Research by Ellen Oettinger White – Unclear territory: Clear zones, roadside trees, and collaboration in state highway agencies

May 3, 2023


The American Association of State Highway and Transportation Officials (AASHTO) issues guidance for highway agencies to maintain clear zones adjacent to the roadbed, free of trees, to reduce the severity of run-off-the-road crashes. Some departments of transportation (DOTs) are clearing trees beyond the standard clear zone for road safety, creating friction between units of different disciplines.

Following an analysis of roadside tree literature, I use semi-structured interviews with agency staff to illuminate how perceptions of trees—either as safety hazards or as beneficial environmental assets—are considered by practitioners at state highway agencies.

Results indicate that engineering leadership understands roadside tree management as a nuanced issue. The benefits of trees are understood by most staff though are rarely a sufficient counterweight for perceived safety issues. Maintenance staff are motivated more by budgets or contracts than by research or federal guidance. An interdisciplinary staff structure, robust communication practices, and stronger environmental policy can improve DOT collaboration.

Ellen Oettinger White, Unclear territory: Clear zones, roadside trees, and collaboration in state highway agencies, Transportation Research Part D: Transport and Environment, Volume 118,
2023, 103650, ISSN 1361-9209,

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