Hard shoulder running (HSR) has been increasingly used as a sustainable and viable way to increase road capacity. This study investigated the safety effect of HSR on freeways in South Korea using the empirical Bayes method. This study found an increase in the total number of crashes. In terms of crash severity, a higher proportion of crashes (25.3%) on 2(3)-lane sections were found to be serious (involving injuries and/or fatalities) compared to those on 4(5)-lane sections (3.6%). Also, a positive relationship was found between the length of the hard shoulder running and changes in crash frequencies. Thus, hard shoulder running on lengthy 2(3)-lane freeways should be avoided.

This paper provides research results of a study to assess the driver performance levels of a 2+1 road, a special type of road involving intermediate cross section that is applied where a four-lane roadway construction is unjustifiable and the use of a two-lane road design may not provide the desired level of mobility. Despite increased driver safety, the use of the 2+1 road involves a problem that the South Korean government cannot assess the mobility effects of 2+1 roads, because the current Korean Highway Capacity Manual lacks the level of service procedure for 2+1 roads. Hence, research is required to provide potential measures of effectiveness for describing traffic flows in 2+1 roads and establish a reliable level of service analysis procedure. To address this issue, we applied the following approach: (1) existing research concerning 2+1 road design and flow performance was reviewed; (2) a field study was conducted in 2+1 roads with video cameras and traffic detectors to investigate traffic flow conditions; (3) candidate measures of effectiveness for describing traffic flow in 2+1 roads were identified based on field study results as well as TWOPAS simulation efforts; and (4) an analysis procedure applicable to determine levels of traffic flow service for 2+1 roads was proposed. We also examined how our proposed procedure would perform based on a case study. It was found that the percent time spent following would represent the most appropriate measures of effectiveness and that realistic output may be produced with our proposed procedure.