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Chapter Five. Saturation Headways
Pages 31-50

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From page 31... ... Saturation headway is also one of the primary input parameters marred for He proposed capacity procedure descnbed in chapter three of this report RESEARC:EI HYPOTHESES: FACTORS AFFECTING SATURATION HEADWAYS Past studies and close observation of traffic operations as part of this study provide evidence that the saturation headway for a vehicle at an AWSC intersection is a function of both traffic flow characteristics as weD as intersection geometry. Since the saturation headway is the key parameter to be used in the estimation of He approach capacity, it is important to understand and quantify the factors that affect it. Read the entire page →
From page 32... ... HYPOTHESIS TESTIN~GROIJP 1 SITES Analysis of Eight Degree of Conflict Cases It was ~n~dady proposed Hat eight degree of conflict cases are required to Filly descnbe the conditions faced by the subject approach driver. These cases are described Table 35. Read the entire page →
From page 33... ... tw~tai1 z Cntical tw~tail ID _ 3.86 1.90 3855 2 4.78 2.43 1874 -21.68 0.00 2.33 0.00 2.58 Reiect 3 5.88 2.89 1073 4 5.89 2.79 934 4.15 0.44 2.33 0.22 2.58 Accent 2 4.78 2.43 1874 5.88 2.89 1073 -17.39 0.00 2.33 0.00 2.58 Re ect J Table 38. Hypothesis Tests: Consolidation of Headway Cases Stan Headway Case Mean Vanance Observations Z Test Results Computed z value P(Z<=z) Read the entire page →
From page 34... ... Frequency Distributions for Degree of Conflict Cases 15 ^10 S O Saturation Headways, Case Single Lane Sites Site ~ H - dwarfs Capacity 1200 800 400 . -o Figure 11. Read the entire page →
From page 35... ... 1' t:.:-:: -- :::::-:.:-:-:-:::.:::::-:::::.::-::::::::::::::::::::::::: :::::::::::: :::::-::: :::-::::::-:-:-:-: ::-:: E:::::::::::::::::: -:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::- :::::::::::::::::: :::::::::::: ::::::::::::::: -:::::.:.- :.:.:::.:::.:::.:. -::::::::::::::::::::::::::: Ista~cs I I T T I 1~ T=g Movement LT ~111 Me" 3.92 1 3.92 Variance 2.S6 1 L74 Observations 367 1 3063 Z Test Results Computed z value -0.04 P(Z<=z) Read the entire page →
From page 36... ... Headway Case 4-Turning Movement Difference in Means Tests TH 7.34 3.84 1148 RT S.32 3.31 293 S.57 0.00 2.33 0.00 2.Sg Reject P :::: '''-'' '''''''' ''' :$ ~ Stadstics 1 1 1 1 1 1 Tuming Movement LT TH LT RT ~ Mean 8.00 7.34 8.00 6.63 1 Variance S.11 3.84 S.11 3.6S Obsenrations 32S 1148 32S 226 Z Test Results Computed z value 4.83 7.68 ~ P(Z<=z) one-tail 0.00 0.00 \| z Cntical one-tail 2.33 2.33 p(z<=z) Read the entire page →
From page 37... ... bservadons 1 106 1 270 1 270 1 51 1 70 1 51 l \| ' Test Results l Computed z value 2.00 -0.40 -0.40 P(Z<~) one-tail 0.02 0.34 0.34 z Critical one-tail 2.33 2.33 2.33 P(Z<=z) Read the entire page →
From page 38... ... Hypothesis Tests. Vehicle Type Mean Mown Variance Observations I' 2;2'22 '' "' "' '' ':""'' "'"'"''I'' '' ~ '2 I"''"" "'" ''' ' ' ' ~ i.,. Read the entire page →
From page 39... ... Saturation Headways for Various Conflicting Vehicle Movements for Group 1 Sites 1 ' 2 2 222 ' 22 'I''' - ' '1 '' ' ' ' I'' '"''""'' ' '' ;':~''1"'' " "' '''''''''''''' -1"''''* Read the entire page →
From page 40... ... The effect of time in queue on Be saturation headway was not listed earlier as a specific hypothesis tom However, Me influence of time in queue of the subject vehicle has been suggest to adversely affect the critical gap and follow up time for TWSC intersections. ~ addition, Were was some concern that sites from this current sty with low volumes may result In lower pressure on the subject approach Diver Bus affecffng the comparability of saturation headway values between sites. Read the entire page →
From page 41... ... Table 52. Hypothesis Test 2 for Each Degree of Conflict Case Sacs Mean Variance Ions Z Test Remlts Computed z value P(Z<=z) Read the entire page →
From page 42... ... .. , 2 ; Statistics Mean Variance Ob~ons 7.34 2.62 29S 7.37 4.20 1699 9.31 6.81 142 ALSO g.S2 427 Z Test Results Confuted z value P(Z<=z) Read the entire page →
From page 43... ... two~ail 0.02 0.00 O.OS z Critical two~ail 2.S8 2.S8 2.S8 HO: (~ are identi~t Accept Reject Ac~xpt Table 56. Hypothesis Tests for Groups 1, 2, and 3 'tadstics - 1 1 1 1 1 Geometric Group 3a-NC1 3~NC1 3a-NC2 3~NC2 Mean 4.3S 4.13 S.19 4.71 Variance 1.4S 1.39 2.8 2.03 Observations 214 1493 121 llOS Z Test Results Con~uted z vatue 2.SO 3.04 P(Z<=z) Read the entire page →
From page 44... ... Hypothesis Tests for Group 4 Staff - cs Geometric Group 4a 4b 4a 4b Mean 7.19 7.77 9.43 10.S7 Variance 2.96 4.13 S.3S lS.05 Observations 1 236 1 439 1 114 1 197 Z Test Results Computed z value -3.92 -3.2S P(Z<=z) one-tail 0.00 0.00 z Critical one-tail 2.33 2.33 P(Z<=z) Read the entire page →
From page 45... ... NumVeh is He number of opposing and conflicting vehicles faced by He subject driver. REGRESSION ANALYSIS-GROllPS 14 SITES The analysis presented ~ the previous sections showed that the most significant factors affecting saturation headway were the mining movement of the subject vehicle, the degree of conflict fat by the subject vehicle, the vehicle type, and the geometry of the intersection. Read the entire page →
From page 46... ... For 4-leg intersections, increasing only the number of opposing^lanes from one to two does not significantly increase the saturation headway. But increasing the number of conflicting lanes, if the number of opposing lanes increases from one to two, does increase the saturation headway by 0.56 to 0.57 seconds. Read the entire page →
From page 47... ... Regression Models for Saturation Headways~roups 5 and 6 Sites The saturation headway for heavy vehicles is I.6 seconds higher than for passenger cars, for the Group 5 sites. There were not sufficient heavy vehicles In the Group 6 Ma for a s~isticaDy-signiiicant estimate of this factor to be made. Read the entire page →
From page 48... ... Hypothesis 2 The saturation headway of the subject vehicle is dependent on intersection geometry, particularly He number of lanes on the conflicting approaches, the opposing approach, and the subject approach. Finding Creasing the number of lanes on the conings approaches, while maintaining a single lane on~the opposing approach does not significantly increase the saturation headway of the subject approach driver. Read the entire page →
From page 49... ... Finding The same analysis shows thatch saturation headway of He subject approach driver is affected by He specific combination of He directional movements of the subject, opposing, and conflicting approach vehicle. This finding is supported by a comparison of the saturation headway values for venous movement interaction combinations. Read the entire page →
From page 50... ... ,- O.S -0.7 1.6 Notes: Case is the degree of conflict case. Bumped is the number of opposing and conflicting vehicles faced by the subject approach driver. Read the entire page →

From page 31...

... Saturation headway is also one of the primary input parameters marred for He proposed capacity procedure descnbed in chapter three of this report RESEARC:EI HYPOTHESES: FACTORS AFFECTING SATURATION HEADWAYS Past studies and close observation of traffic operations as part of this study provide evidence that the saturation headway for a vehicle at an AWSC intersection is a function of both traffic flow characteristics as weD as intersection geometry. Since the saturation headway is the key parameter to be used in the estimation of He approach capacity, it is important to understand and quantify the factors that affect it.

Chapter Five. Saturation Headways Pages 31-50

Chapter Five. Saturation Headways
Pages 31-50