Analysis of Signalized Intersections
What is Intersection analysis Inverse application of the signal timing design In signal timing design, green times are estimated to provide necessary capacity In intersection analysis, signal timing is known and used to estimate the existing capacity 2
Two methods Critical Movement Approach Apply adjustment factors to the demand volume HCM Methodology Saturation flow rates are reduced to reflect non-ideal prevailing conditions 3
Steps for Critical Movement Approach 1. Identify the lane geometry and use 2. Identify hourly demand volumes 3. Specify the signal timing 4. Convert demand volumes to equivalent passenger-car Volumes 5. Convert passenger-car equivalents to through-car equivalents 6. Convert Through-car equivalents under prevailing conditions to though-car equivalents under ideal conditions 7. Assign lane flow rates 8. Find critical-lane flows 9. Determine capacity and v/c ratios 10. Determine delay and level of service 4
Identify hourly demand volumes 1. Proportion of heavy vehicles 2. Proportion of local buses 3. Lane widths 4. Approach grade 5. Parking conditions on approach 6. Pedestrian interference levels 5
Identify hourly demand volumes 1. Proportion of heavy vehicles 2. Proportion of local buses 3. Lane widths 4. Approach grade 5. Parking conditions on approach 6. Pedestrian interference levels 6
Identify signal timings g = G + y + ar l l 1 2 g G y ar l 1 l 2 Effective green time Actual green time Actual yellow time Actual all-red time Start-up lost time Clearance lost time 7
Convert Demand Volume to Equivalent Passenger Car Volume V = VP E + VP E + V (1 P P ) pc HV HV LB LB HV LB 8
Passenger-car Equivalents for Local Buses (Stop in Travel Lane) 9
Passenger-car Equivalents for Local Buses (Stop in Parking Lane) 10
Convert Passenger-Car Equivalent to Through-Car Equivalent Left Turn Vehicles Protected left turns = 1.05 Permitted depends on opposing flow and number of opposing lanes Right Turn Vehicles Depends on the pedestrian volume in conflicting crosswalk 11
Through Car Equivalent for Left-Turning Vehicles 12
Through Car Equivalent for Right-Turning Vehicles 13
Though-car equivalents under ideal conditions v = V tcu PHF * f * f * f * f w g p LU Adjustment factor for: Lane width Grade Parking Lane utilization 14
Lane Width Adjustment 15
Grade Adjustment 16
Parking Adjustment 17
Lane Utilization Adjustment 18
Assign Lane Flow Rates Where a separate LT lane exist, assign all LT tcus to this lane group. If more than one lane exists, divide the tcu/h equally among the lanes Where a separate RT lane exist, assign all RT tcus to this lane group. If more than one lane exists, divide the tcu/h equally among the lanes For all mixed lane group(lt/th/rh, LT/TH, TH/RT)divide the total tcu/h equally among all lanes, except that all LT tcus must be in the LH lane and all RT tcus in RH lane 19
Find Critical Lane Flow Rates for Each Signal Phase From A1 to A3 Ring 1 148+420=568 Ring 2 203+330=533 Maximum = 568 From B1 to B3 Ring 1 120+380=500 Ring 2 220+250=570 Maximum = 570 1138 20
Capacity and v/c Ratio c = 1900( g / C) i n c = 1900( g / C) SUM i X = v / c i i i n i i= 1 X = v / c c i i i= 1 From A1 to A3 Ring 1 148+420=568 Ring 2 203+330=533 Maximum = 568 From B1 to B3 Ring 1 120+380=500 Ring 2 220+250=570 Maximum = 570 1138 21
Delay and Level of Service d i d 1i d 2i PF d d PF d = * + i 1i 2i Approach delay for lane group i Uniform delay for lane group I Overflow plus random delay for lane group i Progression adjustment factor 22
Uniform Delay and Overflow delay Uniform Delay: d 1i 0.5 C[1 ( g / C)] = i 1 [min(1, X )*( g / C)] Overflow Delay: 16X d = 225[( X 1) + ( X 1) 2 + i ] 2i i i cn i i 2 i i 23
Progression Factor 24
Level of Service 25
Example 26
Step 1 and 2: Geometry and volume 27
Step 3:Signal Phase 28
Step 4: Conversions to Equivalent Passenger Car Flow EB Through movement 1100 veh/h, 10% heavy vehicle and 20 buses/hour Heavy=1100*10%*2.0=220 Bus=20*3.1=62 Passenger_car=1100*(1-10%)-20=970 Total=Heavy+Bus+Passenger_car=1252 29
Step 4: Conversions to Through-Car Equivalent EB left turn Protected, equivalent=1.05 NB left turn One-way street, No conflicting through Go through pedestrian crosswalk Pedestrian volume 100 ped/h Treated like right turn, equivalent=1.21 30
Step 5: Conversions to Equivalent Under Ideal Condition No parking, fp=1.0 EB lane width is 11 feet, fw=0.97 EB Through has two lanes f=0.952 31
Step 6: Assign Flow to Lanes WB approach 183 tch/h for right turn and 1242 for through Total 1424 uniformly split between two lanes Leftmost lane 712 through only Rightmost lane carries 183 right turn and 1241-712=529 through 33
Step 6: Assign Flow to Lanes 34
Step 7: Critical Volume 35
Step 8: Capacity and v/c ratio 36
Step 8: Capacity and v/c ratio 37
Step 9: Delay and LOS Uniform Delay: 38
Step 9: Delay and LOS Overflow Delay: 39
Step 9: Delay and LOS Total Delay = d1*pf+d2: 40
Steps for HCM Approach 1. Input data 2. Define movement groups and adjusted flow rate 3. compute lane group flow rate 4. input or compute phase duration 5. Compute capacity 6. Compute delays and LOS 41
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Step 2: Movement and lane groups 43
Step 3: Estimating the Saturation Flow s = s Nf f f f f f f f f f f 0 w HV g p bb a LU RT LT Rpb Lpb Adjustment factors include: Lane width Heavy vehicles Grade Parking Local bus blockage Area type Pedestrian/bicycle interference 44
Adjustment for Lane Width f = w 0.96 Lanes width less than 10 ft f = w 1.0 Lane width between 10 and 12.9 ft f = w 1.04 Lane width larger than 12.9 ft 45
Adjustment for Heavy Vehicles f = w 0.96 Lanes width less than 10 ft f = w 1.0 Lane width between 10 and 12.9 ft f = w 1.04 Lane width larger than 12.9 ft 46
Adjustment for Grade f g = 1 G/ 200 G Grade in % 47
Adjustment for Parking P = N m 18 0.9 ( ) 3600 f p = ( N 1) + N P N 18N 0.1 ( m ) f p = 3600 0.05 N 48
Adjustment for Local Bus Blockage B = 14.4N 1.0 ( B ) 3600 f bb = ( N 1) + N B N 14.4N ( B ) f p = 3600 0.05 N 49
Adjustment for Type of Area CBD location: f = a 0.9 Other location: f = 1.0 a 50
Adjustment for Lane Utilization f LU = v g v N g1 v g vg1 Demand flow rate for the lane group Demand flow rate for highest lane volume N Number of lanes in the lane group 51
Adjustment for Protected Turns f = 0.85 For exclusive RT lane RT f = 0.95 For protected LT lane LT 52
Adjustment for Pedestrian and Bicycle Interference with Turns Estimate Pedestrian Flow Rate During Green Phase Estimate the Average Pedestrian Occupancy in the Conflict Zone Estimate the Bicycle Flow Rate During the Green Phase Estimate the Average Bicycle Occupancy in the Conflict Zone Estimate the Conflict Zone Occupancy Estimate the Unblocked Portion of the Phase Determine Adjustment Factors 53
Step 4: Determine Lane Group Capacities and v/c Ratios Capacity of a lane group c = s ( g / C) i i i v/c ratio of a lane group X i v = i = c i ( v/ s) i ( g/ C) i Critical v/c ratio for intersection X = Cmin c i i C ( v/ s) *( max ) C L max 54
Step 5: Critical Lane Group Identification 55
Step 6: Estimate Delay and LOS d = d + d + d 1 2 3 d 1 Uniform Delay d 2 Incremental Delay d 3 Additional Delay Per Vehicle Due to Queue 56
Step 6: Estimate Delay and LOS d 1 0.5 C[1 ( g/ C)] = 1 [min(1, X)*( g/ C)] 2 8kIX d = 900 T + [( X 1) + ( X 1) 2 + ( ) ] 2 ct d 3 + 2 2 2 b e eo e eo b 3600 Q Q Q Q Q Q = ( t + ) vt 2 2c 2c 57
Step 6: Aggregate Delay d A = i i dv i v i i d I = A i dv A v A A 58
Step 7: Interpret the Results v/c ratios X for every lane group Critical v/c ratio X for the intersection Delays and LOS for each lane group Delays and LOS for each approach Delays for overall intersection 59
Step 7: Interpret the Results Scenario I: Xc<1.0,all Xi<1.0, no capacity deficiency Scenario II; Xc<1.0,some Xi>1.0, reallocation of green time needed Scenaio III: Xc>1.0,some or all Xi>1.0, change of phase plan, cycle length, or physical design is needed 60
Example 61
Volume Adjustment 62
Saturation Flow Rate Estimation 63
Saturation Flow Adjustment 64
Saturation Flow Adjustment 65
Saturation Flow Adjustment 66
Saturation Flow Adjustment 67
Saturation Flow Adjustment 68
Capacity Analysis 69
Delay and LOS 70
What is the result if applying HCM to the former Critical Movement analysis example? 71
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