Safety Performance of Part-Time Shoulder Use on Freeways, Volume 1: Informational Guide and Safety Evaluation Guidelines (2021) / Chapter Skim
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4 Shorter implementation timeframe than a conventional widening project. Some PTSU projects have been interim in nature and eventually were removed when a subsequent widening project occurred (Jenior 2016)
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5 Safety Performance Before/after studies of facilities on which PTSU operation was implemented have shown operational improvements. Specific findings include the following: Following implementation of PTSU on US 2 in Washington, an empirical Bayes evaluation showed a 15 percent increase in expected crash frequency.
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6 The first four variables in the aforementioned list are incorporated in a PTSU operation adjustment factor (AF)
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7 A similar table of AF values was prepared for the PTSU-related AFs included in the PDO crash prediction model. The AF values for the PDO model follow the same trends as those for FI crashes but tend to be about 10 percent larger in value (i.e., AFPDO ≈ 1.1 × AFFI)
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8 Table 2. Comparison of predicted severity distribution for freeway segments.
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9 when PTSU operation is not allowed. Additional information on how values in the table were calculated are presented in the NCHRP Project 17-89 Final Report.
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10 Shoulder Open versus Shoulder Closed – The safety performance of PTSU sites with the shoulder closed to traffic and the shoulder open to traffic was compared. This analysis was conducted with a dataset consisting of 48 observations per site -- one observation for each weekday hour and one for each weekend hour of the study period.
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11 Left-side versus Right-side PTSU – The ability to assess the safety performance of left-side versus right-side PTSU was limited by the relatively small number of left-side PTSU sites in the NCHRP Project 17-89 dataset. Within this limited dataset, the analysis results indicate that there is no practical difference between the crash potential of sites with right-side PTSU and the crash potential of sites with left-side PTSU.
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