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Beyond Level of Service –
Towards a Relative
Measurement of Congestion
in Planning Transport
Lauren Walker and Tony Franso...
What is level of service?
A way of translating quantitative traffic performance measures
into a quality of service.
Aims t...
What is level of service?
Level of service is a useful performance measure:
• Widely accepted
• Simply distils complicated...
Drivers perceive and value aspects of congestion in
different ways
Problems with level of service
Weinstein (2006)
Congest...
Drivers perceive and value aspects of congestion in
different ways
Problems with level of service
Papadimitriou et al (201...
Takes a simplistic view of congestion as a universal sign of
network failure
Problems with level of service
Source: Strong...
Doesn’t allow for ‘prioritisation’ of congestion
• Primary freeway function is to carry large volumes of traffic at high
s...
Problems with level of service in
traffic forecasting
Strategic models do not handle delay at intersections well
Link-base...
Problems with level of service in
traffic forecasting
Difficulties in specifying ‘capacity’ in strategic models
Minderhoud...
Problems with level of service in
traffic forecasting
Speed-flow curves tend to overestimate traffic volumes
under congest...
Problems with level of service in
traffic forecasting
Tolerance to congestion will likely grow into the future
Cameron (19...
Methodology
Two-fold approach:
1. Identify a VC ratio at which poor level of service is almost certainly due
to excess dem...
ResultsIdentify a VC ratio at which poor level of service is almost certainly due to excess demand
rather than misspecific...
Results
Develop simple indices to weight the importance of VC ratio in the
evaluation of link performance
Methodology
Index Justif...
Results
Less Important
More Important
Results
Better amenity
Worse amenity
Results
Less Dense
More Dense
Results
Fewer modes/
travel speeds
More modes/
speeds
Develop simple indices to weight the importance of VC ratio in the
evaluation of link performance
Methodology
Density of
h...
Results
• The measure allows transport planners to more easily isolate
the relative importance of poor traffic level of service in...
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Beyond Level of Service – Towards a relative measurement of congestion in planning transport

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Lauren Walker & Tony Fransos

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Beyond Level of Service – Towards a relative measurement of congestion in planning transport

  1. 1. Beyond Level of Service – Towards a Relative Measurement of Congestion in Planning Transport Lauren Walker and Tony Fransos Veitch Lister Consulting
  2. 2. What is level of service? A way of translating quantitative traffic performance measures into a quality of service. Aims to provide qualitative descriptions of: • Traffic flow stability • Ability of drivers to select desired speeds and to easily manoeuvre • Incidence of queuing Adopted by the Highway Capacity Manual and by Austroads
  3. 3. What is level of service? Level of service is a useful performance measure: • Widely accepted • Simply distils complicated engineering analysis with a highly recognisable measurement scale (A, B, C etc.) • Uses quantitative performance measures (such as volume-capacity ratios) that are readily available from strategic models as inputs
  4. 4. Drivers perceive and value aspects of congestion in different ways Problems with level of service Weinstein (2006) Congestion is subjective, not objective. Perceptions vary from person to person, cultural context to cultural context. Arizona DOTTS 4273 Virginia DOT
  5. 5. Drivers perceive and value aspects of congestion in different ways Problems with level of service Papadimitriou et al (2010) Field survey indicated a significant variation in tolerance to various VC ratios from driver to driver Hostovsky et al (2004) Focus group found that different types of road users valued different aspects of service quality: •Urban commuters value travel time reliability •Rural commuters value manoeuvrability and presence of HCVs •Commercial vehicle drivers value consistent trip times and ability to maintain constant speeds
  6. 6. Takes a simplistic view of congestion as a universal sign of network failure Problems with level of service Source: Strongtowns.orgSource: The Age High Street, Northcote King Street, Newtown Source: SMH Taylor (2002) ‘Long queues at restaurants…are seen as signs of success’ ‘Traffic congestion is an inevitable by-product of vibrant, successful cities.’
  7. 7. Doesn’t allow for ‘prioritisation’ of congestion • Primary freeway function is to carry large volumes of traffic at high speeds for longer distances – minimal interaction with surrounding land uses • Established inner city areas support other important functions (retail, commercial activity, active/public transport users) as well as conveying traffic Problems with level of service
  8. 8. Problems with level of service in traffic forecasting Strategic models do not handle delay at intersections well Link-based VC ratios only account for a small component of variation in travel speeds Skabardonis (2008) Found that VC ratios account for ~30% of variations in travel speeds on arterial roads – single timing offsets were almost equally as impactful
  9. 9. Problems with level of service in traffic forecasting Difficulties in specifying ‘capacity’ in strategic models Minderhoud et al (1997) Three types of road capacity : •Design capacity: the maximum volume ‘that may pass a cross section of a road with a certain probability under predefined road and weather conditions’ •Strategic capacity: ‘the maximum traffic volumes a road section can handle’ •Operational capacity: ‘the actual maximum flow rate’
  10. 10. Problems with level of service in traffic forecasting Speed-flow curves tend to overestimate traffic volumes under congested conditions
  11. 11. Problems with level of service in traffic forecasting Tolerance to congestion will likely grow into the future Cameron (1996) Level of service measures have not kept pace with changing travel patterns since their initial development in the 1960s. As the public now expects higher levels of congestion, this higher tolerance should be reflected in level of service measures. Clark (2008) Drivers in larger cities, such as in inner-Sydney, have a much higher tolerance to traffic delays than drivers in regional environments. Also, a maximum category of level of service is probably not ‘as bad as it gets’ – a new level of service measures ‘beyond F’ should be considered.
  12. 12. Methodology Two-fold approach: 1. Identify a VC ratio at which poor level of service is almost certainly due to excess demand rather than misspecification of capacity 2. Develop simple indices to weight the importance of VC ratio in the evaluation of link performance
  13. 13. ResultsIdentify a VC ratio at which poor level of service is almost certainly due to excess demand rather than misspecification of capacity
  14. 14. Results
  15. 15. Develop simple indices to weight the importance of VC ratio in the evaluation of link performance Methodology Index Justification Calculation Strategic importance Simple measure of the importance of a link in a city's network Count of appearances of a link in the free flow minimum time paths Density of human activity Indication of the number of residents/workers potentially impacted by traffic on each link Association each link with the average of the population and employment per length of road within an area (SA2) Amenity Traffic noise generated is a pragmatic proxy for amenity: - higher volumes of traffic reduce ambient quality - higher speeds increase safety issues - higher numbers of heavy vehicles produce more noise and emissions - links without crossings and large lanes numbers decrease the permeability of the surrounding area Based on approach from Tripathi, Mittal and Ruwali (2012), which is proportional to traffic volume, speed and %HCVs Modal compatibility The diversity of speeds and modes that use a link Shannon's diversity index for speed and volume separately, combined with Shannon’s diversity index range of modes
  16. 16. Results Less Important More Important
  17. 17. Results Better amenity Worse amenity
  18. 18. Results Less Dense More Dense
  19. 19. Results Fewer modes/ travel speeds More modes/ speeds
  20. 20. Develop simple indices to weight the importance of VC ratio in the evaluation of link performance Methodology Density of human activity index
  21. 21. Results
  22. 22. • The measure allows transport planners to more easily isolate the relative importance of poor traffic level of service in the context of an entire network, based on key-weighting factors. Conclusions

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