Table 3. Incidence rate of violating traffic light signals by bus drivers (Changsha city, 2013).

Independent variables	Number of observations	Incidence rate		Adjusted IRR (95%CI)
		%	(95% CI)
Total	5612	2.2	(1.9, 2.7)
Week
Weekdays	2787	2.4	(1.9, 3.2)	1.00
Weekend	2825	2.0	(1.6, 2.6)	0.92	(0.64, 1.33)
Time period
Off-peak hours	2803	2.3	(1.8, 3.0)	1.00
Peak hours	2809	2.1	(1.7, 2.7)	0.92	(0.65, 1.30)
Weather
Sunny day	2186	2.7	(2.1, 3.4)	1.00
Cloudy day	2521	1.6	(1.2, 2.2)	0.60	(0.39, 0.93) *
Rainy/snowy day	715	3.1	(2.0, 4.6)	1.07	(0.62, 1.82)
Foggy/windy/dusty day	190	2.6	(1.1, 6.0)	1.21	(0.44, 3.29)
Installed camera
Without	1259	2.5	(1.7, 3.5)	1.00
With	4353	2.2	(1.8, 2.6)	0.81	(0.54, 1.22)
Presence of traffic police
Without	5440	2.2	(1.9, 2.6)	1.00
With	172	2.9	(1.3, 6.6)	1.35	(0.55, 3.33)

*: P < 0.05;

IRR: incidence rate ratio.