Distribution of lost time in traffic on national expressways in Japan 2019, by cause
In 2019, the leading cause for time lost on national expressways in Japan was when traffic slowed down below designated average speed but stayed above 40 kilometers per hour, which accounted for 46 percent of all person-hours lost of the 30 most-congested sections. When congestion forced traffic to slow even further down, the cause was still primarily traffic concentration.