Variable Speed Limit System - Tasman Highway
The Tasmanian Government has introduced a new way to improve traffic flow and safety on the Tasman Highway between Liverpool Street, Hobart and the Cambridge Road Interchange, including the Tasman Bridge.
Along this section of the highway existing static speed limit signs are being replaced with electronic variable speed limit signs operating 24 hours a day. Variable Speed Limit (VSL) signs are used in other parts of Australia and are similar to the signs in school speed zones around Tasmania.
The benefit of a VSL system is its ability to respond to changing road conditions such as traffic congestion, a crash or weather conditions such as rain, ice or wind. VSL systems have been shown to improve safety and traffic flow.
Progress Report - September 2013
The new Variable Speed Limit (VSL) system on the Tasman Highway including the Tasman Bridge is working well and initial results indicate that it has already helped reduce crashes. The VSL system went 'live' on 21 January this year and operates over a 9km stretch of the Tasman Highway between Liverpool St in Hobart and the Cambridge Road Interchange.
This section of road has one of the State's highest crash rates compared to other roads in Tasmania - particularly rear-end crashes. The new electronic speed limit signs, adjust speed limits to better match the prevailing conditions and alert drivers to potential hazards, such as a crash, traffic congestion or icy conditions.
During the past six months, the system has shown that the majority of drivers are obeying the lowered speed limits, especially during peak hour travel times. This is really positive and shows that motorists have really embraced this new technology.
No significant road crashes have occurred during the peak morning period since the VSL system went 'live'. In fact, initial data indicates that there has been a 57 per cent overall crash reduction over a 24 hour period from end of January to mid July 2013. Ongoing monitoring, evaluation and improvements to the system will continue over the next 6 months, and we will have definitive crash analysis in the next three years.
Since the 'go live' date, the system had been activated most mornings during peak hour travel times, to assist in managing traffic flow for inbound traffic. The road section at Tunnel Hill is notorious for icy conditions and the road ice detector was fully automated in May. The system has also been used to assist in traffic management for road works along this section of the Highway.
When the new system became operational in January, there was a grace period for enforcement. This was to give motorists time to become familiar with how the new signs work. As of Monday 30 September 2013, motorists are warned that they risk being booked if they exceed the posted speed limit.
The Variable Speed Limit system is a great example of how we're using cutting-edge technology to improve road safety for all motorists.
Frequently Asked Questions
What is a Variable Speed limit?
Most speed limits are fixed and apply at all times. A variable speed limit is one that can be altered to respond to changing traffic and road conditions, such as bad weather conditions including rain, ice or wind, a crash or traffic congestion.
Whatever the speed limit is set to, it is still a regulatory speed limit and must not be exceeded. Under the Australian Road Rules, electronic speed limit signs are treated the same as static speed signs.
The sign sets a maximum speed limit and invariably a lower safer speed will be required. Remember it's a driver's responsibility to drive to the traffic and road conditions.
What does a Variable Speed Limit look like?
Variable speed limits are set using high-visibility electronic signs that can display different speeds. They are similar to the signs you might have seen operating in school speed zones in Tasmania and on roads in other parts of Australia.
The speed limit is displayed with white numbers surrounded by five red circles. Most of the time, the speed limits shown on the electronic signs will reflect the existing speed limit for that section of the highway, and during this time the five red circle will be static. When the speed limit is reduced three of the five circles will continually flash until the limit returns to the normal limit.
What are the benefits of Variable Speed Limits?
Variable speed limits have been shown to improve safety and improve traffic flow. In heavy traffic conditions, lowering the speed limit can help smooth traffic flow, as vehicle speeds tend to even out, lane changing is reduced and drivers are less frustrated by irregular traffic flow.
Changing the speed limit to match the prevailing conditions alerts drivers to potential hazards. These may be hazards that are not readily visible, either because of the curve of the road, or weather conditions such as ice or gale-force winds, or a stationary traffic queue has formed further ahead.
Importantly, lowering the speed of traffic approaching a crash site reduces the likelihood of secondary crashes.
Where is the Variable Speed Limit going to apply?
The variable speed limit zone will apply to the Tasman Highway between Liverpool St Hobart and the Cambridge Road Interchange, including the Tasman Bridge.
There will be signs at the entry points to the variable speed limit zone advising drivers that they have entered the zone and alerting them to be aware that the speed limit might change.
Why are Variable Speed limits going to be used here?
This section of the Tasman Highway gets congested during peak times. This section of road also has a high crash rate compared to other roads in the State. This means that at peak times, even a minor crash has the potential to significantly impact a large volume of traffic.
How will different speed limits be chosen?
The system is designed with in-road detectors and sensors located on structures, which continually monitor traffic and road conditions. The system will automatically detect an incident such a crash, or when traffic is being congested, or the road is wet, icy or high winds on the bridge and will raise an alert to the system operator.
The system operator will use live CCTV to verify the alert and can respond by implementing a designated response plan to cover the section of highway where the incident has occurred.
What speed limits will be displayed?
The speed limits will reflect the normal limits and only be reduced to address an incident, such as crash, traffic congestion, adverse weather conditions or high-wind on the Tasman Bridge. The total road length of the system is divided into smaller sections so that only the section or sections affected by the incident will be reduced, whilst other sections may operate under the normal speed limit.
Electronic speed signs are linked to an individual section, meaning all the signs linked to an individual section are forced to display the same speed limit. There are 14 individual sections, which gives the system great flexibility and ensures lower speed limits are only operating where they are needed.
Drivers therefore need to be vigilant and take notice of the speed limit displayed on each of the electronic signs.
The speed limit will never be displayed a speed lower than 40 km/h, and never a speed higher than 110 km/h on the highway between Rosny and Cambridge Interchange. On the Tasman Bridge and the western approach to the bridge the speed limit will never be higher than 70 km/h.
What do I do if a Variable Speed Limit sign is on?
The speed limit displayed on an electronic sign in the variable speed limit zone is a regulatory speed limit, indicates the maximum limit and must not be exceeded, just like a normal static speed limit sign.
If you drive past an electronic sign that is displaying a speed limit that is different to the speed limit on the previous section of road, you must smoothly adjust your speed to comply with the new speed limit.
What do I do if a Variable Speed Limit sign is not displaying a number?
The system has back-ups in the event of a power or other type of system failure. This means that it is unlikely that you will pass any sign that is not displaying a number.
In case there is a problem with the electronic signs, there will be static signs at the entry points to the variable speed limit zone and at critical points within the zone, to tell you what the speed limit is. These signs show the speed limit number in a red circle and have the words "WHEN SIGN ABOVE IS BLANK". This means that these signs only apply if the electronic sign is not displaying a number.
Remember the Australian Road Rules: If you pass an electronic sign that is blank and it does not have a static sign underneath it, the speed limit displayed on a previous sign continues to apply.
What will the CCTV cameras be monitoring?
The variable speed limit cameras and the wet and icy traffic system camera will only view the road condition - the video footage is not stored or used for any other purpose. The CCTV cameras are not speed cameras and only there to allow system operators to monitor and verify traffic and road conditions.
What happens if I've just passed a sign displaying one speed limit and it changes to a lower speed limit? Can I get booked?
Enforcement of the speed limit will incorporate a 'time lag' to allow for those drivers who have recently passed the sign just before it changed to a different speed limit. The system has been designed to ensure that inconsistencies are not possible. The system logs all speed limit changes, with time and date and stored securely and are retrievable only by system operator will appropriate authorization.
This system is not about speed enforcement, but improve the safety of all road users and improving the reliability of the journey.
Why has system take so long to turn on?
The system has evolved through engagement with various stakeholders and consists of many different components which have been tested rigorously which takes considerable time and our aim is to implement a system that runs smoothly.
What periods will the system be monitored and what happens outside these periods?
The system is situated with our Traffic System Group, who will provide the resource to monitor and operate the system during the morning and afternoon peak periods on weekdays. Technicians will also be available to operate the system on weekdays between the peak periods if necessary, due to the system raising an alert.
After hours the system will not be monitored unless there is a planned event, such as road works that would benefit from a lower speed limit. This means the normal speed limit will operate. Our on-call staff technicians have remote access to the system.
At a later stage, will this system be able to operate without operator supervision?
All variable speed limit systems in Australia operate under supervision. However, the aim is for these systems to eventually have the ability to implement a response plan without operator supervision.
Is this a stand alone system or can it be expanded to cover other highways?
Yes, the design enables the current system to be expanded to cover other highways. However, there is no plan to roll this out further.
Will the system be evaluated and how?
Yes, our aim is to evaluate the system to determine the benefits and whether any changes are needed. Traffic and crash data has been collected before the system went live and these will be repeated at various times after the system is in operation. Study of the before and after data will reveal the safety benefits and impact to traffic flow conditions.
Research from other systems introduced has indicated the safety benefit ranges between 20 to 35% reduction in number of crashes.