Traffic Capacity Analysis Concepts Chapter 9

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• Traffic Capacity Analysis Concepts (Chapter 9)
• Capacity vs. Level of Service
• Capacity
• Prevailing Conditions
• Segment analysis
• Peak 15-minute

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• Reasonable Expectancy
• Capacity in VPH or Per./hr.
• Level of Service
• Speed and Travel Time
• Density
• Delay
• Other Measures

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• MOEs for different facility types
• Freeway basic section?Density
• Two-lane highways ?Percent time delay
• Signalized Intersection ?average individual
  stopped delay
• Arterial ?Average travel speed

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• Volume to Capacity Ratio
• Volume of present or future conditions
• Capacity of section based on prevailed traffic
• LOS f(V/C)

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• Basic Capacities
• Multi-lane Uninterrupted
• 2400 pcphpl under prevailing conditions
• Two-lane Rural
• 2800 pcph total of both directions

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• Signalized Intersections
• 1800 pcphgpl
• capacity per lane of clock time
  18001800-3600(21)/60/3600810
• Deviations from ideal conditions require
  correction factors f

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• Geometric Conditions
• Alignment Design Speed
• 55 mph ?2250pcphpl
• Mountainous Terrain
• No Passing ?reduction of 22
• Lane width ? 12 feet
• Shoulder width ? 6 feet
• Correction factor ? fw

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• Grades
• General Terrain, and Segment Specifics ? fg
• Traffic Conditions
• Directional Distribution ? fd
• Lane Distribution equilibrium among lanes
• Heavy Vehicle Impacts ? fHV

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• Different ways to estimate PCE
• Based on
• Speed
• Gaps
• Delay
• Chapter 12, page 300

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• Control Conditions
• Speed Limits
• Lane-use Control
• Traffic Signals
• Stop Yield Signs

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Problem 7-10
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• Mean41.07 mph, SD 7.54
• P5040.1 mph, P8548.0 mph
• 10 mph pace (35.5-45.5 mph) 79 - 24 55 veh.
  in the pace
• 95 conf. U41.071.96(.6)39.9 to 42.25 mph
• 99.7 conf. U41.073.00(.6)39.3 to 42.87
• Es/n0.57.54/1570.50.6 mph

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• N3.84s2/e23.84(7.54)2/(2.5)235
• Normal Approximation test
• SD(7.542/157)(6.912/100).5 0.916 mph
• Z(41.07-40)/0.9161.168
• Prob. (Z?1.168)0.8786lt0.95
• The difference in observed average speeds must
  therefore be considered to be not significant.

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• Problem 8-1
• Accidents Rates
• 360/1230 accidents /100MVM 360/0.5720 acc. /
  100,000 pop. 360/3.5102.9acc./10,000 reg. Veh
• Fatality Rates
• 15/121.25 fatalities/ 100MVM 15/0.530
  fatalities/ 100,000 pop. 15/3.54.28
  fatal./10,000 reg. Veh.

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• Hourly Exposure Rates
• 12,000,000/20400,000 hr. of exp. 360/.40900
  acc./ 106 hr. of exp. 15/0.437.5 fatal/ 106
  hr. of exp.

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• Problem 8-4
• Possible causes of accidents
• Lack of an exclusive left-turn phase for the
  NB-SB approaches.
• Offset of the NB-SB approaches.
• Side-swipe accidents may be due to shifting of
  vehicle path.
• Rear-end due to short amber interval, and other
  factors

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• Measures to improve the situation
• Introduce protected LT phase, no permitted
  option.
• Install additional signal heads
• Install additional guide markings
• correct deficiencies in clearance and pedestrian
  crossing time

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• Problem 8-5
• Normal Approximation
• Z15-25/(1525)0.50 1.58
• Zcrit_at_5 Confidence Level 1.98
• Zlt Zcrit no significant reduction
• Chi-Square Test
• From figure 8-9, for x25, v40, the point lies
  below the Chi-Square curve, reduction is NOT
  significant