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    <title>Transport Research International Documentation (TRID)</title>
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    <copyright>Copyright © 2026. National Academy of Sciences. All rights reserved.</copyright>
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    <managingEditor>tris-trb@nas.edu (Bill McLeod)</managingEditor>
    <webMaster>tris-trb@nas.edu (Bill McLeod)</webMaster>
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      <title>Accident relationships to exposure at traffic signals</title>
      <link>https://trid.trb.org/View/1199954</link>
      <description><![CDATA[Road accidents are a serious social problem and the most common locations are intersections.  In Western Australia in 1989 about 25% of accidents were concentrated at 491 intersections controlled by traffic signals. There has been little information about typical patterns and predictions of accidents at these sites despite the high frequency.  Traffic signals are designed to reduce the accident severity of intersections with high traffic flow although the total number of accidents may increase after installation.  Research and experience suggested that accidents and traffic flow are correlated.  However these effects had not been quantified. This thesis investigates the accident relationship to traffic flow measures of exposure using readily available data from 121 sites.  Complete intersections, individual approaches and the effect of some basic site factors are investigated.  Five accident groups are considered in detail; rear end, right angle, indirect right angle, sideswipe (same direction) and total accidents.  Predictive numerical models of these accidents have been developed.  The specific accident types account for about 90% of accidents at traffic signals. Signal sites with a high accident frequency should be treated to enhance road safety.  Individual approaches become the focus of investigation to determine where the hazards are highest and what countermeasures are used. The identification of hazardous locations has been crude with limited justification since traffic flows have not been properly considered.  The use of accident rate (accidents per vehicle) provides a biased perspective by targeting sites with lower traffic flows.  It is suggested that sites which exhibit a higher than normal accident exposure relationship can be identified as most suitable for treatment.]]></description>
      <pubDate>Fri, 24 Aug 2012 16:52:29 GMT</pubDate>
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      <title>DIAGNOSTIC METHODOLOGY FOR THE DETECTION OF SAFETY PROBLEMS AT INTERSECTIONS</title>
      <link>https://trid.trb.org/View/726695</link>
      <description><![CDATA[There is an established consensus among traffic safety researchers that a nonlinear relationship exists between traffic exposure and safety.  This relationship is reflected by the safety performance functions (SPFs) calibrated for various classes of roads and intersections.  One of the main uses of SPFs is to identify locations with potential for accident reduction.  While this application is certainly important, the use of SPFs provides no information related to the nature of the accident occurrence.  Without being able to relate accident frequency and severity to roadway geometrics, traffic control devices, roadside features, roadway condition, driver behavior, or vehicle type, it is not possible to develop effective countermeasures.  A methodology was developed to provide guidance in diagnostics of safety problems, recognition of accident patterns, and development of appropriate countermeasures.  Considering that traffic accidents can be viewed as random Bernoulli trials, it is possible to detect deviation from the statistical process by computing observed cumulative probability for each of the accident characteristics. Detection of an accident pattern at an intersection suggests the presence of an element in the roadway environment that triggered a deviation from a random statistical process in the direction of reduced safety.  Identification of such an element always provides a critical clue to accident causality.]]></description>
      <pubDate>Fri, 11 Oct 2002 00:00:00 GMT</pubDate>
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      <title>ESTIMATION OF SAFETY AT SIGNALIZED INTERSECTIONS (WITH DISCUSSION AND CLOSURE)</title>
      <link>https://trid.trb.org/View/301420</link>
      <description><![CDATA[Models to estimate the safety of a signalized intersection on the basis of information about its traffic flow and accident history are provided.  They are based on data from 145 intersections in Metropolitan Toronto.  Several insights were obtained during the development of the models.  First, logically sound models require that the frequency of collisions be related to the traffic flows to which the colliding vehicles belong and not to the sum of the entering flows.  Second, it is therefore necessary to categorize collisions by the movement of the vehicles before the collision and not by the initial impact type, as is customary.  Third, the relationship between collision frequency and the related traffic flows is at times unexpected in form.  For each of the 15 accident patterns, an equation is given to estimate the expected number of accidents and the variance using the relevant traffic flows. When data about past accidents are available, estimates based on traffic flow are revised with a simple equation. Several practical questions can now be answered.  Given the traffic flow for a signalized intersection, one can predict how many and what kinds of accidents should be expected to occur on it; one can also show the probability density function (pdf) of the estimate.  Knowledge of the pdf allows the determination of what an unusually high number of accidents would be on such an intersection.  If the traffic flow of the intersection changes from year to year, one can estimate what changes in safety should be attributed to changes in flow.  Also, one can correctly compare the safety of several intersections that have different flow patterns. Most important, one can estimate safety when both flows and accident history are given and, on this basis, judge whether an intersection is unusually hazardous.  This method of estimation is recommended for accident warrants in the Manual on Uniform Traffic Control Devices.]]></description>
      <pubDate>Sat, 30 Sep 1989 00:00:00 GMT</pubDate>
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      <title>A METHOD FOR DETERMINING THE ACCIDENT POTENTIAL OF AN INTERSECTION</title>
      <link>https://trid.trb.org/View/179453</link>
      <description><![CDATA[The paper describes an investigation into the feasibility of predicting the accident potential of an intersection by the application of a model, based on accident occurrences at individual conflict points, within a signal controlled four-legged intersection with two-way flow on each leg. The model developed involved the stratification of intersection movements into individual turning movements resulting in nine conflict types, giving rise to 24 conflicting flows and 36 conflict points.  The stability of the accident rate for each conflict type is investigated, and a relationship derived which was sensitive to changes in traffic volumes. Comparisons were made between actual and predicted annual numbers of accidents at 30 junctions of the type described in Pretoria and Johannesburg.  The average difference was found to be 16 per cent for an annual total of 468 accidents.  Results also indicate that the accident rates derived for the nine different types of conflict could be used to predict accidents at similar types of intersection with similar flow patterns.  (TRRL)]]></description>
      <pubDate>Fri, 28 May 1982 00:00:00 GMT</pubDate>
      <guid>https://trid.trb.org/View/179453</guid>
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      <title>RELATIONSHIP OF ACCIDENT PATTERNS TO TYPE OF INTERSECTION CONTROL</title>
      <link>https://trid.trb.org/View/34981</link>
      <description><![CDATA[The change in accident patterns accompanying a change in intersection control was investigated.  The investigation include a review of previously made studies, an analysis of before and after accident data, and a detailed statistical analysis of a large, specially assembled, nationwide accident data base.  Analysis of variance and regression techniques was used to show that the relationship of accident patterns to type of control must be represented by a complex model and that a simple-signal-no-signal division cannot explain changes in accident patterns.  A large number of different measures of effectiveness that describe changes in accident patterns were computed and analyzed. Hypothesis testing revealed that, although there was a definite shift in the distribution of accident types, there was no evidence that signalization, by itself, would lead to a significant decrease in net accident-related disutility, especially for traffic signals not warranted by traffic volume.  No conclusive evidence was found to justify a general reduction of minimum volume requirements for rural conditions or high-accident locations.]]></description>
      <pubDate>Tue, 16 Dec 1975 00:00:00 GMT</pubDate>
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