FAQs

• Traffic counts conducted on Vincent Street and Melvista Avenue showed that the 85th percentile speed approximately 10 km/h above the posted speed limit. 
• 17 crashes were reported between 2017 to 2021. 
• Due to the number and severity of crashes, the location qualifies for the National Black Spot Fund. 
• The proposed initiative would reduce motorists’ speed and severity of crashes.
• The City of Nedlands is committed to providing an active, safe, and inclusive community.

The flat-top speed plateau with a slope of 15(horizontal):1(vertical) was selected as a traffic calming device due to the following reasons: 

• Evidences suggests that speed plateau’s can reduce vehicle speeds to approximately 30km/hr. 
• Previous research has shown that speed humps or plateaus are more effective at controlling vehicle speed than horizontal deflection. 
• Typically, when horizontal deflections are installed, they are designed to still maintain access for larger vehicles such as buses and waste vehicles and lose the ability to slow down passenger vehicles. 
• horizontal deflection treatments require more space within the road reserve than a plateau or hump. 
• Spacing of horizontal deflections can be difficult when trying to fit treatments between existing site constraints such as residential crossovers, street trees, streetlights, and drainage pits. 
• As such speed plateaus allow more flexibility in their installation location to target areas of concern along a route.

Speed plateaus are most effective when they are placed at spacing of 80m to 120m apart. The following considerations were given in-relation to the placement of a speed plateau:

1. Spacing between two consecutive plateaus varies between 80 m to 120 m.
2. Location of the existing streetlight.
3. Location of the existing crossovers.
4. Maintaining a minimum 1.0m clearance to the wing of any existing crossover.

Speed plateaus can be bicycle friendly if speed plateaus are designed and constructed properly. The proposed plateaus are designed with 15(horizontal):1(vertical) slope. This slope is considered to be acceptable for cyclists.

The proposed plateaus will maintain 0.3m (300mm) clearance from the edge of Vincent Street allowing for stormwater flow. Therefore, it can be considered that the proposed plateaus would not have any detrimental impact on stormwater flow.

Speed Plateaus have the following advantages and disadvantages:

Advantages:

1. Slows vehicles to about 25 - 30 km/hr. at the device.
2. When used in series reduces vehicle speeds along the entire length of the street.

1. They can be designed to limit discomfort to cyclists, buses, commercial vehicles, etc.
2. They are relatively low cost to install and maintain.
3. They may be discouraged through traffic (rat-running).

 Disadvantages

1. The traffic noise level may increase just before and after the device due to braking, acceleration and the vertical displacement of vehicles and their goods.
2. They may divert traffic to nearby streets without LATM measures.
3. They are uncomfortable for vehicle passengers and cyclists.
4. They may adversely affect access for buses, commercial vehicles, and emergency vehicles.

Although the proposed speed plateau has some disadvantages, it is expected that treatment would reduce the speed on Vincent Street and at Vincent Street – Princess Road and Vincent Street – Melvista Avenue – Adelma Road Intersections. Reduced speed would reduce the likelihood and severity of crashes.    

The project will be funded 100% by the Federal Government via the National Black Spot Program.

The project is likely to commence and be completed in the 2023/24 financial year.