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Travel Time Survey
Twice a year Transit conducts Travel Time Surveys in Auckland, Wellington, Tauranga and once a year in Christchurch, to monitor congestion and improve the efficiency and operation of state highways.
For the surveys, Global Positioning System (GPS) instrumented vehicles are driven over specific sections of state highways and local roads during three peak travel time periods each day, on five consecutive week-days.
Auckland Free Flow Traffic at night
Although congestion is an experience that many people encounter on a daily basis, the scale and effects of congestion across a network are impossible to quantify through casual observation.
The combination of Global Positioning System and Geographical Information System technology enables Transit to create a quantifiable measure of the time that is lost as a result of congestion. This helps Transit and road controlling authorities to gain an appreciation of where congestion occurs, trends in the performance of the state highway network, as well as being able to report on specific route travel times.
Other measures Transit is using to monitor and manage congestion include the introduction of ramp signals at on-ramps in Auckland over the next two years, to improve traffic flows and make journey times more reliable.
Transit also manages and monitors traffic across all Auckland state highways and local roads in collaboration with local councils at its ATTOMS Traffic Management Centre. Regular updates to radio stations and variable messaging signs are some of the ways Transit keeps drivers informed to improve travel time reliability.
Measures like this, combined with Travel Time Surveys, enable Transit to better target congestion management.
Background
Transit's use of GPS technology to conduct its Travel Time Surveys provides a measure of the variability of journey times experienced by road users. Variability of travel times can be a source of frustration for road users, and can have a significant economic effect due to the uncertainty of trip duration, for instance, on freight movements and deliveries.
Auckland Free Flow Traffic The network covered in each city for the Travel Time Survey is:
- Auckland 270km of monitored network
- Wellington 160km of monitored network
- Christchurch 170km of monitored network
- Tauranga 130km of monitored network - (including Saturday).
- The road network and speed limits covered by the survey area in each city is different. The data therefore reflects different road types and conditions so results between cities are not suitable for comparison.
- Average speeds are derived using GPS Data
- The Congestion Indicator is a comparison between the average measured speed, and the speed limit.
- Travel Surveys provide a 'snapshot' of road congestion that can be compared between years in each city.
A noticeable seasonal pattern emerging from the surveys is that November statistics appear more favourable than those of March, particularly in the morning peak period. This trend is so significant, that a direct comparison between March and November survey results is not relevant. The reason for this difference is still being investigated. Travel time survey comparisons are drawn on an assessment of the annual results, comparing, for example, March 2006 with March 2005.
Understanding Change over Time / Change in Speed Maps
A noticeable seasonal pattern emerging from the surveys is that November statistics appear more favourable than those of March, particularly in the morning peak period. This trend is so significant, that a direct comparison between March and November survey results is not relevant. The reason for this difference is still being investigated. Travel time survey comparisons are drawn on an assessment of the annual results, comparing, for example, March 2007 with March 2006.
However, these averaged figures can disguise improvements or deterioration in travel speeds or delays on specific parts of the survey network.
To demonstrate this, Transit has prepared maps showing the change in average speeds for traffic heading into the city in the morning peak period.
To produce the maps, the average travel time speeds derived from the earliest two comparable March travel time survey results are combined and averaged together. These are compared with the average of the two most recent March travel time surveys. The differences in speed are then mapped across the surveyed network. This technique provides an easy identification of areas where congestion has changed significantly over time.
Different colours are used to demonstrate changes in travel speed i.e.: dark green equals increase of 10km/h or more, dark red equals decrease of 10km/h or more.
The maps can be downloaded from the links below.
Travel Time Survey Results
| Title | Download |
|---|---|
| Auckland Survey Results - March 2007 | PDF (52KB) |
| Auckland Congestion Monitoring Map - March 2007 | PDF (372KB) |
| Tauranga Survey Results - March 2007 | PDF (48KB) |
| Tauranga Congestion Monitoring Map - March 2007 | PDF (160KB) |
| Christchurch Survey Results - March 2006 | PDF (36KB) | Christchurch Congestion Monitoring Map - March 2007 | PDF (196KB) |