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43 4. Compare these numbers of crashes and injuries reduced the treatments that should be applied to them. Again, the and lives saved to your statewide intersection goal and choice between which procedure is appropriate is defined by calculate the proportion of your total goal that this three factors whether or not treatment effectiveness is represents. known, whether the jurisdiction has inventory data that can 5. To calculate approximately how much you will have to be linked to their crash data, and whether the crashes are expand the intersection part of your HCL program to "mileposted" or not. Exhibit V-1 will guide the user to the meet your goal, divide 1.0 by the proportion from the pre- appropriate procedure. vious step. For example, if the fatality and injury savings from your current program is 20 percent of your goal, Procedure 1 Choosing Intersection then you will have to identify and treat five times as many Treatments and Target Populations intersections in the future (i.e., 1.0 / 0.20 = 5). When Treatment Effectiveness Is Known, and Both Crash and Non-Crash The user will then need to make the determination of whether Data Are Available enough sites with high numbers of intersection crashes can be identified. Usually the HCL program has identified more in- The following text identifies the data needed for con- tersections that can be treated. This full "census" of potential ducting Procedure 1, followed by the individual steps in the HCL sites can be examined to determine whether enough sites procedure. with high numbers of intersection crashes are available. In most cases, if a stretch goal has been set, the answer will be Data Needs "no." In that case, the user should consider adding system im- provements to the plan. The following are the specific data needed to use Procedure While all states and some local jurisdictions have proce- 1 when choosing and targeting intersection treatments. dures in place to identify and treat high-crash locations, it is noted that an improved methodology is currently being de- A specified effectiveness level (CRF or AMF) for each veloped by FHWA in the SafetyAnalyst program described in treatment to be examined the preceding section (also see The "Treatment Effectiveness" section under each treat- This set of the software tools for safety management of spe- ment in each NCHRP Report 500 guide provides a descrip- cific highway sites includes a series of procedures that will tion of what is known about CRFs. It is important that the allow the user to identify high-crash locations or sites with user review the material in the guides for a given treatment. potential for safety improvement, diagnose potential treat- Valuable information about the stability of the CRF, cau- ment sites to identify correctable crash patterns, conduct an tions about the use of the treatment and other essential- economic analysis to assure a minimum B/C ratio, and de- information is included there, but will not be repeated here. velop a combined treatment program which maximizes the For a significant proportion of the treatment strategies benefits that can be gained from a given total treatment defined in the six guides covered in this section, a specific budget. The network-screening tools within SafetyAnalyst AMF is not presented. Since the preparation of some of the provide a good approach for applying Procedure 1. earlier guides, additional information on treatment CRFs If preliminary analysis indicates that even an enhanced has been developed in both NCHRP Project 17-25, and in and expanded high-crash location program will not meet the preliminary work for the Highway Safety Manual. The goal, then the users will need to add systems-based treatment AMFs from NCHRP Project 17-25 have been published in programs to the effort. Indeed, the four procedures de- NCHRP Research Results Digest 299 (27). The AMFs devel- scribed earlier and detailed below are developed to assist the oped in NCHRP Project 17-27 will be incorporated in the user in identifying intersections to treat and to help define forthcoming Highway Safety Manual. Inventory Data Available and Linkable to Crashes? Treatment Yes No Effectiveness Mileposted Crashes Mileposted Crashes Unmileposted Crashes Known? Yes Procedure 1 Procedure 2A Procedure 2B No Procedure 3 Procedure 3 Procedure 3 Some known, Procedure 4 Procedure 4 Procedure 4 some unknown Exhibit V-1. Guide to choice of procedures based on knowledge of treatment effectiveness and crash data quality.

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44 A computerized crash data file which includes sufficient for the Minimum Inventory of Roadway Elements crash details to isolate target crash types (angle, sideswipe, (MIRE). turning, rear-end, and head-on crashes), and potential tar- A computer program that will examine each intersection get populations that will be affected by each treatment and calculate the number of target crashes (e.g., angle, Here, the user will need to examine the data formats for turning, sideswipe, run-off-road crashes, rear-end, and variables in their crash file to identify variables and codes head-on) that have occurred at each intersection in the within variables that can be used in determining whether or past 3 to 5 years. not each crash in the file is a "target crash." Crash databases This program exists in some jurisdictions, but may not often categorize crash data for a given crash into up to three exist in others. If not, a knowledgeable computer analyst subfiles general accident/crash variables, variables for each can build one. The program will require that counts of vehicle in the crash, and variables for each occupant in the target crashes can be made and "attached to" each inter- crash. In general, the analyst will need to first screen to de- section within an agency's jurisdiction (or this could be termine if the crash is an intersection or non-intersection done for all of the intersections on a particular route). crash, and then examine the different crash types within The program must then be able to examine each inter- those that are intersection-related. Since "intersection section and record the total number of crashes in an out- crashes" can include both those in the intersection itself and put file, along with the route number and an intersection on the intersection approaches (e.g., rear-end crashes), the identifier. The process would be repeated for all routes in analyst will usually have to include those crashes that are the system. coded as both "intersection" and "intersection-related." The Computerized traffic count data that can be linked to the variables needed to determine whether a crash is a "target intersection inventory data (unless it is contained in that crash" or not, for intersection crashes, can usually be found database). in one of the first two subfiles crash or vehicle data. Crash While the procedure can be operated without comput- files differ from jurisdiction to jurisdiction. While certainly erized count data, these data are often available in state not always the case, the following variables (or similar vari- DOT files that have an intersection inventory system. This ables) listed in Exhibit V-2 will be used in this determination. is not always the case in urban systems. If available, the Computerized intersection inventory data that can be traffic count information can be used to further target the linked to the crash data by location of the crash potential treatment sites in two ways. First, if the user only A few state DOTs have computerized intersection in- wishes to treat "high-volume" intersections, these data can ventory files for the full state highway system that can be be used to screen out "low-volume" intersections prior to linked to crashes, since both the intersections in the inven- running the computer program. Second, after the program tory file and the crashes are identified by "addresses" usu- has been run, the identified sites can be further screened by ally route and milepost or GIS coordinates. Most local ju- a given AADT level, or the sites can be sorted by AADT to risdictions (i.e., counties, towns, townships, and cities) do assist the user in final site choice. not have such an inventory system. For jurisdictions that Unit cost for each treatment both original implementa- do not have an inventory file, Procedures 2A and 2B below tion costs and annual maintenance costs can be used. The NCHRP Report 500 guides do not provide treatment A recommended set of data elements for inclusion in costs due to differences between states and expected intersection inventories is under development by FHWA changes over time. The user will need to obtain information Crash Type Variable Crash Database Subfile Intersection or Intersection- Relation to Junction Crash related Location Type Angle Crashes Accident/Crash Type Crash Sequence of Events Crash or Vehicle First Harmful Event Crash Most Harmful Event Vehicle Left- and Right-turning Same as Angle Same as Angle Crashes 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. Crash variables and subfile location by crash type.

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45 on such costs, either from vendors or from other jurisdic- CF = (Ann. Cost)(Target B/C)/(Eff)(Avg. Crash Cost) tions that have used the treatment. The guides do provide Where: "Information on Agencies or Organizations Currently Im- CF = Critical annual frequency of target crashes per in- plementing This Strategy" that could be contacted for help tersection to consider the strategy to be cost effective. under each of the treatment strategies. (The guides provide Ann. Cost = The annual cost of the improvement per only early users, and surrounding jurisdictions may have implemented the treatment after the guide was completed.) intersection. If it is a construction improvement, it is Finally, the user will need an estimate of annual mainte- the construction costs annualized over the expected nance cost (per intersection or intersection approach) for life of the improvement. Target B/C = The B/C ratio defined by the user. It is each treatment to be analyzed. Since maintenance includes "replacement after a crash" in some cases, the user may usually between 1.0 and 2.0. In the FHWA Sample have to make estimates of the number of expected crashes Plan for intersections (25), a value of 2.0 is used. Eff = The estimated effectiveness of the treatment per year and the amount of expected damage. Again, past users of the treatment can be of assistance here. strategy in reducing targeted crashes, expressed as a proportion (i.e., the CRF/100). This can be extracted from NCHRP Research Results Digest 299 (27) or from Procedure other sources. The general procedure for choosing and targeting treat- Avg. Crash Cost = The average economic cost per ments with known effectiveness levels was provided in Section crash for the target crash type that will be affected by III above. The following text will expand that description this treatment strategy. The following estimates were while focusing on intersection treatments designed to reduce based on costs from Table 10 of Crash Cost Estimates intersection-related crashes. Because the user needs to under- by Maximum Police-Reported Injury Severity Within stand the computerized procedure in order to input the Selected Crash Geometries (22), and represent compre- correct values and tailor it for their own jurisdiction, the hensive costs in terms of 2001 dollars. Comprehensive following provides the details of each step and sub-step. cost estimates include not only the monetary losses as- sociated with medical care, other resources used, and 1. Specify the types/classes of intersections that are poten- lost work, but also non-monetary costs related to the tial targets for the treatments. reduction in the quality of life. The cost for each crash Because the choice of treatments, the treatment ef- type is shown in Exhibit V-3 for two ranges of speed fectiveness, and the treatment cost per intersection may limits: 45 mph and 50 mph. The former should be differ by intersection class/type, the user will need to useful for urban crashes, and the latter for rural specify the types/classes of interest e.g., four-leg rural crashes. intersections, three-leg urban intersections, rural 3. Using the inventory file, stratify potentially treatable unsignalized intersections, urban signalized intersec- intersections by intersection class. tions. If desired, these potential treatment sites could This stratification will result in a file of intersections be further screened by AADT level (e.g., only "high- for each of the intersection classes under consideration volume" intersections). for each treatment. 2. Develop critical crash frequencies for each candidate 4. Link target crashes with intersections from the appro- treatment type (e.g., left-turn lane) for each intersection priate inventory data file, and then perform a computer class of interest. The "critical frequency" is the fre- screening of all intersections that are potential treat- quency of target crashes per intersection that, if treated, ment locations to determine which intersections have will result in crash-injury reductions whose economic crash frequencies that exceed the critical crash fre- benefit will exceed implementation costs by some fac- quencies calculated above. tor. In the FHWA Sample Plan for intersections (25), This will be done using the computer program de- the target benefit to cost ratio used was 2.0 or greater. scribed above, and will be done independently for each These "critical frequencies" must be developed for each of the intersection types under consideration. candidate treatment being examined. If the same treatment Note that if the treatment being considered is for is to be used on different intersection classes, it will be nec- three-leg intersections (i.e., the user is searching for a essary to develop different critical frequencies for each "system" of three-leg intersections to correct with, say, treatment by intersection class if the treatment cost per unit left-turn lanes), this step will require that the user's in- length or treatment effectiveness varies by intersection tersection inventory system can identify the locations of class. The following formula is used: three-leg intersections. If no such data are available, then

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46 Crash Type Traffic Control Speed Limit Comprehensive Category Cost/Crash* < 45 mph $22,000 Signalized > 50 mph $75,000 Angle/turning Crashes < 45 mph $32,000 Unsignalized > 50 mph $96,000 Signalized or < 45 mph $16,000 Sideswipe Crashes Unsignalized > 50 mph $55,000 Signalized or < 45 mph $24,000 Rear-end Crashes Unsignalized > 50 mph $33,000 Signalized or < 45 mph $16,000 Head-On Crashes Unsignalized > 50 mph $88,000 Run-Off-Road Fixed Signalized or < 45 mph $67,000 Object Crashes Unsignalized > 50 mph $107,000 * Cost in 2001 dollars (22) Exhibit V-3. Crash cost by crash type, traffic control and posted speed limit. the user will have to use either Procedure 2A or 2B in- The summing of goal-related crashes or injuries will be stead of this Procedure 1. done by using a computer program to estimate the an- 5. Review the computer output for "below-threshold" nual number of such target crashes for all intersections intersections. selected for treatment. Users with full crash and inven- The computer program will only detect intersections tory systems who have developed the [computer] pro- that exceed the critical crash-frequency threshold. This gram will have the ability to link such goal-oriented tar- will leave intersections that do not meet the threshold. get crashes to each intersection selected and to sum the The user may desire to manually examine each of the in- total over all intersections. The best annual estimate will tersections under consideration within each intersection be one based on more than 1 year of past data (3 to class and determine whether or not these "below-thresh- 5 years) and then dividing by the number of years used. old" intersections should be treated. The logical first an- 7. Repeat the above steps for each potential treatment type. swer is "no," since the intersections did not meet the crit- The above steps are then repeated for the second and ical threshold. However, there may be times when all or subsequent potential treatment types. In each case, criti- some of these intersections should be included in the cal crash frequencies are calculated for each intersection treatment program. class, the computer program is used to identify treatment 6. Estimate the expected crash/injury reductions on all intersections, and decisions are made whether to treat the identified target locations. any "below-threshold" intersections. However, a correc- The results of this step will be used in Step 9 below in tion is needed for intersections that have been identified determining whether or not the goal is reached. Here, for for more than one treatment type, as detailed in the each treatment location within a given intersection class, following step. the user will need to determine the number of crashes 8. Correct for multiple treatments on the same intersection. and injuries that will be reduced by this treatment. This Since many intersection treatments affect the same type will be done by summing up all pertinent crashes or crash of target crash, the above procedure will identify the same injuries for all intersections to be treated, and then mul- intersection as a potential for treatment in many cases. In tiplying this total by the estimated effectiveness level for these cases, the user has two options: (1) choose only one the treatment under consideration. treatment for each of these intersections, or (2) choose to CI reduction = (CI at intersections) Eff implement two or more treatments at the same intersection. Under Option 1, the user would compare the lists of Where: potential treatment intersection sites from Step 5 above, CI = "Goal-related" crashes or crash injuries and would decide which treatment to place at each inter- Eff = treatment effectiveness section where two or more treatments could be imple- The definition of "goal-related" crashes or injuries is, as mented. That intersection (and its related goal-oriented implied, based on the nature of the overall goal that has crashes or injuries) is then removed from the list of inter- been established. If the goal is oriented to fatal and injury sections for all other treatments. target crashes, then these will be accumulated. If the goal Under Option 2, the user must develop some measure is total target crashes, then these will be accumulated. of combined effectiveness for the two or more treatments