The Department of Infrastructure, Energy and Resources (DIER) recognises that there is community concern regarding congestion on key urban roads in Greater Hobart and that appropriate measures need to be put in place to manage traffic growth and delays.
Traffic congestion occurs when the number of vehicles travelling on a road approaches or exceeds the number of vehicles the road was designed to carry. Congestion is a time and location specific event - for example, it occurs during the morning or at certain intersections - and may have complex underlying causes (e.g. capacity of the road, availability of alternative ways to travel, traffic signal co-ordination, etc). For further information on congestion, refer to Congestion in Greater Hobart http://www.dier.tas.gov.au/plans_and_strategy.
Traffic congestion is generally most pronounced in the morning and late afternoon - referred to as the AM and PM peak - which largely reflects work and school start and end times. While there are different ways to measure congestion, average travel time (the time it takes to travel a particular route) and speed provide two accurate and easily understandable indicators of congestion and the actual experience of road users.
Improving our understanding of how the road network performs is critical to the development of responses that improve reliability and accessibility for road users. In this context, DIER has undertaken a travel time and speed survey on key roads within Greater Hobart. The survey provides information on the actual performance of the network, and compliments existing key initiatives such as the Greater Hobart Household Travel Survey and recent development of the Greater Hobart Urban Travel Demand Model.
Greater Hobart travel time and speed survey, 2011
In July/August 2011, DIER undertook a survey of travel times and speeds during the AM, PM and off-peak periods on the following major roads in Greater Hobart:
- Brooker Highway (Brighton to Hobart city roundabout)
- Southern Outlet (Margate to Macquarie St intersection)
- South Arm Highway (Lauderdale to Davey St intersection)
- Tasman Highway (Sorell to Davey St intersection)
- East Derwent Highway (Bridgewater to Davey St intersection)
The survey examined entire routes from these outer suburbs of Hobart, as well as looking at the inner-most 10km sections closest to the Hobart CBD where the majority of traffic volumes are concentrated.
Five runs were undertaken on each of the above routes, in both directions, for the AM peak (8-9am), off-peak (9.30am-4.30pm) and PM peak (5-6pm) periods. A 'floating car' method was used, which attempts to keep the car in an average position within the general traffic flow.
What does the survey find?
Peak and off-peak travel time
- For most routes the AM peak inwards run had longer travel times - between three and seven minutes - when compared to other times of the day. The exception was the Southern Outlet which experienced a longer PM peak travel time.
- The Brooker and East Derwent Highways had the longest AM peak travel times for the inner 10km routes to the CBD (15 minutes and 16 minutes respectively).
- South Arm Highway experienced the longest AM peak travel time per kilometre for the entire length (at 75 sec/km).
- Delays were generally confined to specific sections of the network. Delays outside peak periods were minimal.
- Delays in the PM peak were shorter than the AM peak, with the exception of the Southern Outlet.
- The Tasman and East Derwent Highways experienced journeys around 6 minutes shorter in the off-peak than in the AM peak for the entire route and around 5 minutes shorter for the inner 10km. The inner 10km for these routes experienced less delay from off-peak travel times - at 2 minutes and 1 minute respectively.
- The Brooker Highway experienced only around a three minutes shorter journey in the off-peak compared to the AM peak for the entire route and the inner 10km. This indicates that the Brooker Highway is busy throughout the day.
- Overall the results showed that the delays at peak periods are not significant. For the 10km inner segments the longest delay from off-peak in the AM peak was around 5 minutes and the longest PM peak delay was around 2 minutes.
- Significant delays can occur as a result of specific events such as a crash or bad weather.
Comparison to 2006 Travel Time Survey Results
Note: 2006 and 2011 travel time surveys are 'point in time' snapshots that should not be used to infer trend. Comparisons provide an indication only and will need to be supported by future surveys to confirm changes in travel times.
- The 2011 survey showed a slight improvement in AM peak travel times compared to 2006 data.
- Comparisons were variable for other time periods.
The Travel Survey collects information on what (and where) delay is occurring and can indicate how the situation may have changed over time. However, the survey can not provide reasons for why the situation may have changed. There are many factors that can influence traffic flows, from increased traffic volumes and specific infrastructure and traffic control measures to behavioural changes such as peak-spreading (people choosing to travel earlier or later to avoid more congested conditions) and local and global economic challenges that can affect travel patterns.
Network changes that may have affected travel times (in particular the improvement in AM peak travel) include:
- Changes in signalisation at specific intersections to improve inbound AM flows (for Brooker Highway);
- Introduction of clearway and slip lane on Macquarie St (for Southern Outlet);
- Reconfiguration of Mornington roundabout (for South Arm);
- Signalised entry onto Tasman Highway from Penna Rd - Midway Point (for Tasman Highway).
Some improvements were still being undertaken at the time of the survey (including the Kingston Bypass and work at the Brighton Hub and Brighton Bypass). These recently completed and planned improvements should positively impact on travel time and reliability, and we will be able to gauge their effect by conducting future surveys. The impact of Variable Speed Messaging (VSM) - soon to be introduced on some routes - will also be a factor in future surveys.
Regular travel time and speed surveys are an effective way to understand the performance of the road network and individual routes, supporting better transport planning and traffic management. DIER is currently investigating options to undertake regular (annual) surveys of key routes to enable reliable comparisons between years and routes, over time.