Click for next page ( 4


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 3
3 CHAPTER 2 Synthesis of Current Repair Criteria for Longitudinal Barriers with Crash Damage 2.1 Objective agency's jurisdiction. The repair policies section, the crux of the survey, was intended to provide insight into what thresholds The purpose of this chapter is to synthesize current U.S. are currently used to determine barrier repair needs, how dam- and Canadian criteria for repair of damaged flexible or semi- aged sites are prioritized, timelines for repairs, documented rigid longitudinal barriers. cases of impacts into damaged barriers, and whether the agency would benefit from more quantitative barrier repair guidelines. 2.2 Methodology This chapter presents a summary of the survey results on the guardrail inventory and repair policies sections. The general methodology for this study was to both examine the available literature and conduct a survey of transportation agencies to ascertain current damaged barrier repair thresholds 2.3 Results among transportation agencies in the U.S. and Canada. The 2.3.1 National Guardrail Repair Guidance literature review focused on available national guardrail repair guidance and individual agency guidelines for the repair and National guidance regarding the repair of w-beam barri- maintenance of semi-rigid and flexible longitudinal barriers. ers is provided by the FHWA's "W-Beam Guardrail Repair: These individual agency guidelines generally fell into two cat- A Guide for Highway and Street Maintenance" (2008). This egories: (1) maintenance manuals that describe conditions document provides highway maintenance personnel with a that warrant repairs on a particular barrier and (2) mainte- comprehensive overview of the importance and logistics of nance assessment criteria that are used to assess the barrier w-beam barrier repair. Guidance is provided on determining condition against a reference condition. Maintenance assess- whether repair is necessary, based on a site visit and a classifi- ment criteria typically evaluate barrier functionality but can cation of the damage severity. A damaged barrier is classified also include other factors such as aesthetics. Although mainte- into one of three categories, as summarized in Table 1. nance assessment criteria may not be directly linked to barrier According to the FHWA guidelines, each transportation repair, they have been included as they are a gauge of barrier agency should develop guidelines for the timing of repair for condition. each damage category. The FHWA report recommends that Using the findings from the literature survey, a survey in- timing be based upon the expected frequency with which the strument was developed for distribution to U.S. and Canadian damaged section will be struck, the severity of impact to the transportation agencies. The 22 question survey was organized damaged section, and agency resources. Despite the relatively into the following five sections: quantitative description of the damage categories shown in Table 1, the guidelines appear to have been developed based Inventory of Guardrail and Median Barriers; on previous state experience with w-beam barrier and engi- Repair Policies; neering judgment. The report does not reference either tests Non-Crash Related Damage/Deterioration; or quantitative analysis as the basis for the guidelines. Notification and Repair Responsibilities; and The American Association of State Highway and Trans- Inspection Policies and Procedures. portation Officials (AASHTO) also provide guidelines on longitudinal barrier maintenance in their Maintenance Man- The purpose of the barrier inventory section was to under- ual (AASHTO, 2007). Although comprehensive in terms of stand the types of barriers most used within a particular what types of damage requires repair, little is provided in terms

OCR for page 3
4 Table 1. Guardrail damage classification details (FHWA, 2008). Damage Category Damage Attributes (1) Non-Functional Rail element is no longer continuous 3 or more posts broken off or no longer attached to rail Deflection of rail element more than 18 in. Rail element torn Top of rail less than 24 in. (2) Damaged but Rail element is continuous (can be bent or crushed significantly) should function 2 or fewer posts are broken or separated from the rail element adequately under Deflection of the rail element is less than 12 in. majority of impacts (3) Damaged but Rail element is continuous (can be crushed or flattened) should not impair the No posts are broken off or separated from the rail element guardrail's ability to Deflection of the rail element is less than 6 in. perform of quantitative guidelines. For instance, w-beam guardrail criteria and 3 maintenance manual criteria). For the purpose repair is recommended when a "deep pocket in the rail line" of this study, "quantitative" was defined as both objective and exists, with no mention of a length or depth threshold. Other measurable. A guideline indicating that posts out of alignment examples of guardrail damage requiring repair include "sec- more than 305 mm (12 inches) horizontally require repair, tions torn loose from posts," "rail section flattened," or an for instance, would be considered "quantitative." However, "anchor at either end of a run broken loose." a guideline indicating that barriers need to be repaired if 5% of the barrier is not functional would not be classified as "quantitative" as there is no measurable definition of "not 2.3.2 Published State Transportation Agency functional." For transportation agencies, quantitative barrier Guidelines for Damaged Barrier Repair repair criteria are important for consistently and objectively The literature review included published guidelines from identifying barrier damage that requires repair. 26 U.S. state transportation agencies relating to the mainte- As additional quantitative barrier repair criteria were iden- nance and/or performance assessment of longitudinal barrier. tified via the survey responses, all quantitative criteria were Of these 26 agencies, only 9 were found to have quantitative combined and discussed further in the survey results section. longitudinal barrier repair criteria (6 maintenance assessment Table 2 summarizes selected agency barrier repair thresholds Table 2. Selected state transportation agencies with non-quantitative guardrail repair guidelines. Agency Type* Criteria Description/Excerpt (Reference) Alabama DOT MM Repair or replacement of guardrail sections, posts and hardware due to crash damage or normal deterioration. (AL DOT, 2005) Idaho MM Any guardrail that is damaged. Most guidance is with respect to Transportation upgrading non-standard guardrail to standard hardware if it is Department damaged. (ID TD, 2008) Indiana DOT MM Maintain guardrail to assure that it will function as designed. Repairs of non-functional barrier should be performed within 5 working days. (IN DOT, 2001) Kentucky MA Measure and record the total linear feet of guardrail that is Transportation damaged to the extent that structural integrity or functionality is Cabinet (TC) lost. (KY TC, 2000) Michigan DOT MM Only a description of how repair work should be completed. No criteria for when guardrail is considered deficient or should be repaired. (MI DOT, 2004) Montana DOT MM "Guardrails are repaired and replaced in order to maintain its structural integrity" (MT DOT, 2002a) North Carolina MA Threshold condition is "Guardrail damaged or not functioning as DOT designed." (NC DOT, 1998; NC DOT, 2004) Oregon DOT MM Description only of the work involved. Maintain, repair, realign, or replace guardrail to preserve or restore the installation to its designed condition. (OR DOT, 2004) South Carolina MA Threshold condition: "Guardrail damaged or not functioning as DOT designed." (SC DOT, 2004) Utah DOT MA Each guardrail run should function as intended - all posts, blockouts, panels, and connection hardware shall be in place. (UT DOT, 2004) * MM denotes criteria present in a maintenance manual; MA denotes maintenance assessment criteria.

OCR for page 3
5 that were not classified as quantitative. The prevailing mainte- Concrete, cable barrier, strong post thrie beam, and the weak nance manual and maintenance assessment damage threshold post w-beam were ranked second through fifth, respectively, is stated as "damage that affects the structural integrity of the based on the responding agencies providing detailed barrier barrier." For maintenance assessment criteria, several agen- information. The distribution of barriers identified in this cies even rate barriers in terms of a percentage that is "func- survey appears similar to that reported by Ray and McGinnis tional" without specifically defining damage that impairs (1997). Note, however, that the Ray and McGinnis study did barrier functionality. Without an objective definition of the not request agencies to report barrier mileage. damage that affects barrier integrity, maintenance personnel Approximately 60 percent of responding agencies (23 of 39) tasked with evaluating barrier repair need may have signifi- indicated the presence of specific guidelines for determining cantly different interpretations of what damage impairs bar- when a guardrail needs to be repaired. Of these 23 agencies, rier functionality. The fact that the majority of state agencies however, only 7 were classified as "quantitative" with 2 of these employ this blanket statement without accompanying quan- agencies previously identified through the literature review. In titative guidelines underscores the importance of developing general, the quantitative guidelines resulting from the survey a better understanding of how quantifiable barrier damage were similar to those found through the literature review. For correlates to subsequent impact barrier performance. the purpose of this study, the quantitative criteria found via the Also evident from this literature review is the variation survey and literature review have been combined and shown in between maintenance manuals and maintenance assessment Tables 36. Tables 35 summarize the metal beam barrier cri- criteria even within the same jurisdiction. For instance, North teria while Table 6 summarizes the criteria for cable barriers. Carolina had quantitative barrier repair guidelines in the main- Each criterion was classified based on the barrier component tenance manual but no quantitative guidelines for mainte- to which it refers, i.e., the rail element, the posts/blockouts, or nance assessment (see Table 2). It should be noted that these the connections. For the rail element and post/blockout cat- criteria for a given agency are not required to coincide as these egories, the criteria have been further classified into 3 general manuals are typically developed independently. In addi- damage types: (1) deflection, (2) tearing/breaks and/or punc- tion, maintenance assessment criteria are not necessarily tures, or (3) deterioration. The transportation agencies using used by maintenance personnel to justify barrier repair and each of these criteria are listed on the right hand side of the may include factors other than the safety performance of the table and grouped into one of two categories: maintenance or barrier in their scope. For all the published maintenance assess- maintenance assessment. Again, note that for the same agency, ment manuals found in this study, however, functionality was maintenance manual-based criteria and maintenance assess- a main component of barrier condition. Another observation ment criteria are not necessarily the same. The Ohio DOT, for from these published guidelines was that there was little dis- instance, has quantitative criteria for both barrier mainte- tinction between the repair thresholds based on barrier appli- nance and maintenance assessment; however, as indicated cation, e.g., on the roadside or in the median. in the table, these criteria are not the same. Another exam- ple is the Indiana DOT that has quantitative maintenance assessment criteria, but the maintenance manual uses only a 2.3.3 Analysis of Survey Responses non-quantitative "functional/non-functional" criterion and A total of 39 transportation agencies responded to the survey. thus was not included in the tables. Note that references From the United States, there were responses from 29 trans- for each agency's barrier repair criteria appear next to the portation agencies from the continental states as well as agency name. Hawaii and Puerto Rico. From Canada, there were responses Current FHWA guidelines for metal beam barriers have from a total of 8 Canadian Provinces: Alberta, British Colum- been provided for reference and are the thresholds to distin- bia, Manitoba, New Brunswick, Nova Scotia, Ontario, Prince guish between the "minor damage" and "damaged but should Edward Island, and Quebec. Approximately 38 percent of the function adequately under majority of impacts" categories. No respondents (15 agencies: 11 U.S. States, 3 Provinces, and FHWA guidelines were found for cable barriers. The majority Puerto Rico) provided detailed information for guardrails of the criteria listed in the table are those used to distinguish within their respective jurisdictions. In total, these agencies between minor damage and damage that needs to be repaired provided an inventory in excess of 37,000 miles of longitudinal (or results in a "deficient" rating in terms of maintenance barrier (no distinction was made between roadside and median assessments). Some agencies also have (or only have) criteria barriers). The strong-post w-beam barrier was the most fre- for severely damaged barriers; these criterion are marked with quent barrier type, accounting for roughly 60 percent of total an asterisk. barrier length by the responding state agencies. Excluding For metal beam barrier rail elements, the most prevalent the two agencies that reported no use of strong-post w-beam quantitative criterion for repair was barrier deflection with (South Carolina and British Columbia), the average use of a majority of agencies using the FHWA-endorsed 152 mm strong-post w-beam barriers was approximately 75 percent. (6 inches) threshold. Maintenance assessment procedures

OCR for page 3
6 Table 3. Summary of quantitative damaged barrier criteria: metal beam barrier rail elements. Maintenance Maintenance Assessment Washington State (2006) North Carolina (2000) Pennsylvania (2006) Nova Scotia (2006) Montana (2002b) California (2006) Wisconsin (2004) Wyoming (2006) Missouri (2003) Category Type Criteria Description Indiana (2006) Quebec (2004) Florida (2007) FHWA (2008) Ohio (2005) Ohio (2004) Iowa (2004) Rail Element Deflection Deflection > 76 mm (3 in.) X Deflection > 152 mm (6 in.) X X X X Deflection > 152 mm at any point in 3.6 m section X X X X * Deflection > 305 mm (12 in.) X * Deflection > 457 mm (18 in.) X Rail flattening > 50% thickness X X Rail flattening > 30% height X > 50% crushed X X > 50% torn X X Rail distortion > 25% of rail section length X Any rail flattening (even if <152 mm deflection) X X X X Rail height varies > +/- 51 mm (2 in.) from 706 X mm (27 in.) standard height Rail height varies > +/- 76 mm (3 in.) from 706 X mm (27 in.) standard height Rail height < 610 mm (ground to top of rail) X X Rail height > 762 mm (ground to top of rail) X Tearing/Breaks Horizontal tear > 25 mm wide and 305 mm long X & Punctures Any length vertical tear X * Any splits or tearing X X > 50% torn X Non-manufacturer hole in rail > 25 mm diameter X > 3 Non-manufacturer holes in rail X Deterioration Any structural corrosion X X X * Maintenance criteria is used to indicate a threshold for severe barrier damage (e.g., immediate repair). X Agency uses the criteria to determine barrier repair need (maintenance column only) or barrier deficiency (maintenance assessment column only). in Missouri, however, allow only a 76 mm (3 inches) deflec- tions, most maintenance assessment criteria rate a barrier as tion threshold for guardrails. Even with severe metal beam deficient if one or more bolts are missing while maintenance barrier damage, there are variations; the California mainte- assessment in Wyoming specified 4 or more missing bolts. nance manual specifies 305 mm (12 inches) of rail deflec- Interestingly, none of the quantitative maintenance criteria tion while the North Carolina maintenance manual specifies used a threshold for missing bolts. 457 mm (18 inches). With respect to rail flattening, two states Similar variations can be found with respect to cable bar- (Montana and Washington State) specify guardrail deficient rier repair/assessment criteria. The overall number of criteria if rail flattening is present even if the barrier was not deflected pertaining to cable barriers, however, was substantially less more than 152 mm (6 inches). The maintenance assessment than that of metal beam barriers. Notable differences include procedures in Iowa were the only guidelines that prescribed criteria for cable sag which varies from 38 mm (1.5 inches, specific thresholds for rail flattening: 50 and 30 percent of the Iowa maintenance assessment) to 51 mm (2 inches, Ontario cross-section thickness and height, respectively. For damage maintenance manual) up to 152 mm (6 inches, Pennsylvania to posts, a majority of the agencies used a threshold of one maintenance assessment). For broken posts, a majority of or more broken or cracked posts. Two exceptions were Ohio agencies used a threshold of one or more (Ohio, Quebec, and and Indiana maintenance assessment procedures which pre- Montana) while Ontario uses 3 or more consecutive posts. scribed two or more broken or cracked posts. For post deflec- In general, maintenance assessment criteria employed by Iowa tion, a majority of the agencies used horizontal distance out were found to be the most quantitative and comprehensive of alignment; a notable exception was Pennsylvania and Nova with respect to both flexible and semi-rigid longitudinal bar- Scotia which use post angle. For metal beam barrier connec- rier assessment.

OCR for page 3
7 Table 4. Summary of quantitative damaged barrier criteria: metal beam barrier post and blockouts. Maintenance Maintenance Assessment Washington State (2006) North Carolina (2000) Pennsylvania (2006) Nova Scotia (2006) Montana (2002b) California (2006) Wisconsin (2004) Wyoming (2006) Missouri (2003) Category Type Criteria Description Indiana (2006) Quebec (2004) Florida (2007) FHWA (2008) Ohio (2005) Iowa (2004) Ohio (2004) Posts & Deflection Deflection > 76 mm (3 in.) X Blockouts Deflection > 152 mm (6 in.) X X X X Post angle > 15 angle from vertical X Post angle > 20 angle from vertical X * Deflection > 305 mm (12 in.) X * Deflection > 457 mm (18 in.) X 1 or more twisted/misaligned blockouts X X 3 or more continuous twisted/misaligned X X blockouts > 10% of blockouts twisted X Tearing/Breaks 1 or more broken/cracked posts X X X X X X X X X 2 or more broken/cracked posts X X *3 or more broken posts X 1 or more missing blockouts X X X X 3 or more continuous missing blockouts X X X Deterioration 1 or more rotten posts X 2 or more continuous rotten posts X X X Rotten post ( > 50% cross section) X > 10% of posts/blockouts deteriorated or rotten X Any structural corrosion X X * Maintenance criteria is used to indicate a threshold for severe barrier damage (e.g., immediate repair). X Agency uses the criteria to determine barrier repair need (maintenance column only) or barrier deficiency (maintenance assessment column only). Table 5. Summary of quantitative damaged barrier criteria: metal beam barrier connections. Maintenance Maintenance Assessment Washington State (2006) North Carolina (2000) Pennsylvania (2006) Nova Scotia (2006) Montana (2002b) California (2006) Wisconsin (2004) Wyoming (2006) Missouri (2003) Category Type Criteria Description Indiana (2006) Quebec (2004) Florida (2007) FHWA (2008) Ohio (2005) Iowa (2004) Ohio (2004) Connections Integrity Loss Splice damage (< 32 mm of rail material left at any X point around the bolt) 1 or more missing/loose/damaged splice bolts X Loose/missing or damaged hardware X 1 or more missing bolts X X X X X X 1 or more posts separated from rail X X 4 or more missing/loose bolts in single section X *Bolts are missing or torn through rail element X * Maintenance criteria is used to indicate a threshold for severe barrier damage (e.g., immediate repair). X Agency uses the criteria to determine barrier repair need (maintenance column only) or barrier deficiency (maintenance assessment column only).

OCR for page 3
8 Table 6. Summary of quantitative damaged barrier criteria: cable barrier. Maintenance Maintenance Assessment North Carolina (2000) Pennsylvania (2006) Washington (2006) Montana (2002b) California (2006) Wisconsin (2004) Missouri (2003) Ontario (2003) Indiana (2006) Quebec (2004) Category Type Criteria Description Ohio (2005) Iowa (2004) Ohio (2004) Rail Element Deflection *Cable is on the ground X X X Top cable height varies > +/- 51 mm (2 in.) from 762 X X mm (30 in.) standard height Spacing between cables > 76 mm (3 in.) X Horizontal deflection > 76 mm (roadside cable barrier) X Horizontal deflection > 25 mm (median cable barrier) X Horizontal deflection > 152 mm (6 in.) X Tearing/Breaks Any broken cable strands X Frayed cable X * Broken cable X X X Deterioration Any structural rust X Cable sag > 38 mm (1.5 in.) between posts X Cable sag > 51 mm (2 in.) X Cable sag > 152 mm (6 in.) X Posts Deflection Post angle > 15 angle from vertical X Tearing/Breaks 1 or more broken posts X X X 3 or more consecutive posts missing/broken X Missing first 2 posts adjacent to anchor(s) X * 4 or more posts knocked down X Deterioration Any structural rust X Connections Integrity Loss Missing cable hooks (unsecured cables) X X Damaged cable hooks X Corroded cable hooks (unsecured cables) X * Maintenance criteria is used to indicate a threshold for severe barrier damage (e.g., immediate repair). X Agency uses the criteria to determine barrier repair need (maintenance column only) or barrier deficiency (maintenance assessment column only). For 27 different minor barrier damage types, respondents does not need to be repaired. Rail deflection only and post/ were asked to indicate whether the damage type would be rail defection less than 6 inches appear to be the least likely repaired and the corresponding repair priority. A total of to be repaired with 50 and 27 percent repair percentages, 33 respondents filled in this information in whole or in part; respectively. the remaining 6 agencies did not provide any information. A total of 34 agencies provided repair priority information Table 7 summarizes the responses by indicating the percent- for each damage type. Respondents were asked to categorize age of agencies that would repair the particular guardrail repair priority into one of 4 categories: (1) repair immediately, damage. For each damage type, the number of respondents (2) repair as part of scheduled maintenance, (3) do not repair, for which it is based has also been listed. Note that not every and (4) at the discretion of maintenance personnel. Again, agency provided a repair indication for each damage type; in not all 34 agencies indicated repair priority for all damage most cases, the agency did not provide a response or, in fewer types. On average, however, there were 27 respondents for each instances, provided alternate responses (other than the yes/no damage type. Figure 2 is a summary of the top 10 damage cat- specified by the survey instructions). There appears to be a egories based on the percentage of respondents indicating the consensus among respondents that post/rail deflection in damage should be repaired as soon as possible. Not surpris- excess of 152 mm (6 inches) and vertical rail tears need to ingly, post and rail deflections in excess of 152 mm (6 inches), be repaired. Splice damage, cable tension loss, damage to rail tears, and damage to cables ranked as high-priority repairs. cables, soil erosion around posts, and bent or missing cable With the exception of erosion of soil around posts, there is very hooks had repair percentages in excess of 90 percent. There good agreement between these top 10 and the top 10 presented appears to be no particular consensus on what damage type in Table 7.

OCR for page 3
9 Table 7. Agency guardrail repair priorities by damage type. Damage Type / Description % Agencies that would Repair # of Respondents Post/rail deflection > 6 in. (152 mm) 100 30 Rail tear (vertical) 100 28 Loss of tension (cable barrier) 96 25 Damage to cable 96 24 Erosion of soil around posts 96 23 Bent or missing hooks (cable) 95 22 Snowplow damage 95 19 Splice damage 92 26 Missing bolts/hardware 92 25 Cable sag 91 22 Rail tear (horizontal) 89 28 Missing blockout 89 28 Loose bolts/hardware 87 23 Mowing damage 83 18 Rail flattening 81 27 Post wood rot 81 21 Slope-related barrier lean 79 24 Tear in steel post 78 27 Bolt pulled-through rail 77 26 Twisted blockout 77 26 Insect damage 68 19 Rail/post corrosion or rust 67 18 Cracked wood post 64 22 Holes > 1 in. (25 mm) in rail 58 24 Rail deflection only 50 22 Post/rail deflection < 6 in. (152 mm) 27 22 With respect to known cases of a vehicle impacting a pre- In New Hampshire, the only details provided were that sec- viously damaged barrier, 32 of 39 respondents indicated no ond impacts do not happen often. documented cases. Three other responding agencies did not Two-thirds of responding agencies (26 of 39) indicated that provide an answer to the question while two agencies an- more quantitative guidelines for the repair of guardrail would swered "unknown." Only two agencies (Oklahoma and New be beneficial. Eleven agencies (28 percent) indicated that more Hampshire) indicated documented cases of a vehicle impact- quantitative guidelines would not be beneficial to their organi- ing a damaged barrier. In Oklahoma, the single case identi- zation; however, only two (California DOT and Florida DOT) fied a vehicle impacting a Truck Mounted Attenuator (TMA) of these agencies reported quantitative barrier repair guide- that was in place (presumably in front of the damage section). lines. Of the remaining two agencies, one indicated that more Post/rail deflection > 152 mm 50 Damage to Cable 41 Rail Tear (horizontal) 39 Rail Tear (vertical) 37 Splice Damage 36 Loss of tension (cable barrier) 30 Cable Sag 30 Snowplow damage 23 Missing Blockout 19 Missing bolts/hardware 17 0 10 20 30 40 50 60 Percentage of Respondents Indicating To Repair ASAP Figure 2. Damage type ranked by ASAP repair priority.