Trees and landscape in the roadside can have a positive effect on driver behavior and perception, resulting in better safety performance.
A study of Texas urban roads showed a 46% decrease in crash rates across the 10 urban arterial and highway sites after landscape improvements were installed. After the improvements, the number of collisions with trees declined by 71%. Another study found that placing trees and planters in urban arterial roadsides reduced mid-block crashes by 5% to 20%.
All types of roadside treatments—roadside landscaping, median landscaping, and sidewalk widening with tree planting—positively affected vehicle safety outcomes. A marked decrease in the number of pedestrian fatalities was also noted—from 18 to 2 after landscape improvements.
Drivers seeing natural roadside views show lower levels of stress and frustration compared to those viewing all-built settings.
Commuting can be one of the most pervasive stressful experiences of urban life. Stress indicators—such as increased blood pressure—are associated with longer or more difficult commutes. Other affects have also been associated with commuting—lowered job satisfaction, higher illness and absenteeism rates, and lower performance on various cognitive tasks. Incorporating vegetation in roadside landscaping is one way to ease driving stress.
Drivers viewing natural roadsides exhibit lower levels of stress and frustration compared to those viewing built settings. In one lab study, drivers were presented with a stress-causing stimulus and their reactions measured in the course of recovery. Study participants seeing more natural roadside scenes returned to normal baseline measures faster. An “immunization effect” was also detected—the initial exposure to a natural roadside setting decreased the magnitude of stress response to subsequent stressful tasks. Parkway design and roadside vegetation appear to have restorative effects in reducing frustration.
Support for this summary was provided by the national Urban and Community Forestry program of the USDA Forest Service, State and Private Forestry. Green Cities: Good Health summary prepared by Kathleen Wolf, Ph.D., June 29, 2010.
 Mok, J.-H., H.C. Landphair, and J.R. Naderi. 2006. Landscape Improvement Impacts on Roadside Safety in Texas. Landscape and Urban Planning 78:263-274
 Naderi, J.R. 2003. Landscape Design in the Clear Zone: Effect of Landscape Variables on Pedestrian Health and Driver Safety. Transportation Research Record 1851:119-130.
 Mok, J.-H., H.C. Landphair, and J.R. Naderi. 2003. Comparison of Safety Performance of Urban Streets Before and After Landscape Improvements. Proceedings of the 2nd Urban Street Symposium (Anaheim, California). Transportation Research Board, Washington DC.
 Wolf, K.L. 2003. Freeway Roadside Management: The Urban Forest Beyond the White Line. Journal of Arboriculture 29, 3:127-136.
 Ulrich, R.S., R.F. Simons, B.D. Losito, E. Fiorito, M.A. Miles, and M. Zelson. 1991. Stress Recovery During Exposure to Natural and Urban Environments. Journal of Environmental Psychology 1:201-230.
 Kaplan, S. 1995. The Restorative Benefits of Nature: Toward an Integrative Framework. Journal of Environmental Psychology 15:169-182