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TRANSPORT and ROAD RESEARCH LABORATORY

Department of the Environment Dep~rtment of Transport

TRRL LABORATORY REPORT 774

ACCIDENTS AT OFF-SIDE PRIORITY ROUNDABOUTS WITH MINI OR SMALL ISLANDS

by

Hilary Green

Any views expressed in this Report are not necessarily those of the Department of the Environment

or of the Department of Transport

Accident Investigation Division Safety Department

Transport and Road Research Laboratory Crowthorne, Berkshire

1977 ISSN 0305-1293

CONTENTS

Abstract

1. Introduction

2. Data collection

3. Method of analysis

4. Results

4.1 All injury accidents

4.2 30/40 mile/h speed limit areas

4.3 Fatal and serious accidents

4.4 Higher speed limit areas

4.5 Type of road user involved in accidents

5. Conclusions

6. Acknowledgements

7. References

8. Appendix

Page

1

1

2

3

4

4

4

6

6

8

8

9

9

28

0 CR.OWN COPYRIGHT 1977

Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged

Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on ! st April 1996.

This report has been reproduced by permission of the Controller of HMSO. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.

ACCIDENTS AT OFF-SIDE PRIORITY ROUNDABOUTS WITH MINI OR SMALL ISLANDS

ABSTRACT

Injury accidents were studied at 150 junctions and roundabouts before and after the installation of single or multiple islands, kerbed or unkerbed. 132 of these, considered separately, were previously govemed by 30 or 40 mile/h speed limits with (A) priority control, (B) traffic signals, or

(C) roundabouts.

Type (A) 88 sites, had statistically significant reductions of 34 and 46 per cent in all injury and in fatal plus serious injury accidents respectively whether unkerbed sites were included or not.

Type (B) 13 sites, all types combined, showed a statistically significant decrease in fatal plus serious accidents of 62 per cent.

Type (C) 31 sites all kerbed. All types except single kerbed island sites with 3 arms showed a statistically significant increase of 91 per cent for all accidents and rather more for fatal plus serious especially when 2 multiple systems were included (200 per cent).

Accidents involving two-wheeled motor vehicles at type A sites, and those involving pedal cycles at type C sites, expressed as proportions of the total, were significantly reduced.

In higher speed limit zones the changes in all accidents at a few sites, type (A) - 10 sites and (C) - 8 sites, were statistically significant and gave indications endorsing the results above.

1. INTRODUCTION

In the course of track experiments at the Transport and Road Research Laboratory in 1971, it was demon-

strated that the capacity of roundabouts could be increased by enlarging the area available to traffic, i.e., by

reducing the size of the roundabout island and/or by increasing the entry widths at the "give way" line. In

addition, traffic was required to obey the rule of "priority to the right", which gives priority to vehicles

negotiating the junction and thereby prevents the traffic from 'locking'. This rule had been introduced

permanently in November 1966 at all roundabouts after a successful experimental period.

The Transport and Road Research Laboratory was associated with a number of trims involving conversion

from large to small island roundabouts and following the issue of Technical Memorandum H7/71 by the

Department of the Environment, which made recommendations for the design of off-side priority roundabouts with small central islands, the layouts at a number of roundabouts throughout the country (mostly, but

not exclusively, in built-up areas) were adapted to meet these principles. Various experimental layouts were introduced, such as a single island with a hollow centre (this is effectively two islands and, shape apart, is

similar from the point of view of traffic movements to a 'double mini', which consists of two small circular islands separated by an elongated strip); a multiple system consisting of a small island for each approach arm,

again with a hollow centre; and a ring system as at Hemel Hempstead, with a large roundabout around which two-way movements are permitted with a small island at each approach area. Plans of some of the schemes are shown in Fig. 1. Recommendations for all types of roundabout design were consolidated in Technical Memorandum H2/75.

Small island roundabouts taking up much less space than a conventional roundabout could now be considered for use at junctions where previously a large roundabout would not have been possible. As a result, most o f the conversions have been at major/minor junctions which previously had priority control only,

together with a few which were previously controlled by traffic signals. Normally, according to the Technical Memorandum H2/75, the diameter o f the small island roundabout should be about one-third of that for the circle inscribed within the total junction area. At sites where this would be less than 4 metres, and space at

a premium such that even the smallest roundabout would obstruct the turning movements of some commercial vehicles or buses, a kerbless island was designed with diameter between 1 and 4 metres. It was constructed to be level with or just proud of the surrounding surface, sometimes employing a different material, and it could

be very slightly raised at the centre or sometimes merely a solid circle of white thermoplastic with or without a ring of studs. This kerbless type of roundabout was surrounded by three broad white arrows painted on the

road surface and a special advance warning sign was used. Ideally, there should have been no other furniture on the centre island, unlike the kerbed types which could be larger in diameter and were allowed a variety of bollards, upright chevron signs and lighting colunms.

Although no longer recommended, there were in this study a number of roundabouts with islands of diameter less than 4 m which had kerbsand/or furniture which effectively prevented vehicles from crossing over them. The term 'mini' has been retained to describe them though they have been grouped with small islands ifl the analysis, likewise, a ring of studs is also no longer recommended.

2. DATA COLLECTION

A survey of mini-roundabouts in England and Wales by the County Surveyors' Society culminated in a list of 114 sites of all types that had been installed before August 1972. This list (see Table 4) with some data from

the report was used as the basis for this investigation but extra information on a more uniform basis was required. A questionnaire was sent to each relevant local authority requesting full details about the changes at each site together with the record of injury accidents from 1.1.67 - 31.3.73 (see Table 5). Although the earlier accident records no longer exist in all cases, some authorities were able to supply more up-to-date data

as well as extra information about new sites, some of which were included in this study. Preliminary analyses were reported in TRRL Leaflets LR 393 I. For a number of sites the data had been updated to May 1975.

The effect of mini-roundabout schemes might not be the same at sites with different forms of control

previously or subject to different speed limits. There were very few sites in 70 mile/h speed limit areas and although the small sample did not allow a very satisfactory analysis this was done in the hope of revealing

some indication of their safety performance. Every' site is unique and, therefore, there could be no entirely standard treatment for the conversion. Some sites were converted at little cost, consisting mainly of paint

markings on the road surface, whilst at others more elaborate and expensive improvement schemes incorpor-

ated the re-surfacing of the junction, considerable changes in the old kerb lines, new or improved standard

street lighting including high intensity lighting on the new centre island, new pedestrian crossings and the re-

siting of old ones with pedestrian barriers etc. Some schemes entailed the complete closure of an arm o f the

2

junction or sometimes one arm was made one-way only or certain turns were prohibited. One authority (Newcastle Upon Tyne) had installed 40 small islands whilst in others there might be only one isolated mini.

Some were used principally by local drivers, and might or might not be heavily trafficked at peak times,

whereas others might be subject to dense holiday traffic especially during summer weekends.

3. METHOD OF ANALYSIS

From the foregoing, it is obviously not possible to assess the effect on accidents of installing a small island

without also including effects arising from all the other changes that have taken place at the junction.

Neither can it be assumed that any part of the change in the numbers or type of accidents is due solely to the

presence of the mini or small-island roundabout itself, as any of the accompanying alterations at the junction

may have contributed to the change. All that can be considered is the composite effect due to all the

measures that are usually incorporated whenever a small island is installed and due also to the particular

environment, traffic and otherwise, in which it is situated, but taking into account any major common factors

by grouping where possible. In any case it was not possible to consider the effect of any change separately

for any individual site since the numbers of accidents at each were invariably too small to yield a significant

result. It was therefore necessary to group the data and to assess the average total effect due to all the changes

within each group, bearing in mind the possible effects of the other measures mentioned above which vary

from site to site and from group to group.

As discussed previously, a variety of types of small island roundabouts and combinations of islands were

adopted for converting the junctions, which had previously been controlled by three different systems. The~

installation of traffic signals or a large roundabout at uncontrolled junctions generally results in a reduction

of accidents, so the effect on accidents of changing to a mini or small-island roundabout might be expected

to depend amongst other things on the previous form of control. In order to test whether there were any

such differences, the sites were separated according to their earlier forms of control, i .e.:-

Group A

Group B

Group C

junctions formerly with priority control, which were generally minor road junctions with a

major road

junctions formerly controlled by traffic signals

junctions formerly controlled by an old-style large roundabout.

These groups were then sub-divided according to the new form of control, as follows:-

(i) single mini island roundabouts having a diameter iess than 4 metres and with no kerbs,

(ii) single small or mini island roundabouts with kerbs and sometimes other furniture effectively preventing

traffic from traversing it,

(iii) those with split islands or a multiple arrangement of islands.

There were so few of each kind in (iii) that they had to be combined but of course there may be

significant differences in their safety characteristics. For sub groups (i) and (ii) it was sometimes possible to

make further breakdowns according to the number of arms at the junction. Some sites could not be used if

there had been major changes during the 'before' and 'after' periods apart from those at the time of the

roundabout installation. One which obviously could not be used was a new junction on a new road. One or

two old roundabout sites which have been included in the analysis were abandoned later and reverted to

3

other controls after fairly short trial periods due to their poor safety record. Some arms were made dual

whilst other arms were closed altogether.

The new style roundabouts came into operation all on different dates with varying 'before' and 'after '

periods, so the normal 'before and after' chi-squared test could not be used. A method (see Appendix)

suitable for such a situation had already been devised by J C Tanner2; for the present analysis the number

of accidents expected in the 'after ' period at each test site, if national trends had applied, was derived from

the ratio between the relevant 'before' and 'after ' periods of the numbers of injury accidents on all A roads

in Great Britain with appropriate speed limits (or B roads where applicable in built-up areas). These ratios

are listed in Table 5 together with the numbers of injury accidents 'before' and 'after' at each site.

Fatal plus serious accidents were treated separately and for these it was possible to use fatal and serious

accidents at junctions on A or B roads with the appropriate speed limit in Great Britain as a better control.

The reason for this was that, before 1969, junction accidents were not recorded for slight accidents in the

national statistics Stats 19.

4. RESULTS

4.1 All injury accidents

The results of the analysis of all accidents for each sub-group are shown below.

A statistically significant value of chi-squared (×2) implies that the effect of such installations on

safety is not the same at all places which, in general, confirms the remarks mentioned earlier. For the group

as a whole, the average numerical amount of the effect is shown by k. An improvement is denoted by the

amount k is less than unity and a worsening by the amount k is greater than unity, the results being multiplied

by 100 to express them as percentages. The level of the statistical significance of k was obtained from the

calculation of ' t ' (see Appendix).

4.2 30/40 mile/h speed limit areas

Looking at Table 1 it ~ be evident that for sites with major/minor priority control 'before', this

provision of mini or small-island roundabouts, kerbed and unkerbed, resulted in reductions of between

28 -37 per cent in all injury accidents which were Statistically significant at the 5 per cent level or better

for each of the groups considered, although in some cases there were variations in the effect between sites

in the sample. The only reservation attaching to this beneficial result was that, unfortunately, there were

insufficient 5-arm sites and those with multiple island installations for separate assessment.

The same remark applies to the small sample of junctions which were previously controlled by traffic

signals. There was great variability between the sites and the observed decrease in accidents in the group

as a whole was not statistically significant; but at least there was no evidence of any increase in accidents.

For the former old-style roundabouts the situation was rather different, with the value of 'k ' substantially

greater than unity for sites with more than 3 arms. There were only 5 sites in the 3-arm sample and the change

at these was not statistically significant but since their 'k ' value was so much less than for the other types

they were treated separately.

4

TABLE 1 Mini roundabouts - significance tests - all injury accidents

A: MAJOR/MINOR PRIORITY CONTROL

SPEED LIMIT 30 or 40 mile/h

MINI KERBLESS

3-arm singles

total - all 3 & 4-arm singles

MINI OR SMALL ISLAND

3-arm singles

4-arm singles

total (incl. 5-arm singles, all multiples)

TOTAL KERBED AND UNKERBED

SPEED LIMIT > 40 mile/h

(3 and 4-arm singles)

B: TRAFFIC SIGNALS BEFORE


KERBED MINI OR SMALL ISLAND

3, 4 and 5-arm singles

Total (incl. unkerbed minis and

multiples)

C: OLD STYLE ROUNDABOUTS


SMALL ISLAND

3-arm singles

4-arm singles

4 and 5-arm singles

Total (excl. 3-arm but incl.

3 multiples)

SPEED LIMIT ~> 40 mile/h

singles 3-arm (2) 4-arm (4)

5-arm (1) double (1)

Number NO. OF k of ACCIDENTS ( ) sig level

sites ' of k Before After

21 109 71

26 148 84

.72 (5%)

.66 (1%)

31 216 77 .63 (0.1%)

26 258 154 .71 (2%)

62 531 243 .66 (0.1%)

88 679 327 .66 (0.1%)

10 105 41 .50 (5%)

111 70 .75 (>10%)

13 257 127 .75 (>10%)

5 32 35

20 120 189

23 163 220

1.09 (> 10%)

2.04 (0.1%)

1.93 (0.1%)

26 228 296 1.91 (0.1%)

57 114 1.88 (1%)

Significant difference

between sites (X 2 )

No

No

No

Yes

Yes

Yes

Yes

Yes

Yes

No

Yes

Yes

Yes

Yes

5

As for the remainder, there were only a sufficient number of sites with 4 arms to be treated separately,

which resulted in an increase in accidents of over 100 per cent. When three 5-arm sites were included, and

finally three sites with multiple islands, the results were increases of over 90 per cent. All these changes were

significant at the 0.1 per cent level and there w~re significant differences between sites.

~,.3 Fatal an3 serious accidents

Table 2 repeats the analysis in Table 1 for fatal and serious accidents only where, of course, the

numbers of accidents were substantially reduced. However, there were still changes which were statistically

significant at the 5 per cent level or better, including again the 3-arm single kerbed mini and small island

roundabouts with priority control previously, where k was lower than for all injury accidents although the

standard error was much larger. This also applied to the combined analysis of the old traffic signal sites where

the result had not been statistically significant when all injury accidents were considered. This time it was

not possible tO test the 3-arm sites after conversion of the old-style roundabouts.

4.4 Higher speed limit areas

Data were available for some sites where the speed limit was over 40 mile/h or was different on

different arms of the junction. Those parts of the 'after' period subsequent to November 1973 were affected

by the lower speed limits in operation during and since the fuel shortage. The experimental and control

data were assumed to be equally affected in this way. However, this assumption is probably not entirely

justified in the case of old style roundabouts, as high speeds would not be possible at these sites anyway,

making them likely to be less influenced by the new limits. In this case the value of 'k ' shown may over-

estimate any increase in accident rate.

There were 10 sites of type (A) in this sample with higher speed limits, all single small island roundabouts,

6 junctions with 3 arms and 4 with 4 arms. The results are shown in Tables 1 and 2. There was a reduction of

50 per cent of all accidents and this result was significant at the 5 per cent level. For fatal and serious accidents

the reduction was 77 per cent and this was significant at the 0.1 per cent level. In both cases there were differences between sites.

The rest of the sample in the higher speed limits range were previously old style roundabouts (C) and

consisted of 8 single small roundabouts (2 3 arm, 4 4 arm and 1 5 arm) together with one multiple system.

The analysis of this combination for all accidents resulted in a statistically significant increase of 88 per cent

(at the 1 per cent level). For fatal and serious accidents the increase was 153 per cent (also at the 1 per cent

level) and for the latter there was no variation between sites. Although the sample was very small it endorses

the earlier results for groups A and C and emphasizes the fact that great care is necessary when shrinking the

central islands of old-style roundabouts.

6

TABLE 2

Mini roundabouts - significance tests - fatal and serious accidents

A:

B :

C:

MAJOR/MINOR PRIORITY CONTROL

BEFORE SPEED LIMIT 30 or 40 mile/h

MINI KERBLESS

3-arm singles

total -- all 3-arm and 4-arm singles

MINI OR SMALL ISLAND

3-arm singles

4-arm singles

total (incl. 5-arm singles, all multiples)

TOTAL KERBED AND UNKERBED

SPEED LIMIT > 40 mile/h

(3 and 4-arm singles)

TRAFFIC SIGNALS BEFORE


KERBED MINI OR SMALL ISLAND

3, 4 and 5-arm singles

total (incl. unkerbed minis and multiples)

OLD STYLE ROUNDABOUTS


3-arm singles

4-arm singles

4 & 5-arm singles

total (excl. 3-arm but incl. 2 multiples)

SPEED LIMIT > 40 mfle/h

3-arm (2) 4-arm (4)

5-arm (1) double (1)

Number • of sites

21

26

31

25

61

87

10

NO. OF ACCIDENTS

Before After

24 14

36 18

58 15

55 29

129 44

165 62

k ( ) sig level

o f k

.65

.61

(10%)

(10%)

.45 (1%)

.68 (10%)

.52 (0.1%)

Significant difference

between sites (×2)

No

No

9 .23

7 .41

16 .38

No

Yes

Yes

13

50

.54 (0.1%)

18

Yes (0.1%)

(i0%)

(5%) 54

Yes

Yes

5

20

23

25

5

22

27

5

31

35

40 73

1.88 (5%)

1.86 (5%)

3.00 (0.1%)

12 32 L53 (1%)

No

No

No

No

7

4.5 Type of road user involved in accidents

TABLE 3

Changes in the proportions of pedestrians, motorcycles and pedal cycles involved in accidents

after conversion to mini-roundabouts - 30/40 mile/h speed limit areas

TYPE OF CONTROL BEFORE

A: PRIORITY

B: TRAFFIC SIGNALS

C: OLD STYLE ROUNDABOUTS

PERCENTAGE OF ACCIDENTS INVOLVING:

Pedestrians

Before After

25 21

23 18

23 21

2-wheeled Motor vehicles

Pedal cycles

Before After Before After

23 16" 13 15

12 14 6 6

21 26 23 12"

* Change statistically significant at the 5 per cent level (no other change sig. at 10% level or better).

The percentages of accidents involving pedestrians, pedal cyclists, and motor cyclists before and after

conversion are shown in Table 3. With two exceptions, compared with all other types of accident involvement,

the observed differences are not statistically significant at the 10 per cent level or better for any of these

particular road users. That is to say that the effects of the conversion on these road users cannot be regarded

as being different from those indicated for all road users in Tables 1 and 2. One exception was for sites

with priority control 'before' where motor cyclist involvement fell on average from 23 to 16 per cent, so

that these riders gained greater-than-average benefit. The other exception was for the conversion from old

style roundabouts, where pedal cycle involvement in relation to other road users was almost halved, leaving

their risk almost the same as before conversion.

5. CONCLUSIONS

The provision of mini or small island roundabouts at the sample of junctions in built-up areas studied here

has been beneficial, in general, so far as accidents are concerned, except where kerbed minis and small

islands have replaced old-style roundabouts when there was a significant increase of about 90 per cent.

This latter result emphasises the need for care in the conversion of old-style roundabouts, and current design

recommendations (H2/75) specify criteria for achieving adequate deflection of crossing movements.

(Deflection is particularly important at 4-way junctions where crossing movements predominate and where

normal road alignment often makes adequate deflection difficult to achieve with small central islands.)

It is fair to say that many of the converted roundabouts in the present study represent early designs, some

probably with inadequate deflection (compare for example, the inscribed circle diameters and central

island sizes for the relevant roundabouts in Table 4). The effect on accidents of the more recent design

requirements is being monitored. Additionally, it should be pointed out that old-style roundabouts are

generally converted to increase junction capacity; the present study has not been directly concemed with

assessing how the resulting accident rates compare with those arising from other means (eg traffic signals)

of achieving a corresponding increase in capacity.

8

The greatest improvements appear to be gained by the sample of junctions, now with kerbed or un-

kerbed islands, with simple priority control before, although here there were significant differences in

behaviour between sites. This was also the case for the traffic signal controlled junctions which, due to the

combination of this and possibly the sparseness of the data, only yielded statistically significant reductions

in fatal and serious accidents.

Results of a small sample of (A) and (C) type sites, where the junctions had speed limits of over

40 mile/h on one or more arms, endorsed the f'mdings for these in the built-up areas.

For all types of island, with more data collected from many more sites, it should be possible to

consider the effects of different features, good and bad, at least in the first instance for the old major/minor

sites. Eventually criteria could be established for the best modifications at each site to ensure traffic safety.

6. ACKNOWLEDGEMENTS

The work described in this report was carried out in the Accident Investigation Division (Head: Miss B E

Sabey) of the Safety Department of TRRL. The author is grateful to Mr A R MeUors and to all the local

authorities who supplied the data for this report.

7. REFERENCES

. TRANSPORT AND ROAD RESEARCH LABORATORY. Accidents at offside priority roundabouts.

TRRL Leaflet LF393, Issue 2, Crowthorne, 1975. (Transport and Road Research Laboratory).

2. TANNER, J C. A problem in the combination of accident frequencies. Biometrika, 1958, 45 (3/4).

9

TABLE 4 Site data

(Extra site numbers in brackets)

No: in CSS

Report

1

2

17

18

19

23

26

27

41

57

62

63

67

100

(2)

(11.) (12) (13) (36) (37) (49)

105

(3)

(43) (46)

(50)

5

12

10

Location Grid Re/.

SITES WITH PREVIOUS PRIORITY CONTROL

Sites now with kerbless mini-roundabouts

3-arm/unctions

Dunstable, Beds. B489/B4541

Luton, Beds. A505

Chelmsford, Essex. A414/A1016

Chelmsford, Essex. A1099/A1113

Chelmsford, Essex. B1007/Longstomps Ave.

Maldon, Essex. A414/B1018

Wickford, Essex. A129/A132

Wickford, Essex. A129/A132

Ware, Herts. A10/A119

Ealing, Middx. Argyle Rd/Ruislip Rd East.

Hillingdon, Middx. B466/B472

Hillingdon, Middx. B466/Field End Rd.

North Walsham, Norfolk. B 1150/Kings Arms St.

Highbridge, Somerset A38T/B3139

Windsor, Berks. Winkfield Rd B3022/Clewer

Hill Rd.

Chesham, Bucks. A416/B485

Hastings, Sussex. A21/A2101

Leighton-Linsdale, Beds. A418/B4032

Amersham, Bucks. A413/A355

Amersham, Bucks. A404/A404 (Spur)

Castleford, Yorks. A656/A655

4-arm junctions

Dorking, Surrey A25/West St/Vincent Lane

Hillingdon, Middx. Pield Heath Rd/Royal

Lane (Unclass:)

Salford, Lancs. Camp St/Frederick Rd (B6168)

Paignton, Devon. Dartmouth Rd/The Riviera

A379/B3201

Normanton, Yorks. A655/B6133

Sites now with small or kerbed mini-

roundabouts

3 ,arm/unct ions

Marlow, Bucks. A404/A4155

Poole, Dorset. A35/Upton Rd/Creekmore lane

TL

TL

TL

TL

TL

TL

TL

TL

TL

TQ

TQ TQ

TG

ST

SU

SP

TQ SP

SU

SU

SE

TQ

TQ

SX

SE

SU

SZ

007214

094214

701072

714070

702048

850070

747936

746933

362132

161824

106887

106886

282300

319472

953755

962013

801116

913251

961972

975980

430258

162494

067821

889602

386227

848866

003931

Date Island Installed Diameter

metres

16.05.70

13.03.71

22.11.70 -

14.06.71 -

04.72

26.04.72

14.06.71 -

14.06.71 -

05.71

15.09.70 -

6.07.70

6.07.70

11.71

28.03.72

05.72

10.72 -

12.72

06.73

09.72

06.72

2.74

02.72

07.72

05.72

04.72

06.74

10.69 3.0

04.72 4.0

Inscribed Circle metres

3O

22

24 16

28

14

20

22

21

2O

14.5

21

21

18

21

24.5

18

20

16

19

20

30 x 25

2 7 x 1 7

25

38

T A B L E 4

Site data (Continued)


No: in CSS

16

29

30

34

35

36

43

47

53

59

65

72

73

75

77

78

82

83

93

98

99

101

114

(6) (7)

(14)

(15) (16)

Location

Blackmore, Essex. Blackmore Rd/Nine Ashes Rd

(Unclass:)

Filton, Glos. B4056. Southmead Rd/Golf

Course Lane

N. Warnborough, Hants. A32 Priors Corner

Bishops Stortford, Hefts. A120/B1004

Bishops Stortford. AI20 The Causeway/

Bridge St

Broxbour_ne, Herts. A10/Bell Lane

Welwyn G.C., Herts. A6129/B190

Manchester. A34/B5093

Bexley, Kent. North Cray Rd A223/

Vicarage Road (B2210)

Harrow, Middx. A410/A4090

Pontllanfraith, Mon. A472/A4048

Newcastle, North 'I'd A696 Ponteland Rd/

Fensham Hall Drive

Newcastle North 'i'd A6125/B6439

Newcastle North 'I'd A696/B6336

Newcastle North 'I'd Westmorland Rd/

George St (B 1600)

Newcastle North 'I'd A193/B1311 Shields Rd/

Byker Bank

Newcastle North 'I'd A193/A187 Shields Rd/

Fossway

Newcastle North 'I'd B 1600 Portland Rd/

TL

SO

SU

TL

TL

TL

TL

SJ

TQ

TQ

ST

NZ

NZ

NZ

NZ

NZ

NZ

Warwick St.

Newcastle, North 'I'd. A696 Barrack Rd/

Strawberry Place

Bristol, Somerset. A38

Bristol, Somerset. Fishponds Rd A432

Ilchester, Somerset A303T/A37

Todmorden, Yorks. A646/A6033

Kippax, Yorks B6137/C284

Newcastle, North 'I'd. A186 Walker Rd/

Allendale

Sunderland A690 Durham Rd/North Moor Lane

Longrock, Cornwall. A30/A394

Bristol, Somerset. Sussex Place B4052/ Ashley Rd B4051

NZ

NZ

ST

ST

ST

SD

SE

NZ

SW

ST

Grid Ref.

603019

359179

731514

548221

548221

367067

523211

865939

497733

123908

177956

231657

252639

243644

240639

266647

273650

258650

243645

571709

614751

524233

936241

416302

278637

501313

598743


metres

9.12.71 7.3

5.02.71 1.4

8.01.72 6.0

06.72 3.5

06.72 3.5

01.71 4.6

01.72 12.5

10.08.69 3.0

14.11.71 3.0

19.04.70 4.6

15.09.71 6.1

05.69 8.5

10.69 9.0

31.08.70 3.5

11.70 5.0

25.01.71 3.5

15.06.71 4.0

23.06.71 3.5

23.05.72 3.5

16.08.70 3.6

09.71 2.0

21.05.71 4.3

03.72 3.6

07.72 2.2

12.07.72

9.72 20

1.73 8

4.73 1.5


22

23

34

25

25

30

29

28

21

28

28

20.5

30

21

23

18

26

25

23

26

26

40

24

19

50

24

18 11

TABLE 4 Site data (Continued)


No: in CSS

Report

(34)

6

24

31

32

48

52

54

55

61

71

74

79

80

81

87

88

89

91

92

103

108

(17)

(18) (44)

(53)

(54)

60

86

12

Location

Wellingborough, Northants. Westfield Rd A5128

Northampton Rd A45

4-arm junctions

Cheadle Hulme, Cheshire A5149

Nazeing, Essex. Nazeing Rd/Middle St (Unclass:)

Portsmouth, Hants A288

Portsmouth, Hants A3019

Manchester B 5167/B5093

Bamet, Herts. Hampden Way/Osidge La. B1453

Brent, Middx. Preston Rd/Woodstock Hill

(Unclass)

Bromley, Kent. Plaistow La/Orchard Rd

(Unclass:)

Hillingdon, Middx. Rickmansworth Rd/

Breakspear Rd (Unclass:)

Newcastle, North 'l'd B1307/B 1309

Newcastle, North 'I'd. B6326

Newcastle, North 'I'd. B6325/B6328

Newcastle, North 'l'd. B 1313 Welbeck, Allendale

Newcastle North ' l 'd A695/A1881

Newcastle. North 'l'd A188

Newcastle. North 'I'd A188

Newcastle. North 'I'd A187

Newcastle North ' l 'd B6332

Newcastle. North 'I'd A186/B 1313

Ipswich, Suffolk A 1071

Winterbourne, Wilts. A338

Hitchin, Herts. A505/Stotfold Rd

Pool, Redruth, Cornwall A30

Stockport, Cheshire. Lower Hillgate/

Wellington St

Windsor, Berks. A308 Maidenhead Rd/

Parsonage Lane

Hertford. A414/A119

5-arm junctions

Harrow, Middx. A312/B457

Newcastle, North 'l'd B1313

SP

SJ

TL

SZ

SU

SJ

TQ

TO

TQ

TQ NZ

NZ

NZ

NZ

NZ

NZ

NZ

NZ

NZ

NZ

TM

SU

TL

SW

Grid Re/'.

SU

TL

TQ NZ

Date Installed

882675 3.74

879861 11.70

408050 25.04.72

636990 04.71

638004 20.07.70

849929 14.02.71

286942 8.04.70

183878 2.04.71

411698 11,71

052906 2.07.69

256653 05.69

214653 01.70

200651 28.02.71

276644 4.06.71

273652 14.06.71

270669 15.12.71

2760672 17.12.71

274650 27.01.72

238637 7.03.72

295649 26.03.72

182452 03.71

178356 31.07.70

204305 07.72

669415 06.73

11.72

954769 11.73

329126 3.73

147869 30.01.72

283645 24.10.71

Island Inscribed Diameter Circle

metres metres

3.0 22

8.9 26

3.0 33

3.0 26

3.0 25

6 28

4.0 27

6 25

4.0 26

5.0 25

6.0 24

7.5 30

5.5 31

6.5 26

5.0 27

5.0 25

4.O 3O

6.5 30

2.5 27

3.0 22

4.0 32

4 20

4 23

3 23

4.5 21

3.0 30

7.0 33

No: in CSS

Report

4

44

(55)

25

102

45

46

(10)

(40)

69

85

15

8

11

42

90

13

112



Location Grid Ref.

Sites now with double, split mini-roundabouts

or ring systems

4-arm junctions

Farnham Royal, Bucks. A355/B416 SU

Welwyn G.C., Herts. B195 TL

Exeter, Devon. A377 Bonhay Rd/St David's Hill SX

SITES PREVIOUSLY CONTROLLED BY

TRAFFIC SIGNALS

Sites now with kerbless mini-roundabouts

3-arm junctions

S. Benfieet, Essex. BlO06/B1014

Ilchester, Somerset A303T/A37

Sites now with small roundabout

3-arm junctions

Peterborough, Hunts. AI5/A605 TL 192979

Tunbridge W, Kent. A26/A267 TQ 582388

Newcastle, North'l'd. A1. Park Terrace NZ 249655

Amersham, Bucks. A413/A416 SU 963972

4-arm junctions

Longbenton, North'l'd. A188/A191 NZ 271683

Newcastle, North'l'd. A1/A189 NZ 247669

5-arm junctions

Gateshead, Durham. A6083/A6082 NZ 274627

Sites now double, split mini- or small

roundabouts or ring systems

4-arm junctions

Truro, Cornwall. A39/A390 SW 822439

Upton, Dorset. A35/A350 SY 981932

Welwyn G.C. Herts. A1000/B195 TL 739122

Newcastle, North'l'd. A696/A6125 NZ 246645

SITES PREVIOUSLY OLD STYLE ROUNDABOUTS

Sites now with small roundabout

3-arm junctions

Poole, Dorset. A348/A3049 SZ

Pontefract, Yorks. A645/A639 SE

960830

524212

913934

TL 779860

ST 522227

038937

453215

Date Installed

29.02.72

1.06.72

04.73

19.05.70

26.05.71

10.68

1 7 . 0 5 . 7 1

17.12.72

10.72

24.03.70

17.10.71

07.71

12.05.71

22.06.70

06.71

8.02.72

26.05.72

5.01.72

Island Inscribed Diameter Circle

metres metres

3.8 + 2.0

2 x 3.0 18 + 35

2 x 2.0 45 + 28

- 17

- 19

3.0 19

1.5 28.5

6.5 25

4 24

2.5 24

9.0 35

2.0 22

13.7 27

2xZerc 45+27

15.0 31"

2 x 3.5 46 + 29

4.0 38

9.5 33.5

13

No: in CSS

Report

113

(1)

(9)

14

50 66

76

104

106

107

(5) (8)

(19)

(20)

(32)

03) (35)

(41) (45)

(47)

(48)

(51)

(52)

7

(21)

(22)



Location

Skipton, Yorks. A65/A59

Sutton-In-Ashfield, Notts. Portland Square B6022

Teeside. A1085/Longlands A172

4-arm junctions

Blaydon, Durham. A694/A608 Syston, Leics. A607

Kings Lynn, Norfolk. A47/A148

Newcastle, North'l'd. A186

Ipswich, Suffolk. A12T/A 1071

Guildford, Surrey. A3/A320

Halesowen, Worcs. A458/A4034

Teeside. A1027/Oxbridge Lane

Teeside. A 1027/Durham Road

Brighton, Sussex. Aquarium Roundabout A23/A259

Letchworth, Herts. Norton Way S/Birds Hill/

Station Road

Teeside. Ormesby Village A171/Cargo Fleet Lane

Leicester. Chapel Lane/Welford Rd. A50

Derby. A5111 Queensway/Broadway/ Kedleston Rd.

Newbury, Berks. A34/A343

Stoke-on-Trent, Staffs. Joiners Square A50/A52

Sunderland, Durham A19/B1405 Ryhope Rd. Queen Alexandra Rd.

Sunderland, Durham. Chester Rd A183/ Springwell Rd.

Leeds. A62/A6110 Gelderd Road Leeds. A63/A64

5-arm junctions

Runcorn, Cheshire. A533

Sheffield, Yorks. Brook Hill/Bolsover St.(A)

Bedford, Beds. Prebend St/Midland Rd (A)

Grid ReL

SD 989516

SK 496589 NZ 503193

NZ 198624

SK 462311

TF 562319

NZ 294657

TM 150446

TQ 998508

SO 982848

NZ 430186

NZ 433206

TQ 314039

TL 221328

NZ 532175

SK 596014

SK 338376

SU 470665

SJ 883474

NZ 406547

NZ 366557

SE 275313

SE 361356

SJ 351382

SK 344873

TL 044496


metres

03.70 4.9

10.71 2.5

05.71 3.0

22.09.71 6.0 22.05.72 3.0

04.71 3.0

15.09.70 12.0

04.72 12.0

10.71 18.0

03.72 6.5

24.03.72 12

22.06.72 18

07.72 7.5

06.71 9

12.72 14 05.08.73

04.72-12.73 07.08.71

02.72 3

05.72 12.5

04.74

02.74

02.73

04.72 12 + 14

10.72 17.5

6.72 3


25

25

34

42

42

40

58

36

55 x45

60

49

30

42

40 + 30

40

60 + 80

75

26

14



No: in CSS

Report

21

(39)

(56)

Location

Site now double, split mini- or small

roundabout or ring system

4-arm junctions

Colchester, Essex. A12T/A134

Colchester, Essex. St. Andrews Ave. A137/

Harwich Rd. A133

Swindon, Wilts. County island ?oundabout

A420/A345

Grid Ref.

TL 992260

TM 012255

SU 159849

Date Installed

6.72

12.72

9.72

Island Diameter

metres

4 x zero

2 x 2


63

50 + 37

15

0 Gh

X X 0 0 ~ 0-1

I ' ~ Ox C~

Z o

lm

o

A

e-, . ~ 0 .~ ~ oa

I-- '~

" 0

c- O

¢.)

0 ' . 0 o o

O l 0 0

O l Oh

Z m

o o ~ ~ ~-

o ~ ~, ~ ,o ~ o < ;~

TABLE 5 Accident data tor each site

No: in C.S.S.

Report

1.

.

17.

18.

19.

23.

26.

27.

41.

57.

62.

63.

67.

100.

(2)

(11)

(12)

Inclusive Dates

1. After 2. Before

Injury Accidents 1. After 2. Before

Injury Accidents in GB on A or B roads with

30/40 mile/h Speed Limit Ratio. After : Before

A. SITES WITH PREVIOUS PRIORITY CONTROL Sites now with kerbless mini-roundabouts

3-arm junctions

6 . 7 0 - - 4.75 1 .67- - 1.70

4 . 7 1 - 1.75 1.68 - 10.70

1 2 . 7 0 - 12.74 12.67 - 10.70

7.71 - 12.74 1 . 6 8 - 5.71

5 . 7 2 - 12.74 1 . 6 8 - 3.72

5 . 7 2 - 12.74 1 . 6 7 - 3.72

7.71 - 12.74 1 . 6 8 - 5.71

7.71 - 12.74 1 . 6 8 - 5.71

6.71 - 12.74 1 0 . 6 9 - 3.71

1 0 . 7 0 - 3.74 1 . 6 7 - 8.70

1 0 . 7 2 - 9.73 1 . 6 9 - 6.70

1 0 . 7 2 - 9.73 1 . 6 9 - 6.70

1 2 . 7 1 - 4.75 1 . 6 7 - 10.71

4 . 7 2 - 12.74 1 . 6 7 - 2.72

6.72 - 12.74 1 . 6 9 - 4.72

5 3 1.49

4 1.31

9

14 1.36 23

5 6 .99

1 .60 5

2 .48

0

3 4 .99

2 8 .99

4 2.26 1

5 9 .92

1 .66 2

1 .66 2

1 2 .64

3 4 .50

2 .74 2

4 .37

9

4 1.05

4

Fatal & Serious Accidents 1. After 2. Before

0 1

2 2

4 6

1 0

0 1

0 0

2 0

0 1

0 1

1 1 . 7 2 - 1.75 1 . 6 7 - 9.72

1 . 7 3 - 1.75 1.71 - 11.72

0 0

Fatal and Serious Accidents in GB at junct ions on A or B

roads with 30/40 mile/h Speed Limit Ratio. After : Before

1.43

1.24

1 .30

.94

.57

.94

.94

2.13

.90

.64

.61

.47

.71

.35

1.01

17

T A B L E 5

Accident data for each site (Continued)

No: in C.S.S.

Report

(13)

(36)

(37)

(49)

105.

(3)

(43)

(46)

(5o)

5.

12.

16.

29.

30.

34.

35.

36.

Inclusive Dates

1. After 2. Before

7.73 - 1.75 1 . 6 7 - 5.73

1 0 . 7 2 - 1.75 1 . 7 0 - 8.72

7 . 7 2 - 1.75 1 . 7 0 - 5.72

3 . 7 4 - 5.75 8 . 7 2 - 1.74

4-arm junctions

3.72 - 1.75 1 .67 - 7 . 7 1

8 . 7 2 - 9.73 1 . 6 9 - 6.72

1 . 7 3 - 12.74 1 . 7 0 - 12.71

5 . 7 2 - 1 2 . 7 4 1 . 6 9 - 3.72

7 . 7 4 - 5.75 6 . 7 2 - 5.74


1 11

2 10

4 16

5 10



.23

.85

1 .03

.76

.60

.32

.94

.79

Sites now with 3oarm junctions

1 1 . 6 9 - 3.73 1 0 . 6 6 - 8.69

5 . 7 2 - 3.73 1 . 7 0 - 1.72

1 . 7 2 - 9.73 1 . 6 8 - 11 .71

3.71 - 3.73 1 . 6 8 - 1.71

2 . 7 2 - 1.73 1 . 6 7 - 8.71

7 . 7 2 - 3.73 1 . 6 9 - 2.72

7 . 7 2 - 3.73 1 . 6 9 - 2.72

2 . 7 1 - 1.73 1 0 . 6 8 - 9.70

1 0

.44

kerbed mini or small roundabout

4 1.12 11

0 .43

1

0 0

2 .65 2

0 4 .21

1 7 .23

2 14 .23

4 2 .98


1 0

0 0 ¸

0 2

2 5

0 0

1 0



.22

.81

.97

.57

.32

.91

.74

1.10

.41

.20

.22

.22

.95

1 8

TABLE 5 Accident data for each site (Continued)

No: in C.S.S. Report

43.

47.

53.

59.

65.

72.

73.

75.

77.

78.

82.

83.

93.

98.

99.

101.

114.

(6)

(7)

Inclusive Dates

1. After 2. Before

2.72 -- 12.72 1.65 - 10.71

9 . 6 9 - 4.73 1 . 6 6 - 6.69

1 2 . 7 1 - 4.74 1 . 6 7 - 9.71

4 . 7 0 - 9.73 1 . 6 7 - 3.70

1 0 . 7 1 - 2.73 1 . 7 0 - 7.70

1 . 7 0 - 6.72 1 . 6 7 - 4.69

11.69 - 10.73 1 . 6 7 - 9.69

9 . 7 0 - 10.73 1 . 6 7 - 7.70

1 2 . 7 0 - 10.73 1.67 - 10.70

2.71 - 10.73 1.67 -- 12.70

7.71 - 10.73 1 . 6 7 - 4.71

7.71 - 10.73 1 . 6 7 - 4.71

6 . 7 2 - 10.73 1 . 6 7 - 4.72

9 . 7 0 - 10.73 1 . 6 8 - 7.70

10.71 - 10.73 1 . 6 9 - 8.71

6 . 7 1 - 3.73 1 . 6 7 - 3.71

4 . 7 2 - 3.73 1 . 6 7 - 12.68

8.72 - 11.73 1 . 6 7 - 6.72

8.12 - 10.73 1 . 6 7 - 6.72


1 22

8 3

1 16

1 0

7 11

0 0

5 16

4 16

10 14

2 10



.13

.99

.49

1.04

2.52

1.04

1.42

.86

.65

.52

.52

.26

1.22

.78

.42

.23

1 10

.22

Fatal & Serious Accidents 1. After~ 2. Before

0 2

1 0

2 3

4 5

0 3

0 0


roads with 30[40 mile/h Speed Hmit Ratio. After : Before

.12

.97

1.00

.84

.62

.5O

.50

.24

1.18

.75

.40

.23

.21

1 9


No: in C.S.S.

Report

(14)

(15)

(16)

(34)

.

24.

31.

32.

48.

52.

54.

55.

61.

71.

74.

79.

80.

81.

Inclusive Dates

1. After 2. Before

10.72 - 12.74 1.68 - 11~71

2 . 7 3 - 1.75 2.71 - 12.12

5 . 7 3 - 3.74 1 . 7 0 - 3.73

4 . 7 4 - 3.75 1.71 - 2 .74




.56

1.00

.27

Sites now with kerbed 4-arm junctions

1 2 . 7 0 - 3.73 1 . 6 8 - 10.70

4.72 - 12.74 1 . 6 8 - 3.72

4.71 - 12.74 1.67 - 10.70

8.70 - 12.74 1 . 6 7 - 3.70

3 . 7 1 - 1.75 1 . 6 7 - 1.71

5 . 7 0 - 12.73 1 . 6 7 - 12.69

5 . 7 1 - 3.73 1 . 6 7 - 2.71

1 2 . 7 1 - 6.74 1 . 6 9 - 8.71

7 . 6 9 - 9.73 1 . 6 7 - 5.69

7.69 - 12.74 1 . 6 7 - 4.69

2.70 - 12.74 1 . 6 7 - 12.69

3.71 - 12.74 1 . 6 7 - 1.71

7.71 - 12.74 1 . 6 7 - 4.71

7.71 - 12.74 1 . 6 7 - 4.71

.30

6 12

8 21

15 22

12 2 4

6 12

5 14

9 10

6 4

14 3

12 5

7 22

mini or small roundabout

1 8 .81

0 4 .62

.93

1.30

.90

1.18

.44

.93

1.71

2.27

1.56

.88

.77

.77

Fatal & Serious Accidents • 1. After 2. Before

0 0

0 0

0 1

0 2

0 I

0 1

0 1

0 1

Fatal and Serious Accidents in GB at junctions on A or B


.52

.28

.79

.59

.88

1.25

.86

1.14

.43

.90

1.64

2.15

1.49

.84

.73

.73

"20


No: in C.S.S.

Report

87.

88.

89.

91.

92.

103.

108.

(17)

(18)

(44)

(53)

(54)

60.

86.

4 .

44.

(55)

Inclusive Dates

1. After 2. Before

1 . 7 2 - 12.74 1 .67- - 11.71

1 . 7 2 - 12.74 1 . 6 7 - 11.71

2 . 7 2 - 12.74 1 . 6 7 - 12.71

4.72 - 12.74 1 . 6 7 - 2.72

4 . 7 2 - 12.74 1 . 6 7 - 2.72

4 . 7 1 - 2.75 1 . 6 9 - - 2 . 7 1

8.70 - 12.74 1 . 6 7 - 5.70

8 . 7 2 - 2.74 1 . 6 7 - 6.72

7 . 7 3 - 1.75 2.71 - 3.73

1 2 . 7 2 - 12.74 1.71 - 10.72

1 2 . 7 3 - 5175 1 1 . 7 0 - 10.73

4 . 7 3 - 6.75 1 . 7 0 - 2.73

5-arm junctions

2 . 7 2 - 9.73 1 . 6 7 - 12.71

11.71 - 10.73 1 . 6 7 - 9 . 7 1


13 15

4 10

2 18

5 13

1 2

Injury Accidents in GB on ~A or B roads with


.58

.58

.55

.50

.50

1 . 7 3

1 . 2 4

.28

.71

1.12

.46

.64

.32


0 4

1 4

0 1

Sites 4-arm junctions

3 . 7 2 - 1.75 1 1 . 6 8 - 10.71

7.72 - 12.74 1.65 - 10.71

5 . 7 3 - 6.75 1 . 6 9 - 3.73

5 20

.41

now with double split mini-roundabouts or ring systems

3 .93 15

1 .33 12

1 .48 3

0 6



.55

.55

.52

.48

.47

1 . 6 4

.26

.69

.45

.61

.30

.39

.88

.31

2 1

25.

102.

45.

46.

(10)

(40)

69.

85.

15. 10.71 - 12.74

.

11.

42.

90.

13.

2 2


No: in C.S.S.

Report

Inclusive Injury Injury Accidents in GB i Fatal & Dates Accidents on A or B roads with

1. After 1. After 30/40 mile/h Speed Limit 2. Before 2. Before Ratio. After : Before

I

B. SITES PREVIOUSLY WITH TRAFFIC SIGNALS Sites now with kerbless mini-roundabout 3-arm ]unctions !

6.70 - 12.74 6 1.67 - 4.70 4 i 1.31 1

6.71 - 12.74 1 £ 1 . 6 7 - 3.71 14 .80 2

Sites now with kerbed mini- or small roundabout 3-arm junctions

1 0 . 6 8 - 12.74 13 C 1.67 - 9.68 11 3.41 4

6.71 - 12.74 7 C 1 . 6 7 - 4.71 6 .79 3

1.73 - 10.73 1 (3 1 . 6 7 - 11.72 28 .13 3

1 1 . 7 2 - 1 .75 4 1 . 7 0 - 9.72 5 .80

4-arm ]unctions i

4 . 7 0 - 12.74 13 2 1 . 6 7 - 2.70 16 1.43 2

11.71 - 12.74 26 5 1 . 6 7 - 9.71 32 .64 4

5-arm ]unctions 6 i

7.68 - 7.71 13 1.02

Sites now with double, split mini-roundabouts or ring systems 4-arm ]unctions

6 . 7 1 - 1.75 6 0 6 . 6 9 - 4.71 26 1.83 5

7 . 7 0 - 2.75 3 1 1 . 6 7 - 12.69 10 1.48 4

7.71 - 12.74 18 3 1.65 - 10.70 50 .54 : 14

3.72 - 10.73 23 3 1 . 6 7 - 1.72 42 .32 9

Serious Accidents 1. After 2. Before

0 0

C. SITES PREVIOUSLY WITH OLD STYLE ROUNDABOUT Sites now with a small roundabout 3-arm ]unctions ]

6 . 7 2 - 2.75 11 , ~, 1 . 7 0 - 12.71 5 l.~J

Fatal and Serious Accidents in GB at junctions on A or B


1.26

.76

3.34

.75

12

1.37

.61

.97

1.75

1.41

.52

.29

1.24


No: in C.S.S.

Report

112.

113.

(1)

(9)

14.

50.

66.

76.

104.

106.

107.

(5)

(8)

(19)

( 2 0 )

(33)

(32)

(35)

Inclusive Dates

1. After 2. Before

1.72 - 1 1 . 7 3 1.67 - 10.71

4 . 7 0 - 12.73 1 . 6 7 - 2.70

11.71 - 12.74 1 .70 - 9 .71

6.71 - 12.74 1 . 7 0 - 4.71

4-arm junctions

10.71 - 12.74 1 . 6 7 - 2.71

6.72 - 12.74 1.69 -: 4.72

5.71 - 12.74 1.68 - 2 .71

1 0 . 7 0 - 12.74 1 . 6 7 - 8.70

4 . 7 2 - - 6.75 1.69 - 9 .71

1 1 . 7 1 - 1.75 1 . 6 7 - 3.71

4 . 7 2 - 1.73 1.67 -- 10 .71

4 . 7 2 - 12.74 1 . 7 0 - 2.72

7 . 7 2 - 12.74 1 . 7 0 - 12.71

8 . 7 2 - 1.75 1 . 6 8 - 3.72

7.71 -- 12.74 1 . 6 8 - 2.71

2 . 7 4 - 4.75 1 . 7 0 - 4.73

1.73 - 12.74 1.71 - 1 1 . 7 2

1 . 7 4 - 4.75 1 . 6 8 - 3.72


5 15

8 6

4 4

7 2

7 4

12 5

39 24

16 13

10 7



.38

1.15

1.77

2.61

.74

.75

1.11

1.12

1.13

.73

.17

1.22

1.21

.56

1.06

.34

1.01

12 7

.28


0 1

6 2

0 0

6 3

0 2

0 0

1 0

Fatal and Serious Accidents in GB at junc t ions on A or B


.36

1.10

1 .72

2.48

.70

.70

1.05

1 .06

.69

.16

1.14

.53

1 .00

.26

2 3

T A B L E 5


(41)

(45)

(47)

(48)

(51)

(52)

7.

(21)

(22)

21.

(39)

(56)

No: in C.S.S. Report

37.

38.

39.

24

Inclusive Dates

1. After 2. Before

9 . 7 1 - 8.74 7.69 - 6.71

3 . 7 2 - 12.75 1 . 6 9 - 12.71


6.72 -- 5.69 --

5.74 - 4.71 --

3 . 7 4 - 6 . 7 2 --

3.73 - 1 .72 -

23 8

4.75 2 4.72 9

4.75 5 3.74 5

5.75 5 1 . 7 4 7

5.75 13 1 . 7 3 8

16 9

9 17

6 17


30/40 mile/h Speed l i m i t Ratio. After : Before

1 .43

1 . 2 2

.92

.31

.69

1 .95

.58

.34


5-arm junctions

4 . 7 2 - - 2.75 1 .67 - 9 . 7 1

1 1 . 7 2 - 3.75 1 .66 - - 8.72

7 . 7 2 - 4.75 1 . 6 7 - 4.72

Sites now double 4~arm junctions

8 . 7 2 - 12.74 1 . 6 8 - 4.72

1.73 - 12.74 1 . 7 0 - - 1 1 . 7 2

43 26

.50

split mini-roundabouts or ring systems

.55

13 7 .66

.78

0 0

2 2

1 2

1 0 . 7 2 - 2.75 9 . 6 9 - 8.72

• 20 32

Injury Accidents in GB on A roads with

Speed l i m i t s > 40 mile/h Ratio After : Before

Inclusive Dates

1. After 2. Before


D. SITES IN AREAS WITH SPEED LIMITS > 40mph Sites with major/minor priority control before

0 1

26 8

6 . 7 2 - 12.74 1 . 6 9 - 4.72

9.71 - 1.73 1 . 6 7 - 6 . 7 1

12 5

Fatal and Serious Accidents i in GB at junctions on A or B :oads with 30/40 mile/h Speel Limit Ratio. After : Before

1.13

.86

.30

9 . 6 9 - 12.74 1 . 6 7 - 7.69

13 13 .77

0 3 .32

11 22 2.04


2 9

0 2

1 11

.67

1 .86

.54

.31

.46

.54

.65

1 .94

.31

.75

Fatal and Serious Accidents i n GB at junct ions on A roads with Speed Limits> 40 mile/h

Ratio After : Before

TABLE 5


40.

84.

109.

(23)

(24)

(25)

(26)

(4)

20.

33.

110.

(27)

(28)

(29)

(30)

(31)

Inclusive Dates

1. After 2. Before

6.71 - 12.74 1.67 - 11.70

10.71 - 12.74 1 . 6 7 - 8.71

9 . 7 2 - 5.75 1 . 6 7 - 7.72

10 .72 - 1.75 2 . 7 1 - 8.72

10 .72 - 12.74 1 . 6 7 - 8.72

3 . 7 3 - 1.75 1 . 6 7 - 12.72

8 . 7 1 - 5.75 1 . 6 7 - 6.71


6

25

Injury Accidents in GB on A roads with

Speed l imi ts> 40 mile/h Ratio After : Before

.89

.68

.46

1 . 4 5

.39

.30 0

22

Sites with traffic signals before

4"72-12"74 I 9 I 1 . 6 8 - 2.72 32

Sites previously old style roundabouts

7 . 7 1 - 12.74 15 1 . 6 8 -

4 . 7 0 -

1 . 6 7 -

3 . 7 1 -

1 . 6 7 -

12.72 -

1 . 6 9 - -

8.71 - 6.68 -

5 . 7 2 -

1 . 7 0 -

5.72 -

1 . 7 0 -

4.71 17

12.74 23 12.69 6

5.75 14 1.71 2

5.75 15 3.72 13

2.74 6 6.71 8

12.74 17 12.71 4

12.74 22 12.71 5

12.74 2 1 . 7 3 2

.81

.65

1 . 0 5

1.55

.98

.72

.85

1 . 3 0

1 . 3 0


0

12

10 3

5 0

2

0

4.73 -

1 . 7 0 - - .53 1

0

Fatal and Serious Accidents in GB at junctions on Aroads with Speed Limits > 40 mile/h

Ratio After : Before

.86

.65

1 . 3 9

.37

.28

.77

.63

1 . 0 2

1 . 4 9

.94

.69

.82

1 . 2 7

1 . 2 7

.52

2 5

r~

e n

I

I

c.~ Q;

" r " - ~ . - .

r - i . o

> r ' o O - -

E~oo_~

~ ~ ~ ' ~

¢¢J I,-

0

Z D 0 n-

u.i ..I >- I -

i . .cn

¢'~ i,t,, Z O D

Ilc_l

LM > 0 z ~ O ~

, _ LIL

/",'o,,',,

i"i/ " r

o

\ /,'l :- ~ /:/

:i,/l

0

Z

0

,-I >. I -

Z

0

,..,1 a .

X Ill

Il l

0

I W

0

° ~ IL

8. A P P E N D I X -

Extract f rom 'A Problem in the combinations of accident frequencies' (J C Tanner, Biometrika Vol. 45,

Dec 1958, pp 3 3 1 - 3 4 2 )

Let N = Number of sites from which data are to be combined

b i = Number of accidents in the before period at site i (i = 1,2 . . . . . . . N)

a i = ' . . . . . after . . . . i "

C i = Ratio of accidents after to before in the control area for site i (assumed free from error)

n i = a i + bi; then k i = ai/biC i measures the apparent effect of the change at the ith site.

k is the ratio of accidents after to the number that would have been expected if the change

had no effect. n i k i s the solution of the equation ~ 1 + k C i = ~ b i . . . . . . . (1)

The sampling variance of log k is approximately

Var l o g e k = (1 + 0 ) ( 1 + 2 )

ni

KC i n i

(1 + KCi)2

w h e r e 0 = ( N 2 1 - 1 ) N

( ~ ni )2

(a i - kb i Ci)2 X 2 =

k C i n i

. . . . . . . ( 2 )

and K is the true value o f k i

(i.e. the value k i would take

if b i and a i took their

expected values)

. . . . . . . ( 3 )

If ×2 is significant we may conclude that there are real differences in the effect between sites.

error S.E. (Logek) = ~var log e k~ ½ . . . . . . . (4) Standard

where K = k

Putting K = 1 in equation (2) t - l°ge k S'E' l°gek . . . . . . . (5)

If t is significant we conclude that the average effect of the measure at all the sites studied was to reduce

accident frequency if k is less than 1.

28

(1130) Dd443233 1,500 7/77 H P L t d S o ' t o n G1915 PR1NTED IN ENGLAND

ABSTRACT

Accidents at off-side priority roundabouts with mini or small islands: HILARY GREEN: Department of the Environment, Department of Transport, TRRL Laboratory Report 774: Crowthorne, 1977 (Transport and Road Research Laboratory). Injury accidents were studied at 150 junctions and roundabouts before and after the installation of single or multiple islands, kerbed or unkerbed. 132 of these, considered separately, were previously governed by 30 or 40 mile/h speed limits with (A) priority control, (B) traffic signals, or (C) roundabouts.

Type (A) 88 sites, had statistically significant reductions of 34 and 46 per cent in all injury and in fatal plus serious injury accidents respectively whether unkerbed sites were included or not.

Type (B) 13 sites, all types combined, showed a statistically significant decrease in fatal plus serious accidents of 62 per cent.

Type (C) 31 sites all kerbed. All types except single kerbed island sites with 3 arms showed a statistically significant increase of 91 per cent for all accidents and rather more for fatal plus serious especially when 2 multiple systems were included (200 per cent).

Accidents involving two-wheeled motor vehicles at type A sites, and those involving pedal cycles at type C sites, expressed as proportions of the total, were significantly reduced.

In higher speed limit zones the changes in all accidents at a few sites, type (A) - 10 sites and (C) - 8 sites, were statistically significant and gave indications endorsing the results above.

ISSN 0305-1293

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