire page →
From page 700... ... 700 Table B-2. Data Needs for Calibration of Chapter 18 and 19 Predictive Models continued Chapter Data Element Data Need Default Assumption Required Desirable ROADWAY SEGMENTS 19―Ramps For ramps and collector-distributor (C-D) Read the entire page →
From page 701... ... 701 Table B-2. Data Needs for Calibration of Chapter 18 and 19 Predictive Models continued Chapter Data Element Data Need Default Assumption Required Desirable INTERSECTIONS 19 -- Ramps For all crossroad ramp terminals: Area type (rural or urban) Read the entire page →
From page 702... ... 702 If data for some required elements are not readily available, it may be possible to select sites in Step 2 for which these data are available. For example, in calibrating the predictive models for freeway segments, if data on the radii of horizontal curves are not readily available, the calibration data set could be limited to tangent freeways. Read the entire page →
From page 703... ... 703 Within the first two to three years after a jurisdiction-specific SPF is developed, calibration of the jurisdiction-specific SPF may not be necessary, particularly if other default values in the predictive models were also replaced with locally-derived values, as explained in Section B.1.3. If jurisdiction-specific SPFs are used in a predictive method, they need to be developed with methods that are statistically valid and developed in such a manner that they fit into the applicable predictive method. Read the entire page →
From page 704... ... 704 Table B-3. Crash Distributions in Chapter 18 and 19 Predictive Models That May Be Calibrated to Local Conditions Chapter Table or Equation Number Site Type Distribution That May Be Calibrated to Local Conditions Roadway Segments Intersections 18 -- Freeways Table 18-6 X Crash type for multiple-vehicle crashes Table 18-8 X Crash type for single-vehicle crashes Table 18-10 X Crash type for ramp-entrance-related crashes Table 18-12 X Crash type for ramp-exit-related crashes 19 -- Ramps Table 19-6 X Crash type for multiple-vehicle crashes Table 19-9 X Crash type for single-vehicle crashes Table 19-16 X Crash type for signal-controlled ramp terminal crashes Table 19-21 X Crash type for one-way stop-controlled ramp terminal crashes Table 19-45 X Crash type for all-way stop-controlled ramp terminal crashes B.1.3.1. Read the entire page →
From page 705... ... 705 The distribution is categorized by two crash severity levels and two area types. If sufficient data are available, the values in Table 18-10 may be updated. Read the entire page →
From page 706... ... 706 a joint distribution of two variables for each area type. Therefore, for a given area type, sufficient data for calibrating the distribution requires a set of one-way stop-controlled ramp terminals that have collectively experienced at least 200 intersection-related crashes during a recent one- to three-year period (i.e., 200 crashes in the entire time period) Read the entire page →
From page 707... ... 707 Each calibration site should be selected without regard to the number or severity of crashes reported during the calibration period. In other words, calibration sites should not be selected to intentionally limit the calibration database to include only sites with either high or low crash frequencies. Read the entire page →
From page 708... ... 708 B.1.1.4. Step 4 -- Apply the applicable predictive method to estimate the predicted average crash frequency by severity for each site during the calibration period. Read the entire page →
From page 709... ... 709 Where: Pp, aS, ac, at, KAB = predicted probability a severe crash (i.e., K, A, or B) for all crash types at at all sites aS and all cross sections or control types ac; and N p, w(i) Read the entire page →
From page 710... ... 710 B.2.1. Determine whether the EB Method is Applicable The applicability of the EB Method to a particular project depends on the type of analysis being performed and the type of future project work that is anticipated. Read the entire page →
From page 711... ... 711 B.2.2. Determine whether Observed Crash Data are Available for the Project and, if so, Obtain those Data If the EB Method is determined to be applicable to a given project, then it should be determined whether observed crash data are available directly from the jurisdiction's crash record system, or indirectly from another source. Read the entire page →
From page 712... ... 712 Crash Type Considerations For projects that consist of one site, Figure B-1 indicates that the first consideration is whether the applicable predictive model is specific to one crash type (i.e., multiple-vehicle crashes or single-vehicle crashes) Read the entire page →
From page 713... ... 713 If the crashes cannot be assigned to individual sites, then the project-level EB Method is applicable. This method is described in Section B.2.5. Read the entire page →
From page 714... ... 714 Taper point Exit Ramp with Taper Design Entrance Ramp with Parallel Design Ramp Exit Length Ramp Entrance Length * Read the entire page →
From page 715... ... 715 Any crashes that occur in a ramp speed-change lane associated with a ramp-to-ramp junction are assigned to the originating ramp (i.e., they are not assigned to the merging or diverging ramp) Read the entire page →
From page 716... ... 716 kw, x(i) Read the entire page →
From page 717... ... 717 Chapters 18 and 19 present worksheets that can be used to apply the site-specific EB Method as presented in this section. Section B.2.6 explains how to use Equation B-5 to estimate the expected average crash frequency for a time period other than the crash period, such as the time period when a proposed future project will be implemented. Read the entire page →
From page 718... ... 718  = = cn j jfikyixiwp types crash all k sites all i fiatacaSp NN 1 ,) Read the entire page →
From page 720... ... 720 period can be designated as the reference year. It is the year for which the expected average crash frequency will be estimated in Step 5. Read the entire page →
From page 721... ... 721 N1, aS, ac, at, fi, r = expected average crash frequency for all sites aS and reference year r assuming perfect correlation among sites (includes all cross sections ac and fatal-and-injury fi crashes of all crash types at) (crashes/yr) Read the entire page →
From page 722... ... 722 study period (as represented by the values of the associated CMFs) Read the entire page →
From page 723... ... 723 = severities all l lzkyixiwe types crash all k sites all i asatacaSe NN * Read the entire page →
From page 724... ... 724 N* e, aS, ac, at, fi = total expected number of crashes for all sites aS and all years in the study period (includes all cross sections ac and fatal-and-injury crashes fi of all crash types at) Read the entire page →
From page 725... ... 725 ( ) zyXwzyXwmzyXwzyXwjzyXwspfjzyXwp CCMFCMFCMFNN ,,,,,,,,,,,2,,,,1,,,,,,,,,, ×××××=  Where: Np, w, X, y, z, j = predicted average crash frequency for year j for site type w, X-lane cross section, crash type y, and severity z (crashes/yr) Read the entire page →
From page 726... ... 726 2 1 ,,,,, ,,,,* ,,,,         =  = cn j jzyXwp zyXwp zyXwp N V k Where: k* Read the entire page →

From page 693...

... 693 APPENDIX E PROPOSED HSM APPENDIX B FOR PART C APPENDIX B―SPECIALIZED PROCEDURES COMMON TO CHAPTERS 18 AND 19 TABLE OF CONTENTS List of Figures ................................................................................................................................ 694 List of Tables ..................................................................................................................................