oliver carsten institute of transport studies leeds univ
TRANSCRIPT
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Institute for Transport Studies
Lower speeds and Intelligent Speed Adaptation: what do they deliver for safety and CO2
?
Oliver CarstenInstitute for Transport StudiesUniversity of Leeds
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ISA-UK (2000-2006) CfIT ISA (2007-2008)
The evidence base: two projects
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Terminology
•
Advisory ISA: Informs the driver of the speed limit and warns the driver when the limit is being exceeded (= enhanced SatNav)
•
Voluntary (or Overridable) ISA: The information on speed limit is linked to the vehicle’s engine management system and perhaps additionally to the braking system —
the system comes on with the vehicle
ignition, but it may be overridden by the driver at will
•
Mandatory ISA: Works like Voluntary ISA, but without the option to override
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Our vehicles
•
Voluntary system that limited speed to the prevailing limit (no acceleration beyond limit)
•
Drivers could override at will
•
Vibration on throttle pedal to prevent over-
throttling
30 30
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Some of our fleet in the ISA-UK project
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Field trial timings
0 12 24 36
Trial 4
Trial 3
Trial 2
Trial 1
2004 2005 2006
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The ISA field trials database
•
Driving by 79 drivers over 6 months–
1 month without ISA (baseline)
–
4 months with Voluntary ISA
–
1 month with ISA again off
•
Total mileage: 429,487
–
With speed limit information: 354,592
–
For ISA active phase:
218,790
–
All at 10Hz
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Speed profile by time on 30 mph roads
0%
2%
4%
6%
8%
10%
12%
14%
16%
18%
20%
0 10 20 30 40 50 60 70 80 90 100
Prop
ortio
n of
jour
ney
Vehicle speed (mph)
Mandatory
Voluntary
Baseline
Mandatory
Voluntary
Baseline
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Safety
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Accident prediction and cost-benefit analysis (latest version)
“Recipe”:•
Predict traffic growth (DfT advice)
•
Predict accident trends without ISA•
Predict additional safety impact of ISA (via observed change in speed patterns)–
Depends on ISA type and road type
•
Analyse costs and benefits over 60 years from 2010
•
Scenario-based approach
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Method for estimating accident reductions with ISA
•
Based on models from the literature of relationships between speed and crash risk (e.g. Kloeden et al., 2001, 2002)
•
These models have been calculated from real-world data
•
They are not drawn from the police reported contributory factors for accidents
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Use of data from ISA field trials to provide speed profiles
Baseline: data collected from Phase 1 (i.e. no ISA)
Voluntary ISA: data collected from Phase 2 (i.e. the ISA system was overridable)
“Mandatory” ISA: data collected from Phase 2 excluding when ISA was overridden
Phase 1 Phase 2 Phase 3
Without With Without 1 month 4 months 1 month
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Estimated impact of Advisory ISA on speed
•
Obtained from:Shift from Baseline (no ISA) to Voluntary ISA
x Adjustment factor from LAVIA trial in France, i.e.
LAVIA Advisory speed reduction
——————————————— LAVIA Voluntary speed reduction
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Predicted risk reduction by type of ISA
Reduction in Injury Accidents with ISA
ISA Variant Overall Reduction
Advisory ISA −2.7%
Voluntary (Overridable) ISA −12.0%
Mandatory (Non-Overridable) ISA −28.9%
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Emissions
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Emissions modelling using recorded speeds from ISA-UK trials
Done two ways:
1.With detailed second-by-second GAMs models
2.With more aggregated speed-emissions curves
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Input into GAMs
speed (km/h)
acce
lera
tion
(km
/h/s
)
-10
-5
0
5
10
0 50 100 150
Baseline Driving
0 50 100 150
Driving with ISA Engaged Counts
1248173468137276557
1124227045839252186773770676121
Driving on 70 mph roads
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GAMs modelling
Speed Limit (mph)
Change with Voluntary ISA
Change with Mandatory
ISA20 0.0% +0.1%
30 −0.4% −0.4%
40 −1.2% −1.2%
60 +0.3% +0.3%
70 −3.4 % −5.8%
Speed-emissions curves
Speed Limit (mph)
Change with Mandatory
ISA30 +2.8%
40 +2.8%
60 +0.4%
70 −4.2%
CO2
emissions from UK field trial speed profiles
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Network micro-simulation modelling
•
4 networks:
1.
Rural –
A614
2.
Urban –
Sheffield S10
3.
Urban –
Sheffield Sheaf Valley
4.
Motorway –
A1(M) near Gateshead
•
AIMSUN micro-simulation model modified to cater for Voluntary ISA
•
For emissions, used speed-emissions curves
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Critical mass effect?
Urban – All vehicles Urban – Cars Urban – HGVs
0
5
10
15
20
25
0 20 40 60 80 100
% Spe
eding
0
5
10
15
20
25
0 20 40 60 80 100
% Spe
eding
0
2
4
6
8
10
12
14
0 20 40 60 80 100
% Spe
eding
Rural – All vehicles Rural – Cars Rural – HGVs
0
1
2
3
4
0 20 40 60 80 100
% Spe
eding
0
1
2
3
4
5
0 20 40 60 80 100
% Spe
eding
0
10
20
30
40
50
60
70
80
0 20 40 60 80 100
% Spe
eding
Motorway – All vehicles Motorway – Cars Motorway – HGVs
0
2
4
6
8
10
0 20 40 60 80 100
% Spe
eding
0
2
4
6
8
10
12
0 20 40 60 80 100
% Spe
eding
0
1
2
3
4
5
6
0 20 40 60 80 100
% Spe
eding
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The future(s)
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Predicted ISA penetration under the Market Driven scenario
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
2010 2020 2030 2040 2050 2060 2070
Prop
ortion
of ISA system
s in veh
fleet
Voluntary
Advisory
Non‐ISA
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Predicted ISA penetration under the Authority Driven scenario
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
2010 2020 2030 2040 2050 2060 2070
Prop
ortion
of ISA systesm
in veh
flee
t
Mandatory
Voluntary
Advisory
Non‐ISA
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Crash reduction over time for Market Driven ISA
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
2010 2020 2030 2040 2050 2060 2070
Acciden
t redu
ction rate
Fatal
Serious
Slight
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Crash reduction over time for Authority Driven ISA
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
2010 2020 2030 2040 2050 2060 2070
Acciden
t redu
ction rate
Fatal
Serious
Slight
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Predicted safety outcomes
Slight Crashes Serious Crashes Fatal CrashesMarket Driven 4% 8% 13%Authority Driven 15% 25% 30%
Crashes Saved 2010 to 2070
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Predicted environmental outcomes
CO2 (tonnes x 106)
Fuel (litres x 106)
Market Driven 4.139 6,460Authority Driven 16.303 25.436
Savings in emissions and fuel 2010 to 2070
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Source of ISA benefits over 60-year period
Implementation Scenario
ISA Benefits (£1m) % Due to Accident SavingsFuel CO2 Accidents TOTAL
Market Driven £446 £196 £32,808 £33,450 98%
Authority Driven £1,740 £773 £85,122 £87,636 97%
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Do the benefits outweigh the costs?
•
Benefit to cost ratios (accidents + fuel + CO2
):
–
Market Driven scenario 3.4
–
Authority Driven scenario
7.4
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Conclusions
•
The safety benefits of ISA are very considerable
•
The harder the push for ISA and the “stronger”
the system, the greater the benefits
•
The environmental benefits of ISA are real–
There may be benefits on roads other than 70 mph roads
•
In cost-benefit terms the environmental impact is much less than the safety impact
•
Much of the potential of ISA, e.g. to replace traditional and costly traffic calming, was not counted
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