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APPENDIX
G
In order to determine if changing speed limits has much effect on traffic speeds, speed studies were undertaken on a selection of arterial roads in the metropolitan area. Four sites for each category of road and speed limit were surveyed.
An LTI 20/20 laser speed gun, which allows very precise measurement of individual vehicle speeds, was used for the surveys. The gun operates by transmitting a very narrow beam of infra red light at the moving vehicle.
The survey targeted only cars and only free speed vehicles with at least four second headways were considered. This was difficult to achieve at certain locations due to relatively high traffic volumes and heavy platooning.
A sample size of 100 cars per direction was chosen to provide estimation of mean speeds within + 0.75 km/h accuracy assuming a 7.5 km/h standard deviation.
Speeds of traffic are generally highest between midnight and dawn and lowest during morning and evening peak hours. Therefore, surveys were conducted during off-peak hours and during week-days only.
The 'before' surveys were carried out about one month before the speed zones were changed and the 'after' surveys about two months after.
All the sites chosen were mid-block sections of roads within the metropolitan area. They were at least 200 metres away from the influence of traffic signals, pedestrian crossings, bus shelters, shops and kerbside parking.
At sites where the influence of traffic lights was unavoidable, vehicles were sampled only during the green signal phase. Accelerating and overtaking vehicles were excluded.
Care was taken to minimise the influence of people mistaking the survey vehicle for an unmarked police car, as the Victoria Police have been operating speed cameras since 1989 from vehicles parked on kerbs.
The local Police were informed about the surveys to ensure that speed samples were not collected during periods when police enforcement was taking place in the vicinity.
The results and main conclusions drawn from the study are outlined in the following section.
Road Dir 85th % ile % Mean speed Std Z-sta Are means
Speed Compliance (km/h) Deviation t equal at
(km/h) Before Before (km/h) 95%
Before After After Before confidence?
After After
Canterbury East 73 73 73 69 17 78 14 89 65.8 66.1 6.7 5.4 -0.41 Yes No
Rd Blackburn West 66.6 63.4 6.9 5.2 4.32
Heidelberg East 73 71 76 74 12 75 13 80 66.7 66.2 6.5 6.3 0.59 Yes No
Rd Fairfield West 68.6 66.4 7.7 7.3 2.08
Doncaster East 73 77 80 74 21 58 10 65 66.3 69.3 7.1 7.6 -2.82 No Yes
Rd West 69.6 67.7 8.6 6.5 1.66
Doncaster
East
South Rd East 72 74 74 72 28 70 20 82 65.2 67.7 7.1 6.0 -2.89 No Yes
Moorabbin West 66.2 65.9 6.7 5.4 0.49
The increased speed limit on divided urban arterials from 60 km/h to 70 km/h had a mixed impact on mean speeds. The mean speeds in the before and after samples were equal within 95 percent confidence interval in only four of the eight studies.
If the 85th percentile speed is used as an indication of compliance with the speed limit, the majority of motorists complied with the new 70 km/h limit. This suggests that most motorists consistently ignored the former 60 km/h limit at the survey locations on these divided arterial roads.
Road Dir 85th % ile % Mean speed Std Z-sta Are means
Speed Compliance (km/h) Deviation t equal at
(km/h) Before Before (km/h) 95%
Before After After Before confidence
After After ?
Bell St East 77 73 76 73 73 77 82 72 70.6 65.2 6.8 7.8 5.04 No No
Preston West 70.5 66.0 6.7 6.9 4.83
F'tree Gully East 79 78 81 80 73 52 58 44 71.7 70.4 6.6 7.6 1.21 Yes Yes
Rd Oakleigh West 74.3 72.2 7.1 8.2 1.81
East
North Rd East 81 80 78 78 62 45 74 47 73.5 72.1 7.5 7.2 1.37 Yes Yes
Oakleigh West 71.4 71.4 6.4 7.8 0.07
South
Manningham East 81 79 82 79 65 38 55 37 73.0 72.5 7.8 7.8 0.43 Yes No
Rd Lower West 75.6 72.3 7.4 7.0 3.28
Templestowe
The decreased speed limit on divided urban arterials from 75 km/h to 70 km/h did not impact mean speeds at five of the eight study locations. In six of the eight studies, the 85th percentile speeds ranged from 78 km/h to 80 km/h while the mean speeds were about 71 km/h. There were 5 km/h and 3 km/h reductions in mean and 85th percentile speeds respectively on one of the roads.
Generally, there was a slight reduction in compliance with the new 70 km/h limit compared with the former 75 km/h limit. This suggests that motorists have continued to drive at a speed that they feel is appropriate on these roads, regardless of the speed limit.
Road Dir 85th % ile % Mean speed Std Z-sta Are means
Speed Compliance (km/h) Deviation t equal at
(km/h) Before Before (km/h) 95%
Before After After Before confidence?
After After
Boronia Rd East 80 82 82 80 64 83 53 87 73.5 75.4 6.0 6.6 -2.49 No No
Wantirna West 75.4 73.8 6.9 6.3 2.00
Princes Hwy East 87 85 83 88 51 76 48 59 76.3 75.4 8.5 7.9 0.66 Yes No
Oakleigh West 75.3 78.7 7.0 9.8 -2.41
Springvale Nth 81 83 83 82 61 79 52 82 73.9 74.8 7.2 7.5 -0.82 Yes Yes
Rd Forest Sth 75.4 74.5 6.3 7.9 0.89
Hill
Stud Rd Nth 82 82 84 85 54 83 44 70 74.7 73..8 7.1 7.8 0.90 Yes Yes
Rowville Sth 76.7 77.7 6.6 6.7 -1.17
The increased speed limit on divided urban arterials from 75 km/h to 80 km/h did not impact mean speeds at five of the eight study locations. In the before and after surveys, the 85th percentile speeds generally ranged from 80 km/h to 85 km/h while the mean speeds were about 75 km/h.
Again, this suggests that motorists have continued to drive at a speed that they feel is appropriate on these roads.
Road Dir 85th % ile % Mean speed Std Z-sta Are means
Speed Compliance (km/h) Deviation t equal at
(km/h) Before Before (km/h) 95%
Before After After Before confidence
After After ?
Hallam Rd Nth 82 74 80 78 66 98 61 88 73.4 67.7 7.9 7.1 3.40 No Yes
Hallam Sth 73.8 71.1 6.6 7.8 1.62
Mickleham Rd Nth 80 89 79 93 65 40 60 41 72.9 81.8 7.1 7.2 -8.80 No No
Tullamarine Sth 74.1 83.1 6.9 7.2 -9.02
Wellington East 81 84 84 85 57 70 55 55 74.0 77.5 7.7 7.6 -3.25 No No
Rd Rowville West 75.0 78.7 7.5 6.3 -3.78
Reynolds Rd East 79 85 78 85 70 78 74 67 71.9 75.6 7.2 7.1 -2.49 No No
Warrandyte West 72.6 77.2 6.3 6.9 -3.34
West
The increased speed limit on undivided urban arterials from 75 km/h to 80 km/h led to increases in mean speeds at six of the eight study sites and a decrease at one site. Only one location out of eight had mean speeds which were equal within 95 percent confidence interval.
Road Dir 85th % ile % Mean speed Std Z-sta Are means
Speed Compliance (km/h) Deviation t equal at
(km/h) Before Before (km/h) 95%
Before After After Before confidence
After After ?
Nepean Hwy Nth 74 77 72 74 26 55 31 68 65.5 70.1 7.7 6.3 -4.72 No No
Chelsea Sth 64.3 68.1 6.7 6.1 -4.70
Smithfield East 73 77 69 76 36 52 36 64 64.4 70.3 7.6 5.7 -4.75 No No
Road West 63.2 68.3 6.3 7.6 -3.29
Kensington
Hammond Rd Nth 69 69 72 74 33 92 28 75 63.3 62.1 6.8 6.3 0.93 Yes Yes
Dandenong Sth Sth 64.4 64.9 7.7 8.1 -0.27
Kingston Rd East 75 76 72 77 10 68 34 68 68.5 67.9 6.3 6.7 0.45 Yes Yes
Heatherton West 64.8 67.5 7.9 8.0 -1.44
The increased speed limit on undivided urban arterials from 60 km/h to 70 km/h led to increases in mean speeds at four study locations and no significant change at the other four locations.
Road Dir 85th % ile % Mean speed Std Z-sta Are means
Speed Compliance (km/h) Deviation t equal at
(km/h) Before Before (km/h) 95%
Before After After Before confidence?
After After
Elgar Rd Nth 71 71 73 71 36 42 28 32 63.3 61.9 5.9 6.4 1.25 Yes Yes
Box Hill Sth 64.9 62.7 6.9 7.0 1.52
Centre Rd East 66 65 67 70 50 70 41 44 60.3 57.6 7.5 7.4 1.63 Yes Yes
Bentleigh West 61.3 62.8 5.0 7.7 -1.01
Grimshaw Rd East 68 71 67 68 44 38 51 29 61.5 62.6 5.3 7.1 -0.83 Yes No
Bundoora West 60.4 62.9 6.3 6.2 -2.12
Lower East 66 66 71 69 57 52 31 44 60.2 60.0 4.7 6.1 0.21 Yes Yes
Heidelberg West 63.6 62.6 6.4 6.3 0.86
Rd Ivanhoe
Eight undivided arterial road studies were undertaken at four sites as control sites where the speed limits did not change. Seven of the eight locations had mean speeds which were equal within 95 percent confidence interval for the before and after surveys for both directions.
These surveys determined that the sites had similar mean speeds after the majority of the speed zone changes had occurred in the metropolitan area. This implied that general speed patterns in the metropolitan area did not vary significantly between the two sets of surveys.
The revised speed limits led to mixed effects on spot speeds at the eight study locations. Generally, motorists appeared to drive at speeds which they perceive to be appropriate for a given set of road conditions and not the speed limit.
_________________________________________________________________________
Source: Royal Automobile Club of Victoria Ltd, Submission to the Inquiry into the Revision of Speed Limits in Victoria, September 1994.
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