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Trong qua trinh phat trin cac phng phap nghin cu iu kin xe chay ngi ta a s dung tiu chi nng lng gm: Tap m gia tc , gradient tc Gv, tap m nng lng, gradient nng lng Ge.Kt qua nghin cu chi tiu cht lng xe chay co th tip nhn thng s cua dong giao thng, c goi la tap m gia tc. Ly do: co 2 nguyn nhn. Th nht, chi tiu nay quan h vi 3 b phn c ban cua dong giao thng nh: lai xe, ng va iu kin xe chay. Th hai, thng s nay ban cht la chi s cua chuyn ng u.Trn ng vi lu lng xe it, khng bi gii han t do di chuyn, lai xe thng c gng chuyn ng u vi tc thun li cho minh. Khi tng lu lng xe chy n mc m tc chy xe mong mun b hn ch li, ngi li xe phi di chuyn sang hng khc v tng tc vt cc xe t ang chuyn ng vi tc thp hn, dn n tn sut ln hn v lch tc so vi chuyn ng u. Nh vy, c th thy rng s thay i gia tc theo thi gian mang tnh cht ngu nhin, v bn cht th gia tc phn phi theo quy lut chun.S u n ca chuyn ng c th miu t bng i lng c trng l lch ca cc gi tr ngu nhin ring phn ca gia tc so vi gi tr ca gia tc trung bnh lch qun phng trung bnh ca gia tc.

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Tp m gia tc - lch qun phng trung bnh ca gia tc, c th c xem nh l lch tc ca xe t so vi khi chuyn ng u hay c coi l ch s ca s u n ca chuyn ng. Thut ng tp m c s dng ch ra rng, s vi phm tnh u n khi chuyn ng so vi tp m ca tn hiu, gy ra bi cc nhiu trn knh tivi. Tng nng lng cua dong cac phng tin giao thng c hinh thanh t ng nng chuyn ng cua cac xe t va ni nng (tap m gia tc). Phu thuc vao trang thai cua dong giao thng tng quan gia nng lng co ich (ng nng) va nng lng khng co ich (tap m gia tc) se thay i. tng hiu qua hoat ng cua h thng giao thng cn phai tng nng lng toan phn cua dong giao thng, ng thi c gng giam tap m gia tc (hinh 1)

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Hinh 1. Cac c trng nng lng cua dong giao thng va quan h cua chung vi cac ai lng: Z h s lam vic; E/T: ty s gia ng nng va nng lng toan phn; J/T: ty s gia ni nng va nng lng toan phn.Nu gi v(t) v a(t) l tc v gia tc ca t thi im t, th gia tc trung bnh ca t trong thi gian T l:

(1) lch qun phng trung bnh s i vi n i lng ngu nhin x1, x2, , xn c xc nh theo cng thc:

(2)(2)

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Trong : : Gi tr trung bnh ca i ln ngu nhin x.T phng trnh (1) v (2) ta xc nh c tp m gia tc c xc nh theo cng thc:

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Trong : v0 v vT l tc khi bt u v kt thc ca an ng nghin cu (chiu di an ny > 0,5km). Nu nh gi tr ca V=const th:

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Trong : v l ln chun ca bin thin tc ; n - s ln bin thin tc trong thi gian t.Theo cc kt qu thc nghim nghin cu thit lp c tp hp cc gi tr tp m gia tc i vi cc trng thi khc nhau khi xe chy: < 0,2m/s2 iu kin chy xe thun li; = 0,2m/s2 0,45m/s2 iu kin xe chy mc trung bnh; > 0,45m/s2 iu kin xe chy phc tp.Tp m gia tc c mi lin h cht ch vi lu lng xe chy.

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Vi du: v = 0,5m/s v cc s liu v thay i tc th hin bng 1.

Hnh 2. th bin i tc xe chy trn an ng nghin cu

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= 0,48 m/s2

S khoangThi gian kt thuc cua khoang, sVn tc cui cua khoang, m/sS ln thay i tc t, sn2/ti012345678910110368101315182225273014141314,515,515,514,51413,513,51311-02320211014-33223234323-0,001,334,502,000,002,000,330,250,000,505,33Tng cng3025,64

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Khi anh gia cac iu kin xe chay trn cac ng ph chinh tr chuyn ng khng u, cn phai xt n thi gian bi dng lai trn cac nut giao thng co iu khin, ni dong xe bi un laiKhi thi gian bi dng lai la ang k thi tap m gia tc s khng th hin tng ng vi mc xu i cua iu kin xe chay, dn n kha nng s dung no khi anh gia ln cua thi gian b dng lai l han ch. Han ch nay lam cho vic s dung tap m gia tc nh la tiu chi anh gia hiu qua cua cac phng phap t chc giao thng trn cac ng ph chinh l khng thch hp.Trong mt vai trng hp khi xe b chm lai trn cac giao ct co iu khin co th ghi nhn gia tri tap m gia tc be hn so vi khi xe chay lin tuc. gia tri thp cua tap m gia tc, vi du, khi co un tc giao thng, gy ra mc thp t chc giao thng va dong giao thng co mt cao. Cho nn s dung tap m gia tc nh la tiu chi anh gia cht lng t chc giao thng i vi ng ph co tc xe chay cao chi co hiu qua khi xe chay khng bi gian oan.

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Nh vy, c 2 tiu ch: tp m gia tc v tc hnh trnh (tc trung bnh trn hnh trnh cho trc, c xt n thi gian xe b tr trn cc nt giao thng v do nh hng ln nhau ca cc xe trong dng xe. Tp m gia tc th hin r tnh khng u ca ch tc xe chy, nhng khng th hin y khi dng xe b tr; tc hnh trnh nh gi c s chm dng, nhng khng miu t c dao ng ca ch t tc . nhn c tiu ch tan din v khch quan, c th nh gi chuyn ng ca dng xe khi n tc giao thng, xut t s tp m gia tc v tc hnh trnh trn an nghin cu, c gi l gradient tc .Gv= /vctrong vc tc hnh trnh, m/sGradient tc quan h tuyn tnh vi tc hnh trnh, thi gian ca chuyn i, thi gian xe b chm dng. Gradient tc l cc ch tiu thng tin v tnh trng n tc giao thng nhiu hn so vi tp m gia tc. Gv < 0,05 (1/s) - iu kin chy xe thun li;Gv = 0,05-0,10 (1/s) - iu kin chy xe trung bnh;Gv > 0,10 (1/s) - iu kin chy xe phc tp;

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Khi phn tch ch tc xe chy chng minh rng, cng vi vic tng tc xe chy v tip tc chy xe ch ny lm gim cc gi tr tc thi v gi tr trung bnh ca gia tc. T cng thc xc nh gi tr tp m gia tc (6) cho thy r khi xe chy vi tc cao th gi tr gim. Kt qu, khi xe chy tc cao khng xt ti mt trong cc mu thun c bn ca chuyn ng tc - mi nguy him. Tuy nhin cc tnh tit ny thng khng c xem xt khi xc nh ch tc ti u theo ln ca tp m gai tc.Bi vy, hng tip theo l pht trin tiu ch trn c s nh gi lch qun phng trung bnh ca cc gi tr aivi so vi gi tr trung bnh av. Cc tiu ch ny c gi l tp m nng lng.

(7)

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Trong : m Khi lng ca t.

E =mv2/2Trong : ai, vi l cc gi tr tc thi ca gia tc v tc , m/s2 v m/s; av gi tr trung bnh ca tch tc v gia tc trn an nghin cu, m/s3; n s ln o tc v gia tc.ng nng ca t c xc nh theo cng thc:

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Trong khong thi gian dt gia 2 ln o (2-3s) khi lng ca t khng thay i, c th cho rng, s thay i nng lng c c trng bi tch s ca gia tc v tc .Khc vi gia tc ln av tng nhanh cng vi vic tng tc khi chuyn ng khng u, cn trong trng hp tin gn n ch n nh khi chuyn ng, gi c mc tc cao hn 40-45 km/h. Phn bit c tnh nguyn tc ny cho php nhn c nh gi chnh xc hn ch chuyn ng vi tc tng i cao.Tp m nng lng him khi c s dng nh gi cc iu kin chuyn ng, kinh nghim s dng n khng nhiu. Trn c s cc s liu c, c th cho rng cc iu kin chuyn ng l phc tp (kh khn) khi tp m nng lng cao hn 4-5 m2/s3. Gradient nng lng Ge l tng hp cc tiu ch. Cng thc tnh tan xc nh n khi bin i tp m nng lng:

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Cc nghin cu thc nghim c thc hin bi gio s V.V. Girianvi ch ra rng, nh hng thc s ln nht n gradient nng lng l thi gian chm dng v tnh khng u ca chuyn ng. Mc tc ng ln nhau ca cc nhn t ny vi gradient nng lng l nh nhau. Cc tnh cht nh vy cho php p dng thnh cng gradient nng lng nh gi hiu qu cc cc phng php t chc giao thng trn mng li giao thng c iu khin n tn hiu.Nh kt qu ca cc nghin cu ny thit lp c cc quan h sau gia gradient nng lng v cc c trng c bn ca dng giao thng:- Cng vi vic tng lu lng xe chy gradient nng lng tng ln, c ngha l tiu chun phn nh s thay i v cht ca trng thi dng giao thng, xy ra khi thay i mc n tc giao thng (hnh 3a)- Tng tc hnh trnh v gim thi gian chm dng dn n gim gradient nng lng (hnh 3b)

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Hnh 3. S ph thuc ca gradient nng lng:a- vo h s lm vic Z; b- vo khang thi gian trung bnh chm dng t trn hnh trnh.

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- Nng cao n nh ch tc gp phn gim gradient nng lng;- S khng ng nht thnh phn dng xe dn n tng gradient nng lng;- Cc iu kin giao thng c th bc u nhn nh c nh cc gi tr sau ca gradient nng lng: + Ge < 0,3 m/s2 thun li;+ Ge = 0,30-0,55 m/s2 trung bnh;+ Ge > 0,55 phc tp;

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Khi tin hnh cc nghin cu vi mc ch nh gi cc iu kin chy xe theo tiu ch nng lng cn phi o cc gi tr tc thi ca vn tc vi v gia tc ai trong khang thi gian nht nh t. Khi la chn tnh phn tn ca php o cn thit phi xt n: cc khang thi gian b vic vo s cc s liu tn cng x l s liu hn, cn cc khang thi gian ln d b st cc thng tin v s thay i ch chuyn ng. Trn c s cc nghin cu c tin hnh ti MADI cc ch tiu Ge c tnh ton vi t=2s.Vic xut hin cc nhm ch tiu v nng lng i hi tin hnh phn tch hp l nh gi cc iu kin xe chy v ln ca cc ch s ny, xc nh phm vi hp l p dng chng. Mi mt trong cc ch tiu c mt vi c im nh hng n nh gia thc t cc iu kin xe chy. Xc nh phm vi p dng hp l cc ch tiu cn phi da vo nh gi cc gi tr c th ca c trng chuyn ng trn ng t. Cc gi tr ny c th c xc nh t s ph thuc n nh v ch yu gia cc ch tiu v tng hp cc nhn t, th hin qu lut ca dng giao thng, cc phng php t chc giao thng, cc iu kin xe chy. Tt c cc yu nh hng n cc ch tiu, c th chia lm 2 nhm: trc tip v gin tip. Bi v cc phn tch cc ch tiu c hnh thnh trn c s nh gi s thay i ch tc , cc yu t lin quan n nhm trc tip, phi l cc c trng trc tip ca ch tc . Cc yu t ny c th c o c chnh xc v c i chiu vi ln ca cc ch tiu i vi bt k an ng no thuc mng li ng ph v trong bt k khong thi gian no. Cc yu t trn gm: tc , phng sai ca tc , thi gian chm dng, s lng cc trm dng...

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Nhm cc yu t gin tip bao gm cc yu t nh hng n ln ca cc ch tiu do s tn ti ca tc ng ln nhau trong h thng chuyn ng ng. Cc yu t gin tip cng c th l: lu lng, mt , thnh phn dng xe hay ng mt chiu, hai chiu, cc phng php iu khin n tn hiu... nhn c cc quan h ng tin cy gia cc ch tiu v cc yu t gin tip cn phi h cc yu t ny khng phi l cc yu t c lp nhau, m s thay i mt nhn t co th dn n thay i nhn t khac. Bi vy, quan h gia cac yu t gian tip va trc tip cn phai anh gia s thay i ng thi cua cac yu t va tac ng gia chung.

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Khi thit lp pham vi ap dung hp ly cac tiu chi, vic xac inh cac gia tri gii han i vi cac mc thun li xe chay khac nhau, tinh trang giao thng trong cac iu kin phc tap khac nhau la bai toan quan trong nht. Vic chia cac tiu chi thanh cac nhom ng nht cho phep phat hin cac tinh trang va iu kin xe chay, ma mt trong s cac tiu chi co th th hin chinh xac. Chng han, i vi tc hanh trinh nhn c cac kt qua sau (bang 1).

Cac gi tri cua cac tiu chiTc hanh trinh, m/s45678910111213Tap m gia tc, m/s2 > 0,55 < 0,55Tap m nng lng, m2/s3e < 4,36,1> e > 4,3e > 6,1Gradient tc , 1/sGv>0,110,11>Gv>0,0870,0650,55Ge

Cho nn, cac khoang tc c chia ra, ma mi mt trong cac tiu chi co th phn bit c chinh xac. Tap m gia tc co th phn bit c, khng phai la tp hp tt ca cac gia tri tc , ma chi la hai khoang chia (v > 9m/s, v

Vi vic s dung thng tin tng t v thi gian chm dong, tn sut dng xe ngi ta a chinh xac pham vi ap dung cac tiu chi:- Tap m gia tc cho it thng tin v tc hanh trinh, nhay yu vi s thay i thi gian chm dong, anh gia s khng u n chua chuyn ng khach quan. Trn mang giao thng co iu khin ap dung no khi chiu dai cua mt oan ng > 500-600 m;- Nh gradient tc anh gia tt cac iu kin xe chay kho khn khi tc hanh trinh < 30 km/h, thi gian chm dong > 5s/phut, tn sut dng xe > 0,6 ln/phut, nhay yu vi s thay i cua tc cac iu kin t do. Ap dung hp ly trn cac ng ph chinh;- Vi tap m nng lng phn bit tt cac iu kin khi tc hanh trinh > 30 km/h, no khng nhay khi anh gia xe chay vi tc thp va chm dong. Nn ap dung trn cac ng chinh xe chay khng phai dng;- Vi gradient nng lng la tiu chi chinh xac nht anh gia s thay i chm dong, phn bit tt cac iu kin kho khn xe chay. Khuyn khich pham vi ap dung Mang li giao thng co iu khin, cac ng chinh xe khng dng.

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