ML20149E834

Applicant Exhibit A-24,consisting of Undated Article, Effect of Roadway & Environmental Factors on Capacity of Traffic-Signal Approach

ML20149E834
Person / Time
Site:	Seabrook
Issue date:	11/06/1987
From:	AFFILIATION NOT ASSIGNED
To:
References
OL-A-024, OL-A-24, NUDOCS 8802110294
Download: ML20149E834 (5)

Text

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.Gt \ Jo -qqs/vvf n T //,/t /2 7 0'dITED oR k~ '88 FEB -f A9 :28 0FFICE OF syg A,;y 00CKEimc A SER.qcf.

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33 l

T:Te effect of roacway l

and environmenta factors on t:Te i

l capacity cf a traffic-signal  !

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l approach i capasits ' i uartirynal control led interseetton is knuteu hs the sacacities of the

.ndnidual approa,hes to the intersection.

- There are two ty pes of factor which af fect the capaesty of an approach: roadway 4 and environmental factors. discussed in this chapter, and traffic and control factors discussed in uhaoter 31 l The roadw n and envirnnmental factors that control the capacity of an approach are  !

the physical I.n out ut the approach. in particular its width, the radii along w hich let'.. {

or right turning sehicles have to travel, and the grac'ient of the approach and its exr.  ;

from the inter >eetion. '

• The e::pacin os an approach is measured indeper.dently of trattie and control factors and is expressed as the saturat<on flow.

3 Saturation flow is defined as the maximum flow. expressed as equnalent passenger

• cars. that can enns the stop li,e of the approach when there is a continuous green signal -

indication and a continuous queue of vehicles on the approach.

Observauon> ot traffic Ilow made by the Road Research Laborate : at intersections .

in the London area and also in some of the larger cities. suppiementnt by controlled , ,

escenments at the (..horatory test track hoe shown that the saturatten tiowm '

expressed in pnwneer ear units per hour with ne parked venisles n linen by l a

s = S30w p.e.u./h l

l ', . ' where w is the width of the approach in metres. l This formula n appheable to approach widths greater than a .s m at widths less than

l. 5 5 m the relationship is not knear and saturation flows may he estimated from table 33.1.

'- 282 g d

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TRAFFIC SIGN AL APPROACit: CONTROLLING FACTORS

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TAllLE 33.1 4 00 4 50 5 20 f 3-no J do ) 63 wino 1875 19n0 195n  ::50 2700 3ips u.fu 1350 ._

1 These satulation 110ws have to be amended for the etfeet of gradient. This moditica- ,

tiui ha, been veported as a decrease or merease of 3 per cent in the saturation flow for i evers 1 ;er cent of uphill or downlull eradient of the approash. ihe gradient ot the approuh was .fetined as the aserage slope between thg stop luie and a point on the approxh ni m betore it. At the sites where these obwrvation> were made, the slope connnued through the interseenon.

wheie whistes crossing the stop kne have then to travel unmediately around a curve the rate of dncharge across the stop line will be reduced. lhis occurs frequently when nglit turnmg vehicles are al.le to discharge during a nght turtung phase. Test track expenments have shown that the saturauon llow for right turning streams may be obtamed from 1800 '

s=i+lSOM i

or 1600 p.c.u.!h f 3000 i p.e.u.;h for double. file streams s = i + l 32.'r or 2700 p.e.u.th {

where r = turning radius m metres. e ,

l The environment also has an effect on.the saturation tiow of an approach and l.while it 6 is dif ficult to define this ef fect precisely.generalised moditiestion factors are often app _

Where a sue is designed with . good environment, that is dual carnageway approaches.

[ no nonceable pedesinan mterf erersce. no parked velocles no interferences to trattic -

l i 11mv trom oght turnmg veh,eles, good visibility and adequat<. turna.g radii then the b .

l I saturauun slow is taken as 100 per cent of the standstd vr.;ue. i f It however a site is designed with poor environment. that is low average speeds, l interierence from standing vehicles and right turning vehicles. poor visibility ar;d poor  :

aligmnent, then the saturation tiow is taken as 85 per cent of the standard v Jue. ~. I Determination of the sattwation flow of a traffic signalapproacle i

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f l T.i determi se the saturation flow of an approach select one in which there is a scri.  ;

( ' tinuous queue even it the end of the green period. Avoid situations a which right.

j turnmg schicles have an errahe elTect on the traffic flow. Fct ease of observaJunl '

preferable to seleet an approash that is restricted to straight ahead snd left' tarnm vehicles.  : ,

U>ing a stopwatch note the number, type and turning inovement of each vehicle; .

ernssing the stop line durmg each successive 01 minute interval of the green andl '

penod. At the end of the amber period there will normally be an interval {ofless 0-l minute. Note the length of this interval and also the number and type of vehicles

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284 TR.\FFIC SIGNAL CONTROL crossmg the stop line m the mterval. These miervals are subsequently referred to as last saturated mtenals.

If at any time the flow on the approach is not saturated, then obsenations should l

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be discontmued until the flow reaches saturation level again. '

l Ifit is not found poonble to obserse vehicle type then only the number and turning movement of schicles shouid be noted. At the complet rm of observanons a separate

, enunt is then necessary to dese:nnne the composition of the traftie slow.

The observations given m table 33.2 were obtamed at a traffic sienal controlled '

interseenon in the City of liradford. In tfUs instance observations were made of mi. sed ' '

vehicles travelling straight ahtad, l

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TA11LE 33.2 Observed discharge of schicles across the stop line Tirne i minu te) 02 0 01 03 oe n- 5 No. ut ychicles crossinit stophne 60 76 71 78 79 No. on'sa tursted intervals observed 32 32 32 32 32 Dinharre per o-1 rnin 1 88 2-48 2 22 2 44 247 l

' Total duration of the last satu ated intervals = 142 seconds Total number of vclueles crossing stop line = 41.

Discharge per 01 minute dunng last saturated interval = (41-6t/142

= l 74 schicles.s l

During the first and last saturated miervals there is a loss of capacity becabe of the

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effect of vehicles accelerstmg hum the stationary position at the commencement of the green penod and decelerating dunng the amber period.

The tiow during the remainder of the observed periods represents the maximum discharge possible and their ruean value gives the saturation flow for the approach

- 2 48 + 2 22 + 2 44 + 2 47 i

s3tutullon flow 8 '

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= 140 vehicles per 01 minute '

) = 1440 vehulesih I

This value rr.ust now he eo.nerted to traffic signal passenger :ar units and a sub.,idiary traffic count is required to det;rmme the composition of the traffic. '

Observe the composition and turmng movemer;ts of the traf fie flow for a period of j 30 minutes and at similar rm e to when the ongmW observations were made. The i following composition of ira!ise was nor-ed on the approach where the llow lieures I given in tabla 33.2 were cbserted tusing the equivalent effects of vanous vehicle types  ;

given in chapter 34) heavs schides 14 per tent  :

bines 5 per cent motor cycles 6 per cent pnvate ears 75 per cent all vehicles proceed strair.ht ahead i

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s - w . . w. 3 w g .~. ,

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TR.\FFt(' 5IGNAL APPROACll: CONTROLLIM; F \CTORS 255 t The passenser < : equnalent of the ilow is then k l

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di I 4 x t 75 + 0 05 x 2 25 + 0 06 x 0-33 + 0 75 x i = l lo . 't+

4 Saturanon flow = I 4481 = l 16 .' '

1070 p.c.u.,b. '

l The deuen tiene even in Road Research Teclurical Paper in k I'Itn) p.e.u.th f or a , 1 J oS in lane widih.

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i renhlenn 1 Four ditTerim it.itfis .sunal approaches are beribed below. I' lace them m the order of '. )

their trallie capasit .

i ta s An approash anh good enuronmental conditions where all schides discharge ,

straight astou the meersection and where the approach width is 7.20 m.

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(bl An appro.wh with poor environmental conditions with a continuous uphill gradient .

l of 3 per cent. .sne.e iil sehisles disharce straicht asross the meer esnon and where the  ;,

approach width > lh (il m.

ic) An appro.nh with normal environinental conditions f rom winsh all vehicles turn l.

right in a doub'e h!e sticam on a path with a radius of 30 m. l

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l (d) An appro.un woh evod etnironmental conditions aild downii.ii yeadient ol 4 per . .

eent. where a;i emues diwharge str.iight aeruss the intersecuen and w heie the approach i .

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width is 5 20 m. l

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The trattie'earaunes <.! the approachts . ire: '-

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, (a) saturanon ilow = 550 x 7-30 = 4015 p.e.u.lb -

i l i plus enviromnental Iactor of 20'c l

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= 4015 x l 2 l

= 4818 p.e.u./h .N l (b) saturation tiow = 550 x 10 50 = 5775 p.e.u./h ]

minus enviromneni.ii taetor et 15.;  !

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[ = 5775 x 0 85 .

= 490') p.e.u.i h ".,

!, minus gradient c tTeet af] < 37 '..; )

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= 4407 p.c.u./h .

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I i 24, TR.'.FFIC SIGNAL CON TROL 3000

.i ia saturation slow = p.e.u./ h i: I + l 52/r I. . l I.

3000 j-.t 1 + l 52/30

= '857 p.e.t../h ,

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.., idi saturation flow = 2700 p.e.u./h (table 33.11 -

rios environmental faster of 20'/c

= 2700 x I : r-

= 3:40 p.e.u.ili

. liin gradient elTect of 4 x 37'

= 3240 x l 12 (

" = 3629 p.c.u.!h 1 t he order of capacity of the approaches is (a). (hi (dl. (c).

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