Reduction of travel speeds in the Melbourne CBD after installation of repeater speed signs: Results of a quasi-experimental before-after study with comparison sites

Transport Accident Commission (TAC) research indicates many drivers claim to often be
unaware of the speed limit. Drivers may be genuinely unsure of the speed limit if there is
inadequate signage, that is, if there are not enough repeater speed signs (RSS).
Previous research found RSS to be ineffective in changing vehicle speeds in areas with
speed limits over 80 km/h, however, there is no published research regarding the
effectiveness of RSS alone in reducing speed in areas of lower speed limits (e.g. 50
km/h). In this study, RSS were installed on two routes in the Melbourne CBD, and a
Before-and-After study with comparisons was conducted. Vehicle speeds were
measured for two 14 day periods; the first prior to installation of RSS, and the second
after installation. Changes in average vehicle speed on the treatment routes after
installation of RSS were compared to changes in vehicle speeds on the comparison
routes over the same time-frame. Considering the effectiveness of RSS might vary
according to the day of the week and time of day, the recording periods were
categorised into six time periods. There was a strong net reduction in mean speed after
installation of RSS during all six time periods, the minimum being a net 1.59 km/h
reduction during the day on weekdays, to the maximum of a net 3.63 km/h reduction on
weekend nights. The proportion of speeding vehicles was also significantly reduced.
These results indicate that installation of RSS can effectively reduce travel speeds in 50
km/h speed zones.