05 HCM 2010 Procedure - Kittelson & Associates, Inc.

HCM 2010 Analysis ProcedureRoundabout Traffic Operations AnalysisShort Course

Highway Capacity Manual 2010Roundabouts ProcedureHighway Capacity Manual 2010Roundabouts Procedure

Largely based on research documented in NCHRP Report 572

Procedure is:Anchored to empirical U.S. performanceAble to analyze multilane roundaboutsAble to be calibrated

Comparing HCM 2010 Procedure to NCHRP Report 572Comparing HCM 2010 Procedure to NCHRP Report 572

The HCM 2010 incorporates several modifications to the NCHRP Report 572 procedure, including:

The HCM procedure provides a separate capacity calculation for the left and right lane of a two-lane entry. NCHRP Report 572 computes capacity and performance measures for only the critical lane of an approach.Additional guidance provided on lane use and lane utilization factorsCalculation using either 15-minute volumes or hourly volumes modified by a PHFCalculation of control delay and queues using vehicles per hour instead of passenger car equivalents per hour (heavy vehicles handled differently)Control delay equation includes additional term for yield control

HCM 2010 Analysis ProcedureHCM 2010 Analysis Procedure

Step 1: Convert movement demand volumes to flow rates

Step 2: Adjust flow rates for heavy vehicles

Step 5: Determine the capacity of each entry lane and bypass lane as appropriate in passenger car equivalents

Step 8: Compute the volume-to-capacity ratio for each lane

Step 9: Compute the average control delay for each lane

Step 10: Determine LOS for each lane on each approach

Step 11: Compute the average control delay and determine LOS for each approach and the roundabout as a whole

Step 12: Compute 95th percentile queues for each lane

Step 3: Determine circulating and exiting flow rates

Step 4: Determine entry flow rates by lane

Step 7: Convert lane flow rates and capacities into vehicles per hour

Step 6: Determine pedestrian impedance to vehicles

Step 1: Convert movement demand volumes to flow ratesStep 1: Convert movement demand volumes to flow rates

Use peak 15-minute volumes and multiply by 4 to directly measure an hourly flow rate for those peak 15 minutes, ORUse hourly volumes and a peak hour factor to get an estimated hourly flow rate for those peak 15 minutes

PHFVv i

i =

where:vi = demand flow rate on approach i, veh/hVi = demand volume on approach i, veh/hPHF = Peak Hour Factor

HCM 2010, Equation 21-8

Step 2: Adjust flow rates for heavy vehiclesStep 2: Adjust flow rates for heavy vehicles

Convert trucks to passenger car equivalents (pce)

HCM 2010, Exhibit 21-10

HV

ipcei f

vv =, ( )111

−+=

TTHV EPf

where

v i,pce = demand flow rate for movement i (pc/h),

vi = demand flow rate for movement i (veh/h),

fHV = heavy-vehicle adjustment factor,

PT = proportion of demand volume that consists of heavy vehicles, and

ET = passenger car equivalent for heavy vehicles.


HCM 2010, Equations

21-9, 21-10

Step 3: Determine circulating and exiting flow ratesStep 3: Determine circulating and exiting flow rates

Circulatory volume = sum of movements as shown

Step 3: Determine circulating and exiting flow rates (cont.)Step 3: Determine circulating and exiting flow rates (cont.)

Exit volume = sum of movements as shownDeduct right-turn movement if it is using a bypass lane

Step 4: Determine entry flow rates by laneStep 4: Determine entry flow rates by lane

Check for fixed or de facto lane assignments


Step 4: Determine entry flow rates by lane (cont.)Step 4: Determine entry flow rates by lane (cont.)

If only one lane is available for a given movement, 100% of that movement is assigned to that lane.

210290130

210420

210290130

500130


Check to see if a turning movement creates a de facto lane assignment.

610290130

LTs dominate left lane, create de factoLT lane. THs are assumed to use only the right lane.

515515

420 (= 290 + 130)

610


Lane flow by lane assignment case:

Default values for %LL, %RL:

HCM 2010, Exhibits 21-14, 21-21


Adjustments can be made to account for downstream destinations, geometric effects, etc.

210590130

465465

The downstream on-ramp creates a lane imbalance at this intersection that should be accounted for in the analysis.

450 of the 590 are turning right onto a freeway on-ramp immediately beyond this intersection

580 (= 130 + 450)

350 (= 210 + 140)

0

200

400

600

800

1,000

1,200

1,400

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000

Conflicting Flow Rate (pc/h)

Cap

acit

y (p

c/h

)

Dashed regression extrapolated beyond the data

Capacity of one-lane entry or right lane of two-lane entry against two conflicting lanes

Capacity of left lane of two-lane entry against two conflicting lanes

Capacity of one-lane or either lane of two-lane entry against one conflicting lane

Step 5: Determine capacity of each entry lane and bypass laneStep 5: Determine capacity of each entry lane and bypass lane


0

200

400

600

800

1,000

1,200

1,400

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000


Cap

acit

y (p

c/h

)





Capacity: 1 laneCapacity: 1 lane

0

200

400

600

800

1,000

1,200

1,400

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000


Cap

acit

y (p

c/h

)





Capacity: 2x1 laneCapacity: 2x1 lane

0

200

400

600

800

1,000

1,200

1,400

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000


Cap

acit

y (p

c/h

)






Right Turn Bypass LanesRight Turn Bypass Lanes

Right turn volume excluded from roundabout entry volume for roundabout capacity calculations.Separate capacity calculation may be required for bypass lane.Two types:

Yielding bypass lane (Type 1)Non-yielding bypass lane (Type 2)

Yielding Bypass Lane (Type 1)Yielding Bypass Lane (Type 1)

Terminates at a high angle -yielding to exiting trafficCapacity approximated using the appropriate single-lane (1x1) or multilane (1x2) capacity formulaTreat the exiting flow from the roundabout as the conflicting flow

Non-Yielding Bypass Lane (Type 2)Non-Yielding Bypass Lane (Type 2)

Merges at a low angle with exiting traffic or forms a new lane adjacent to exiting traffic. Capacity is expected to be relatively high due to a merging operation between two traffic streams at similar speeds.

Step 6: Determine pedestrian impedance to vehiclesStep 6: Determine pedestrian impedance to vehicles

Single-lane case

0.80

0.85

0.90

0.95

1.00

0 100 200 300 400 500 600 700 800 900 1,000

Conflicting circulating flow (pc/h)

Entr

y ca

paci

ty a

dju

stm

ent

fact

or, f

ped

Step 6: Determine pedestrian impedance to vehicles (cont.)Step 6: Determine pedestrian impedance to vehicles (cont.)

Double-lane case

0.80

0.85

0.90

0.95

1.00

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800

Conflicting circulating flow (pc/h)

Entr

y ca

paci

ty a

dju

stm

ent

fact

or, f

ped

Step 7: Convert lane flow rates and capacities into veh/hStep 7: Convert lane flow rates and capacities into veh/h

where:

vi = flow rate for lane i (veh/h),v i,PCE = flow rate for lane i (pc/h),fHV,e = heavy-vehicle adjustment factor for the entry lane,ci = capacity for lane i (veh/h),c i,PCE = capacity for lane i (pc/h),fped = pedestrian impedance factor,fHV,i = heavy-vehicle adjustment factor for movement i.

eHVPCEii fvv ,,= pedeHVPCEii ffcc ,,=

PCEeRPCETPCELPCEU

PCEeReRHVPCETTHVPCELLHVPCEUUHVeHV vvvv

vfvfvfvff

,,,,,

,,,,,,,,,,, +++

+++=

Step 8: Compute volume-to-capacity ratio for each laneStep 8: Compute volume-to-capacity ratio for each lane

Calculated as follows:

HCM 2010 does not set target values for xFor design purposes, often desirable to design for value of 0.85, or a different value under appropriate circumstances

i

ii cvx =

Step 9: Compute average control delay for each laneStep 9: Compute average control delay for each lane

where:D = control delay, s/vehx = volume-to-capacity ratioc = capacity, veh/hT = time period = 0.25 h

( ) [ ]1,min5450

600,3

11900600,3 2 xT

xcxxT

cd ×+

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡⎟⎠⎞

⎜⎝⎛

+−+−+=

0

10

20

30

40

50

60

0 400 800 1200 1600 2000 2400

HC

M 2

010

Co

ntr

ol D

elay

(s)

Entering flow (veh/h)

Capacity = 400 veh/h 800 veh/h 1200 veh/h 1600 veh/h 2400veh/h

2000veh/h

Graphical Depiction of HCM 2010 Control Delay EquationGraphical Depiction of HCM 2010 Control Delay Equation

Note: Assumes T=0.25 h

Step 10: Determine LOS for each laneStep 10: Determine LOS for each lane

LOSControl Delay

(s/veh)

A 0 − 10

B > 10 − 15

C > 15 − 25

D > 25 − 35

E > 35 − 50

F > 50

Same as for other unsignalized intersections

Step 11: Compute control delay and LOS for approaches and roundabout as a wholeStep 11: Compute control delay and LOS for approaches and roundabout as a whole

Can be used for comparison with signalized and AWSC intersections

∑∑

=

ii

iii

V

VDD onintersecti

where:Dintersection = intersection control delay, s/vehDapproach i = control delay on approach i, s/vehVapproach i = volume on approach i, veh/h

Step 12: Compute 95th percentile queue for each laneStep 12: Compute 95th percentile queue for each lane

where:Q95 = queue length, vehx = volume-to-capacity ratioc = capacity, veh/hT = time period = 0.25 h

( ) ⎟⎠

⎞⎜⎝

⎛

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡⎟⎠⎞

⎜⎝⎛

+−+−=600,3150

600,3

11900 295

cT

xcxxTQ

Graphical Depiction of HCM 2010 95th Percentile Queue EquationGraphical Depiction of HCM 2010 95th Percentile Queue Equation

0 0.2 0.4 0.6 0.8 1.0 1.2 1.41

2

3

4

5678910

20

30

40

5060708090100

∞

Exp

ecte

d M

axim

um N

umbe

r of V

ehic

les

in Q

ueue

, Q95

[veh

]

v/c Ratio [-] FHWA Exhibit 4-10, p. 95

Example ProblemExample Problem

Adjusted Roundabout

volumes

271

246

693

222

847

344

602

0

200

400

600

800

1,000

1,200

1,400

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000


Cap

acit

y (p

c/h

)





Example Problem: Capacity CalculationExample Problem: Capacity Calculation

246

(NB

)

NB = ~880

SB = ~900

222

(SB

)

WB = ~620

599

(WB

)

EB = ~56069

3 (E

B)

Example Problem: V/C CalculationExample Problem: V/C Calculation

Northbound Approach:Entering volume = 602 veh/hCapacity = 880 veh/hV/C Ratio = 602 / 880 = 0.68

Repeat calculation for other approaches

Example Problem: V/C ResultsExample Problem: V/C Results

V/C Ratio

Entry capacity (pce)

Conflicting volume (pce)

Entering volume (pce)

WBEBSBNB

Approach Control Delay (s/veh)

Intersection Control Delay (s/veh)

95th %ile Queue (veh)

0.550.94

621905

599222

344847

0.68

884

246

602

-

-

-

-

-

-

-

0.48

565

693

271

-

-

0

10

20

30

40

50

60

0 400 800 1200 1600 2000 2400

HC

M 2

010

Co

ntr

ol D

elay

(s)

Entering flow (veh/h)

Capacity = 400 veh/h 800 veh/h 1200 veh/h 1600 veh/h 2000 veh/h 2400veh/h

602

12

Example Problem: Control Delay Calculation (Northbound Approach)Example Problem: Control Delay Calculation (Northbound Approach)

Note: Assumes T=0.25 h

Example Problem: Delay ResultsExample Problem: Delay Results

V/C Ratio




WBEBSBNB




0.550.94

621905

599222

344847

0.68

884

246

602

-

12

-

33

-

13

21

0.48

565

693

271

-

12

Example Problem: 95th Percentile Queue (Northbound Approach)Example Problem: 95th Percentile Queue (Northbound Approach)

0 0.2 0.4 0.6 0.8 1.0 1.2 1.41

2

3

4

5678910

20

30

40

5060708090100

∞

Exp

ecte

d M

axim

um N

umbe

r of V

ehic

les

in Q

ueue

, Q95

[veh

]

v/c Ratio [-]

0.68

~5.5

884*0.25 = 221

Example Problem: Delay ResultsExample Problem: Delay Results

V/C Ratio




WBEBSBNB




0.550.94

621905

599222

344847

0.68

884

246

602

6

12

15

33

4

13

21

0.48

565

693

271

3

12

05 HCM 2010 Procedure - Kittelson & Associates, Inc.

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