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 A tree-lined street is certainly more beautiful than the alternative. But few people think about how trees enhance our traffic safety…
Basically, trees slow us down and calm us down, with narrower streets, extended curbs, and roundabouts. Tall trees make a street feel narrower, which slows cars down. Closely spaced trees give the perception of speed (they go by very quickly) slowing drivers down. Conversely, a treeless street is perceived as wide and free of hazard, which increases speeds.
Trees can serve as a buffer between moving vehicles and pedestrians.
Street trees also forewarn drivers of upcoming curves. If the driver sees tree trunks curving ahead before seeing the road curve, they will slow down and be more cautious when approaching curves.
And streets without shade break down faster and become more hazardous. The asphalt paving on streets contains stone aggregate in an oil binder. Without tree shade, the oil heats up and volatizes, leaving the aggregate unprotected. Vehicles then loosen the aggregate and much like sandpaper, the loose aggregate grinds down the pavement. Streets should be overlaid or slurry sealed every 7-10 years over a 30-40 year period, after which reconstruction is required. A slurry seal costs approximately $0.27/sq. ft. or $50,000/linear mile. Because the oil does not dry out as fast on a shaded street as it does on a street with no shade trees, this street maintenance can be deferred. The slurry seal can be deferred from every 10 years to every 20-25 years for older streets with extensive tree canopy cover.
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