Skip to main content

Understanding and Communicating Reliability of Crash Prediction Models (2021) / Chapter Skim
Currently Skimming:


Pages 73-89

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 73...
... 71 Chapter 7. Reliability Associated with Predicting Outside the Range of Independent Variables: Problem Description and Procedure for Practitioners Background Crash prediction models (CPMs)
Read the entire page →
From page 74...
... 72 discussion of the functional form of CPMs and SPFs, since they influence the guidance that is provided in the subsequent sections. Functional Form of CPMs and SPFs When CPMs are used to predict the number of crashes at sites whose site characteristics (especially, AADT)
Read the entire page →
From page 75...
... 73 Where 𝐢𝑀𝐹 , β„Žπ‘–π‘”β„Ž π‘‘π‘Ÿπ‘Žπ‘“π‘“π‘–π‘ π‘£π‘œπ‘™π‘’π‘šπ‘’ π‘π‘Ÿπ‘Žπ‘ β„Ž π‘šπ‘œπ‘‘π‘–π‘“π‘–π‘π‘Žπ‘‘π‘–π‘œπ‘› π‘“π‘Žπ‘π‘‘π‘œπ‘Ÿ π‘“π‘œπ‘Ÿ π‘šπ‘’π‘™π‘‘π‘–π‘£π‘’β„Žπ‘–π‘π‘™π‘’ π‘π‘Ÿπ‘Žπ‘ β„Žπ‘’π‘  𝑏 , β„Žπ‘–π‘”β„Ž π‘‘π‘Ÿπ‘Žπ‘“π‘“π‘–π‘ π‘£π‘œπ‘™π‘’π‘šπ‘’ π‘π‘Žπ‘™π‘–π‘π‘Ÿπ‘Žπ‘‘π‘–π‘œπ‘› π‘π‘œπ‘’π‘“π‘“π‘–π‘π‘–π‘’π‘›π‘‘ π‘“π‘œπ‘Ÿ π‘šπ‘’π‘™π‘‘π‘–π‘£π‘’β„Žπ‘–π‘π‘™π‘’ π‘π‘Ÿπ‘Žπ‘ β„Žπ‘’π‘  𝑃_β„Žπ‘£ π‘π‘Ÿπ‘œπ‘π‘œπ‘Ÿπ‘‘π‘–π‘œπ‘› π‘œπ‘“ 𝐴𝐴𝐷𝑇 π‘‘π‘’π‘Ÿπ‘–π‘›π‘” β„Žπ‘œπ‘’π‘Ÿπ‘  π‘€β„Žπ‘’π‘Ÿπ‘’ π‘£π‘œπ‘™π‘’π‘šπ‘’ 𝑒π‘₯𝑐𝑒𝑒𝑑𝑠 1,000 π‘£π‘’β„Ž/β„Žπ‘œπ‘’π‘Ÿ /π‘™π‘Žπ‘›π‘’ For single-vehicle crashes: Equation 64 𝐢𝑀𝐹 , 𝑒 , Where 𝐢𝑀𝐹 , β„Žπ‘–π‘”β„Ž π‘‘π‘Ÿπ‘Žπ‘“π‘“π‘–π‘ π‘£π‘œπ‘™π‘’π‘šπ‘’ π‘π‘Ÿπ‘Žπ‘ β„Ž π‘šπ‘œπ‘‘π‘–π‘“π‘–π‘π‘Žπ‘‘π‘–π‘œπ‘› π‘“π‘Žπ‘π‘‘π‘œπ‘Ÿ π‘“π‘œπ‘Ÿ 𝑠𝑖𝑛𝑔𝑙𝑒 π‘£π‘’β„Žπ‘–π‘π‘™π‘’ π‘π‘Ÿπ‘Žπ‘ β„Žπ‘’π‘  𝑏 , β„Žπ‘–π‘”β„Ž π‘‘π‘Ÿπ‘Žπ‘“π‘“π‘–π‘ π‘£π‘œπ‘™π‘’π‘šπ‘’ π‘π‘Žπ‘™π‘–π‘π‘Ÿπ‘Žπ‘‘π‘–π‘œπ‘› π‘π‘œπ‘’π‘“π‘“π‘–π‘π‘–π‘’π‘›π‘‘ π‘“π‘œπ‘Ÿ 𝑠𝑖𝑛𝑔𝑙𝑒 π‘£π‘’β„Žπ‘–π‘π‘™π‘’ π‘π‘Ÿπ‘Žπ‘ β„Žπ‘’π‘  The next section provides an overview of the goodness-of-fit measures that can be used assess the performance of different calibration and re-estimation options for predicting outside the range of independent variables. Following that is a discussion of different options illustrated using HSIS data from California freeways from 2005 to 2014.
Read the entire page →
From page 76...
... 74 Equation 65 𝑀𝐴𝐷 βˆ‘ |𝑦 𝑦 |𝑛 where: 𝑦 = predicted values from the SPF. 𝑦 = observed counts.
Read the entire page →
From page 77...
... 75 Equation 68 𝐢𝑉 𝑉 CC Where: CV = coefficient of variation of the calibration factor. C = estimate of the calibration factor.
Read the entire page →
From page 78...
... 76 The following five options were examined: ο‚· Option 1: Perform calibration ο‚· Option 2: Adjust parameter/coefficient for AADT and perform calibration ο‚· Option 3: Estimate calibration function or SPF by modifying the coefficient for AADT and perform calibration ο‚· Option 4: Estimate calibration function or SPF and perform calibration ο‚· Option 5: Estimate calibration function or SPF with different parameters for AADT and the other factors, and perform calibration Some of these options (e.g., Options 1 and 2) would be easier for practitioners to apply.
Read the entire page →
From page 79...
... 77 Equation 71 𝑁 𝐢𝐹 𝑁 Β  Option 4: Estimate calibration function or SPF and perform calibration This option also involves the estimation of a calibration function, but unlike Option 3, the coefficient for all the terms in the SPF/CPM are estimated. If the NSPF includes CMFs (also called SPF adjustment factors)
Read the entire page →
From page 80...
... 78 Figure 14. For Option 2, a few values on the change AADT parameter were investigated, and the best one was used to compare with the other options.
Read the entire page →
From page 81...
... 79 Table 32. Testing Results for Multi-Vehicle Crashes (Rural 4-lane flat terrain freeways)
Read the entire page →
From page 82...
... 80 Β  Β  Β  Β  Figure 10. CURE Plots for MV Crashes - Option 1 Β  Β 
Read the entire page →
From page 83...
... 81 Figure 11. CURE Plots for MV Crashes - Option 2Β 
Read the entire page →
From page 84...
... 82 Β  Figure 12. CURE Plots for MV Crashes - Option 3Β  Β  Β 
Read the entire page →
From page 85...
... 83 Figure 13. CURE Plots for MV Crashes - Option 4
Read the entire page →
From page 86...
... 84 Figure 14. CURE Plots for MV Crashes - Option 5Β 
Read the entire page →
From page 87...
... 85 Single-Vehicle Crashes The evaluation results for single-vehicle crashes are shown in Table 33. Overall, Option 5 has very good performance, and Option 1, Option 3, and Option 4, have comparable results and are good candidates for the second-best performance.
Read the entire page →
From page 88...
... 86 Total Crashes (TOT) The results for total crashes are shown in Table 34.
Read the entire page →
From page 89...
... 87 These results indicate that Option 5 generally performs the best, while Option 1 has the worst performance based on all criteria except MAD and Modified R2. Generally, Option 2 performs reasonably well compared to Option 1.
Read the entire page →

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.