U.S Forest Service facts and figures and new traffic safety studies detail many urban street tree benefits. Once seen as highly problematic for many reasons, street trees are proving to be a great value to people living, working, shopping, sharing, walking and motoring in and through urban places.
For a planting cost of $250-600 (includes first 3 years of maintenance) a single street tree returns over $90,000 of direct benefits (not including aesthetic, social and natural) in the lifetime of the tree. Street trees (generally planted from 4 feet to 8 feet from curbs) provide many benefits to those streets they occupy. These trees provide so many benefits that they should always be considered as an urban area default street making feature.
With new attentions being paid to global warming causes and impacts more is becoming known about negative environmental impacts of treeless urban streets. We are well on the way to recognizing the need for urban street trees to be preferred urban design, rather than luxury items tolerated by traffic engineering and budget conscious city administrators.
The many identified problems of street trees are overcome with care by designers. Generally street trees are placed each 15- 30 feet. These trees are carefully positioned to allow adequate sight triangles at intersections and driveways, to not block street luminaries, not impact utility lines above or below ground. Street trees of various varieties are used in all climates, including high altitude, semi-arid and even arid urban places.
The science of street tree placement and maintenance is well known and observed in a growing number of communities (i.e. Chicago, Illinois; Sacramento, Davis, California; Eugene, Oregon; Seattle, Redmond, Olympia and Issaquah, Washington; Charlotte, N.C.; Keene, New Hampshire and Cambridge, Mass). Although care and maintenance of trees in urban places is a costly task, the value in returned benefits is so great that a sustainable community cannot be imagined without these important green features.
Properly placed and spaced urban street trees provide these benefits:
Increased motorized traffic and pedestrian safety (contrary to engineering myths). See below article for details on mode safety enhancements. See especially the compilation of safety benefits detailed in, Safe Streets, Livable Streets, by Eric Dumbaugh Journal of the American Planning Association, Vol. 71, No. 3, Summer 2005. One such indication of increased safety with urban street trees is quoted from this document:
“…Indeed, there is a growing body of evidence suggesting that the inclusion of trees and other streetscape features in the roadside environment may actually reduce crashes and injuries on urban roadways. Naderi (2003) examined the safety impacts of aesthetic streetscape enhancements placed along the roadside and medians of five arterial roadways in downtown Toronto. Using a quasiexperimental design, the author found that the inclusion of features such as trees and concrete planters along the roadside resulted in statistically significant reductions in the number of mid-block crashes along all five roadways, with the number of crashes decreasing from between 5 and 20% as a result of the streetscape improvements. While the cause for these reductions is not clear, the author suggests that the presence of a well defined roadside edge may be leading drivers to exercise greater caution.”