Driver's Attitudes toward Speed Limits
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Transcript of Driver's Attitudes toward Speed Limits
SPEED LIMITS: planning perspectives SPEED LIMITS: planning perspectives and driversand drivers’’ attitudes in Greeceattitudes in Greece
Petros VythoulkasBasil Psarianos Pavlos Chorianopoulos
Faculty of Rural and Surveying EngineeringNational Technical University of Athens
Eva KasapiMinistry of Environment, Regional Planning and Public Works
11stst INTERNATIONAL SYMPOSIUM ONINTERNATIONAL SYMPOSIUM ONFREEWAY AND TOLLWAY OPERATIONSFREEWAY AND TOLLWAY OPERATIONS
TRB Freeway Operations Committee TRB Freeway Operations Committee Athens 2006Athens 2006
safety, environmental
andenergycosts
mobilityand
economiccosts
• Speed may affect the severity and risk of accidents. • But unreasonably low speed limits increase drivers’ violation
of the speed limits
Setting speed limits: a complex tradeSetting speed limits: a complex trade--offoff
speed
• Investigate drivers’ speed choice behaviour and their attitudes towards speed limits
• Review the current practices in setting speedlimits.
• Directions for future research
OObjectivesbjectives
DriversDrivers’’ speed choicespeed choice
Most drivers select a reasonably safe speed for the conditions under which they travel
They select their selfself--optimum speedoptimum speed primarily on the basis ofTravel time minimisationAccident risk minimisationMinimisation 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 awarenessJourney characteristics
Speed choices are analysed based :
a) on actual speed data collected through the use of radarmeters at 15 stations along the rural highway network ofGreece.
b) on a dataset collected through a questionnaire surveythat was conducted at 5 motorway toll plazas in Greece.
Driver speeds in the trunk road network in GreeceDriver 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.
Motorway with local speed limit 90 km/hMotorway with local speed limit 90 km/h
probability distribution of observed speeds in motorway with speed limit 90 km/h
0%2%
8%
11%
7%
12% 12% 11%
7%5%
3% 2%0%
21%
0%
5%
10%
15%
20%
25%
85 90 95 100 105 110 115 120 125 130 135 140 145 150
observed speed
0%
20%
40%
60%
80%
100%
120%
histogram Cumulative Probability Distribution
V85 = 127 km/hSpeed limit
Probability distribution of observed speeds in Probability distribution of observed speeds in motorway section with local speed limit 90 km/hmotorway section with local speed limit 90 km/h
85%
1,5%
Motorway with general speed limit 120 km/hMotorway with general speed limit 120 km/h
Cumulative probability distribution of observed speeds in the left and right lane of motorway with speed limit 120 km/h
0%
20%
40%
60%
80%
100%
120%
90 100 110 120 130 140 150 160 170 180 190 200
Left laneRight laneboth lanes
140 152 157
5,6%
19,3%
31,7%
85%
Speed limit
Probability distribution of observed speeds in motorway Probability distribution of observed speeds in motorway with general speed limit 120 km/hwith general speed limit 120 km/h
Speed (km/h)
Roadside surveysRoadside surveys
• Self reported speed and relation to drivers’characteristics
• Drivers’ attitudes towards speed limits
Histogram and cumulative probabality distribution of self reported speeds in motorways with with speed limit 120 km/h
0% 1% 0%
5%
1% 1%
26%
3%1%
6%8%
29%
6%
12%
0%
5%
10%
15%
20%
25%
30%
35%
70 80 90 100 110 120 125 130 135 140 150 155 160 170 180 190 200 220
self reported speed (km/h)
0%
20%
40%
60%
80%
100%
120%
cum
ulat
ive
prob
abili
ty d
istri
butio
n
Histogram Cumulative probability distribution
V85 = 140 ~150 km/h
Self reported speeds in motorways with general Self reported speeds in motorways with general speed limit 120km/hspeed limit 120km/h
Distribution of self reported speed in motorways with speed limit 120 km/h by driver's age
18%
24%
42%
37%
34%
34%
14%
14%
15%
10% 11%
9%
23%
32%
25%
31%
25% 27
%
41%
46%
13%
5%
17%
11%
16%
24%
13%
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
18 - 24 25 - 34 35 - 44 45 - 54 55 - 64 > 65 Sampledriver's age
= < 80 km/h 81 - 100 km/h 101 - 120 km/h121 - 130 km/h 131 - 140 km/h > = 141 km/h
Self reported speed and driverSelf reported speed and driver’’s age s age in motorways with general speed limit 120 km/hin motorways with general speed limit 120 km/h
Distribution of self reported speed in motorways with speed limit (120 km/h) by vehicle engine size
7%9%
7% 8%
50%
43%
29%26%
7%
34%
64%
25%
8%
17%20% 21%
0%
10%
20%
30%
40%
50%
60%
70%
<= 1100 1101 - 1400 1401 - 1800 1801 - 2300 > 2300 sample
= < 80 km/h 81 - 100 km/h 101 - 120 km/h121 - 130 km/h 131 - 140 km/h > = 141 km/h
Self reported speed and vehicle engineSelf reported speed and vehicle engine’’s power s power in motorways with general speed limit 120 km/hin motorways with general speed limit 120 km/h
Distribution of self reported speed in motorway and trip frequency
5%14%
3%
16%7%
20%
10%
42% 43% 41%49%
63%67%
46%53%
44%
57%
36%30%
13%
44%
0%
10%
20%
30%
40%
50%
60%
70%
80%
almostevery day
1 - 2 days/week
once in afortnight
once amonth
severaltimes a
year
1 - 3 timesa year
Sample
< 110 km/h 110 - 130 km/h > 130 km/h
Self reported speed and frequency of useSelf reported speed and frequency of usein motorways with general speed limit 120 km/hin motorways with general speed limit 120 km/h
Linear regression coefficientsCoef value t
(Constant) 109,94 13,19
AGE 18 - 24 29,961 5,22
AGE 25 - 34 27,864 5,85
AGE 35 - 44 19,266 4,04
AGE 45 - 54 21,596 4,56
AGE 55 - 64 20,229 4,10
ENGINE > 2300 cc 24,926 3,61
Frequency: Almost every day 6,593 1,82
GENDER -6,011 -1,93
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
Relationship between self reported speed and personal Relationship between self reported speed and personal characteristics of drivers characteristics of drivers
Reference values:Reference values:
- Age > 65
- Engine =< 1100 cc
- Frequency 1- 3 /year
- Gender male
- Not involved in accident
- No speeding ticket
- Do not consider safety as a reason for conforming with speed limit
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
Exceeding the motorway speed limit:Exceeding the motorway speed limit:Factors affecting driver choices Factors affecting driver choices
Binary Binary logitlogit coefficientscoefficients
Reasons that car drivers conform with the Reasons that car drivers conform with the motorway general speed limit (motorway general speed limit (120km/h120km/h))
Driver’s speedReasons for conforming with speed limit
% of drivers
Drivers who Conform with speed limit
Others F sig
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
Reasons for exceeding the speed limit
% of drivers
Enjoy speeding 4,8% 149 130 10,1 0,00
Drivers who exceed the speed limit
Others F sig.
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
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
Reasons that drivers exceed the motorway general Reasons that drivers exceed the motorway general speed limit (speed limit (120km/h120km/h))
DriversDrivers’’ views on the views on the 120km/h120km/h general speed limit on general speed limit on motorways motorways
Drivers' views on the level of speed limit in motorways (120km/h)
65%
31%
5%
120
138
112
0%
10%
20%
30%
40%
50%
60%
70%
It's very high andshould be decreased
It's about right It's very low andshould be increased
% o
f driv
ers
100
110
120
130
140
150
mea
n sp
eed
(km
/h)
Speed limits should never be exceeded
8%
42%
10%
35%
5%
126
139
152
131
114
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
StronglyAgree
Agree Neitheragree notdisagree
Disagree StronglyDisagree
%D
river
s
110
120
130
140
150
160
mea
n sp
eed
(km
/h)
Should drivers exceed speed limits?Should drivers exceed speed limits?
Speed limits should never be Speed limits should never be exceededexceeded
Speed limits are lower than the speed limit for safe driving, and thus they could be exceeded by 10 km/h or more
2%
36%
14%
46%
2%
151
137
124
100
138
0%
10%
20%
30%
40%
50%
60%
StronglyAgree
Agree Neither agreenot disagree
Disagree StronglyDisagree
% o
f Driv
ers
90
100
110
120
130
140
150
160
mea
n sp
eed
(km
/h)
Should drivers exceed speed limits?Should drivers exceed speed limits?
Current Speed limits are lower than the limit Current Speed limits are lower than the limit for safe driving and thus could be exceeded for safe driving and thus could be exceeded
by 10 km/h or even more by 10 km/h or even more
Speed limits are inaccurateDrivers can judge whether they can drive slowly or fast .
9%
59%
12%18%
2%
150
134130
123
137
0%
10%
20%
30%
40%
50%
60%
70%
StronglyAgree
Agree Neither agreenot disagree
Disagree StronglyDisagree
% o
f driv
ers
110
120
130
140
150
160
mea
n sp
eed
(km
/h)
Should drivers exceed speed limits?Should drivers exceed speed limits?
Speed limits are inaccurate Speed limits are inaccurate Drivers can judge for themselves whether Drivers can judge for themselves whether
they should drive slowly or fastthey should drive slowly or fast
Main findings from surveysMain 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.
Self optimum speed :Self optimum speed :
Social optimumSocial optimumCost of travel time
Accident costs
Environmental costs
Energy costs
Enforcement cost
drivers can impose significant risks drivers can impose significant risks and uncompensated costs on othersand uncompensated costs on othersDifferent drivers have different risk Different drivers have different risk tolerancestolerancesMay have inadequate information May have inadequate information and/or misjudge roadway conditions, and/or misjudge roadway conditions, and own and vehicle capabilitiesand own and vehicle capabilitiesMay misjudge the effect speed on May misjudge the effect speed on accident probability and severity accident probability and severity
Reasons for regulating driversReasons for regulating drivers’’ speedspeed
Driver tries to minimise travel time, perceived risk of accident perceived risk of being caughtfuel cost
Different approaches in setting speed limitsDifferent approaches in setting speed limits(Fildes et al. for Austroads 2005)
Engineering Engineering Road geometry, Traffic speeds, Accident data, Traffic volumes, Roadside development.
DriversDrivers’’ ChoiceChoiceDrivers select a reasonable and safe travel speed.The posted speed limit is the 85th percentile driving speed.
Economic OptimisationEconomic OptimisationAll 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 MinimisationHarm MinimisationLife and health cannot be measured in monetary terms. Fatalities or serious casualties is not considered as an inevitable cost of increased mobility.
Economic optimisation approachEconomic 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
Road accident costsRoad 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 issueDifferent methods
Human Capital ApproachWillingness to Pay
can lead to significantly different costs of accidents
The number of Road accidents The number of Road accidents (Nilsson (1984)(Nilsson (1984)
NA = (VA/VB)p * NB
NA = number of accidents After the speed change
VA = mean or median speed After
NB = number of accidents Before the speed change
VB = mean or median speed Before
p = 4 for fatal accidents 3 for serious injury accidents2 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
Travel time costsTravel time costs
TimC = Traffic Volume * Travel Time * VoTrequires reliable estimates of the value of time
Vehicle operating costsVehicle operating costs
OpC = Traffic Volume * distance* Fuel Consumption * fuel cost
- Reliable Fuel consumption functions are available for differenttypes of vehicles
- Fleet composition data should be available
Traffic emissions costsTraffic emissions costs
• Hydrocarbons and other organic compounds (VOC), benzene, 1,3-butadiene
• Carbon monoxide CO• Nitrogen Oxides NOx• Particular Matter (PM) –
particles emitted from the exhaust
• CO2: is a main contributor to global warming.
Atmospheric emission pollutants which are normally regarded as the ones of most concern include:
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0 20 40 60 80 100 120 140 160 180
speed (km/h))
ΝΟ
x em
issi
ons
(gr/k
m)
Euro III_< 1.4 l Euro III_1.4 - 2.0 l Euro III_> 2.0 l
Euro IV_< 1.4 l Euro IV_1.4 - 2.0 l Euro IV_> 2.0 l
NOx emissions rates
0 20 40 60 80 100 120 140 160 180Speed (km/h)
Extensive database of vehicle Emission functions is provided by the UK Dept of Environment
Traffic emissions costsTraffic 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 compositionCost of different pollutants has not been estimated in Greece
Noise pollution impactNoise 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
All relationships for estimating 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) ]Accident frequency is related to speed variance.
Intensity of speed enforcement affects speed distribution
But cost of intensive enforcement can incur high costs Speed limit
Speed limits, speed distribution and Speed limits, speed distribution and speed enforcementspeed enforcement
Low/moderate enforcement
Intense enforcement
Further research in• Effect of level of enforcement on speed distribution• Speed – accident relationships• Reliable estimates of accident, pollution costs
Future researchFuture research
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.