Rail Operation Design

7/26/2019 Rail Operation Design

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OPERATIONAL DESIGN

Rail Operation Design

The purpose of this section is to give an elementaryidea of how the concepts of capacity, volume, headway,and safety considerations are used in rail and bus operation

design.We have seen that volumemay be defined as the

number of vehicles passing a fixed point on the guideway ina unit of time. Volume is related to headway given by

3600 (9)Vh


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Similarly, capacity is related to headway as given by the equation

where cv , is the theoretical vehicular capacity or maximum volume(veh/hr), and hmis the minimum headway (sec). Theoreticalpassenger capacity is given by

where

cp= theoretical passenger line capacity (number of passengers)

p= vehicles/train

N= maximum passenger per vehicle

3600 (10)

v m

ch

3600 (11)p v

m

pNc pNc

h


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If practical vehicular capacities are to be considered, the ratioof practical to theoretical vehicular line capacities is introduced.This ratio, called the guideway utilization factor, is denoted by .

Therefore, actual vehicle capacity is given by

A load factor is usually used to express the percentage of vehicle

occupancy; hence,

where is the load factor. When the load factor = 1, it denotes

that the vehicle is fully occupied. The maximum number ofpassengers who can theoretically be squeezed into a vehicle iscalled its crush load, and therefore the load factor can exceed 1.00during, say, rush hours.

3600 (12)

m

ch

3600Actual passenger capacity (13)

m

p N

h


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In rail design particularly, safe stopping distance is amajor concern. A safety factor is used for safe design on thebrick-wall-stop (BWS) concept.Say, for example, that whenthe lead vehicle on a track stops instantaneously, thefollowing vehicle must be able to stop safely, with a factorof safety of K. K can be assumed to be 1.5. The followingvehicle in such cases is considered to stop with constantdeceleration. Based on this principle,

where

vo= cruise speed (ft/sec)L= vehicle length (ft)

d= deceleration rate (ft/sec2)

Minimum headway, (14)2

om

o

Kv pLh

d v


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Therefore, w e can now write the theoretical capacityequation as

For maximum capacity, we differentiate cpwith respect tovoand obtain

and if we substitute voin Equation (14), we get

3600 (15)2

po o

pNc Kv d pL v

2

for maximum capacity (16)opLd

v K

2 (17)m

pLKh

d

and the maximum theoretical capacity 2546N pd LK


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The basic line-capacity equation tells us that if we wishto increase the line capacity, we could achieve it in one offive ways (Yu, 1982):

1. Increase the number of passengers carried by eachvehicle.

2. Increase the length of the trains.

3. Decrease the minimum allowable headway.4. Improve the load factor.

5. Improve the guideway utilization.


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Example 4: Rail Operation Design

A transit authority needs to design a rapid rail line to meetpeak-hour demand of 10, 000 passengers per hour, with a requiredspeed of 35 to 40 ft/see (24 to 27 mph). The following assumptionsare made: deceleration 2ft/sec2. safety factor K =1.35; minimumheadway = 120 sec; maximum headway = 240 sec; load factor = 0.9;guideway utilization factor = 0.6. station platform limit =10 vehicles(maximum); car length =70 ft; car capacity =130 passengers. Howmany cars should a train consist of to provide adequate passengervolume capacity? What will be the corresponding headway?


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Solution

1. Determine headway

3600

13010,000 3600 0.6 0.9

Therefore, 0.03957

x x

x

x

x

x x

Nc p

h

p

hp h


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2. Examine computed headways and train size. From the brick-

wall-stop (BWS) concept:

2 2 ando x

pLd pLKv h

K d


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3. Evaluate. Examination of the preceding table should be based onthree criteria: (a) computed speed should be in the range 35 to 40ft/sec; (b) minimum headway = 120 sec; (c) BWS hoshould be less

than 120 sec.

4. Conclusion. Six-or seven-car trains are all right.

Six-car train: speed 35.28 ft/sec. hx=151.63 sec

Seven-car train: speed 38.10 ft/sec. hx=176.91 sec

Discussion

These results are meant for peak-hour service. Naturally, for

off-peak hours, the train lengths will be different, depending onwhat policy headways are needed.


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Bus Operation Design

Buses in mixed traffic represent the most common operatingscenarioin North American cities and rural areas for small and largebuses, both standard and articulated, and for both fixed-route anddemand-responsive services. Exceptions occur when busways ordowntown bus lanes are provided in larger cities with very highcapacity routes. Because a bus operates much like other vehicles in

traffic lanes, its impact on the overall vehicle capacity of the lanemay be calculated as if it were another vehicle, using methods givenin Chapter 7. Bus vehicle capacity is calculated in similar manner asthat for exclusive urban street bus lanes, except that theinterference of other traffic on bus operation must be accounted for.This traffic interference is greatest when off-line stops are used and

buses must wait for a gap in traffic to merge back into the street.Some states have laws requiring motorists to yield to busesreentering a roadway; motorists'compliance can reduce or eveneliminate the reentry delay.


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For the purpose of determining capacity, a bus lane is any lane on aroadway in which buses operate. It may be shared with other traffic or itmay be used exclusively by buses (TRB, 2000).The capacity of a critical bus

stoplocated along the lane significantly influences the vehicle capacity ofa bus lane. Typically, the stop with the highest volume of passengers or aninsufficient number of loading areas is the critical stop. Bus lane capacityis also affected by the following:

Bus lane type: The vehicle capacity procedures identify three types of buslanes. Type 1 bus lanes have no use of the adjacent lane; Type 2 bus laneshave partial use of the adjacent lane, which is shared with other traffic;and Type 3 bus lanes provide for exclusive use of two lanes by buses.

Skip-stop operation: Bus lane capacity can be increased by dispersing busstops, so that only a portion of the buses use the bus lane stop at aparticular set of stops. This block-skipping pattern allows for a faster tripand reduces the number of buses stopping at each stop, although itincreases the complexity of the bus system for new riders and mayincrease passenger walking distances to bus stops.


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Platooning: When skip stops are used, gathering buses intoplatoons at the beginning of the skip-stop section maximizes theefficiency of the operation. Each platoon is assigned a group of

stops, and the platooned buses travel as trains past the skip-stopsection. The number of buses in each group ideally should equalthe number of loading areas at each stop.

Bus stop location:Far-side stops provide the highest bus lane

capacity, but other factors

for example, conflicts with othervehicles, transfer opportunities, and traffic signal timing

also mustbe considered when siting bus stops.


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The design of a bus route is somewhat different from raildesign operation and the differences will be evident from thedescription that follows. Ultimately, an operation planwould

contain information regarding the adopted headway, cycle time,terminal time, fleet size, and the commercial speed.

Again, the capacity of a transit route is the product of thepassenger capacity per vehicle and the maximum number ofvehicles that can travel on that route. The last term is usually thecapacity of the busiest stop on the route. An expression for the

headway of a bus stop is

where hmis the minimum headway between buses (minutes), and td

is the average dwell time in seconds.

2 60 (18)m dh t


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Dwell time is the amount of time a bus spends whilestopped to service passengers. When buses operate inmixed traffic and stop in a travel lane, the reduction in theroadway capacity is directly related to the amount of timethe buses stop. It is the time required to serve passengersat the busiest door plus the time required to open andclose the doors. A value of 2 to 5 seconds for door openingand closing is reasonable for normal operations.


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Dwell time can be assumed to be 60 seconds for centralbusiness district (CBD), transit center, major on-line transfer point,or major park-and-ride stops; 30 seconds for major outlying stops;

15 seconds for typical outlying stops. Dwell time, td, is bestmeasured in the field for determining capacity and LOS of anexisting transit line. Equation (19) can be used to compute dwelltime.

where

td= dwell time, s

Pa = alighting passengers per bus through the busiest door duringpeak 15-min(P)

ta

= passenger alighting time, sec/person (s/p)

Pb= boarding passengers per bus through busiest door during peak15-min(P)

tb = passenger boarding time (s/p)

toc= door opening and closing time (s)

(19)d a a b b oct P t P t t


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Estimates of hourly passenger volume are required for thehighest-volume stops. The peak-hour factor (PHF) is used to adjusthourly passenger volumes to reflect 15-minute conditions.

where

PHF = peak-hour factorP = passenger volume during peak hour (P)

P15= passenger volume during peak 15min (P).

If buses operate at frequencies longer than four buses perhour scheduled, the denominator of Equation (20) should beadjusted accordingly. Typical PHF values range from 0.60 to 0.95 fortransit service with a value close to 1.0 indicating possibleinadequate service of the route.

15 (20)4(PHF)

PP


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Table 10-9 provides boarding and alighting times for baseconditions. If standees are present, 0.5 seconds should be added tothe boarding times shown. The base values are multiplied by 1.2 for

heavy two-way flow through a single door. Similarly the multiplyingfactor is 0.6 and 0.9 for a double-stream door or for a low-floor bus,respectively. The frequency of service is given by

where

f = frequency (buses/hr) required

n = demand for service (passengers/hr)

N = maximum number of passengers per bus

Usually, the bus company decides the minimum headway, andthis figure is set in multiples of 7.5 or 10 minutes for the sake ofcoordinating the operation of several bus routes operating.

(21)n

fN


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The capacity of a bus route is governed by four factors: thestreet capacity, the bus station platform capacity, the vehiclecapacity, and the headway. Each of the first three factors is

independent of one another, and the headway is influenced by allthree. Vehicle capacitydepends on two factors: seating capacityand standing capacity. A load factor is often used to measure seatavailability, and a load factor of 1.0 indicates that every seat isoccupied.

The passenger capacity of a bus is given by

where

Ct= total passenger capacity per vehicle

Ca

= vehicle seating capacity

Cb= vehicle standing capacity

= fraction of Cballowed

Hence, capacity Rcof a bus routing during any time period is

+ c (22)t a bc c

60 60( ) (23)

t a bc

m m

c c cR

h h


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The fleet size, or the number of vehicles needed to serve a particularroute, can be determined, based on the time it takes a bus to complete around trip. Thus,

where

tR= round-trip travel (hr)

d= distance of a round trip (mi or km)

vc= average vehicle speed or commercial speed (mph or km/hr)

A minimum layover and recovery time(say, 10 minutes) is provided atthe end of each round trip. The number of vehicles needed (fleet size) canbe determined from

whereNfis the fleet size, and S is the service frequency, which equal1/headway.

(24)Rc

dt

v

(25)Rf R tN Sth


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Example 5

A bus system needs to be set up between the WashingtonState University Campus and the University of Idaho, a distance of8.5.mi. The operating time is 30 min. It has been estimated that thepeak-hour demand is 400 passengers/hr and 45-seater buses areavailable, which can safely accommodate 20 standees. Design thebasic system and determine the fleet size, assuming that the policyheadway is 30 min and that the minimum terminal time is 7.5 min,which may be revised if necessary.


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Solution

0Operating speed, 60 / 60 8.5 / 30 17.0mph; operating time

Policy headway = 30 min (which is arbitrary)

Terminal time = 7.5 min

60(45 20)

Headway, 60 / 9.75min(adopt 10 min)400

Cycle time, 2(

o o

m t c

v L t t

h c R

T

0

'

' '0

'

) 2(30 7.5) 75min

Fleet size, / 75 / 10 7.5 8 vehicles

Revised cycle time, / 8 10 80min

Revised terminal time, ( 2 ) / 2 80 (2 30) / 2 10min

Commercial speed, / 120 / 120(8.5) / 80 1

t

f

f

c R

t t

N T h

T N h

t T t

v d t L T

2.75mph


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'

In summary,

Headway, 10minCycle time, 80min

Fleet size, 8 vehicles

Terminal time, 10min

Commercial speed, 12.75mph

f

c

hT

N

t

v

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Rail Operation Design