TABLE 1—

Wet Day Crash Rates Relative to Dry Day Crash Rates

	Fatal Crashes,IRR (95% CI)	Nonfatal-Injury Crashes, IRR (95% CI)	Property-Damage-Only Crashes, IRR (95% CI)
Dry days	1.00	1.00	1.00
Rain days relative to dry days	1.06 (1.06, 1.07)	1.19 (1.18, 1.19)	1.15 (1.14, 1.16)
Nonfirst snow days relative to dry days	0.84 (0.83, 0.85)	1.24 (1.22, 1.26)	1.78 (1.74, 1.82)
First snow days relative to nonfirst snow days	1.30 (1.21, 1.38)	1.13 (1.05, 1.21)	1.00 (0.90, 1.10)

Note. IRR = incidence rate ratio; CI = confidence interval.