ROAD RESEARCH LABORATORY

Ministry of Transport

RRL REPORT LR 118

EFFECT OF THE ADVISORY "GIVE W A Y " RULE

ATUXBRIDGE .CIR C U S ROUNDABOUT

by

C.R.. Faulkner

CROWTHORNE

ROAD RESEARCH LABORATORY

1967

CONTENTS

Abs t r ac t

1. In t roduc t ion

2. B e f o r e - a n d - a f t e r s tudies

2 .1 Capac i ty and p r e c e d e n c e

2 .2 J o u r n e y t i m e s

2.3 Gap a c c e p t a n c e , and a l t e rna t ing sequences of e n t e r i n g and c i r c u l a t i n g vehic les

3. Conc lus ions

4. Acknowledgemen t

5. R e f e r e n c e s

Page

I

i

2

2

6

9

10

11

11

(C) CROWN COPYRIGHT 1967 E x t r a c t s f r o m the text may be reproduced

p rov ided the sou rce is acknowledged

Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on I 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.

EFFECT

AT

OF THE A D V I S O R Y

UXBRIDGE CIRCUS

" G I V E - W A Y " RULE

R O U N D A B O U T

ABSTRACT

Traffic movements at Uxbridge Circus roundabout on Western Avenue (A40) were studied before and after the introduction in November 1966 of the advisory give-way rule for roundabouts.

As this roundabout was near several involved in the long 83-site experiment it was not surprising to find that drivers were mostly obeying the convention of right-hand priority before the announcement of the rule. No overall significant changes were found in capacity, precedence, or gap acceptance, or in the distribution of vehicles in peak period flow. There was no increase in the proportion (less than 10% of cars observed) which were delayed for 20 seconds or more after passing a point 50 yards before the roundabout.

There was evidence of a slight reduction o f approach speeds. There was also evidence that the formalisation of the priority rule tended to increase the difficulty on one part of theroundabout , where peak congestion was already being caused by a restricted exit road.

i . INTRODUCTION

The a d v i s o r y r i g h t - h a n d p r i o r i t y ru le fo r the e n t r a n c e s to r o u n d a b o u t s was in t roduced in N o v e m b e r , 1966 fo l lowing Road R e s e a r c h L a b o r a t o r y e x p e r i m e n t s which had t aken p lace at s e v e r a l s i t es d u r i n g the p r e v i o u s t e n y e a r s , and a l a r g e r sca le e x p e r i m e n t at 83 s e l e c t e d roundabou t s .

Studies of veh i c l e s e n t e r i n g and c r o s s i n g a r oundabou t on W e s t e r n A v e n u e (A40) w e r e a l r e a d y in p r o g r e s s a t th is t i m e in p r e p a r a t i o n f o r an e x p e r i m e n t on the use of l anes within roundabou ts . This p a r t i c u l a r r o u n d a b o u t though not i n v o l v e d in the 83-s i t e e x p e r i m e n t was v e r y c lose to s o m e of t h e m . M o s t d r i v e r s u s i n g th i s

r o u n d a b o u t b e f o r e N o v e m b e r 1966 a l r e a d y u s e d t he c o n v e n t i o n of r i g h t - h a n d p r i o r i t y p r e s u m a b l y a s a l a r g e p e r c e n t a g e of t h e s e d r i v e r s h a d e x p e r i e n c e wi th the n e a r b y r o u n d a b o u t s p r e v i o u s l y u n d e r t e s t w i th r i g h t - h a n d p r i o r i t y . T h e s e o b s e r v a t i o n s t h e r e f o r e p r o v i d e a l i t t l e f u r t h e r i n f o r m a t i o n on d r i v e r s ' b e h a v i o u r in r e s p o n s e to t he f o r m a l i s a t i o n of t h e a d v i s o r y r u l e and t he p a i n t i n g of t h e whi t e p r i o r i t y l i n e s on t h e e n t r a n c e s .

The r o u n d a b o u t s t u d i e d i s a t t he j u n c t i o n of A40 and B467 , and is known as U x b r i d g e C i r c u s . A p l a n of t h e s i t e i s g i v e n in F i g u r e 1. O b s e r v a t i o n s b e f o r e any c a r r i a g e w a y m a r k i n g s w e r e p r e s e n t , and b e f o r e the a n n o u n c e m e n t of the g i v e - w a y r u l e , w e r e m a d e b e t w e e n 9 / 8 / 6 6 and 2 1 / 1 0 / 6 6 . O b s e r v a t i o n s a f t e r the r u l e b e c a m e o p e r a t i v e w e r e m a d e b e t w e e n 7 / 1 1 / 6 6 and 2 1 / 3 / 6 7 . E a c h e n t r a n c e to the r o u n d a b o u t w a s m a r k e d by s i n g l e t r a n s v e r s e b r o k e n l i ne w i th s t r o k e s 3 f ee t l ong , 3 f e e t a p a r t . T h e s t r o k e w i d t h w a s m a d e 18 i n c h e s , t he s a m e a s in e x i s t i n g m a r k i n g s on n e a r b y r o u n d a b o u t s w h i c h h a d b e e n i n v o l v e d in t he 8 3 - s i t e e x p e r i m e n t . I t was t hus m o r e e m p h a t i c t h a n t h e w i d t h of 8 i n c h e s w h i c h w a s s p e c i f i e d f o r the g e n e r a l r u l e .

2. B E F O R E - A N D - A F T E R STUDIES

2 . 1 C a p a c i t y a n d p r e c e d e n c e

E x c e p t f o r s h o r t , i r r e g u l a r p e r i o d s , n o r m a l l y b e t w e e n 8 . 0 0 a . m . and 8 . 4 0 a . m . on w e e k d a y s , t h e v o l u m e of t r a f f i c e n t e r i n g U x b r i d g e C i r c u s d id not r e a c h the e s t i m a t e d c a p a c i t y of any of t h e w e a v i n g s e c t i o n s . The m e a n o p e r a t i n g c o n d i t i o n s f o r t h e 8 a . m . - 9 a . m . p e a k p e r i o d on w e e k d a y m o r n i n g s ( exc lud ing Mondays ) a r e g i v e n in T a b l e 1, a n d t h e m e a n o f f - p e a k c o n d i t i o n s b e t w e e n 10 a . m . and 4 p . m . on w e e k d a y s a r e g i v e n in T a b l e 2. T h e m o s t h e a v i l y t r a f f i c k e d w e a v i n g s e c t i o n , on t h e NE q u a r t e r of t h e r o u n d a b o u t , w a s s t u d i e d in de ta i l by t i m e - l a p s e c ine p h o t o g r a p h y .

T h e r e s u l t s of a m i n u t e - b y - m i n u t e c o u n t of m o t o r v e h i c l e s in the NE w e a v i n g s e c t i o n a r e g i v e n in T a b l e 3 , f o r the p e r i o d 8 . 0 5 a . m . - 8 . 2 6 a . m . D u r i n g t h i s p e r i o d t h e r e w a s a p e r m a n e n t queue e n t e r i n g f r o m the B467 r o a d - tha t i s , the d e m a n d e x c e e d e d t h e c a p a c i t y of t h i s w e a v i n g s e c t i o n , and as B l a c k m o r e (1) ha s s h o w n , t h e a v e r a g e f l o w u n d e r t h i s c o n d i t i o n g i v e s a u s e f u l m e a s u r e of the c a p a c i t y . T h e r e s u l t s i n d i c a t e t h a t the c a p a c i t y of the c i r c u l a t i n g r o a d was u n c h a n g e d by t h e i n t r o d u c t i o n of the p r i o r i t y m a r k i n g . R i g h t - h a n d p r i o r i t y b e h a v i o u r w a s a l m o s t u n i v e r s a l at U x b r i d g e C i r c u s even b e f o r e N o v e m b e r 1966, p r o b a b l y due to t h e p r e s e n c e of o t h e r r o u n d a b o u t s in the v i c i n i t y which had b e e n u s e d in t h e e a r l i e r e x p e r i m e n t a l s t u d i e s of t he u s e of " g i v e - w a y " s i g n s . In any h o u r of o b s e r v a t i o n d u r i n g t he o f f - p e a k p e r i o d , v e r y few c a s e s cou ld e v e r be s e e n in w h i c h c i r c u l a t i n g v e h i c l e s gave way to o r w e r e o b s t r u c t e d by e n t e r i n g v e h i c l e s .

2

Calcu la t ion of " p r e c e d e n c e index" as de f ined by H o l r o y d (2), f o r the e n t r a n c e of

the NE weav i ng s e c t i on gave p = 0 .99 b e f o r e , and p = 0 .99 a f t e r the a n n o u n c e m e n t of the p r i o r i t y ru l e .

The p r e c e d e n c e index p is the r a t io of the n u m b e r of e n t e r i n g v e h i c l e s g iv ing way to the to ta l n u m b e r (both e n t e r i n g and c i r c u l a t i n g ) of v e h i c l e s g iv ing way at the beginning of the weaving sec t ion . When p = 1 . 0 , the c i r c u l a t i n g v e h i c l e s t a k e comple te p r e c e d e n c e ove r the e n t e r i n g v e h i c l e s .

In th i s c a s e no e f fec t of the p r i o r i t y r u l e was t h e r e f o r e d e t e c t a b l e f r o m the s tudy of g iv ing-way be ha v i ou r .

TABLE i

Mean O p e r a t i n g Condi t ions a t Uxbr idge C i r c u s Be tween 8 a . m . and 9 a . m .

W e e k d a y s , Exc lud ing Mondays o n

(Total f low about 6000 p c u / h o u r )

p c u / h o u r

T o London

T o

Uxbridge

r

I F r o m London

F rom Uxbridge

50

From

D e n h a m

1320

F r o m Ru i s l i p

30

T o t a l

1400

160 - 650 1000 1810

To Denham 1140 50 - 350 1540

To Ruis l ip 70 370 630 - 1070

T ~ a l 1370 470 2600 13.80 5820

3%

P e r c e n t a g e of heavy

C o m m e r c i a l Vehic les

3% 18% 7%

Data f r o m manua l 6 - minute counts du r ing r a n d o m v i s i t s b e t w e e n 2 8 / 7 / 6 6 and 2 / 3 / 6 7

T A B L E 2

M e a n O p e r a t i n g Condi t ions at U x b r i d g e C i r c u s b e t w e e n 10 a . m . and 4 p . m .

on W e e k d a y s

(Tota l f low about 3000 p c u / h o u r )

F r o m

London i f

F r o m U x b r i d g e

From

D e n h a m From

Ruis l ip p c u / h o u r Total

To L o n d o n - 90 890 50 1030

To U x b r i d g e 100 - 60 300 460

To D e n h a m 930 40 - 130 1190

To R u i s l i p 80 330 130 - 540

T o t a l 1110 460 1080 480 3130

22% 13% P e r c e n t a g e

of h e a v y C o m m e r c i a l

V e h i c l e s

28% 13%

Da ta f r o m m a n u a l 6 - m i n u t e c o u n t s d u r i n g r a n d o m v i s i t s b e t w e e n 28 /7 /66 and 2 / 3 / 6 7

4

TABLE 3

Typ ica l P e a k Ope ra t i on of the NE Weaving Sec t ion of Uxbr idge C i r c u s Roundabout , b e f o r e and a f t e r

a n n o u n c e m e n t of the " G i v e - W a y " Rule

Minute commencing at approximately

08.05 a.m. 06

07 08 09

08. i0 11 12 13 14

08.15 16 17 18 19

O8.2O 21 22 23 24

08.25

Mean (per minute)

BEFORE (7/10/66)

N u m b e r of Moto r V e h i c l e s -

C i r c u l a t i n g

40 16 39 23 34 35 21 43 45 41 29 36 22 36 3O 32 35 34 29 38 28

32.7

E n t e r i n g Tota l

17 57 22 38 15 54 19 42 16 50 17 52 34 55 12 55 16 61 19 60 23 52

I0 46 25 47 17 53 28 58 29 61 20 55 25 59 23 52 23 61 35 63

21.2 5 3 . 9

A F T E R (21/3 /67)

N u m b e r of M o t o r V e h i c l e s -

C i r c u l a t i n g II E n t e r i n g To ta l

37 18 29 25 32 16 22 33 27 26 30 26 39 20 23 29

55 54 48 55 53 56

-59 52

30 39 37 3 0 28 35 26 16 24 17 35 33 30:

29 .5

21 51 21 60 13 50 21 51 26 54 25 60 26 52 36 52 31 55 36 53 20 55 15 48 24 54

24.2 53 .7

NOTE - making a l lowance f o r 3 heavy c o m m e r c i a l v e h i c l e s p e r m i n u t e (pcu = 2 .8) , th is s ec t ion o p e r a t e d a l m o s t e x a c t l y at the c a l - cu la ted capac i ty of 3500 p c u / h r while the queue of e n t e r i n g

veh ic l e s p e r s i s t e d .

D u r i n g peak t ra f f ic condi t ions a l so , the re was no visual evidence of a change in b e h a v i o u r except on the SE q u a r t e r of the roundabout. After the announcement of the p r i o r i t y r n l e , a g r e a t e r t endency was seen for the fo rmat ion of t r ans i en t queues at l e a s t 50 y a r d s long on the en t r ance f r o m London, giving approach delays which a re r e f e r r e d to in pa r ag raph 2 .2 below.

Th i s a p p e a r e d to be due to a combinat ion of th ree re levan t fac tors :

(a) the n a r r o w road f r o m the Southbound exit (to Uxbridge);

(b) a l a rge p ropor t ion of r i g h t - t u r n i n g vehic les f r o m Denham to Uxbridge combin ing with ove r 1000 veh ic l e s per hour s t r a igh t - ahead f rom Ruisl ip to Uxbridge to r educe the n u m b e r of "gaps" avai lable to westbound t raff ic ;

(c) a tendency fo r southbound veh ic l e s to stop on the roundabout ac ross the mouth of the p r e c e d i n g e n t r a n c e when the road to Uxbridge was eonges ted .

The p r i o r i t y ru le tended s l ight ly to act against the common sense of a l lowing westbound t ra f f i c to pass through the southbound queue. Had the capaci ty of the exit road been g r e a t e r the effect would not have o c c u r r e d .

2 .2 J o u r n e y t imes

The a v e r a g e t ime taken to gain a c c e s s to the roundabout f r o m an a r b i t r a r y m a r k 50 y a r d s before each en t r ance was m e a s u r e d before and a f te r the mark ing of the e n t r a n c e s .

The d i s t ance was m e a s u r e d f r o m the cen t re of each en t r ance , and the t ime f r o m the a r r i v a l of the f ront of the veh ic le at the 50 ya rd mark to the passage of the r e a r of the vehic le over the e n t r a n c e m a r k , to the n e a r e s t second.

Queuing t ime on the road m o r e than 50 ya rds before an en t rance was thereby neg lec ted but only in the case of veh i c l e s f r o m Ruisl ip dur ing the morning peak per iod was this of any s ign i f icance . The length and pe r s i s t ence of the Ruislip queue v a r i e d g rea t ly each day in both "be fo re" and "af te r" per iods . Measu remen t s of it w e r e abandoned when it was r e a l i s e d that the resu l t s would desc r ibe local f luctuat ions caused by t ra f f ic as f a r away as ~Ickenham, Hillingdon and Uxbridge, r a the r than any effect of the roundabout mark ings .

Random samples w e r e take n of 100 pr iva te c a r s at each en t r ance , and of 100

hea vy c o m m e r c i a l v e h i c l e s at the W e s t e r n A v e n u e e n t r a n c e s o n l y , to m a k e e a c h e s t i m a t i o n of m e a n a c c e s s j o u r n e y t i m e o v e r t he 5 0 - y a r d a p p r o a c h e s . O b s e r v a t i o n s w e r e m a d e only in c l e a r , d r y , d a y l i g h t c o n d i t i o n s in the a b s e n c e of s k i d - r i s k o r any known o b s t r u c t i o n s to t r a f f i c .

The r e s u l t s a r e g iven in Tab le 4. D u r i n g the c o m p i l a t i o n of T a b l e 4, t he a v e r a g e t i m e s w e r e c a l c u l a t e d s e p a r a t e l y f o r e a c h e n t r a n c e l a n e in e a c h a p p r o a c h r o a d , and i t was found tha t no s i g n i f i c a n t f a c t o r w a s m a s k e d by p o o l i n g a l l t h e r e s u l t s f o r c l a r i t y of p r e s e n t a t i o n .

T A B L E 4

A v e r a g e T i m e T a k e n to Gain A c c e s s to Uxbr idge C i r c u s R o u n d a b o u t F r o m a P o i n t 5 0 Y a r d s

B e f o r e E a c h E n t r a n c e , B e f o r e and A f t e r t he I n t r o d u c t i o n of the Give Way Rule

A p p r o x i m a t e to ta l f low into t he r o u n d a b o u t

( p c u / h o u r )

Mean t i m e to ga in a c c e s s (secs) f o r -

P r i v a t e c a r s (all r o a d s )

Heavy c o m m e r c i a l v e h i c l e s ( W e s t e r n avenue only)

3000

BEFORE

6 . 0 0

6 . 0 5

A F T E R

6 . 5 0

6 . 7 5

6000

BEFORE

1 1 . 7

1 2 . 5

A F T E R

1 2 . 2

15 .3

The o v e r a l l i n c r e a s e in t i m e to g a i n a c c e s s to t h e r o u n d a b o u t , a m o u n t i n g to about ha l f a s e c o n d ( m o r e f o r h e a v y v e h i c l e s in h e a v y t r a f f i c ) i s s t a t i s t i c a l l y s i gn i f i c an t at bo th 3000 p c u / h r and 6000 p c u / h r t o t a l f l o w s .

T h i s i s p a r t l y due to a r e d u c t i o n of the a p p r o a c h s p e e d s of v e h i c l e s wh ich did no t have to give w a y , and p a r t l y to an i n c r e a s e of the d e l a y s to v e h i c l e s which d id give way. Tab le 5 shows the d i s t r i b u t i o n of the t i m e s to ga in a c c e s s , in the r a n d o m s a m p l e s of p r i v a t e c a r s . No r e c o r d w a s m a d e of w h i c h c a r s d id no t give w a y , but f r o m the s y s t e m a t i c sh i f t in the d i s t r i b u t i o n b e f o r e and a f t e r the m a r k i n g of the e n t r a n c e s , i t s e e m s r e a s o n a b l e to s u p p o s e t h a t s o m e of the f a s t e r d r i v e r s a p p r o a c h e d m o r e s l o w l y , e v e n t h o u g h t h e y d id not h a v e to g ive way. T h e i n f e r e n c e would be t ha t the s igh t of the m a r k i n g a h e a d is an e f f e c t i v e r e m i n d e r of the p r i o r i t y r u l e .

7

T h e r e w a s c e r t a i n l y no i n c r e a s e in the p r o p o r t i o n of c a r s which w e r e d e l a y e d

b y m o r e t han 20 s e c o n d s in the a p p r o a c h e s .

T A B L E 5

D i s t r i b u t i o n of T i m e s T a k e n to Gain A c c e s s to U x b r i d g e C i r c u s Roundabout F r o m a Po in t 50 Y a r d s

B e f o r e E a c h E n t r a n c e , B e f o r e and A f t e r the I n t r o d u c t i o n of the Give Way Rule

Type of d r i v e r s

D r i v e r s who m a d e fas t a p p r o a c h e s

Some s l o w e r d r i v e r s ; s o m e d r i v e r s who gave w a y to c i r c u l a t i n g v e h i c l e s

D r i v e r s who s u f f e r e d Long d e l a y s

T i m e to gain a c c e s s ( s e c o n d s , to

n e a r e s t second)

3 4 5

6 7 8 9 10-19

20 -29 30-60 o v e r 60

PRIVATE CARS

P E R C E N T A G E S

B E F O R E (of 800 c a r s )

0 . 9 ) 12 .9 ) 3 7 . 6 23 .8 )

-16.6 ) 11.2 ) 6.7 )53 4 . 3 ) 14.2 )

5 . 2 ) 4 . 0 ) 9 .4 0 . 2 )

A F T E R (of 800 c a r s )

0 . 4 ) 10.1 ) 34 23.5 )

17 .1 ) 10 .0 )

7 .8 ) 5 7 . 7 5 . 7 )

i 7 . i )

4 . 7 ) 3.2 ) 8.3 0 . 4 )

Change

- 3.6%

+ 4 .7%

- 1.1%

T h e v e h i c l e s in the a p p r o a c h s a m p l e s w e r e a l s o c l a s s i f i e d a c c o r d i n g to the r o u t e t h e y fo l l owed t h r o u g h the j u n c t i o n , and about 80% of the t r a f f i c went s t r a igh t

a h e a d .

T h e a v e r a g e to taI j o u r n e y t i m e f r o m the 5 0 - y a r d m a r k to the s t r a i g h t - a h e a d ex i t w a s m e a s u r e d , and the r e s u l t s a r e g iven in Tab le 6. As fo r Table 4, a v e r a g e r e s u l t s c a l c u l a t e d f o r e a c h a p p r o a c h l ane s e p a r a t e l y have been pooled. F o r al l

v e h i c l e s the i n c r e a s e at low t r a f f i c f low, and f o r p r i v a t e c a r s the d e c r e a s e at high t r a f f i c f low, a r e no t s i g n i f i c a n t s t a t i s t i c a l l y . F o r h e a v y c o m m e r c i a l v e h i c l e s at h igh t r a f f i c f low the i n c r e a s e is s i g n i f i c a n t , and i s due to the i n c r e a s e of a p p r o a c h de lay at t h e e n t r a n c e f r o m London .

T A B L E 6

A v e r a g e to ta l j o u r n e y t i m e S t r a i g h t a h e a d t h r o u g h Uxbr idge C i r c u s R o u n d a b o u t

b e f o r e and a f t e r the i n t r o d u c t i o n of the Give Way Rule

A p p r o x i m a t e to ta l f low into the r o u n d a b o u t

( p c u / h r )

Mean to ta l j o u r n e y t i m e ( secs )

Private cars (all roads)

Heavy c o m m e r c i a l v e h i c l e s (Wes te rn Avenue only)

3000

BEFORE

16.1

15.5

A F T E R

16 .5

1 6 . 2

6000

B E F O R E

2 4 . 9

2 5 . 4

A F T E R

2 4 . 0

27~3

2 .3 Gap a c c e p t a n c e s and a l t e r n a t i n g s e q u e n c e s of c i r c u l a t i n g and e n t e r i n g v e h i c l e s

D u r i n g the o p e r a t i o n of the r o u n d a b o u t at 3000 p c u / h o u r t o t a l f l o w , abou t 400 v e h i c l e s p e r h o u r f r o m R u i s l i p e n t e r e d the r o u n d a b o u t wi th abou t 700 c i r c u l a t i n g v e h i c l e s p e r h o u r on t h e i r r i g h t at the e n t r a n c e .

About hal f the e n t e r i n g v e h i c l e s " e n c o u n t e r e d " c i r c u l a t i n g v e h i c l e s in t he s ense tha t one o r m o r e p a s s e d in f ron t of t h e m wh i l e t h e y w e r e w i t h i n abou t a c a r l eng th of the e n t r a n c e , o r whi le t hey w e r e w a i t i n g a t t he e n t r a n c e o r m o v i n g s lowly out into the c i r c u l a t i n g road . F o r t h e s e e n t e r i n g v e h i c l e s , t he g a p s in the c i r c u l a t i n g s t r e a m which e a c h r e j e c t e d , and t he gap w h i c h e a c h e v e n t u a l l y e n t e r e d , w e r e m e a s u r e d on the c ine f i l m r e c o r d .

The r e s u l t s of the a n a l y s i s of f i l m s t a k e n b e f o r e (on 3 0 / 9 / 6 6 ) a n d a f t e r (on 3 0 / 1 / 6 7 ) the m a r k i n g of the e n t r a n c e s a r e g i v e n in F i g u r e 2. T h i s s h o w s that the i n t r o d u c t i o n of the p r i o r i t y r u l e h a d no e f f e c t on gap a c c e p t a n c e .

D u r i n g the p e a k o p e r a t i o n of t h e r o u n d a b o u t at abou t 6000 p c u / h r , to ta l f l ow , i t w a s no t p o s s i b l e to d e s c r i b e gap a c c e p t a n c e s in any s i m p l e m a n n e r .

I n s t e a d , a f r a m e - b y - f r a m e a n a l y s i s of c i n e f i l m was m a d e , of the p a s s a g e of a l l t he v e h i c l e s a c r o s s a t r a n s v e r s e l i n e t h r o u g h the c e n t r e of the NE w e a v i n g s e c t i o n a n d in t h i s way the e n t i r e s t r e a m was d i v i d e d in to a l t e r n a t i n g s e q u e n c e s of " c i r c u l a t i n g " and " e n t e r i n g " v e h i c l e s a c c o r d i n g to the o r i g i n of t h e i r e n t r y i n to t h e w e a v i n g s e c t i o n . T h e s e q u e n c e s r a n g e d f r o m i to 31 v e h i c l e s . F i g u r e 3 s h o w s t h e c u m u l a t i v e d i s t r i b u t i o n of v e h i c l e s in t e r m s of the s i z e of the g r o u p in w h i c h e a c h m o v e d , and i t i s a p p a r e n t tha t t h e e n t e r i n g s t r e a m , queu ing to wai t f o r " g a p s " , ga in a c c e s s to the r o u n d a b o u t in c o n s i d e r a b l y s h o r t e r s e q u e n c e s t h a n t h e c i r c u l a t i n g s t r e a m . S ince the " b e f o r e " and " a f t e r " r e s u l t s h a v e s i m i l a r d i s t r i b u t i o n s i t i s c o n c l u d e d t h a t n e i t h e r s t r e a m has ga ined o r l o s t p r i o r i t y a s a r e s u l t of t he m a r k i n g of t he e n t r a n c e s and a n n o u n c e m e n t of the "g ive -way" r u l e .

3. CONC LUSIONS

3 . 1 D r i v e r s a t U x b r i d g e C i r c u s m o s t l y a c c e p t e d the c o n v e n t i o n of r i g h t - h a n d p r i o r i t y b e f o r e N o v e m b e r 1966, and no o v e r a l l change in t h e i r b e h a v i o u r w a s found a f t e r t he " g i v e : w a y " m a r k i n g s and the a d v i s o r y r u l e c a m e in to

o p e r a t i o n .

3 . 2 T h e c a p a c i t y of t he on ly w e a v i n g s e c t i o n wh ich o p e r a t e d at i t s t h e o r e t i c a l l i m i t was u n c h a n g e d by m a r k i n g t he e n t r a n c e to it wi th the " g i v e - w a y " l i n e .

3 . 3 T h e r e was no c h a n g e in gap a c c e p t a n c e b e h a v i o u r by d r i v e r s e n t e r i n g at m o d e r a t e f l o w l e v e l s .

3 . 4 T h e r e was a l s o no c h a n g e in t he d i s t r i b u t i o n of the s e q u e n c e s of c i r c u l a t i n g a n d e n t e r i n g v e h i c l e s on a w e a v i n g s e c t i o n at peak f low.

3 . 5 M o r n i n g p e a k c o n g e s t i o n w a s o b s e r v e d at t he S o u t h e r n e x i t , c a u s e d by the low c a p a c i t y of t he B467 r o a d to U x b r i d g e , and when th i s o c c u r r e d the " g i v e - w a y " r u l e i n c r e a s e d a t e n d e n c y f o r c i r c u l a t i n g v e h i c l e s to s t op a c r o s s the m o u t h

of t he p r e c e d i n g e n t r a n c e .

3 . 6 T h e e n t r a n c e m a r k i n g s a p p a r e n t l y c a u s e d s o m e d r i v e r s to a p p r o a c h the r o u n d a b o u t a t s l o w e r s p e e d s , bu t t h i s d id no t i n c r e a s e d e l a y s . The m a r k i n g s h e l p e d to g i v e p r e c i s i o n and e m p h a s i s t o the r u l e , wh ich was a l r e a d y p r o v i n g e f f e c t i v e at s o m e r o u n d a b o u t s in the o u t e r London a r e a .

10

4. ACKNOWLEDGEMENT : .

Thanks a r e due to Mr. H . J . Wood, the Eng inee r and Su rveyo r of the London Borough of Hill ingdon, and Mr. Lipwick of his s taff , fo r t h e i r i n t e r e s t in this s u r v e y , and ass i s tance in cont rac t ing for the c a r r i a g e w a y mark ings .

5. REFERENCES

i . F . C . BLACKMORE, "P r io r i t y at roundabouts . " Traf f ic Eng. and Cont ro l , 1963, 5, (2), p .104-106.

. E . M . HOLROYD. "Measur ing p r e c e d e n c e at roundabouts . " R . R . L . Labora to ry Note No. LN/650/EMH.

11

RUISLIP I , B~67 W - - - - - ~ E

B&6? UXBRIDGE

LONDON A/,O

Diameter of centrat istQnd 200ft Width of circutatlng road /,Oft

Fig.1. UXBRIOGE CIRCUS ROUNDABOUT

100

O I

O . O U U

~a

O

U ~t t,. I l l 0.

60

60

/,0

20

I I I ! I I

J C ~ " I I I 1 2 3 4 5

(Seconds)

/

Gap in circulat ing steam

Circulating stream approximately 700 vehicles Ih.

Entering stream approximately 400 vehicles/h. Data from cine film taken at 4 frames per second

Before O 3019166 After • 301116"/

Fig.2. GAP ACCEPTANCES BY DRIVERS ENTERING THE N E WEAVING SECTION OF UXBRIOGE

CIRCUS BEFOREANO AFTER THE ANNOUCEMENTOF THE GIVE-WAY RULE

R.118. 2.

I I I l I

g ° ~ J~

& ¢11

P 0 Q .

:3 E

¢ J

io0

8O

60

AO

Entering

l ~ ~ / 0

20,

I l I I 5 10 15 20

Number of vehicles in sequence

I 25

I 30

Circutating stream approximately 1850 vehicles Ih Entering stream approx~matety 1350 vehicles/h

Before O circulating A entering7/10/66 After • c i rcuta t ing • entering21/3/6? Oata from c[ne f i rm record.

Fig.3. DISTRIBUTION OF VEHICLES BY ALTERNATING SEQUENCES IN THE NE WEAVING SECTION OF UXBRIOGE CIRCUS BEFORE ANO AFTER THE ANNOUCEHENT OF THE GIVE WAY RULE

3 9 8 1 9 3 6 5 O L T D 1 1 / 6 7