1.   Second, the event was held on a day when the University, Art College and other institutions were closed, making traffic density much lighter than usual.

2.   The fee is based on traffic density, which is relayed to the transponders by electronic detectors in the pavement.

3.   The measure is intended to prevent head-on collisions and keep traffic density under control.

4.   According to the report, Guangzhou has the highest traffic density in China.