Findings of greek driver's attitudes toward speed limits.

1. 1st INTERNATIONAL SYMPOSIUM ON
FREEWAY AND TOLLWAY OPERATIONS
TRB Freeway Operations Committee
Athens 2006
SPEED LIMITS: planning perspectives
and drivers’ attitudes in Greece
Petros Vythoulkas
Basil Psarianos
Pavlos Chorianopoulos
Faculty of Rural and Surveying Engineering
National Technical University of Athens
Eva Kasapi
Ministry of Environment, Regional Planning and Public Works

2. Setting speed limits: a complex trade-off
safety,
environmental mobility
and and
economic
energy costs
costs
speed
• Speed may affect the severity and risk of accidents.
• But unreasonably low speed limits increase drivers’ violation
of the speed limits

3. Objectives
• Investigate drivers’ speed choice behaviour and
their attitudes towards speed limits
• Review the current practices in setting speed
limits.
• Directions for future research

4. Drivers’ speed choice
Most drivers select a reasonably safe speed for the conditions
under which they travel
They select their self-optimum speed primarily on the basis of
Travel time minimisation
Accident risk minimisation
Minimisation of the Risk of being caught speeding
Fuel economy
The self-optimum speed is related to driver’s
Personal characteristics age, income, driving experience,
risk behaviour, environmental awareness
Journey characteristics

5. Driver speeds in the trunk road network in Greece
Surveys in the context of the research project
“Method for Setting Reliable Speed Limits in Greece”
funded by the Ministry of Environment, Regional Planning
and Planning Works.
Speed choices are analysed based :
a) on actual speed data collected through the use of radar
meters at 15 stations along the rural highway network of
Greece.
b) on a dataset collected through a questionnaire survey
that was conducted at 5 motorway toll plazas in Greece.

6. Motorway with local speed limit 90 km/h

7. Probability distribution of observed speeds in
motorwaydistribution ofwith local speed limitwith speed
probability section observed speeds in motorway 90 km/h
limit 90 km/h
histogram Cumulative Probability Distribution
25% 120%
21%
20%
100%
85%
80%
15%
12%
12% 60%
11% 11%
10%
8%
7% 7% 40%
5%
5% 3%
2% 20%
2%
0% 0% 1,5%
0% 0%
85 90 95 100 105 110 115 120 125 130 135 140 145 150
observed speed
Speed limit V85 = 127 km/h

8. Motorway with general speed limit 120 km/h

9. Probability distribution of observed speeds in motorway
Cumulative probability distribution of observed speeds in the left
with general speed limit 120 km/h
and right lane of motorway with speed limit 120 km/h
120%
100%
85%
80%
Left lane
60%
Right lane
both lanes
40%
31,7%
19,3%
20%
5,6%
0%
90 100 110 120 130 140 150 160 170 180 190 200
Speed limit 140 152 157 Speed (km/h)

10. Roadside surveys
• Self reported speed and relation to drivers’
characteristics
• Drivers’ attitudes towards speed limits

11. Self reported speeds in motorways with general
Histogram and cumulative probabality distribution of self reported speeds in
speed limit 120km/h
motorways with with speed limit 120 km/h
Histogram Cumulative probability distribution
35% 120%
cumulative probability distribution
30%
100%
29% 26%
25%
80%
20%
60%
15%
40%
10% 12%
8% 5% 20%
5% 6% 6% 3%
1% 1% 1% 1%
0% 0%
0% 0%
70 80 90 100 110 120 125 130 135 140 150 155 160 170 180 190 200 220
V85 = 140 ~150 km/h self reported speed (km/h)

12. Self reported speed and driver’s age
in motorways with general speed limit 120 km/h
= < 80istribution of self reported speed in-motorways with speed limit 120 km/h101 -age
D km/h 81 100 km/h by driver's
120 km/h
121 - 130 km/h 131 - 140 km/h > = 141 km/h
50%
46%
42%
41%
45%
37%
40%
34%
34%
32%
35%
31%
27%
30%
25%
25%
24%
24%
23%
25%
18%
17%
16%
20%
15%
14%
13%
14%
13%
11%
11%
15%
10%
9%
10%
5%
5%
0%
18 - 24 25 - 34 35 - 44 45 - 54 55 - 64 > 65 Sample
driver's age

13. Self reported speed and vehicle engine’s power
in motorwaysreported speed in motorways with speed limit120 km/h
Distribution of self with general speed limit (120 km/h)
by vehicle engine size
= < 80 km/h 81 - 100 km/h 101 - 120 km/h
121 - 130 km/h 131 - 140 km/h > = 141 km/h
70%
64%
60%
50%
50%
43%
40%
34%
29%
30%
25% 26%
20% 21%
20% 17%
10% 7% 8% 9% 7% 7% 8%
0%
<= 1100 1101 - 1400 1401 - 1800 1801 - 2300 > 2300 sample

14. Self reported speed and frequency of use
in motorways with general speed limit 120 km/h
Distribution of self reported speed in motorway and trip frequency
< 110 km/h 110 - 130 km/h > 130 km/h
80%
70% 67%
63%
60% 57%
53%
49% 46%
50% 42% 44%
43% 41% 44%
40% 36%
30%
30%
20%
20% 14% 16% 13%
7% 10%
10% 5% 3%
0%
almost 1 - 2 days/ once in a once a several 1 - 3 times Sample
every day week fortnight month times a a year
year

15. Relationship between self reported speed and personal
characteristics of drivers
Reference values: Linear regression coefficients
- Age > 65 Coef value t
(Constant) 109,94 13,19
- Engine =< 1100 cc
AGE 18 - 24 29,961 5,22
- Frequency 1- 3 /year
AGE 25 - 34 27,864 5,85
- Gender male AGE 35 - 44 19,266 4,04
- Not involved in accident AGE 45 - 54 21,596 4,56
AGE 55 - 64 20,229 4,10
- No speeding ticket
ENGINE > 2300 cc 24,926 3,61
- Do not consider safety
Frequency: Almost every day 6,593 1,82
as a reason for
GENDER -6,011 -1,93
conforming with speed
limit Involvement in an accident -5,214 -1,95
Speeding ticket in the last 5 years 6,529 2,75
Safety is a reason for conforming with
speed limit -11,127 -4,01

16. Exceeding the motorway speed limit:
Factors affecting driver choices
Binary logit coefficients
β Sig.
AGE 18 - 24 1,551 0,005
AGE 25 - 34 1,3 0
GENDER (0:male, 1:female) -0,826 0,033
ENGINE > 2300 cc 2,64 0,014
ENGINE 1801 – 2300 cc 0,946 0,014
ENGINE 1401 – 1800 cc 0,601 0,023
SPEEDING TICKET 0,967 0,001
SAFETY is a reason for
conforming with the speed limit -1,002 0

17. Reasons that car drivers conform with the
motorway general speed limit (120km/h)
Driver’s speed
Reasons for conforming with % of Drivers who
speed limit drivers Conform with Others F sig
speed limit
Safety 76,2% 128 142 23,4 0
Risk of getting a speeding
ticket 25,5% 130 136 4,929 0,02
Legislation 14,3% 131 131 0,005 0,94
Fuel cost 4,4% 127 131 0,573 0,45
Driver is not in a hurry 4,1% 121 132 3,059 0,81
Environmental 1,4% 122 131 0,695 0,40
Other reasons 1,4% 127 131 0,128 0,72
Drivers who stated that
they do not conform with
the 120km/h speed limit in
motorways 3,4% 160 130 20,26 0

18. Reasons that drivers exceed the motorway general
speed limit (120km/h)
Drivers who
Reasons for exceeding the % of exceed the Others F sig.
speed limit drivers speed limit
Being in a hurry 42,9% 131 131 0,01 0,91
The limit for safe driving is higher
than 120km/h in motorways 31,3% 138 128 13,1 0
Other reasons 24,5% 134 131 0,36 0,55
Adjusting to the speed of other
vehicles 5,1% 132 131 0,02 0,89
Enjoy speeding 4,8% 149 130 10,1 0,00
Being bored driving at low speed 4,8% 147 131 8,1 0,01
No specific reason 3,4% 133 131 0,11 0,74
Never/rarely exceed the speed
limit 24,5% 116 136 56,5 0

19. Drivers’ views on the 120km/h general speed limit on
motorways
Drivers' views on the level of speed limit in motorways (120km/h)
70% 65% 150
60%
mean speed (km/h)
138 140
% of drivers
50%
40% 130
31%
30% 120
112 120
20%
110
10% 5%
0% 100
It's very high and It's about right It's very low and
should be decreased should be increased

20. Should drivers exceed speed limits?
Speed limits should never be
Speed limits should never be exceeded
exceeded
45% 160
42%
40% 152
35% 150
35%
mean speed (km/h)
30%
%Drivers
139
140
25%
131
20%
126 130
15%
10% 10%
8% 120
5% 114 5%
0% 110
Strongly Agree Neither Disagree Strongly
Agree agree not Disagree
disagree

21. Should drivers exceed speed limits?
Current Speed limits are lower than the limit
for safe driving andkm/h or more 10 thus could be exceeded
Speed limits are lower than the speed limit for safe driving, and thus they could be exceeded by
by 10 km/h or even more
60% 151 160
50% 150
46%
137 138
mean speed (km/h)
140
40%
% of Drivers
36%
124 130
30%
120
20%
110
14% 100
10% 100
2% 2%
0% 90
Strongly Agree Neither agree Disagree Strongly
Agree not disagree Disagree

22. Should drivers exceed speed limits?
Speed limits are inaccurate
Drivers can judge forare inaccurate
Speed limits themselves whether
Drivers can judge whether they can drive slowly or fast .
they should drive slowly or fast
70% 160
60% 150 59%
150
mean speed (km/h)
50%
% of drivers
137 140
40% 134
130
30% 130
123
20% 18%
12% 120
10% 9%
2%
0% 110
Strongly Agree Neither agree Disagree Strongly
Agree not disagree Disagree

23. Main findings from surveys
Current speed limits are exceeded by the vast majority
of drivers.
Speed limit offenders are mostly Young drivers,
Frequent users and drivers of high engine power cars.
Safety is the main reason for conforming with speed
limits.
Being in a hurry is the main reason for exceeding speed
limits.
~40% of drivers consider current speed limits as lower
than the limit for safe driving, and believe that speed
limits could be exceeded by 10km/h or more.

24. Reasons for regulating drivers’ speed
Self optimum speed : Driver tries to minimise
travel time,
perceived risk of accident
perceived risk of being caught
fuel cost
drivers can impose significant risks
Social optimum
and uncompensated costs on others
Different drivers have different risk Cost of travel time
tolerances Accident costs
May have inadequate information
and/or misjudge roadway conditions, Environmental costs
and own and vehicle capabilities Energy costs
May misjudge the effect speed on
Enforcement cost
accident probability and severity

25. Different approaches in setting speed limits
(Fildes et al. for Austroads 2005)
Engineering
Road geometry, Traffic speeds, Accident data, Traffic
volumes, Roadside development.
Drivers’ Choice
Drivers select a reasonable and safe travel speed.
The posted speed limit is the 85th percentile driving speed.
Economic Optimisation
All costs (travel time, injury, death, environmental, energy)
associated with travel are expressed in monetary terms.
The posted speed limit is the speed that results in the lowest cost.
Harm Minimisation
Life and health cannot be measured in monetary terms.
Fatalities or serious casualties is not considered as an
inevitable cost of increased mobility.

26. Economic optimisation approach
(EU-MASTER, Cameron)
Explicit framework that takes account of :
• Road accident costs AccC
• Travel time costs TimC
• Vehicle operating costs OpC
• Traffic emissions costs EmisC
• Noise pollution costs NoisC

27. Road accident costs
AccC = Σi NiA * VAcci
where
NA the number of accidents of category i
Vacc the cost of an accident
Estimation of a fatal accident cost is a controversial issue
Different methods
Human Capital Approach
Willingness to Pay
can lead to significantly different costs of accidents

28. The number of Road accidents
(Nilsson (1984)
NA = (VA/VB)p * NB
NA = number of accidents After the speed change
NB = number of accidents Before the speed change
VA = mean or median speed After
VB = mean or median speed Before
p = 4 for fatal accidents
3 for serious injury accidents
2 for minor injury accidents
Poor estimates of NB can result in highly inaccurate estimates of
NA, particularly in the case of fatal accidents where p = 4
Speed variance is also considered as an important factor

29. Travel time costs
TimC = Traffic Volume * Travel Time * VoT
requires reliable estimates of the value of time
Vehicle operating costs
OpC = Traffic Volume * distance
* Fuel Consumption * fuel cost
- Reliable Fuel consumption functions are available for different
types of vehicles
- Fleet composition data should be available

30. Traffic emissions costs
Atmospheric emission pollutants which are normally regarded as
the ones of most concern include:
Euro III_< 1.4 l Euro III_1.4 - 2.0 l Euro III_> 2.0 l
• Hydrocarbons and other
organic compounds (VOC), Euro IV_< 1.4 l Euro IV_1.4 - 2.0 l Euro IV_> 2.0 l
benzene, 1,3-butadiene 0,8
NOx emissions rates
• Carbon monoxide CO 0,7
• Nitrogen Oxides NOx 0,6
• Particular Matter (PM) –
Ν Ο x e m i s s i o n s (g r / k m )
0,5
particles emitted from the
0,4
exhaust
0,3
• CO2: is a main contributor
to global warming. 0,2
0,1
Extensive database of vehicle
Emission functions is provided by 0,0
0
0
20
20
40
40
60
60
80 100 120 140 160 180
80 100 120 140 160 180
the UK Dept of Environment Speed (km/h)
speed (km/h))

31. Traffic emissions costs
EmisC = Σi Volume Pollutanti * CoPi
where
CoPi the cost of pollutant i.
Traffic emission impact depends on
• the size of the population living in the vicinity of the
road, and who are exposed to emissions, and
• the emission concentration which the population is
exposed to.
Pollutant concentrations at the road side receptors
should be estimated by taking into account the
dispersion and dilution of the pollutants.
Vehicle fleet composition
Cost of different pollutants has not been estimated in Greece

32. Noise pollution impact
Depends on the size of the population living in the vicinity
of the road, and who are exposed to noise.
Noise level depends on speed, traffic volume and form of
roadside development - Estimation of noise level is a
complex problem often requiring specialised SW
Cost and effectiveness of noise barriers should be
compared to cost of reduced mobility due to speed
reduction
Cost of noise pollution – hedonic pricing applied in urban
areas, WTP approaches
Noise pollution cost has not been estimated in Greece

33. Speed limits, speed distribution and
speed enforcement
Low/moderate
All relationships for estimating
enforcement
safety, environmental, energy and
mobility implications are based on
driver speeds - not speed limits.
Nonlinear relationships imply that
speed distributions rather than
mean speed values should be
used.
f( E[v] ) ≠ E[ f(v) ] Intense
Accident frequency is related to enforcement
speed variance.
Intensity of speed enforcement
affects speed distribution
But cost of intensive enforcement
can incur high costs Speed limit

34. Future research
Further research in
• Effect of level of enforcement on speed distribution
• Speed – accident relationships
• Reliable estimates of accident, pollution costs
Complexities and uncertainties related to the estimation of the
monetary values of the various benefits and disbenefits from
speed changes dictate that alternative options that could
improve accident rate should always be considered before
proceeding to speed limit changes.