1. Institute for Transport Studies
Lower speeds and Intelligent Speed
Adaptation: what do they deliver for
safety and CO2?
Oliver Carsten
Institute for Transport Studies
University of Leeds

2. The evidence base: two projects
ISA-UK (2000-2006) CfIT ISA (2007-2008)

3. 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

4. Our vehicles
• Voluntary system that
30 30
limited speed to the
prevailing limit (no
acceleration beyond
limit)
• Drivers could override at
will
• Vibration on throttle
pedal to prevent over-
throttling

5. Some of our fleet in the ISA-UK
project

6. Field trial timings
Trial 1
Trial 2
Trial 3
Trial 4
0 2004
12 2005
24 2006
36

7. 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

8. Speed profile by time on 30 mph
roads
20%
Mandatory
Mandatory
18% Voluntary
Voluntary
Baseline
16%
Baseline
14%
Proportion of journey
12%
10%
8%
6%
4%
2%
0%
0 10 20 30 40 50 60 70 80 90 100
Vehicle speed (mph)

9. Safety

10. 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

11. 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

12. Use of data from ISA field trials to
provide speed profiles
Phase 1 Phase 2 Phase 3
Without With Without
1 month 4 months 1 month
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

13. 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

14. 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%

15. Emissions

16. 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

17. Input into GAMs
Driving on 70 mph roads
Baseline Driving Driving with ISA Engaged Counts
76121
10
37706
18677
9252
5 4583
acceleration (km/h/s)
2270
1124
557
0 276
137
68
34
-5
17
8
4
-10 2
1
0 50 100 150 0 50 100 150
speed (km/h)

18. CO2 emissions from UK field trial
speed profiles
GAMs modelling Speed-emissions curves
Speed Change with Change with
Change with
Limit Voluntary ISA Mandatory Speed Limit
Mandatory
(mph) ISA (mph)
ISA
20 0.0% +0.1%
30 +2.8%
30 −0.4% −0.4%
40 +2.8%
40 −1.2% −1.2%
60 +0.4%
60 +0.3% +0.3%
70 −4.2%
70 −3.4 % −5.8%

19. 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

20. Critical mass effect?
Urban – All vehicles Urban – Cars Urban – HGVs
25 25 14
12
20 20
10
% Speeding
% Speeding
% Speeding
15 15 8
10 10 6
4
5 5
2
0 0 0
0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100
Rural – All vehicles Rural – Cars Rural – HGVs
4 5 80
70
4
3 60
% Speeding
% Speeding
% Speeding
3 50
2 40
2 30
1 20
1
10
0 0 0
0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100
Motorway – All vehicles Motorway – Cars Motorway – HGVs
10 12 6
8 10 5
% Speeding
% Speeding
% Speeding
8 4
6
6 3
4
4 2
2 2 1
0 0 0
0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100

21. The future(s)

22. Predicted ISA penetration under the Market
Driven scenario
100%
Proportion of ISA systems in veh fleet
90%
80%
70%
60%
Voluntary
50%
Advisory
40%
Non‐ISA
30%
20%
10%
0%
2010 2020 2030 2040 2050 2060 2070

23. Predicted ISA penetration under the
Authority Driven scenario
100%
Proportion of ISA systesm in veh fleet
90%
80%
70%
60% Mandatory
50% Voluntary
40% Advisory
30% Non‐ISA
20%
10%
0%
2010 2020 2030 2040 2050 2060 2070

24. Crash reduction over time for
Market Driven ISA
1
Fatal
0.9
Serious
Accident reduction rate
0.8
Slight
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2010 2020 2030 2040 2050 2060 2070

25. Crash reduction over time for
Authority Driven ISA
1
Fatal
0.9
Serious
Accident reduction rate
0.8
Slight
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2010 2020 2030 2040 2050 2060 2070

26. Predicted safety outcomes
Crashes Saved 2010 to 2070
Slight Crashes Serious Crashes Fatal Crashes
Market Driven 4% 8% 13%
Authority Driven 15% 25% 30%

27. Predicted environmental outcomes
Savings in emissions and fuel 2010 to 2070
CO2 Fuel
(tonnes x 106) (litres x 106)
Market Driven 4.139 6,460
Authority Driven 16.303 25.436

28. Source of ISA benefits over 60-year
period
ISA Benefits (£1m) % Due to
Implementation
Accident
Scenario Fuel CO2 Accidents TOTAL Savings
Market Driven £446 £196 £32,808 £33,450 98%
Authority Driven £1,740 £773 £85,122 £87,636 97%

29. Do the benefits outweigh the costs?
• Benefit to cost ratios (accidents + fuel + CO2):
– Market Driven scenario 3.4
– Authority Driven scenario 7.4

30. 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

31. Thank you for your attention!
o.m.j.carsten@its.leeds.ac.uk