This paper documents the calibration of the Highway Safety Manual (HSM) safety performance function (SPF) for rural two-lane two-way roadway segments in Utah and the development of new SPFs through negative binomial regression. Crash data from 2005 to 2007 on 157 selected study segments in Utah provided a 3-year frequency of observed crashes to calibrate the HSM SPF and develop new models. The calibration factor for the HSM SPF for rural two-lane two-way roads in Utah is 1.16, indicating that the original HSM model under predicts crashes in Utah. The HSM suggests that jurisdiction-specific SPFs may predict crashes with greater reliability than calibrated SPFs. The following variables were significant in each of the four models developed by this research: annual average daily traffic (AADT), segment length, speed limit, and the percentage of AADT composed of multiple-unit trucks. AADT and segment length are used in the HSM SPF; speed limit and the percentage of AADT composed of multiple-unit trucks were found to correlate significantly with observed crash frequencies. The fourth negative binomial model developed in the study would be the best SPF to predict crashes on rural highways in Utah. As encouraged by the HSM and contemporary research, the empirical Bayes method can be applied with each jurisdiction-specific SPF because the analysis provided an overdispersion parameter for each model.

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This paper presents an innovative method of visualizing eye-tracking data by using heat maps (color-coded contour maps showing distributed data). Heat maps of eye fixation points were created from data collected while drivers navigated a rural road. Comparable road segments were used to identify how a driver's visual attention changed while the driver approached and navigated a curve and to address how chevrons and time of day affected fixation patterns. Measures of the centroid and dispersion of each heat map were used to quantify the changes in visual behavior. The results suggest that as drivers approach curves, their fixation patterns become more focused, particularly during the daytime, when their gazes are more prone to shift away from the road scene on long tangents. Chevrons are most useful at night and guide drivers to select a narrower field of view on curve approaches. There were no consistent differences in fixation points within curves that had chevrons as compared with curves that did not, for either daytime or nighttime conditions. This finding suggests that drivers derive little benefit from chevrons within the curve as compared with on the approach. This research is particularly valuable because it investigates a new method for evaluating the effectiveness of traffic control devices and characterizing the driving experience.

High-friction surface treatments (HFSTs) are effective at reducing crashes on horizontal curves; however, HFST effectiveness on other roadway sections (e.g., tangents, intersections, intersection approaches) is not well documented. The crash reduction effectiveness of HFSTs in Florida was assessed, and the benefit–cost (BC) ratios for these section types were calculated. The researchers identified 23 HFST projects in Florida and attempted to collect data for each project, including bidding records, roadway geometry, and crash statistics. The cost data were based on the average comprehensive HFST unit cost and scaled by the size of the application. The benefit was estimated on the basis of 5-year extrapolations of average total and wet weather crash reductions. Savings were estimated on the basis of Florida Department of Transportation KABCO severity distribution of the crashes and an average cost per crash. On average, HFST applications on tight curves reduced the total crash rate by 32% and the wet weather crash rate by 75%. The average BC ratio on tight curve sections was between 18 and 26, depending on the benefit calculation method. Wide curve and tangents sections had few accidents initially, and HFST had negligible impact. From a crash perspective, wide curve and tangent HFST applications are not cost-effective. The effectiveness of HFST on intersection and approach applications is still inconclusive. Half the sections had good BC ratios and the other sections had negative benefit (increased crash rates). When considering the application of HFST, the engineer should consider whether there is an existing crash problem and whether it is skid related.

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