Flat top road plateau is also known as a “flat-top road hump” or “raised table”. The height of a plateau ranges from 90mm to a maximum of 100 mm above the existing road surface. The difference in geometry between a “flat top road plateau”(FTRP) and a “Watts profile road hump”(WPRH) is that the former has a flat surface at the top, which usually has a traverse length of between 2 and 6 metres, while a WPRH has a 3.7m long curvy crown.
The difference in functionality is that, individually, a FTRP has a slightly longer distance of influence over vehicle speeds than a WPRH. However, road humps are seldom used in isolation but in successions over a street length. In addition, due to construction methodology WPRH’s are more economical and easier to install than FTRP’s.
The unique advantage of a flat top road hump over a curvy crown road hump is that it can be installed at an intersection to reinforce the Stop/”Give Way” control in the minor legs of an intersection, where motorists have been observed frequently disobeying the regulatory control.
Figure 1 shows a typical “flat top road hump” in mid-block, i.e. a chosen location in a street away from intersections. Figure 2 shows a typical Watts profile road hump.
They may slow vehicles to about 20 to 25 km/h at the device;
When used in series, they would reduce vehicle speeds along the entire length of the street;
It is relatively inexpensive, especially Watts Profile road hump, when comparing with either Blister Island or Slow Point treatments;
They may discourage through traffic; and
Large flat top road plateau may be used to reinforce the regulatory control of “Stop” or ”Give Way” on the minor legs of an intersection, such as Gloucester Street.
They may increase vehicle noise through braking, accelerating and vertical displacement;
They may adversely affect emergency and commercial vehicles;
They may only be used on relatively straight and flat streets;
They do not overcome 'gun barrel' effect on long straight roads; and
Reduction of on-street parking adjacent to the islands.
Well-spaced blister islands reduce speeds along a street.
They can provide refuge for cyclists and pedestrians crossing the street.
When landscaped they can reduce a 'gun barrel' effect on long straight roads and enhance the residential streetscape.
They can accommodate buses and commercial traffic.
Design flexibility allows for a variety of applications over a range of roads having different traffic volumes.
They may impact on property access and egress and reduce road verges due to road widening.
They are expensive to build, especially when relocation of power poles and underground utility services are required.
Their locations are dictated by the available spacing between successive cross-overs - a minimum of 15 metres.
They may increase vehicle noise through braking and accelerating;
They may adversely affect emergency vehicles;
Reduction of on street parking adjacent to the islands.
They may create a squeeze point for cyclists.
They reduce speed at and in the vicinity of device. Typically, single lane devices restrict speeds to about 25 km/h. Two lane devices restrict speed to about 40 km/h.
When used in a series, reduces speeds over the entire length of the street.
May discourage through traffic.
Imposes minimal inconvenience on local residents.
When used to narrow the carriageway provides a shorter crossing distance for pedestrians.
Relatively low cost for single lane slow points.
Possibility of increased noise.
Is contrary to driver expectations if used in isolation.
May restrict emergency vehicles.
Will restrict parking opportunities.
Can present a 'squeeze' point to cyclists if not designed and maintained correctly.
May result in confrontations between opposing drivers arriving simultaneously at a single lane slow point.
Kerbing and signage may be damaged by vehicles travelling at inappropriate speeds.
May not reduce motorcycle speeds.
Relatively high cost for two lane slow points if road widening is required.
They may impact on property access and egress
- Improve traffic safety by reducing traffic speeds.
- Reduce rat-running and limit traffic growth though the suburb.
- Maintain an even distribution of traffic on all roads.
What traffic calming designs are being looked at?
There are a number of traffic calming designs that are being considered for State Street.
Road Humps (Flat top road plateau or Watts profile road hump)
A “Blister island” is a raised, oval shaped island. The island width can vary but ideally should not be less than 3 metres in width to ensure proper deflection. The island length can also vary but should not be less than 10 metres. The island is usually installed in the centre of a road and in the mid-block of a residential street (i.e. a chosen location anywhere in a street away from intersections). The device requires road widening and a minimum spacing of about 15 metres between two successive cross-overs. The device is costly. Its main function is to regulate the speed of larger vehicles such as buses and trucks and can be less effective for passenger vehicles. Figure 3 shows a typical “Blister Island
Slow Point (either a “single lane slow point” or a “two-Lane slow point”)
A slow point is a device intended to reduce vehicle speeds by the creation of a short narrow section of carriageway that motorists must negotiate at low speed. Angled slow points can be either two lane, with or without an angled central median, or one lane. The effectiveness of an angled slow point is dependent on the degree to which the device is angled to the through roadway. Two lane devices generally only maintain deflection if they are constructed with a central median
What are the advantages and disadvantages of the above traffic treatment options?
Road humps (Flat top road plateau or Watts profile road hump)
Slow points (either a “single lane Slow Point” or a “two-Lane Slow Point”)
Will traffic treatments have impact on my property access and egress?
Blister Islands and two lane slow points require a large amount of space. They may have impact on property access and egress. Watts profile road humps require less room than Blister Islands and Slow Points. Road humps would therefore have little impact on property access and egress.
What happens after the community consultation?
After the conclusion of this community consultation, comments will be reviewed, collated and summarised. A report on findings will be presented to the Ordinary Council Meeting to be held in April/May 2018 for deliberation. All respondents to the community consultation will be informed of Council’s decision.
What are the goals of the traffic calming?
There are three main issues that the plan aims to address:
Can I comment on the proposal itself to determine whether it proceeds?
Yes, public comment is now open. Please complete the online survey. Survey closes 15 March 2017.