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Page 89
Suggested Citation:"Appendix C - Traffic Levels and Capacity." National Academies of Sciences, Engineering, and Medicine. 2016. Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual. Washington, DC: The National Academies Press. doi: 10.17226/24610.
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Page 89
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Suggested Citation:"Appendix C - Traffic Levels and Capacity." National Academies of Sciences, Engineering, and Medicine. 2016. Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual. Washington, DC: The National Academies Press. doi: 10.17226/24610.
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Page 91
Suggested Citation:"Appendix C - Traffic Levels and Capacity." National Academies of Sciences, Engineering, and Medicine. 2016. Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual. Washington, DC: The National Academies Press. doi: 10.17226/24610.
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Page 91
Page 92
Suggested Citation:"Appendix C - Traffic Levels and Capacity." National Academies of Sciences, Engineering, and Medicine. 2016. Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual. Washington, DC: The National Academies Press. doi: 10.17226/24610.
×
Page 92
Page 93
Suggested Citation:"Appendix C - Traffic Levels and Capacity." National Academies of Sciences, Engineering, and Medicine. 2016. Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual. Washington, DC: The National Academies Press. doi: 10.17226/24610.
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Page 93
Page 94
Suggested Citation:"Appendix C - Traffic Levels and Capacity." National Academies of Sciences, Engineering, and Medicine. 2016. Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual. Washington, DC: The National Academies Press. doi: 10.17226/24610.
×
Page 94
Page 95
Suggested Citation:"Appendix C - Traffic Levels and Capacity." National Academies of Sciences, Engineering, and Medicine. 2016. Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual. Washington, DC: The National Academies Press. doi: 10.17226/24610.
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Page 95

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

89 A P P E N D I X C C.1 Introduction In the context of emergency responses, knowledge of critical and vulnerable road links or highway structures is of great significance to reduce loss of life and increase the efficiency of transporting resources for recovery. Several state DOTs have adopted processes for the assessing, coding, and marking of highway structures in the event of emergencies resulting from natu- ral or man-made disasters. However, these processes do not consider the different ranges of traffic levels (i.e., AADT) and the composition of traffic (i.e., light vs. heavy vehicles). Public agencies should incorporate traffic levels when coding highway structures in emergency situa- tions to prioritize and identify the most significant roadways when their remaining function has great impact on not only reducing the casualties, but also the performance of the transportation network in post-disaster emergency responses and recovery. Collaboration and coordination among agencies are required to consider the successful practices of other organizations that often respond to such emergencies. This issue relies on capturing these segments before disaster, and trying to keep them func- tional during and after the event. Despite many efforts in this regard, there have been no univer- sal standards about how to code and assess these highway facilities so far. Emergency response relies on transportation network availability since emergency services need to reach the populated area and also the key resources such as hospitals and fire stations. Now, it is the responsibility of police departments to monitor traffic congestions and to provide solutions for effective traffic flow. The responsibility of local fire departments is to define the impact area and evacuate damaged structures (CH2M Hill 2012). The objective of this appendix is to develop a process for incorporating different ranges of traf- fic levels into the assessment, coding, and marking of highway structures in emergency situations. The rest of the appendix is organized into three sections. The section on assessment criteria reviews the different alternatives in the coding and marking processes. The section on traffic levels assessment proposes categories of traffic levels. The last section presents a procedure for implementation. C.2 Assessment Criteria Some of the procedures suggest using these criteria to process the assessment and coding: • Roadway functional classification: It can be treated as the measure of the importance of the roadway in the local transportation network. It also mimics the ability of the facility to accom- modate traffic. It is not a good criteria to replicate the exact features of the facility though. Traffic Levels and Capacity

90 Assessing, Coding, and Marking of Highway Structures in Emergency Situations: Assessment Process Manual • Congestion: Heavily congested roadways cannot accommodate rapid emergency response. At the same time, prediction of post-earthquake traffic patterns would be difficult. So, the “abil- ity to control” highway structures use is of great significance rather than dedicating roadways to emergency services. • Emergency access routes: Rather than routes that are typically important due to daily use, roadways near emergency facilities like hospitals and emergency response staging areas should be taken into consideration. • Interdependent lifelines: Access to the critical utilities should be taken into consideration. • Capacity: Under capacity criteria, the ability of the facility to accommodate freight vehicles, road width, and access control should be taken into consideration. – Roadway width: Number of lanes is mainly categorized in the following three levels.  Low: two or three lanes  Moderate: four or five lanes  High: six or more lanes – Ability to control use: This criterion is basically the ability to manage access through the segments. The number of controlled and uncontrolled intersections plays a critical role in access management. Normally, roads with high ability to control use perform better for commuting between populated areas.  Low: no access control  Moderate: limited access control (such as an expressway)  High: full access control (such as interstate freeway) – Freight access: The level of freight access to the road also plays an important role in emergency responses since it represents the ability of the goods and supplies to reach the populated areas.  Low: highly restricted to truck and oversized load traffic  Moderate: some restrictions for length or width  High: no freight restrictions Figure C-1 shows how to take capacity criteria into consideration (CH2M Hill 2012). These criteria should be considered along with traffic data discussed in the next section. C.3 Traffic Levels Assessment Table C-1 is extracted from the well-maintained Code of Practice for Highway Inspection and Assessment, and it seems that such network hierarchy can be used in the case of assessing and coding prior to traffic level analysis. For general purposes like highway inspections, although it is pretty basic, some agencies categorize highways based on their estimated annual average daily traffic (AADT) level as follows (Rotherham Metropolitan Borough Council 2014): • Traffic Level 1: greater than 80,000 vehicles/day (high) • Traffic Level 2: 50,000 to 80,000 vehicles/day (moderately high) • Traffic Level 3: 20,000 to 50,000 vehicles/day (medium) • Traffic Level 4: less than 20,000 vehicles/day (low) A more elaborate approach is to use average daily traffic (ADT) for the assessment. At the same time, considering the other criteria mentioned in the previous section and the facility types, ADT and AADT are the most-used measurements to address traffic stress levels on the facility: • ADT: the total traffic volume during a given time period, ranging from 2 to 364 consecutive days, divided by the number of days in that time period, and expressed in vehicles per day • AADT: average daily traffic on a roadway link for all days of the week during a period of one year, expressed in vehicles per day

Traffic Levels and Capacity 91 Since the AADT is more stable and is widely used for planning purposes, in this work the research team suggests using AADT for coding a traffic level on a highway structure. In addition, availability of the data justified the use of AADT since most of the DOTs collect and spread these data. It is also worth mentioning that these data are collected based on dif- ferent vehicle classifications. In Oregon, the data are collected through the Transportation Systems Monitoring Unit which has the mission to formulate a system to collect and process traffic-related data on Oregon’s highways. The raw data collected involve traffic volumes, manual counts, and vehicle class. Based on those, flow maps and other information can be drawn (Oregon DOT 2015). The color-coded maps in Figures C-2, C-3, and C-4 were downloaded directly from the Oregon DOT website. For the purpose of this study, incorporation of these maps, and the previ- ous one, can lead to a general consensus on the standard of assessing and coding the highway structures. Table C-2 shows the categories recommended by the Oregon DOT to analyze traffic flow. Source: CH2M Hill (2012). Figure C-1. Assessment criteria.

Facility Type General Description of Type of Road Detailed Description Motorway Limited access motorway regulations apply Routes for fast-moving long-distance traffic. Fully grade separated and restrictions on use. Strategic Route Trunk and some principal ‘A’ roads between primary destinations Routes for fast-moving long-distance traffic with little frontage access or pedestrian traffic. Speed limits are usually in excess of 40 mph and there are few junctions. Pedestrian crossings are either segregated or controlled and parked vehicles are generally prohibited. Main Distributor Major urban network and inter-primary links; short- to medium-distance traffic Routes between strategic routes and that link urban centers to the strategic network with limited frontage access. In urban areas, speed limits are usually 40 mph or less, parking is restricted at peak times and there are positive measures for pedestrian safety. Secondary Distributor Classified road (B and C class) and unclassified urban bus route carrying local traffic with frontage access and frequent junctions In rural areas, these roads link the larger villages and heavy goods vehicle generators to the strategic and main distributor network. In built-up areas, these roads have 30 mph speed limits and very high levels of pedestrian activity with some crossings. On-street parking is generally unrestricted except for safety reasons. Link Road Roads linking between the main and secondary distributor network with frontage access and frequent junctions In rural areas, these roads link the smaller villages to the distributor roads. They are of varying width and not always capable of carrying two-way traffic. In urban areas, they are residential or industrial inter- connecting roads with 30 mph speed limits, random pedestrian movements, and uncontrolled parking. Local Access Road Roads serving limited numbers of properties carrying only access traffic In rural areas, these roads serve small settlements and provide access to individual properties and land. They are often only single lane width and unsuitable for heavy goods vehicles. In urban areas they are often residential loop roads. Source: Rotherham Metropolitan Borough Council (2014). Table C-1. Transportation network hierarchy. Source: Oregon DOT (2015). Figure C-2. Traffic flow map – Oregon 2013.

Source: Oregon DOT (2015). Figure C-3. Traffic flow map – Oregon 2013, Portland area. Figure C-4. Traffic flow map – Oregon 2013, Willamette Valley area. Source: Oregon DOT (2015).

94 Assessing, Coding, and Marking of Highway Structures in Emergency Situations: Assessment Process Manual C.4 Procedure In sum, the assessment, coding, and marking of highway structures should consider a combi- nation of the criteria concurrently; however, it is difficult to consider all the important criteria mentioned in this document. As a rule of thumb, if only the ranges of traffic levels are con- sidered, the following procedure is recommended: 1. Establish a multi-agency coordination mechanism (e.g., Figure C-5) to respond to emergency situations that includes state DOT, emergency management department, and city or local jurisdiction metropolitan planning organizations 2. Identify highways, strategic routes, and primary distributors based on their attributes and the functional classification based FHWA criteria 3. Integrate the lifeline routes and prioritizations into the consideration if this is available 4. Identify critical organizations such as hospitals or fire stations and vulnerable transportation network components (i.e., bridges and overpasses) 5. Identify traffic levels (i.e., AADT) typically as traffic flow maps represented by AADT col- lected by automatic traffic recorder by state DOTs 6. Determine the priority of assessing, coding and marking highway structures in emergency situations. In terms of marking post-disaster damaged highways facilities, one of the approaches imple- mented by the U.S. DOT is that, in some emergency situations, vehicles driving on specific seg- ments are required to have special permits (EPC 2015). Some other agencies implement some restrictions on oversize or overweight trucks and freight vehicles (FHWA 2015b). In some other cases portable changeable message signs are towed to any place they are needed. They can easily be used in emergency situations to convey the appropriate message to achieve traffic manage- ment purposes (Texas DOT 2006). Source: Oregon DOT (2015). Levels AADT Range Color 1 0 1000 2 1001 2500 3 2501 5000 4 5001 10000 5 10001 15000 6 15001 20000 7 20001 30000 8 30001 50000 9 50001 75000 10 75001 + Table C-2. Traffic levels.

Traffic Levels and Capacity 95 Source: EPC (2015). Figure C-5. Example of a multi-agency emergency planning and preparedness diagram.

Next: Appendix D - Equipment List »
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TRB’s National Cooperative Highway Research Program (NCHRP) Research Report 833: Assessing, Coding, and Marking of Highway Structures in Emergency Situations, Volume 2: Assessment Process Manual is intended for managers who will oversee emergency response situations. The report identifies technologies that could be used to assess highway structures in emergency situations. The report addresses technologies that can help with prioritization, coordination, communication, and redundancy.

NCHRP Research Report 833, Volume 1, Volume 2, and Volume 3; along with NCHRP Web-Only Document 223: Guidelines for Development of Smart Apps for Assessing, Coding, and Marking Highway Structures in Emergency Situations provides guidelines for related coding and marking that can be recognized by highway agencies and other organizations that respond to emergencies resulting from natural or man-made disasters.

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