Rain makes the traffic woe of Chinese cities worse. [Photo/IC]

Cities in South China suffered worse congestion in the second quarter this year as a result of heavy rain, a report shows.

The report ranks the congestion level of 60 Chinese cities based on a "delay index" calculated through analyzing data collected from devices installed on vehicles that can record their speed and location.

Beijing is the most congested city with a delay index of 2.16. It means commuters in Beijing spend 2.16 times as much time on rush-hour roads as on the same roads with normal traffic. And congestion costs a Beijing commuter 952.5 yuan ($143) a month on average.

The quarterly report was released on Wednesday by digital mapping and navigation service AutoNavi Software.

The report shows that only five out of the 60 monitored cities had congestion eased in the second quarter compared with the same period last year, indicating "a grim challenge posed by traffic jams".

Southern cities were 4.3 percent more congested on average compared to the same period last year due to widespread heavy rain over recent months, while traffic jams in northern cities were slightly improved compared with last year.

Drivers of Hangzhou, the capital of Zhejiang province, saw the slowest speed in peak hours at less than 21km/h. Beijing recorded an average rush-hour speed of 22.28km/h.

Tianjin, the neighboring port city of Beijing, was most resilient in the face of rain. The city was barely influenced by rainfall while the northeastern city of Shenyang saw the biggest rise in its delay index when rain hit.

Chart by Jin Dan