UNSIGNALISED INTERSECTIONS

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UNSIGNALISED INTERSECTIONS

• TS4273 Traffic Engineering

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Scope and Objectives

• This chapter deals with 3-arm and 4-arm
  unsignalised intersections which are formally
  controlled by the basic Indonesian traffic code
  rule give-way to the left.
• This method assumes right angled intersections in
  flat alignment and is valid for degree of
  saturation less than 0,8-0,9.

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Traffic Safety Considerations

• Effect of intersection layout
• 3-arm with T-shape 40 lower accident rates than
  4-arm.
• Y-shape have 15-50 higher accident rates than
  T-shape.
• Effect of geometric design
• Median (3-4m) on major road reduces the accident
  rates (if the road wider than 10m)

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Traffic Safety Considerations

• Effect of intersection control
• Yield sign control reduces the accident rates 60
  compare to priority from the left
• Stop sign control reduces the accident rates 40
  as compared to yield sign.
• Traffic signal control reduces the accident rates
  20-50 compared to uncontrolled operation.

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Performance Measures of Unsignalised Intersections

• Capacity (C)
• Degree of saturation (DS)
• Delay
• Queue probability

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Range of Variation in Empirical Data for Input
Variables (4-Arm)
Variable Min. Avg. Max.
Approach width (m) 3,5 5,4 9,1
Left-turn ratio 0,10 0,17 0,29
Right-turn ratio 0,00 0,13 0,26
Minor road flow ratio 0,27 0,38 0,50
Light vehicle- 29 56 75
Heavy vehicle- 1 3 7
Motorcycle- 19 33 67
Unmotorised flow ratio 0,01 0,08 0,22
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Range of Variation in Empirical Data for Input
Variables (3-Arm)
Variable Min. Avg. Max.
Approach width (m) 3,5 4,9 7,0
Left-turn ratio 0,06 0,26 0,50
Right-turn ratio 0,09 0,29 0,51
Minor road flow ratio 0,15 0,29 0,41
Light vehicle- 34 56 78
Heavy vehicle- 1 5 10
Motorcycle- 15 32 54
Unmotorised flow ratio 0,01 0,07 0,25
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Definition of Unsignalised Intersection Types in
IHCM (4-Arm)
Type Code Major road approaches Major road approaches Minor road approaches
Type Code No. of lanes Median No. of lanes
422 1 N 1
424 2 N 1
424M 2 Y 1
444 2 N 2
444M 2 Y 2
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Definition of Unsignalised Intersection Types in
IHCM (3-Arm)
Type Code Major road approaches Major road approaches Minor road approaches
Type Code No. of lanes Median No. of lanes
322 1 N 1
324 2 N 1
324M 2 Y 1
344 2 N 2
344M 2 Y 2
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STEP A-1 Geometric Conditions

• Date
• Handle by
• City and province
• Major and minor road names
• Case
• Period
• Sketch of intersection geometry and dimension

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STEP A-2 Traffic Condition

• Sketch of turning movement flow
• Traffic composition
• pcu-factor
• K-factor
• pce-values

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STEP A-2 Traffic Condition
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STEP A-3 Environmental Condition

• City Size (p.3-29 Table A-31 or p.3-34 Table
  B-51)
• Road Environment (p.3-29 Table A-32 or p.3-35
  Table B-61)
• Side Friction (p.3-29 Table A-32 or p.3-35 Table
  B-61)

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City Size Classes CSTable A-31 p.3-29
City Size Inhab. (M)
Very Small ? 0,1
Small gt 0,1 - ? 0,5
Medium gt 0,5 - ? 1,0
Large gt 1,0 - ? 3,0
Very Large gt 3,0
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Road Environment Type RETable A-32 p.3-29
Commercial Commercial land use (e.g. shops, restaurants, offices) with direct roadside access for pedestrians and vehicles
Residential Residential land use with direct roadside access for pedestrians and vehicles
Restricted Access No or limited direct roadside access (e.g. due to the existence of physical barriers, frontage streets etc).
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Side Friction class SF

• Side friction describes the impact of road side
  activities in the intersection area on the
  traffic discharge, e.g. pedestrians walking on or
  crossing the carriageway, angkot and buses
  stopping to pick up or let off passengers,
  vehicle entering and leaving premises and parking
  lots outside the carriageway.
• Side friction is defined qualitatively from
  traffic engineering judgment as high, medium or
  low.

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STEP B-1 Approach Width and Intersection Type
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STEP B-1 Approach Width and Intersection Type

• Average intersection approach width, WI
• WI (a/2bc/2d/2)/4
• If A is only exit
• WI (bc/2d/2)/3
• Road entry widths
• WAC (a/2c/2)/2
• WBD (bd/2)/2

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STEP B-1 Approach Width and Intersection Type

• Average road approach width WAC,WBD (m)
• WBD (bd/2)/2 lt 5,5
• No. of lanes (total for both directions) ? 2
• WAC (a/2c/2)/2 ? 5,5
• No. of lanes (total for both directions) ? 4

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STEP B-1 Approach Width and Intersection Type

• Average road approach widths WAC, WBD and
  Average intersection approach width WI.
• WAC (WAWC)/2 and WBD (WBWD)/2
• WI (WAWCWBWD)/no. intersection arms.

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STEP B-1 Approach Width and Intersection Type
IT Code No. of intersection arms No. of minor road lanes No. of major road lanes
322 3 2 2
324 3 2 4
342 3 4 2
422 4 2 2
424 4 2 4
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STEP B-2 Base Capacity Value C0
Intersection Type Base Capacity C0 (pcu/h)
322 2.700
342 2.900
324 or 344 3.200
422 2.900
424 or 444 3.400
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STEP B-3 Approach Width Adjustment Factor FW

• 422 ? FW 0,70 0,0866 WI
• 424 or 444 ? FW 0,61 0,0740 WI
• 322 ? FW 0,73 0,0760 WI
• 324 or 344 ? FW 0,62 0,0646 WI
• 342 ? FW 0,67 0,0698 WI

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STEP B-3 Approach Width Adjustment Factor FW

• 422 ? FW 0,70 0,0866 WI
• 424 or 444 ? FW 0,61 0,0740 WI
• 322 ? FW 0,73 0,0760 WI
• 324 or 344 ? FW 0,62 0,0646 WI
• 342 ? FW 0,67 0,0698 WI

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STEP B-4 Major Road Median Adjustment Factor FM
Description Type M Median adjustment factor, FM
No major road median. None 1,00
Major road median exists, width lt 3m Narrow 1,05
Major road median exists, width ? 3m Wide 1,20
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STEP B-5 City Size Adjustment Factor FCS
City Size Inhab. (M) FCS
Very Small ? 0,1 0,82
Small gt 0,1 - ? 0,5 0,88
Medium gt 0,5 - ? 1,0 0,94
Large gt 1,0 - ? 3,0 1,00
Very Large gt 3,0 1,05
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STEP B-6 Road Environment, Side Friction
Unmotorised AF FRSU
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STEP B-7 Left-Turning Adjustment Factor FLT
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STEP B-8 Right-Turning Adjustment Factor FRT

• 4-arm
• 3-arm

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STEP B-9 Minor Road Flow Ratio Adjustment
Factor FMI

• 422 (pMI ?0,1-0,9)
• FMI1,19pMI2-1,19pMI1,19
• 424 (pMI ?0,1-0,3)
• FMI16,6pMI4-33,3pMI325,3pMI2-8,6pMI1,95
• 444 (pMI ?0,3-0,9)
• FMI1,11pMI2-1,11pMI1,11

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STEP B-9 Minor Road Flow Ratio Adjustment
Factor FMI

• 322 (pMI ?0,1-0,5)
• FMI1,19pMI2-1,19pMI1,19
• 322 (pMI ?0,5-0,9)
• FMI-0,595pMI20,595pMI0,74
• 342 (pMI ?0,1-0,5)
• FMI1,19pMI2-1,19pMI1,19
• 342 (pMI ?0,5-0,9)
• FMI2,38pMI2-2,38pMI1,49

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STEP B-9 Minor Road Flow Ratio Adjustment
Factor FMI

• 324 (pMI ?0,1-0,3)
• FMI16,6pMI4-33,3pMI325,3pMI2-8,6pMI1,95
• 344 (pMI ?0,3-0,5)
• FMI1,11pMI2-1,11pMI1,11
• 344 (pMI ?0,5-0,9)
• FMI-0,555pMI20,555pMI0,69

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STEP B-10 Actual Capacity C
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STEP C-1 Degree of Saturation DS
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STEP C-2 Delays D (Intersection Traffic Delay
DTI)

• DS ? 0,60
• DTI 2 8,2078DS - (1-DS)2
• DS gt 0,60
• DTI 1,0504/(0,2742-0,2042DS) - (1-DS)2

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STEP C-2 Delays D (Major Road Traffic Delay
DTMA)

• DS ? 0,60
• DTMA 1,8 5,8234DS - (1-DS) 1,8
• DS gt 0,60
• DTMA 1,05034/(0,346-0,246DS) - (1-DS) 1,8

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STEP C-2 Delays D (Minor Road Traffic Delay
DTMI)

• DTMI (QTOTAL x DTI QMA x DTMA) / QMI

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STEP C-2 Delays D (Intersection Geometric Delay
DG)

• DS lt 1,00
• DG (1-DS) x (pTx6 (1-pT)x3) 4xDS
• DS ? 1,00
• DG 4

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STEP C-2 Delays D (Intersection Delay D)

• D DG DTI

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STEP C-3 Queue Probability
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STEP C-4 Evaluation of Traffic Performance

• If the obtain DS values are too high (gt 0,75),
  we should revise our assumptions regarding
  approach width etc and make a new set of
  calculations.

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Perbaikan Simpang Tak Bersinyal di Indonesia

• Perbaikan geometri (sudut radius tikungan)
• Manajemen lalulintas (rambu marka)
• Pengaturan PKL (represif preventif)
• Pulau lalulintas (lebar jalan gt 10 m)
• Lebar median di jalan utama (min 3-4 m)