Centre for Transport Aberdeen 12- 11-08 An Investigation of impacts VMS on safety on Scottish Trunk...

Centre for Transport Aberdeen 12-11-08

An Investigation of impacts VMS on safety on Scottish Trunk

Roads

Wafaa Saleh

TRi, Napier University, Edinburgh


Contents

1. Introduction to VMS2. Literature3. Research gaps4. Main research objectives5. Research methodology 6. Source of data7. Modelling estimation results – accident rates

and accident severity 8. Discussions9. Conclusions and Further Works


Introduction to VMS

• To inform drivers of dangers ahead (e.g., adverse weather, accidents)

• To inform motorists of congestion, roadwork, or speed limits ahead, etc.


Wafaa SALEH

Craig WALKER & Chih-Wei PAI

An Investigation of the impacts of


Literature

• VMS for Speed reduction information and unexpected events

- a 30% - 48% reduction of accident rates

- effective in diverting motorists

- a reduction in speed in upstream but an increase downstream


Research Gap

Results re accidents reductions are not conclusive

Overall reduction in accidents do not mean resulting from VMS

The effect of VMS on accident severity?The interaction effects of other factors with

VMS?


Therefore…

• A review of the literature suggests that while consistent conclusions have been suggesting that a reduction of speed was observed as a result of a sign that urges a reduced speed, there was a concern for an increase in speed downstream

• The net safety effects of such message systems were rather inconclusive in the literature


Research objectives

• To investigate the impacts of VMS on accident rates and severity on Scottish trunk roads

- A before-and-after analysis of accidents at 14 selected VMS sites in Central and North-East Scotland is presented.


Data sources

• The number and locations of accidents at 14 selected VMS sites

- NADICS website

- Glasgow ITS department of the Faber Maunsell Engineering Consultancy

• Other factors that affect accident rates and severity:

- The UK Stats19 accident injury database


Wafaa SALEH

Craig WALKER & Chih-Wei PAI

An Investigation of the impacts of


Data sources

• The number and locations of accidents at 14 selected VMS sites

- NADICS website

- Glasgow ITS department of the Faber Maunsell Engineering Consultancy

• Other factors that affect accident rates and severity:

- The UK Stats19 accident injury database


1.1 Record Type 1.14 Road Type 1.20a Pedestrian Crossing 1.23 Road Surface Condition - Human Control 11 New accident record 1 Roundabout 1 Dry 15 Amended accident record 2 One way street 0 No crossing facility within 50 metres

or 2 Wet / Damp

3 Dual carriageway - 2 lanes physical crossing facility not controlled

3 Snow

1.2 Police Force 4 Dual carriageway - 3 or more lanes by authorised person 4 Frost / Ice 5 Single carriageway - single track road 1 Control by school crossing patrol 5 Flood (surface water over 3cm deep)

1.3 Accident Ref No 6 Single carriageway - 2 lanes (one in 2 Control by other authorised person 6 Oil or diesel each direction) 7 Mud

7 Single carriageway - 3 lanes (two way 1.5 Number of Vehicle capacity) 1.20b Pedestrian Crossing Records 8 Single carriageway - 4 or more lanes - Physical Facilities (two way capacity) 1.24 Special Conditions at Site 9 Unknown 0 No physical crossing facility within

1.6 Number of Casualty 50 metres 0 None

Records 1.15 Speed Limit (mph) 1 Zebra crossing 1 Automatic traffic signal out

4 Pelican, puffin, toucan or similar non-

2 Automatic traffic signal partially defective 1.16 Junction Detail junction pedestrian light crossing 3 Permanent road signing or marking

1.7 Date 5 Pedestrian phase at traffic signal defective or obscured

00 Not at or within 20 metres of junction junction 4 Roadworks present

01 Roundabout 8 Central refuge - no other controls 5 Road surface defective

02 Mini roundabout 9 Footbridge or subway

1.9 Time of Day 03 T or staggered junction 05 Slip road 06 Crossroads 1.21 Light Conditions 1.25 Carriageway Hazards 07 Multiple junction

1.10 Local Authority 08 Using private drive or entrance 1 Daylight: street lights present 0 None

09 Other junction 2 Daylight: no street lighting 1 Dislodged vehicle load in carriageway

3 Daylight: street lighting unknown 2 Other object in carriageway

1.11 Location Junction Accidents Only 4 Darkness: street lights present and lit

3 Involvement with previous accident 10 digit OS Grid Reference number 5 Darkness: street lights present but

unlit 4 Dog in carriageway

1.17 Junction Control 6 Darkness: no street lighting 5 Other animal or pedestrian in carriageway 1 Authorised Person 7 Darkness: street lighting unknown

Easting Northing

2 Automatic traffic signal

3 Stop sign

4 Give way sign or markings 1.22 Weather 1.26 Place Accident Reported 1.12 1st Road Class 5 Uncontrolled 1 Fine without high winds 1 At scene 1 Motorway 1.18 2nd Road Class 2 Raining without high winds 2 Elsewhere 2 A(M) 1 Motorway 3 Snowing without high winds 3 A 2 A(M) 4 Fine with high winds 4 B 3 A 5 Raining with high winds 5 C 4 B 6 Snowing with high winds 1.27 DETR Special Projects 6 Unclassified 5 C 7 Fog or mist - if hazard 6 Unclassified 8 Other

1.13 1st Road Number 9 Unknown

1.19 2nd Road Number

Day Month Year

Hours Mins Hours Mins

24 hour Hours Mins

0

0

1


Years

2.1 Record Type 2.8 Vehicle Movement 2.11 Skidding and Overturning 2.16 First Point of Impact Compass Point

21 New vehicle record 0 No skidding, jack-knifing or overturning 0 Did not impact 3 Offside 25 Amended vehicle record 1 N 5 S Parked: 1 Skidded 1 Front 4 Nearside

2 NE 6 SW not at kerb 2 Skidded and overturned 2 Back

2.2 Police Force 3 E 7 W 3 Jack-knifed 4 SE 8 NW at kerb 4 Jack-knifed and overturned 2.17 Other Vehicle Hit 2.3 Accident Ref No 5 Overturned Ref no of other vehicle

2.4 Vehicle Ref No 2.12 Hit Object in Carriageway 2.18 Part(s) Damaged 2.9a Vehicle Location at Time of

Accident - Road 00 None 06 Bridge - side

0 None 3 Offside 6 Underside

2.5 Type of Vehicle 01 Previous accident 07 Bollard / refuge 1 Front 4 Nearside 7 All four sides 1 Leaving the main road 02 Roadworks 08 Open door of

vehicle 2 Back 5 Roof

01 Pedal cycle 15 Other non-motor vehicle

2 Entering the main road 03 Parked vehicle - lit 09 Central island of

02 Moped 16 Ridden horse 3 On the main road 04 Parked vehicle roundabout 2.21 Sex of Driver 03 Motor cycle 125 cc 17 Agricultural vehicle

4 On the minor road - unlit 10 Kerb

and under (includes diggers etc.)

05 Bridge - roof 11 Other object 1 Male 2 Female 3 Not traced 04 Motor cycle over 125cc 18 Tram / Light rail 2.9b Vehicle Location at Time of 08 Taxi 19 Goods vehicle 3.5

Accident - Restricted Lane/ 2.13 Vehicle Leaving Carriageway 2.22 Age of Driver 09 Car tonnes mgw and under

Away from Main Carriageway Estimated if necessary 10 Minibus (8 - 16 20 Goods vehicle over 3.5

0 Did not leave carriageway passenger seats) tonnes and under 7.5

0 On main carriageway - not in restricted 1 Left carriageway nearside 2.23 Breath Test 11 Bus or coach (17 or tonnes mgw lane 2 Left carriageway nearside and rebounded

more passenger seats) 21 Goods vehicle 7.5

1 Tram / Light rail track 3 Left carriageway straight ahead at junction 0 Not applicable 5 Driver not contacted 14 Other motor vehicle tonnes mgw and over 2 Bus lane 4 Left carriageway offside onto central 1 Positive at time of accident 3 Busway (including guided busway) reservation 2 Negative 6 Not provided

2.6 Towing and Articulation 4 Cycle lane (on main carriageway) 5 Left carriageway offside onto central 3 Not requested (medical reasons) 5 Cycleway (separated from main reservation and rebounded 4 Refused to provide

0 No tow or articulation 3 Caravan carriageway) 6 Left carriageway offside and crossed 1 Articulated vehicle 4 Single trailer 6 On lay-by or hard shoulder central reservation 2.24 Hit and Run 2 Double or multiple trailer 5 Other tow 7 Entering lay-by or hard shoulder 7 Left carriageway offside

8 Leaving lay-by or hard shoulder 8 Left carriageway offside and rebounded 0 Other 2 Non-stop vehicle, 2.7 Manoeuvres 9 Footway (pavement) 1 Hit and Run not hit

2.14 Hit Object Off Carriageway

01 Reversing 12 Changing lane to right

2.25 DETR Special Projects 02 Parked 13 Overtaking moving

2.10 Junction Location of Vehicle 00 None 03 Waiting to go ahead vehicle on its offside at First Impact 01 Road sign / Traffic signal 2.26 Vehicle Registration but held up 14 Overtaking stationary

02 Lamp post Mark (VRM) 04 Stopping vehicle on its offside

0 Not at junction (or within 20 metres) 03 Telegraph pole / Electricity pole Special codes: 05 Starting 15 Overtaking on nearside

1 Vehicle approaching junction or parked at 04 Tree 2 Foreign / Diplomatic 4 Trade plates 06 U turn 16

Going ahead left hand junction approach 05 Bus stop / Bus shelter 3 Military

9 Unknown 07 Turning left bend 2 Vehicle in middle of junction 06 Central crash barrier

08 Waiting to turn left 17 Going ahead right

3 Vehicle cleared junction or parked at 07 Nearside or offside crash barrier 2.27 Driver 09 Turning right hand bend junction exit 08 Submerged in water (completely) Postcode 10 Waiting to turn right 18 Going ahead other

4 Did not impact 09 Entered ditch Special codes: 2 Non-UK resident 11 Changing lane to left 10 Other permanent object 1 Unknown 3 Parked and

unattended

From To 2

0 0

* code 1 - 8 *

0


3.1 Record Type 3.7 Sex of Casualty 3.11 Pedestrian Movement 3.13 School Pupil Casualty

31 New casualty record 1 Male 0 Not a pedestrian 1 School pupil on journey to or from 35 Amended casualty record 2 Female 1 Crossing from driver’s nearside school

2 Crossing from driver’s nearside - masked

0 Other by parked or stationary vehicle 3 Crossing from driver’s offside

4 Crossing from driver’s offside - masked

by parked or stationary vehicle

3.2 Police Force 3.8 Age of Casualty 5 In carriageway, stationary - not crossing

3.15 Car Passenger Estimated if necessary (standing or playing)

6 In carriageway, stationary - not crossing

0 Not a car passenger

(standing or playing), masked by 1 Front seat passenger

parked or stationary vehicle 2 Rear seat passenger

7 Walking along in carriageway - facing

3.3 Accident Ref No 3.9 Severity of Casualty traffic 8 Walking along in carriageway - back to 1 Fatal traffic

2 Serious 9 Unknown or other

3 Slight 3.16 Bus or Coach Passenger

3.4 Vehicle Ref No 0 Not a bus or coach passenger 1 Boarding 2 Alighting

3 Standing passenger

3.10 Pedestrian Location 3.12 Pedestrian Direction 4 Seated passenger

3.5 Casualty Ref No 00 Not a pedestrian Compass point bound

01 In carriageway, crossing on pedestrian

crossing facility 1 N 02 In carriageway, crossing within zig-

zag 2 NE

lines at crossing approach 3 E 3.17 DETR Special Projects

03 In carriageway, crossing within zig-zag

4 SE lines at crossing exit 5 S

3.6 Casualty Class 04 In carriageway, crossing elsewhere 6 SW

within 50 metres of pedestrian crossing

7 W

1 Driver or rider 05 In carriageway, crossing elsewhere 8 NW

2 Vehicle or pillion passenger 06 On footway or verge 9 Unknown 3.18 Casualty 3 Pedestrian 07 On refuge, central island or central 0 Standing still Postcode

reservation

08 In centre of carriageway, not on refuge,

Special codes: central island or central

reservation 1 Unknown

09 In carriageway, not crossing 2 Non-UK resident 10 Unknown or other

Years

3


Analysis of accident rates

• Accident rates

Where k represents accident rates; X = number of accidents, T = time (in years in this

case), L = length (km) of the road in question and Q = flow on the road over the entire year (thus is typically calculated by multiplying the AADT (Annual Average Daily Traffic) by 365 (days in a year))


Effect of VMS on accident rate

• Effectiveness of VMS

AAB

BBA

QTY

QTY

Where YB = Accidents Before, YA = Accidents After TB = Time Before (years), TA = Time After (years) QB = Flow Before, QA = Flow After


Overall accident rate (k) 2000-2006


ROAD VMS CODE X ACCIDENTS

Q (AV.) L (KM) T (YEAR) K (ACCS/108VEH-KM) SE (ACCS/108VEH-KM)

M9 N3 6 17515 2 7 6.70 2.74

W2 5 18006 2 7 5.43 2.43

W3 2 18857 2 7 2.08 1.47

W4 2 18088 2 7 2.16 1.53

A720 M7 9 30401 2 7 5.79 1.93

M8 O3 69 31066 2 7 43.47 5.23

O6 10 26476 2 7 7.39 2.34

O 7 25442 2 7 5.38 2.04

V2 10 26377 2 7 7.42 2.35

O9 18 25036 2 7 14.07 3.32

V1 13 36582 2 7 6.95 1.93

A90 G1 11 12285 2 7 17.52 5.28

G2 4 10871 2 7 7.20 3.60

D6 14 12756 2 7 21.48 5.74


ROAD VMS CODE

ACCIDENT DATA (BEFORE) ACCIDENT DATA (AFTER) K BEFORE VMS

(ACCS/100M VEH-

KMS)

K AFTER VMS (ACCS/100M VEH-KMS)

BEFORE AND AFTER % DIFFERENCE

X Accidents

Q Average

L (km)

T(yr)

X Accident

s

Q Averag

e

L(km)

T(yr)

M9 N3 4 17139 2 5 2 18455 2 2 6.39 7.42 16.09%

W2 4 16571 2 5 1 21592 2 2 6.61 3.17 -52.03%

W3 2 17764 2 5 0 21590 2 2 3.08 0.00 -100.00%

W4 2 17206 2 4 0 19263 2 3 3.98 0.00 -100.00%

A720 M7 4 30042 2 4 5 30881 2 3 4.56 7.39 62.14%

M8 O3 46 30436 2 4 23 31905 2 3 51.76 32.92 -36.40%

Accidents data before and after installing VMS

Total 114 298463

28 60 66 328559

28 38 6.22 5.17 -16.96


Percentage effectiveness of VMS including the control zone information

YB YA XB XA VMS Accs before

Accs after Accs before

Accs after

VMS % EFFECT

EFFECT RANGE

N3 4 2 5 2 25.00% -88.20% 1224.07% W2 4 1 5 2 -37.50% -95.95% 865.03% W3 2 0 5 2 -100.00% 0.00% 0.00% W4 2 0 4 3 -100.00% 0.00% 0.00% M7 5 4 4 3 6.67% -85.45% 682.20% O3 46 23 76 50 -24.00% -84.32% 268.40% O6 6 4 5 2 66.67% -78.99% 1222.36% O 3 4 4 3 77.78% -78.60% 1376.72%

V2 7 3 7 3 0.00% -86.70% 651.94% O9 10 8 9 1 620.00% 9.31% 4642.50% V1 7 6 7 3 100.00% -68.62% 1174.54% G1 8 3 9 1 237.50% -59.06% 2682.30% G2 1 3 4 3 300.00% -73.48% 5932.77% D6 10 4 15 5 20.00% -81.94% 697.14%


Percentage effectiveness of VMS

95% CI VMS ө ESTIMATE % VMS EFFECT 95% CI

EFFECT RANGE

N3 1.160896 16.09% 0.213 6.338 -78.74% 533.82%

W2 0.479663 -52.03% 0.054 4.292 -94.64% 329.17%

W3 0 -100.00% 0.000 0.000 0.000 0.000

W4 0 -100.00% 0.000 0.000 0.000 0.000

M7 1.037703 3.77% 0.279 3.864 -72.13% 286.44%

O3 0.635975 -36.40% 0.386 1.049 -61.45% 4.91%

O6 1.489406 48.94% 0.420 5.278 -57.97% 427.80%

O 1.637746 63.77% 0.367 7.318 -63.35% 631.77%

V2 0.304464 -69.55% 0.079 1.177 -92.13% 17.74%

O9 1.827277 82.73% 0.721 4.630 -27.88% 362.99%

V1 0.577838 -42.22% 0.194 1.719 -80.58% 71.94%


Chi-squared results for the 14 VMS VMS

OBSERVED EXPECTED

Accs before

Accs after

ACCIDENTS PER YEAR

Accs before Accs after

X2

=∑(O-E)2/E

N3 4 2 0.857 4.286 1.714 0.07 W2 4 1 0.714 3.571 1.429 0.18 W3 2 0 0.286 1.429 0.571 0.80 W4 2 0 0.286 1.143 0.857 1.50 M7 5 4 1.286 5.143 3.857 0.01 O3 46 23 9.857 39.429 29.571 2.56 O6 6 4 1.429 7.143 2.857 0.64 O 3 4 1.000 4.000 3.000 0.58 V2 7 3 1.429 4.286 5.714 3.01 O9 10 8 2.571 12.857 5.143 2.22 V1 7 6 1.857 5.571 7.429 0.64 G1 8 3 1.571 7.857 3.143 0.01 G2 1 3 0.571 2.286 1.714 1.69 D6 10 4 2.000 8.000 6.000 1.17


Analysis of accident severity

• Two binary logit models (KSI vs non KSI accident) were estimated

- the overall binary logit model

- the binary logit model conditioned on the absence of VMS (interaction effects of absence of VMS with other variables)


The overall binary logit model VARIABLE

CATEGORIES OF EACH VARIABLE

FREQUENCY COEFFICIENT (P-VALUE)

O.R.

Intercept: -1.876 (0.217) Gender of rider 1. male 136 (76%) 0.044 (0.943) 1.045 2. female 43 (24%) R R Age of rider 1. up to 20 19 (10.6%) -0.456 (0.661) 0.634 2. 21~59 143 (79.9%) -1.017 (0.206) 0.362 3. 60 or above 17 (9.5%) R R Vehicle type 1. car (private car/taxi) 143 (79.9%) -0.835 (0.150) 0.434 2. heavier veh (bus/HGV) 36 (20.1%) R R Accident month 1. spring/summer (Mar-Aug) 84 (46.9%) 0.533 (0.025) 3.237 2. autumn/winter (Sep-Feb) 95 (53.1%) 0.325 (0.006) 1.384 VMS measure 1. no VMS 113 (63.1%) 0.749 (0.186) 2.116 2. automatic signal 66 (36.9%) R R Weather condition 1. fine 118 (65.9%) -0.319 (0.720) 0.727 2. wet 44 (24.6%) -0.602 (0.544) 0.548 3. extreme 17 (9.5%) R R Accident time 1. rush hours (1600-1859; 0700-

0959) 69 (38.5%) 0.533 (0.359) 1.705

2. late night/morning (0000-0659)

10 (5.6%) 1.446 (0.105) 4.246

3. evening (1900-2359) 21 (11.7%) 0.176 (0.849) 1.185 4. late morning/afternoon (1000-

1559) 79 (44.1%) R R

Traffic flow 1. 10000-19999 42 (23.5%) 0.261 (0.688) 1.298 2. 2000-29999 65 (36.3%) 0.079 (0.245) 1.317 3. 30000-39999 72 (40.2%) R R Dependent variable 1. KSI 22 (12.3%) 2. slight injury 157 (87.7%) Classification accuracy 1. the number of KSI that was correctly predicted: 1 (0.6%) 2. the number of Slight injury that was correctly predicted: 156 (99.4%) Observations: 179 McFadden Pseudo R-Square: 0.103

Likelihood ratio 2 : 139.761 (with 115 D.F., p=0.058)


Interaction binary logit model VARIABLE

CATEGORIES OF EACH VARIABLE

FREQUENCY COEFFICIENT (P-VALUE)

O.R.

Intercept: -0.573 (0.784) Gender of driver 1. male 85 (75.26%) -00814 (0.913) 0.923 2. female 28 (24.8%) R R Age of driver 1. up to 20 11 (9.7%) -0.752 (0.628) 0.472 2. 21~59 93 (82.3%) -0.986 (0.339) 0.373 3. 60 or above 9 (8.0%) R R Vehicle type 1. car (private car/taxi) 92 (81.4%) -1.616 (0.029) 0.199 2. heavier veh (bus/HGV) 21 (18.6%) R R Accident month 1. spring/summer (Mar-Aug) 54 (47.8%) 1.607 (0.019) 4.987 2. autumn/winter (Sep-Feb) 59 (52.2%) R R Weather condition 1. fine 748 (65.5%) -0.715 (0.580) 0.489 2. wet 32 (28.3%) -0.552 (0.668) 0.576 3. extreme 7 (6.2%) R R Accident time 1. rush hours (1600-1859; 0700-

0959) 39 (34.54%) 0.809 (0.253) 2.245

2. late night/morning (0000-0659)

5 (4.4%) 0.946 (0.458) 2.576

3. evening (1900-2359) 11 (9.7%) 1.049 (0.297) 2.856 4. late morning/afternoon (1000-

1559) 58 (51.3%) R R

Traffic flow 1. 10000-19999 29 (25.7%) -0.269 (0.747) 0.764 2. 2000-29999 45 (39.8%) 0.372 (0.598) 1.450 3. 30000-39999 39 (34.5%) R R Dependent variable 1. KSI 16 (14.2%) 2. slight injury 97 (85.8%) Classification accuracy 1. the number of KSI that was correctly predicted: 2 (1.8%) 2. the number of slight injury that was correctly predicted: 95 (84.1%) Observations: 113 McFadden Pseudo R-Square: 0.149

Likelihood ratio 2 : 13.698 (with 12 D.F., p=0.320)


Summary and conclusions

• Installation of VMS resulted in all reduction of accident rate (16.9%).

• However, when the control sites were taken into account, installation of VMS might have resulted in an increase in accident rates on the roads upon which they were placed.

• The presence of VMS reduced accident severity at the considered sites.


Further work

• Analysis of accident rates and severity with larger data and wider area coverage

• Taking into account other impacts such as national trends of accidents rates and impacts of speed reductions, etc.

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Centre for Transport Aberdeen 12- 11-08 An Investigation of impacts VMS on safety on Scottish Trunk...

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