Cover Image

Not for Sale

View/Hide Left Panel
Click for next page ( 50

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement

Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 49
49 8. Add new treatments, new targets, or new approaches Unit cost for each treatment both original implemen- (e.g., inclusion of safety treatments in normal mainte- tation costs and annual maintenance costs. nance or rehabilitation efforts) until the goal is met. See discussion under Procedure 1. Again, the FHWA Sample Plan for intersections (25) provides additional discussion of this option. Procedure The following steps are those that would be followed for Procedure 2B Choosing Intersection choosing among intersection treatments with known effec- Treatments and Target Populations When tiveness and targeting these treatments to entire intersection Treatment Effectiveness Is Known and classes in a jurisdiction. Neither Mileposted Crash Data nor Detailed Inventory Data Are Available 1. Develop critical crash frequencies for each candidate The following text identifies the data needed for conduct- treatment type and intersection class of interest. ing Procedure 2B, followed by the individual steps in the The "critical frequency" is the annual frequency of tar- procedure. Note again that since no mileposted crash data get crashes per mile that, if treated, will result in crash- exists, this procedure will only allow the user to identify injury reductions whose economic benefit will exceed intersection types within a given jurisdiction as potential implementation costs by some factor. treatment sites, but not specific intersection locations. It will The same formula and information presented under also not allow the user to target the treatments to specific Step 2 of Procedure 1 above will be used here. locations along the route. 2. Link target crashes to each route in each jurisdiction (but not to a specific point on the route). This will require computer sorting of crashes by each Data Needs named route. Some manual effort will be required to correct misspelled names and to group routes or streets The data needed for Procedure 2B are less than required in that have multiple names. The output of this program either of the previous two procedures. Major differences in- will be a listing of target crashes sorted by route name. clude the fact that no inventory or traffic data are required, Note that multiple years of crashes can be used, and in- and that the crashes do not have to be "mileposted" to a spe- deed the procedure will be more accurate if more than 1 cific location on a specific route. However, each crash record year's crash data (e.g., 3 to 5 years) are used. If multiple must contain information on the county or local jurisdiction years are used, there may be situations where a route was where the crash occurred, along with the name of the renamed during the period. If so, both crashes with the route/street where the crash occurred. original and new name should be accumulated under one route name. A specified effectiveness level (CRF or AMF) for each 3. Develop a spreadsheet that contains the count of target treatment to be examined. crashes for each route (one route per row), along with A computerized crash data file which includes suffi- the mileage for that route. cient crash details to isolate crash types that will be It may be possible for the computer program used to affected by each treatment ("target crashes" e.g., angle sort the crashes in Step 2 to output this count for each crashes, sideswipe crashes, run-off-road crashes, rear- route. If not, the counts can be made manually. The final end crashes, and head-on crashes), which includes output of this step is a spreadsheet containing a total crashes for all potential target populations. Each crash count of target crashes and the length in miles for each record must contain a county or jurisdiction name route under consideration. where the crash occurred, and the name of the route or 4. Calculate the annual crash frequencies per mile for road where the crash occurred. each potential route. Route length information that will provide the length in If a spreadsheet is used, this is a simple step in which miles of each road or route within a county or local juris- the crash count is divided by the route length times the diction that is a potential target for any treatment, or at number of years of crashes used. least the approximate length. 5. Identify routes to be treated by determining which If this information is not available in the user's files, it have calculated annual frequencies per mile that exceed may be available from other sources including road the developed critical crash frequencies per mile. maintenance records, and can be scaled from maps if This is a comparison of the output of Step 4 with the necessary. "critical frequencies" defined in Step 1.