Browsing by Subject "Crash modification factors"
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Item Safety Effects of Left-Turn Phasing Schemes at High-Speed(Minnesota Department of Transportation, Research Services Section, 2007-01) Davis, Gary A.; Aul, NathanThis research describes an effort in estimating crash modification factors (CMFs) associated with different left-turn phasing schemes, at intersections where the major approach speed limit exceeds 40 mph. For installation of signals at previously thru/stop-controlled intersections, rear-end crashes increased while right-angle crashes decreased. Installation of the signal had no effect on either major or minor approach left turn crashes as long as the protected-only left turn phasing was used on the major approaches. At one intersection where a signal was originally installed with permitted/protected phasing on the major approaches, we found evidence for an increase in major approach left-turn crashes, which vanished when the major approach left-turn treatment was changed to protected-only. For several other phasing changes it was not possible to construct an after-treatment data set of sufficient size to permit reliable estimation of an effect. This project also describes a simple simulation model for left-turn cross-path crashes, where a probabilistic gap acceptance model for the turning driver is combined with a standard braking model for the opposing driver. The model characterizes left-turn crashes as resulting when the turning driver accepts a minimal gap and takes an atypically long time complete his/her turn, while the opposing driver takes an atypically long time to react before braking. R reconstruction of an actual fatal crash however was more consistent with the opposing driver reacting normally, but with the turning driver selecting an atypically short gap. Characterizing the rate at which such selection errors occur would then be necessary to accurately predict left-turn crash frequencies.Item Vehicle Automation and Transportability of Crash Modification Factors(Center for Transportation Studies, University of Minnesota, 2019-07) Davis, Gary A; Gao, JingruAlthough the Highway Safety Manual (HSM) now provides empirical tools for predicting the safety consequences of highway engineering decisions, these tools represent the prevailing driver and vehicle conditions in the United States during the last few decades. As automated vehicles improve in capability and increase in market share, these conditions will change, possibly affecting the accuracy of HSM predictions. This report investigates the feasibility of using “transportability” analyses, developed by Judea Pearl and Elias Bareinboim, to assess the “transferability” of crash modification factors (CMF) to new situations. An overview in Chapter 2 concludes that transportability analysis is, in principle, possible provided one can describe a causal mechanism that explains how a CMF works. Chapter 3 then describes developing such an explanation for pedestrian hybrid beacons (PHB). In Chapter 4 the explanatory model developed in Chapter 3 is used to assess the transportability of existing estimates of PHB CMFs to a hypothetical situation where vehicles with autonomous braking are present.