Abstract
This study examined changes in vehicle running speeds before and after the speed limit was raised above 100 km/h on the Tohoku Expressway during 2016–2020. During the period, the speed limit was increased by 20 km/h, but increases in mean speeds were approximately 25% of the speed limit increase. Some drivers increased their speed in response to the raised speed limit, but others did not. ‘Spillover effects’ were observed: vehicle speeds sometimes increased in areas where the speed limit had not changed. Findings indicate the necessity of continual enforcement activities and countermeasures against excessive speeding.
