EFFECTS OF STREET TREE SHADE ON ASPHALT CONCRETE PAVEMENT PERFORMANCE
E. Gregory McPherson and Jules Muchnick
Abstract: Forty-eight street segments were paired into 24 high- and low-shade pairs in Modesto, California, U.S. Field data were collected to calculate a Pavement Condition Index (PCI) and Tree Shade Index (TSI) for each segment. Statistical analyses found that greater PCI was associated with greater TSI, indicating that tree shade was partially responsible for reduced pavement fatigue cracking, rutting, shoving, and other distress. Using observed relations between PCI and TSI, an unshaded street segment required 6 slurry seals over 30 years, while an identical one planted with 12 crape myrtles (Lagerstroemia indica, 4.4 m [14 ft] crown diameter) required 5 slurry seals, and one with 6 Chinese hackberry (Celtis sinensis, 13.7 m [45 ft] crown diameter) required 2.5 slurry seals. Shade from the large hackberries was projected to save $7.13/m2 ($0.66/ft2) over the 30-year period compared to the unshaded street.
Keywords: Avoided repaving costs; pavement distress; tree benefits; urban heat island