Safety Data and Analysis in Developing Emphasis Area Plans (2008) / Chapter Skim
Currently Skimming:
Pages 42-53
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 42... ...
Where the procedure differs between crash types, this will be noted. In addition, the data needed for the different intersection-oriented crash types will differ and will be specified.
|
From page 43... ...
Exhibit V-1 will guide the user to the appropriate procedure. Procedure 1 – Choosing Intersection Treatments and Target Populations When Treatment Effectiveness Is Known, and Both Crash and Non-Crash Data Are Available The following text identifies the data needed for conducting Procedure 1, followed by the individual steps in the procedure.
|
From page 44... ...
• Unit cost for each treatment – both original implementation costs and annual maintenance costs The NCHRP Report 500 guides do not provide treatment costs due to differences between states and expected changes over time. The user will need to obtain information 44 Crash Type Variable Crash Database Subfile Intersection or Intersectionrelated Relation to Junction Location Type Crash Angle Crashes Accident/Crash Type Sequence of Events First Harmful Event Most Harmful Event Crash Crash or Vehicle Crash Vehicle Left- and Right-turning Crashes Same as Angle Same as Angle Sideswipe Crashes Same as Angle Same as Angle Run-Off-Road Crashes Same as Angle plus Number of Vehicles or Units Crash Rear-end Crashes Same as Angle plus Number of Vehicles or Units Crash Head-On Crashes Same as Angle Same as Angle Exhibit V-2.
|
From page 45... ...
4. Link target crashes with intersections from the appropriate inventory data file, and then perform a computer screening of all intersections that are potential treatment locations to determine which intersections have crash frequencies that exceed the critical crash frequencies calculated above.
|
From page 46... ...
The above steps are then repeated for the second and subsequent potential treatment types. In each case, critical crash frequencies are calculated for each intersection class, the computer program is used to identify treatment intersections, and decisions are made whether to treat any "below-threshold" intersections.
|
From page 47... ...
Since no detailed intersection inventory exists in this situation, these data will help in defining potential target locations within different intersection classes or types. • A network screening computer program which can read an input file composed of target crash records sorted by route and milepost, and can count the number of target crashes within a given specified length (e.g., 1 mile)
|
From page 48... ...
under consideration. As noted above under "Data Needs," the network screening program will need to output the total number of target crashes in the specified length and the route number and mileposts for the first and last crash falling in each "window" for which the total number of target crashes exceeds the critical crash frequency.
|
From page 49... ...
for each treatment to be examined. • A computerized crash data file which includes sufficient crash details to isolate crash types that will be affected by each treatment ("target crashes" – e.g., angle crashes, sideswipe crashes, run-off-road crashes, rearend crashes, and head-on crashes)
|
From page 50... ...
provides additional discussion of this option. Procedure 3 – Choosing Intersection Treatments and Target Locations When Treatment Effectiveness in Terms of Crash/Injury Reduction Is Not Known As noted in the preceding section, the three procedures described above allow the user to choose intersection treatments and treatment targets for a given problem while ensuring that the economic value of the crash/injury reductions will exceed the cost of implementing the program.
|
From page 51... ...
within each target crash type. Information on economic cost per severity level within 22 different crash types including different types of run-off-road and head-on crashes can be found in Crash Cost Estimates by Maximum Police-Reported Injury Severity Within Selected Crash Geometries (22)
|
From page 52... ...
Cc* Eff Where: • N = Number of target crashes for the subpopulation or location where the treatment is to be applied • Cc = average economic cost per target crash • Eff = treatment effectiveness, or the percent reduction in target crashes Since different severity levels have different crash costs, the value used for Cc can be a weighted average of the crash costs associated with the crash types likely to be affected.
|
From page 53... ...
b) When possible, formulate an effectiveness estimate that is applicable to particular target crash types only, not to total crashes.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.