3 capacity analysis - 2.ppt

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Transportation Capacity andLevel of Service

CE 426

Weeks 3 –4 Chapter 4

pp. 139-232



10/29/2013 Prepared by: E.M. Parentela2

Objectives

1. Analyze capacity for signalized intersections

2. Identify three types of signal control.3. Define and estimate cycle length and

pedestrian timing.

4. Estimate capacity of transport facility

5. Estimate capacity of pedestrian facilities




Intersection Control

Types of Intersection Control – Yield Signs

– Stop Signs

– Multiway Stop Signs

Warrants: – Total intersection approach volume 500 vph for 8 hours, or 350

vph if the 85th percentile speed of the major road is >40 mph

– Combined volumes of vehicles and pedestrians on minor approach200 units per hour for the same 8 hour, and

– Average delay of vehicles on minor street 30 sec/veh during themaximum hour

Intersection Channelization

Traffic Signals




Signal Control

MUTCD warrants to signalize an intersection:

1. Eight hour vehicular volume

2. Four hour vehicular volume

3. Peak Hour

4. Pedestrian volume

5. School crossing

6. Coordinated signal system7. Crash experience

8. Roadway Network

What are the types of signal operation at signalized intersection?




Three Types of Signal Operation

Pretimed - repeat a preset constant cycle. – does not respond to demand or presence of vehicles or pedestrians.

– suitable in areas with more or less uniform rate of flow.

Semi-actuated – detectors are placed on minor streets only. Themajor street is guaranteed green display except when vehicles aredetected on lightly used minor street. – demand-actuated

– implemented at intersections of a major street and a minor street. .

Fully actuated - detectors are placed on all legs of the intersection. – demand-actuated.

– suitable at intersections with more or less equal demand but fluctuatingflow.



Detectors - autoscope




Detectors –

loop





Signalized Intersection

Signalized intersections

– permit conflicting traffic movements to proceed efficiently and

safely – Separates individual movements in time rather than in space.

– Movements can be grouped and served during separate phases

– Some movements are allowed to proceed during a phase eventhough they cause conflicts (such as pedestrians allowed to crosswhile right-turn movements are occurring)

Two types of movements – Permitted (conflicts with other movements)

– Protected (without conflicts)

How many conflicting movements occur at an intersection?




Signal Timing

Terminologies – pp. 152 – Cycle, Cycle length, interval, phase, offset

Saturation headway, h – average headway that can beachieved by a saturated, stable moving queues of vehicles;around 2-3 sec/veh.

s = 3600/h

s = saturation flow rate (veh/hg/ln)

h = saturation headway (sec/veh)

Capacity of lane (ci)ci = si gi/C

gi = effective green time for lane i

Si = saturation flow rate for lane i

C = cycle length




Signal Timing

Maximum critical volume at intersection

C xt N

hV Lc 360036001

Where:

Vc = maximum sum of critical volume

N = number of phases in the cycle

tL = total lost time/phase (includes start-up, and lost time incurred

as light changes from yellow to all red

C = cycle length

Can be used to determine number of lanes, pp. 159

Can be used to determine minimum cycle length, pp. 160




Signal Timing

Minimum Cycle Length

Desirable Cycle Length

)/()/3600(1

cv PHF h

V

Nt C

c

Ldes

)/3600(1

min

h

V

Nt C

c

L




Signal Timing

Cycle Length – complete sequence of signalindication

Co = optimal cycle length, sec

L = total lost time during a cycle, normally 3.5 secper phase (due to startup delay and clearancelost time)

Yi = sum of the flow ratios (V/S) of criticalmovement i

Yi LC o

1

55.1




Saturation Flow Rate

Saturation flow rate – flow rate the lanegroup can carry for continuous green time(g/C = 1)

So = base saturation flow rate = 1900 pcphgpl

N = number of lanes

f = adjustment factors (lane width, heavy vehicle,grade, parking, bus blockage, lane utilization, leftturn, right turn, pedestrian and bicycles)

Rpb Lpb RT LT LU bb p g HV wo F fl f f f f f f f Nf S S




Signal Timing

Yellow interval – alerts motorists that green light

is about to change to red – eliminates dilemma zone

Gg a

u

u

LW o

o

2min

Where:

λmin = minimum yellow duration, sec δ= perception-reaction time, sec

(around 1 to 1.5 sec to stop) uo= initial speed, ft/sec

a = constant rate of vehicle deceleration

(around 8 to 11.2 ft/sec2,use 11.2 if not given)

W = width of intersection, ft

L = length of vehicle, ftG = grade




Signal Timing

Allocation of Green Times

Gte = total effective green time per cycle

Gei = effective green time for phase i

Actual green time for phase i

xGteY Y Y

Y G i

ei

....21

iitea l GG 11

Gte = C-Sum(Total lost time +All Red)




Signal Timing

Pedestrian Consideration

– for WE>10 ft

– for WE≤10 ft where:

– Gp = pedestrian effective green time, sec

– 3.2 = pedestrian start-up time

– L = crosswalk length, ft

– Sp = average speed of pedestrians (usually taken 4 ft/sec)

– WE = width of the crossing, ft

– Nped = number of pedestrians crossing during an interval

E

ped

p p W

N

S

L

G 7.22.3

ped

p

p N S

LG 27.02.3




Signal Timing Exercise

A B

Lane Width = 15’

L a n e W i d t h 1 8 f t

500

400

500

600

Given:

saturation flow rate= 2000 vph/ln

(vehicle per hour per lane)

lost time = 3.5 sec per phase

85th percentile speed= 40 mph

Required:

Optimal Cycle length

Phase




Bus Capacity

Factors affecting capacity: Dwell time – door opening to

closing

Dwell Time: td = Pata + Pbtb +toc

Pa = alighting passengers (peak 15min)

Ta = alighting time

Pb = boarding (peak 15 min)

Tb = boarding time

Toc = door opening (2 sec) and closing(5 sec) time

Variation of dwell time – standarddeviation (60%; 40-80%)

Clearance time – exit stop toreenter traffic (10 sec)

Failure rate – probability of queuing

Bus stop location nearside

Midblock

farside

Capacity: – Loading Area pp. 177

– Bus Stop pp. 178

– Bus lane pp. 178 Exclusive urban bus lane

Mixed traffic bus lane




Transit Person Capacity

Person Capacity, P, person/hr

P = TLPm (PHF) T = veh cap (trains/hr)

L = length of train (ft)

Pm (linear passenger loading level, person/ft PHF = peak hour factor



Transit Quality of Service

Measures pp. 200-202

LOS

– Frequency of service – Hours of service

– Passenger loads

– Route segment reliability





Pedestrian Facilities

LOS p. 206, 208

Walkways and

Sidewalks

– Pedestrian flow rate

Urban Streets pp. 213

E

p

W

vv

15

15

Vp = pedestriam flow rate

V15 = peak 15-min flow rate

We = effective walkway width

j

i

i

T A

d S

L

LS

Sa = ave ped speed, ft/sec

LT = total length of urban street (ft)

Si = ped walking speeddj = intersection delay




Bicycle Facilities

Exclusive off-street pp. 215

Shared off-street (peds, skateboards, roller skates)

Paths at signalized intersection

On-street bike lanes

Capacity is not critical for the design and analysis of

bicycle facilities Assume 2000 bicylce/hr/lane for saturation flow rate –

uninterrupted flow condition




Airport Runway Capacity

Factors affecting capacity pp. 224

– number and layout of runway

– Separation requirements

– Weather conditions

– Wind direction/strength

– Aircraft (heavy, large, small) pp. 86

– Movements (arr-arr, dep-dep, arr-dep, dep-arr) – Air traffic management (ATM) system performance

– Noise and other env considerations



LAX Runway Capacity

Capacity Benchmark (2004 data)

– 137-148 flights per hour (arrivals and departures) in

Optimum weather (visual approaches/separation)

– 126-132 flights per hour in Marginal conditions,

– 117-124 flights per hour in IFR conditions

With Planned improvements:

– Optimum and Marginal rates = 173 flights per hour

– IFR condition: 128 flights per hour


3 capacity analysis - 2.ppt

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