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3  Introduction 1.1 Background Roadside barriers are often used to shield fixed objects that may be hazardous to errant vehicles within the roadside clear zone. Barriers are also used to prevent vehicles from engaging hazards located behind the barriers, such as steep drop-offs or slopes, and to prevent cross- median crashes. Some locations with limited lateral clearance require roadside barriers to be constructed close to a fixed object or have objects placed on top of a barrier. In these situations, an errant vehicle impacting a roadside barrier risks contacting the fixed object located directly behind or on top of the barrier. Examples of fixed objects often placed close to or on top of barriers include signs, luminaires, overhead sign structures, bridge piers, noise walls, debris fences, and trees. Researchers at the Midwest Roadside Safety Facility (MwRSF) at the University of Nebraska- Lincoln found that breakaway and rigid attachments on barriers may damage the occupant compartment, result in occupant compartment penetration, or cause excessive vehicle accelera- tions (Keller et al. 2003). These conditions could be hazardous to the occupants and may cause a rigid barrier to fail the full-scale crash test safety performance criteria set forth in the Manual for Assessing Safety Hardware, 2nd edition (MASH) (AASHTO 2016) and NCHRP Report 350 (Ross et al. 1993). The zone of intrusion (ZOI) is a measurement of the farthest protrusion of a critical vehicle component behind the top-front corner of a barrier during a crash, as shown in Figure 1. ZOI envelopes were developed by MwRSF researchers to determine critical areas above and behind barriers where fixed objects should not be located unless subjected to full-scale crash testing (Keller et al. 2003). A comprehensive review of full-scale crash testing was conducted to identify the extent that critical components of a pickup or single-unit truck (SUT) would intrude over the top of a barrier (Keller et al. 2003). Critical vehicle components are structural elements that may pose a risk to occupants when loaded and/or may impart a significant load to objects mounted within the ZOI. ZOI envelopes vary for different vehicle and test level (TL) impacts as well as barrier shapes and heights (AASHTO 2011). ZOI was previously determined for NCHRP Report 350 TL-2 through TL-4 (Ross et al. 1993). The test matrix for longitudinal barriers at NCHRP Report 350 TL-2 through TL-5 is shown in Table 1. Impact severity (IS) values used with MASH (AASHTO 2016) testing are higher for test TL-2 through TL-4 impacts than with comparable impacts per- formed under NCHRP Report 350, and the angle of impacts for small cars was increased to be equal to the angle for pickup trucks. An example of the ZOI for NCHRP Report 350 TL-3 barriers is shown in Table 2. Although intrusion varied for single-slope, F-shape, and Jersey barriers, they were combined to form a C H A P T E R 1
4 Zone of Intrusion Envelopes Under MASH Impact Conditions for Rigid Barrier Attachments Figure 1. Vehicle intrusion beyond the front barrier face (Keller et al. 2003). Table 1. NCHRP Report 350 longitudinal barrier test matrix (Ross et al. 1993). Test Designation no. Test Vehicle Vehicle Weight (lb) Impact Conditions Speed (mph) Angle (deg.) 2-10 820C 1,808 44 20 2-11 2000P 4,409 44 25 3-10 820C 1,808 62 20 3-11 2000P 4,409 62 25 4-10 820C 1,808 62 20 4-11 2000P 4,409 62 25 4-12 8000S 17,637 50 15 5-10 820C 1,808 62 20 5-11 2000P 4,409 62 25 5-12 36000V 79,366 50 15 Table 2. NCHRP Report 350 TL-3 lateral intrusion for permanent concrete barriers (Ross et al. 1993). Barrier ZOI (in.) 10.8-degree single-slope 12 F-shape 8 Jersey 18 Vertical 24
Introduction 5  ZOI envelope for all sloped-face barriers. A field site investigation was then conducted to deter- mine the types of devices commonly attached to traffic barriers. Based on the combined results from the crash test review and field investigation, recommendations were made for the safe placement of attachments near traffic barriers under NCHRP Report 350 safety criteria. The recommended ZOI guidelines were included in the AASHTO Roadside Design Guide (RDG) (AASHTO 2011), as shown in Figures 2 through 4. MASH is the current guideline for testing and evaluating roadside safety hardware (AASHTO 2016). MASH included updated test vehicles to represent the current vehicle fleet and modi- fied impact conditions for crash testing roadside safety hardware. These changes altered vehicle interaction with rigid barriers, which may also affect ZOI envelopes developed from NCHRP Report 350 (Ross et al. 1993) or prior test criteria. Moreover, the increase in impact severity of MASH test levels has changed the minimum height required to safely contain and redirect vehicles, particularly at TL-4. Therefore, ZOI envelopes needed to be evaluated and updated to the MASH standards. The test matrices for longitudinal barriers at MASH TL-2 through TL-5 impact conditions are shown in Table 3. While previous studies established ZOI envelopes based on NCHRP Report 350 crash testing (Ross et al. 1993), no studies have been conducted to establish ZOI envelopes for all rigid barrier shapes and test levels based on MASH crash testing. Since MASH vehicles and impact condi- tions result in higher impact severities, these envelopes may need to be modified. Additionally, only select studies have been conducted to evaluate specific objects, such as sign supports and luminaires, when placed adjacent to or on top of barriers. Thus, there is a need to reevaluate the ZOI envelopes for rigid barriers with MASH criteria (AASHTO 2016) to identify the extension of the vehicle behind the top-front edge of a barrier to aid determination if a rigid object located behind a barrier may require full-scale crash testing that would confirm that occupant-risk criteria are not being violated. Figure 2. RDG ZOI with NCHRP Report 350 TL-2 impact conditions (AASHTO 2011).
6 Zone of Intrusion Envelopes Under MASH Impact Conditions for Rigid Barrier Attachments Figure 3. RDG ZOI with NCHRP Report 350 TL-3 impact conditions (AASHTO 2011).
Introduction 7Â Â Figure 4. RDG ZOI with NCHRP Report 350 TL-4 impact conditions (AASHTO 2011). Table 3. MASH longitudinal barrier test matrix for TL-2 through TL-5 (AASHTO 2016). Test Designation No. Test Vehicle Vehicle Weight (lb) Impact Conditions Speed (mph) Angle (deg.) 2-10 1100C 2,420 44 25 2-11 2270P 5,000 44 25 3-10 1100C 2,420 62 25 3-11 2270P 5,000 62 25 4-10 1100C 2,420 62 25 4-11 2270P 5,000 62 25 4-12 10000S 22,000 56 15 5-10 1100C 2,420 62 25 5-11 2270P 5,000 62 25 5-12 36000V 79,300 50 15
8 Zone of Intrusion Envelopes Under MASH Impact Conditions for Rigid Barrier Attachments 1.2 Research Objective The research objective of NCHRP Project 22-34 was to develop ZOI envelopes for a variety of rigid barriers under MASH safety criteria (AASHTO 2016) and develop implementation guid- ance for highway design practitioners. 1.3 Research Scope The research objectives are listed and described below: ⢠Literature review and agency survey. ⢠Rigid barrier crash data analysis. ⢠Identification of barrier height thresholds based on available full-scale crash test data. ⢠Simulation model creation and validation. ⢠Simulation of recommended barrier configurations. ⢠Development and validation of ZOI envelopes based on the fusion of computer simulation and full-scale testing. ⢠Identification of future research needs. Literature was collected on previous ZOI research and past full-scale crash testing and simula- tion studies on rigid barriers. This review included tests conducted according to MASH TL-2, TL-3, TL-4, and TL-5 (AASHTO 2016), and NCHRP Report 350 impact safety criteria for TL-5 (Ross et al. 1993). ZOIs associated with rigid barriers and factors potentially affecting the ZOI were identified, including barrier shape and height, vehicle-barrier friction, vehicle suspension failure, and tire deflation. A survey was sent to each state DOT to identify commonly installed rigid barriers at each test level, including Jersey, F-shape, single-slope, vertical, and low-profile barriers, as well as current ZOI determination practices and placement of breakaway/nonbreakaway systems near rigid barriers. Full-scale crash testing, simulation, real-world crash data, and survey results were analyzed to categorize rigid barriers and identify minimum and maximum barrier heights used at each test level. Next, the lateral and vertical extensions of vehicle components above and beyond the front face of each traffic barrier were evaluated from available rigid barrier crash tests to establish intrusion limits for each barrier class. Prior validated simulations of full-scale crash tests were considered when available. Full-scale crash testing was not conducted with all barrier configurations, and thus Phase I included preliminary estimates of ZOI envelopes and barrier height thresholds for each test level based on available crash test data. Preliminary results and recommendations on refinements and methods to fill gaps from a lack of crash test data were prepared and discussed. Researchers conducted simulation using vehicle models consistent with a MASH 2270P pickup truck, 10000S SUT, and 36000V tractor-trailer. Models were used in conjunction with several barrier shape and height combinations to calibrate vehicle-barrier interactions, and simulations were validated using NCHRP Web-Only Document 179: Procedures for Verification and Validation of Computer Simulations Used for Roadside Safety Applications (Ray, Plaxico, and Anghileri 2011). Validated computer models were used to examine the effects of barrier shape and height on ZOI. Simulation and full-scale crash test results were co-plotted to identify correlations between barrier geometry, vehicle dynamic behaviors, and ZOI envelope shapes. Recommendations for ZOI envelopes were developed based on MASH test level, barrier shape, and barrier geometry (AASHTO 2016) and presented for updating RDG guidelines.
