A CONFLICT STUDY AT A HIGHWAY JUNCTION

A traffic sign with a changing speed limit value was installed in 1985 at a heavily trafficked highway junction located within an 80 kmph speed limit. The sign shows 60 kmph on working days between 6.30-8.00 am and 3.45-4.45 pm. During the 60 kmph speed limit periods the mean vehicle speeds on the main road in the congested direction were always below 60 kmph, and about 6-15 kmph lower than during the corresponding periods in the before-studies. It has to be noted that also traffic volumes had increased by more than 10%. The speeds against the congested direction had not decreased as clearly. Owing to lower driving speeds the number and risk of conflicts, and in particular the severe ones, were also lower during the 60 kmph periods than during the corresponding before-periods. During the periods when the speed limit showed the original value of 80 kmph, vehicle speeds had increased. This resulted in an increase in the number and risk of conflicts. At this congested junction the changing speed limit did not seem to affect the junction's capacity for the left turning vehicles from the minor road. (TRRL)