Evaluation of the use of safety barriers on roundabouts

Roundabouts are standard intersection treatments that can be found throughout the world. They have proven safety benefits over conventional intersections when it comes to crash severity. In certain circumstances it can also be noted that traffic flows can be more efficient with a roundabout arrangement. Over time the design standards of roundabouts have changed and improved. As these developments occur a number of existing roundabouts can remain that were design based on outdated knowledge. This development can leave a legacy of existing roundabouts with known deficiencies causing an unsafe environment for road users. This report has identified that this is a prevalent issue on NSW roads due to a lack of development in standards relating to roundabouts that now can be seen to have promoted geometric deficiencies in high speed roundabouts. As with the design standards, methods to treat design deficiencies and desirable safety outcome have also changed. It is common practice to conduct a cost benefit analysis to determine which treatment is most suitable for the intersection. In previous design development, safety barriers have been excessively used as the treatments are heavily based on benefit cost ratios which they perform well in. These analysis’s suit barriers as they are a cheap solution that reduces the severity of the crash and therefore reduces injury and cost to state. Movement has begun to introduce a safe systems approach to treatments where by treatments to remove the cause of the incidents be a primary focus. This no longer suites safety barriers, as they do not alter the occurrence of crashes only reduce the impact of crashes. Safety barriers are designed to operate in certain circumstances with ideal conditions of impact. Due to the circular nature of roundabouts it is difficult to predict the speed and angle of impact that will be made between a collision with a barrier and a vehicle. This report has found that safety barriers cannot be expected to operate in an ideal manor at roundabout locations. The overriding conclusion of this dissertation is that the treatment of now known geometric deficiencies will provide a reduction in off carriageway crashes that were previously overrepresented on NSW roads and the cause for safety barrier treatments to be installed in roundabout intersection environments. Safety barriers do still have a purpose in these environments as it is necessary to protect hazards that may not be feasible or possible to remove. Safety barriers should be installed after all possible works to reduce the inherent design deficiencies has been completed to reduce any residual risk