DRYSDALE BYPASS – GRUBB RD INTERSECTION

The following extract is from DCSCA’s submission dated 13/12/16 to Vic Roads.

The complete submission will shortly be tagged for complete reference.

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Safety Assessment – Vic Roads Option 3a for the Drysdale Bypass.

Summary

Vic Roads preferred option for the Jetty Rd/Grubb Rd intersection is Option 3a – Signalized intersections with pedestrian crossings located at those intersections.

The DCSCA Committee does not support this option due to safety, traffic efficiency, and environmental and operational concerns and details these concerns.
DCSCA recommends a roundabout system with slip lanes and signalized pedestrian crossings located some distance from the roundabouts, with or without an overpass.
DCSCA believes such systems will be superior to Option 3a in all these respects and presents and recommends two alternative roundabout systems for Vic Roads to evaluate – one with an overpass and one without.
DCSCA has researched international Internet data on the factors affecting safety and the operation of traffic systems and has made the following conclusions: –
• Crashes are invariably caused by an error – e.g. a driver or pedestrian “doing the wrong thing”.
• Errors inevitably will occur and the potential for an error to result in a crash is dependent on the number of collision points (points at which traffic paths cross each other) and the density of traffic.
• The number of collision points is a meaningful measure of the relative safety of a traffic system, e.g. the more the collision points, the more dangerous the intersection.
• A prediction of the number of crashes over a given time period can be made by investigation of the number of collision points and the volume of traffic – i.e. analysis of historical crash data would show that an intersection of a given design with a given number of collision points would have X number
of injury crashes per million vehicles passing through the intersection. This information can be used to predict the number of crashes when considering alternative types of road infrastructure.
• Signalized intersections have significantly more vehicle-to-vehicle collision points than roundabouts and are approximately twice as dangerous with respect to the occurrences of injury crashes.
• Signalized pedestrian crossings at intersections have more vehicle to pedestrian collision points than crossings located at roundabouts and have more “pedestrian incidents” than non signalized crossings at roundabouts.
• Many signal violations occur at higher speeds so the severity of accidents is often high.
• Mobility challenged pedestrians prefer signalized crossings and perceive crossings at roundabouts as challenging.
• A signalized crossing located away from an intersection would have fewer pedestrian to vehicle collision points and would be safer.
• The best way to minimize “pedestrian/vehicle” incidents” and “cyclist/vehicle” incidents is to totally separate these different types of traffic, e.g. underpass. elevated walkway.
• When this cannot be accomplished, the next best way is to minimize the number of collision points between them.
• A traffic option often adopted is to provide a shared path for pedestrians and cyclists separate to the
traffic. Cyclists can then chose between cycling on the road or sharing the footpath with pedestrians.
It would be anticipated that faster cyclists would chose the road, and children on bikes the shared path.
• Slip roads and slip lanes are an effective way of reducing the number of vehicles passing through these collision points. These not only improve safety but also improve traffic flow.
• Roundabouts are more efficient as regards reducing travel times than signalized intersections. With a well-designed roundabout system, delay times are reduced by approx 30% at peak times and are reduced to a minimum at off peak times. With signalized intersections significant delays are experienced at all hours. For example, at a signalized intersection with a four-sequence traffic flow, three of the four traffic streams are facing a red light at all hours of the day and there is a significant “lost time” between phases when no traffic can flow.
• Roundabouts are more fuel-efficient than signalized intersections. The vehicles waiting at traffic lights are idling away using up fuel and this is a significant cost impost on the local community and Australia as a whole.
• Roundabouts have lower environmental impact than signalized intersections and generate significantly lower carbon emissions and noxious gasses. They also result in quieter neighborhoods.
• The new Ausroads recommendations are resulting in the, presumably unintended, outcome of Vic Roads designing roundabouts that are too large to be packaged in restricted urban environments.