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Page 270
Suggested Citation:"Appendix C: Ohio Crash Assignment Rules." National Academies of Sciences, Engineering, and Medicine. 2021. Safety Performance of Part-Time Shoulder Use on Freeways, Volume 2: Conduct of Research Report. Washington, DC: The National Academies Press. doi: 10.17226/26393.
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Suggested Citation:"Appendix C: Ohio Crash Assignment Rules." National Academies of Sciences, Engineering, and Medicine. 2021. Safety Performance of Part-Time Shoulder Use on Freeways, Volume 2: Conduct of Research Report. Washington, DC: The National Academies Press. doi: 10.17226/26393.
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Page 272
Suggested Citation:"Appendix C: Ohio Crash Assignment Rules." National Academies of Sciences, Engineering, and Medicine. 2021. Safety Performance of Part-Time Shoulder Use on Freeways, Volume 2: Conduct of Research Report. Washington, DC: The National Academies Press. doi: 10.17226/26393.
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Page 273
Suggested Citation:"Appendix C: Ohio Crash Assignment Rules." National Academies of Sciences, Engineering, and Medicine. 2021. Safety Performance of Part-Time Shoulder Use on Freeways, Volume 2: Conduct of Research Report. Washington, DC: The National Academies Press. doi: 10.17226/26393.
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Page 273

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272 A P P E N D I X C - O H I O C R A S H A S S I G N M E N T R U L E S Ohio Crash Assignment Rules The Ohio HSIS vehicle subfile contains the direction that each vehicle in a crash came from and was going to. This field has nine possible values – north, south, east, west, northeast, northwest, southeast, southwest, and unknown. The process used to assign directionality (increasing milepost direction or decreasing milepost direction) for the three facilities studied in Ohio was noted in Chapter 4 and is more fully described below. The process of differed for each facility because the geographic orientation of each facility differs. The direction of the first two vehicles was considered when assigning a direction to the crash; approximately 87% of the crashes involved one or two vehicles. The direction of additional vehicles beyond the first two was examined for a sample of the crashes with three or more vehicles and the directions were usually consistent with the first two vehicles. I-71 I-71 is signed as a north/south route, and oriented in the northeast/southwest direction in the study area. Mileposts increase in the northbound direction. Directionality was assigned as follows:  Single-vehicle crashes o Vehicle 1 travelling from north to south or northeast to southwest – decreasing milepost direction and confidence level 1 o Vehicle 1 travelling from south to north or southwest to northeast – increasing milepost direction and confidence level 1 o Vehicle 1 travelled from east to west – decreasing milepost direction and confidence level 2 o Vehicle 1 travelled from west to east – increasing milepost direction and confidence level 2 o Vehicle 1 travelled from north or northeast to any direction not already assigned – decreasing milepost direction and confidence level 2 o Vehicle 1 travelled from south or southwest to any direction not already assigned – increasing milepost direction and confidence level 2 o Approximately 3% of crashes remained after the prior assignments, the majority of which were located within the vicinity of a system interchange with I-275. The majority were coming from the east or west. Vehicles travelling to the south were assigned to the decreasing milepost direction and confidence level 2. Vehicles travelling to the north were assigned to the decreasing milepost direction and confidence level 2 o Less than 1% of crashes remained after the prior assignments. All had Vehicle 1 travelling in a northwest/southeast direction or where travelling to and/or from an unknown direction. These crashes were eliminated from the dataset  Multi-vehicle crashes o Vehicle 1 and 2 travelling from north to south or northeast to southwest – decreasing milepost direction and confidence level 1

273 o Vehicle 1 and 2 travelling from south to north or southwest to northeast – increasing milepost direction and confidence level 1 (this and the prior bullet captured 89% of MV crashes) o Vehicle 1 and 2 travelled from east to west – decreasing milepost direction and confidence level 2 o Vehicle 1 and 2 travelled from west to east – increasing milepost direction and confidence level 2 o Vehicles 1 and 2 travelled from north or northeast to any direction not already assigned – decreasing milepost direction and confidence level 2. In some cases one of the vehicles was travelling from north and one was travelling from northeast o Vehicles 1 and 2 travelled from south or southwest to any direction not already assigned – increasing milepost direction and confidence level 2. In some cases one of the vehicles was travelling from south and one was travelling from southwest o Vehicles travelling to the south were assigned to the decreasing milepost direction and confidence level 2. Vehicles travelling to the north were assigned to the decreasing milepost direction and confidence level 2. o Approximately 2.5% of the multi-vehicle crashes remained after the prior assignments. Many have vehicles traveling in seemingly opposite directions or unknown directions. These crashes were eliminated from the dataset. I-275 I-275 is a beltway route forming a complete loop. Mileposts increase on the inner loop direction of I- 275, which is oriented to the southeast in the study area. Directionality was assigned as follows:  Single-vehicle crashes o Vehicle 1 travelling from east to west or southeast to northwest – decreasing milepost direction and confidence level 1 o Vehicle 1 travelling from west to east or northwest to southeast – increasing milepost direction and confidence level 1 o Vehicle 1 travelled from north to south – increasing milepost direction and confidence level 1 o Vehicle 1 travelled from south to north –decreasing milepost direction and confidence level 1 o Vehicle 1 travelled from east or southeast or south to any direction not already assigned – decreasing milepost direction and confidence level 2 o Vehicle 1 travelled from west or northwest or north to any direction not already assigned – increasing milepost direction and confidence level 2 o Less than 0.05% of crashes remained after the prior assignments and had unknown directions. These crashes were eliminated from the dataset.  Multi-vehicle crashes o Vehicle 1 and 2 travelling from east to west or southeast to northwest or south to north – decreasing milepost direction and confidence level 1 o Vehicle 1 and 2 travelling from west to east or northwest to southeast – increasing milepost direction and confidence level 1 o Vehicle 1 and 2 travelled from north to south – increasing milepost direction and confidence level 1

274 o Vehicle 1 and 2 travelled from south to north – decreasing milepost direction and confidence level 1 o Vehicles 1 and 2 travelled from east or southeast or south to any direction not already assigned – decreasing milepost direction and confidence level 2. o Vehicles 1 and 2 travelled from west or northwest or north to any direction not already assigned – increasing milepost direction and confidence level 2. o Vehicles 1 and 2 travelling to the west or north or northwest not already assigned - decreasing milepost direction and confidence level 2. o Vehicles 1 and 2 travelling to the east or south or southeast not already assigned - increasing milepost direction and confidence level 2. o Approximately 3% of the multi-vehicle crashes remained after the prior assignments and all had unknown directions. These crashes were eliminated from the dataset. I-70 I-70 is signed as an east/west route, with some portions oriented in the northwest/southeast direction in the study area. Mileposts increase in the eastbound direction. Directionality was assigned as follows:  Single-vehicle crashes o Vehicle 1 travelling from east to west or southeast to northwest – decreasing milepost direction and confidence level 1 o Vehicle 1 travelling from west to east or northwest to southeast – increasing milepost direction and confidence level 1 o Vehicle 1 travelled from north to south – decreasing milepost direction and confidence level 2 o Vehicle 1 travelled from south to north – increasing milepost direction and confidence level 2 o Vehicle 1 travelled from east or southeast to any direction not already assigned – decreasing milepost direction and confidence level 2 o Vehicle 1 travelled from west or northwest to any direction not already assigned – increasing milepost direction and confidence level 2 o Vehicle 1 travelling to the southeast from any direction not already assigned - decreasing milepost direction and confidence level 2. o Vehicle 1 travelling to the west from any direction not already assigned - decreasing milepost direction and confidence level 2. o Approximately 1% of crashes remained after the prior assignments. All had Vehicle 1 travelling in a northeast/southwest direction or where travelling to and/or from an unknown direction. These crashes were eliminated from the dataset  Multi-vehicle crashes o Vehicle 1 and 2 travelling from east to west or southeast to northwest – decreasing milepost direction and confidence level 1 o Vehicle 1 and 2 travelling from west to east or northwest to southeast – increasing milepost direction and confidence level 1 o Vehicle 1 and 2 travelled from north to south – decreasing milepost direction and confidence level 2 o Vehicle 1 and 2 travelled from south to north – increasing milepost direction and confidence level 2

275 o Vehicles 1 and 2 travelled from east or southeast to any direction not already assigned – decreasing milepost direction and confidence level 2. o Vehicles 1 and 2 travelled from west or northwest to any direction not already assigned – increasing milepost direction and confidence level 2. o Vehicles 1 and 2 travelling to the west not already assigned - decreasing milepost direction and confidence level 2. o Vehicles 1 and 2 travelling to the east not already assigned - decreasing milepost direction and confidence level 2. o Approximately 2.5% of the multi-vehicle crashes remained after the prior assignments. Many have vehicles traveling in seemingly opposite directions or unknown directions. These crashes were eliminated from the dataset.

Safety Performance of Part-Time Shoulder Use on Freeways, Volume 2: Conduct of Research Report Get This Book
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Part-time shoulder use is a congestion relief strategy that allows use of the left or right shoulders as travel lanes during some, but not all, hours of the day.

The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 309: Safety Performance of Part-Time Shoulder Use on Freeways, Volume 2: Conduct of Research Report describes the development of crash prediction models for freeways with PTSU operation.

Supplemental to the document is a Freeway Analysis Tool, which includes BOS Data, S D PTSU Data, and a Prediction Tool, as well as NCHRP Web-Only Document 309: Safety Performance of Part-Time Shoulder Use on Freeways, Volume 1: Informational Guide and Safety Evaluation Guidelines.

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