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130 In this research study, ZOI envelopes were recommended based on a collection of full-scale test data and simulation results. These ZOI envelope recommendations are useful to deter- mine the minimum lateral and vertical offsets from the barrier that are necessary to mitigate contact between roadside structures and vehicles during an impact. However, there are many instances in which offsets between the top traffic-side face of the barrier and the roadside struc- ture are limited, and structures must be placed within the ZOI envelope. The following sec- tions document research needs for structures that are often located within the recommended ZOI envelopes. 7.1 Median Barrier Sign Supports and Poles Sign supports and luminaires that are used to inform drivers may not have sufficient space in medians to be placed outside of the ZOI from both travel directions. These features are com- monly located within the barrierâs ZOI envelope. Crashworthy combinations of barrier heights, sign support configurations, and potential retrofit or design options to accommodate stiff or rigid structures located within the ZOI are needed. 7.2 Bridge Pier Protection Shielding bridge piers from impacts with vehicles is important for safe, crashworthy designs as well as to reduce the risk of catastrophic structural damage resulting from a crash with a large truck. Some large-truck crashes with reduced-height median barriers resulted in direct impact between the truck and a bridge pier or supporting structure, including a girder or deck. The ZOI envelopes provided by this research may provide guidance for new or retrofit designs to mitigate potential contact between large trucks and bridge structures. However, some existing systems may not have sufficient offset between bridge structures and barrier systems to shield the bridge pier in the event of a large-truck collision. Guidelines are needed for determining the cost-effectiveness, warrants, and best practices for shielding critical structural elements located close to a roadside barrier. 7.3 Guidelines for Mechanically Stabilized Earth (MSE) Walls Although recommendations were provided in this study for rigid barriers consistent with the most commonly used barrier profiles, some types of roadside barriers have a unique configura- tion, including some MSE walls and natural, earthen, or stone walls. Further study is necessary C H A P T E R 7 Future Research Needs
Future Research Needs 131  to determine whether guidelines should be modified to accommodate barriers with unique geometries or materials, which nonetheless satisfy the criterion of less than 10 in. total dynamic deflection. 7.4 Noise Walls and Structural Barrier Attachments Many DOTs have utilized noise walls or debris fences in combination with stiff roadside bar- riers to reduce transportation noise, limit transportation debris from falling off overpasses, or discourage pedestrian crossings in key locations. The stiffness of noise walls and debris fences may vary, but these features can be located within the ZOI envelope depending on barrier height. Guidance is necessary to evaluate the crashworthiness of noise wall and debris fence combina- tions with roadside barriers. 7.5 Pedestrian Protection ZOI envelopes presented in this study may offer some indication of the risk to vulnerable road users, such as pedestrians and bicyclists, located on the nonimpact side of a barrier that is struck by an adjacent impacting vehicle. However, the safety of pedestrians was not an objec- tive of this study. Further research is recommended to evaluate the risk to vulnerable road users during a crash. 7.6 MASH TL-6 Truck-Tank Trailer Combination Vehicle ZOI Guidelines This study focused on the ZOI envelopes of pickup trucks, SUTs, and tractor-van body trailer combination vehicles corresponding to MASH test designation nos. 2-11 and 3-11, 4-12, and 5-12, respectively. Tractor-tank trailer combination vehicles, which are consistent with MASH test designation 6-12, were not considered; these vehicles may experience significantly different intrusion past the barrier than van-body trailers. Previously tested TL-6 barriers were evaluated with 90-in.-tall barriers (Hirsch 1978; Hirsh and Fairbanks 1984; Mak et al. 1988; Whitfield 2018). An ongoing study performed at MwRSF is investigating the crashworthiness of a 62-in.- tall, single-slope median barrier evaluated to MASH 6-12 impact conditions (Vasquez 2020; Stolle et al. 2022). It is anticipated that the ZOI will be determined for that barrier shape. Further research is necessary to evaluate the ZOI of tractor-tank trailer combination vehicles in accor- dance with MASH TL-6 impact conditions, which may better support cost-effective evaluation of bridge pier protection systems. 7.7 In-Service Performance Evaluations (ISPEs) Currently, limited crash data are available to identify how significantly design for ZOI and how vehicle impacts with fixed objects in the ZOI may affect occupant safety. Images of the objects struck behind a barrier system would be helpful to determine the frequency and sever- ity of impacts with objects in the ZOI. Observations of vehicle contact with features located near rigid barriers should be denoted and referenced to the impact location longitudinally and laterally. If possible, those impacts should be correlated with as many of the following factors as possible: vehicle make, model, and production year; impact conditions (speed, angle, and vehicle orientation at the point of impact); barrier geometry; and injury/crash outcome. A useful addition to crash reporting documentation could include binary fields: was a rigid barrier struck? Was an object struck behind the rigid barrier during impact?
132 Zone of Intrusion Envelopes Under MASH Impact Conditions for Rigid Barrier Attachments These data may be difficult to acquire unless the reporting officials are prepared to investigate and determine if such contact occurred. Thus, additional training may be necessary to aid crash investigators to identify subsequent impacts and the features that were struck, along with the components on the vehicle that interacted with the shielded objects. ISPEs would be helpful for passenger vehicles but may be more challenging to acquire regu- larly. However, large-truck crashes, which are less common, may be easier to correlate the truck and trailer component contacts with shielded objects near rigid barriers. It is recommended that ISPE implementation starts with updated data collection for large trucks and utilizes experience gained to update crash documentation needs for passenger vehicles. There are significant difficulties associated with implementing updates to crash reporting forms and data collection as well as a benefit-to-cost for additional time, data storage, management, maintenance, accuracy checks, and training. Since many crash reports are completed by law enforcement officers, who are on a fixed timeline for training before entering the field, proper care should be taken not to burden data collection with unnecessary difficulties and time without a real benefit received. Nonetheless, if ISPE data can be collected, it will significantly aid the understanding of the frequency, severity, outcomes, and circumstances surrounding impacts with features located in the ZOI of rigid barrier systems.
