Road Design

The purpose of this report is to re-evaluate the working widths for concrete barriers currently used by Australian and New Zealand road agencies and document the background behind the recommended revised working widths for the Austroads Guide to Road Design Part 6: Roadside Design, Safety and Barriers (AGRD06). The current practices of the jurisdictions were identified and found to be generally consistent with the values in AGRD06.

The methodology involved a process of review, comparison and development of zones of intrusion (ZOI). Zones of intrusion, included in the US Roadside Design Guide, were based onNCHRP350 tests. In 2022, ZOI values were reevaluated to reflect MASH tests and reported in the NCHRP report 1018. These ZOI values were used as the basis of the values recommended in this report. As part of the research process, the ZOI values were adjusted for 4.6 m high vehicles and subsequently to establish potential working widths consistent with the definition in AGRD06.

Working widths were recommended for inclusion in the AGRD06, which are 1.96 m to 2.58 m for TL-4 and TL-5 containment levels for a 1100 mmm high barrier and 0.81 to 0.94 m for TL-4 and TL-5 containment levels for a 2300 mm high barrier. In addition, this report discusses the appropriate working widths for barriers in tunnels and the reduction of values for roads with lower design speeds.