Signal-controlled intersections
This section describes signal controls. Topics include:
Signalized intersections are controlled by sets of traffic lights. At any given time, vehicles making a particular movement through the intersection will see a particular signal aspect:
Modelers reclassify the aspect into effective green (when the traffic can go) and effective red (when the traffic stops). Note that effective green begins and ends later than actual green (due to reaction times).
A set of signal aspects for all movements through an intersection is called a phase. Note that the total duration of all the phases should be significantly less than the duration of the signal cycle. The difference is primarily due to two factors: lost time while the signals are changing phase and pedestrian phases.
CUBE Voyager offers two ways of modeling the capacity of signals. There is a detailed model of junction geometry, which has been calibrated to traffic conditions in the U.S.(Geometric / HCM model), and there is a model which requires saturation flows to be estimated or measured externally, which has been calibrated to traffic conditions in the U.K.(Saturation Flow model). The detailed model also imposes more constraints on the allowed signal phasing than the saturation flow only model.
CUBE Voyager offers four signal intersection types, i.e. signal saturation flows, signal geometric (HCM), adaptive signal saturation flows, and adaptive signal geometric (HCM).
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Signal, Saturation Flows model: It is developed to model capacities, queues, delays and LOS at fixed time signal controlled isolated intersections. The user inputs include geometric characteristics of the intersection, signal timing arrangements, and demand flow information. The methodology is based on the Catling’s delay method and the TRRL (Transport and Road Research Laboratory, UK) Report 105.
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Signal, Geometric (HCM) model: It addresses the capacities, queues, delays and LOS for lane groups and the LOS for intersection approaches and the intersection as a whole at signalized intersections. Each lane group is analyzed separately in the HCM model. It considers a wide variety of prevailing conditions, including the amount and distribution of traffic movements, traffic composition, geometric characteristics, and details of intersection signalization. The methodology is based on the HCM 2000 signal model.
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Adaptive Signal, Saturation Flows model: It is an advanced model based on the Signal, Saturation Flows model. The model optimizes the signal timing based on the intersection geometric characteristics, signal parameter bounders and demand flow information. The methodology tries to iteratively fit delay parabolas based on three distinct and reasonable signal timing plans, i.e. phase timings and cycle time, and picks the plan at the minimum delay point, until no delay reduction could be reached. The delay is calculated by the Catling’s delay method. The methodology was inspired by the TRANSYT model.
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Adaptive Signal, Geometric (HCM) model: The model is similar as the Adaptive Signal, Saturation Flows model, except the delay is calculated by the HCM 2000 method.
The above intersection types output not only delay, capacity, queue and LOS, but also low flow delay. The low flow delay is a measure commonly used by European users. It is the additional travel time experienced by drivers of each movement at low degree of saturation (flow to capacity ratio << 1). According to Catling’s delay method, the delay at low degree of saturation is almost equal to that occurring when the traffic intensity is uniform. The low flow delay is calculated as the inverse of the capacity for Saturation Flows models, and is calculated as the half cycle time times the square of the red time proportion for Geometric (HCM) models.
A left turn (right turn when LEFTDRIVE=T) which sees a green phase will either be protected (that is, no opposing flow is running) or permitted (that is, the vehicles must give way to some oncoming traffic). Both methodologies can model both permitted and protected phases.
CUBE Voyager does not offer any model of "right turn on red" although this is allowed in many areas of the U.S. (The LEFTDRIVE=T equivalent, "left turn on red", is not permitted in the U.K.) This is best handled by introducing a dummy link into the network, allowing the right-turners to bypass the signal control, and omitting some lane(s) from the definition of the approach.
References
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Catling, I. (1977). A time-dependent approach to junction delays. Traffic Engineering and Control, 18(11), pp. 520-523, 526.
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Kimber, R. M., Mcdonald, M., Hounsell, N. B. (1986). The prediction of saturation flows for single road junctions controlled by traffic signals. Transport and Road Research Laboratory Report RR 67.
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Burrow, I. J. (1987). OSCADY: a computer program to model capacities, queues and delays at isolated traffic signal junctions. Transport and Road Research Laboratory Report RR 105.
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Kimber, R.M. and M.C. Semmens (1983). Traffic signal junctions: a track appraisal of conventional and novel design. Transport and Road Research Laboratory Report RL 1063.
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Transport Research Laboratory. TRANSYT. http://www.trl.co.uk/Transyt.htm
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Transportation Research Board. Highway Capacity Manual 2000.
This section describes generic keywords used for signals:
Note: These keywords are case insensitive. For example, capitalizing as CanShareLeft might improve readability.
This keyword specifies that there is a shared lane to the left of the exclusive lanes for this movement (that is, the movement can share with the movement to its left). Note that this keyword does not mean "can share with left turners" unless either the movement is THROUGH or the movement is on the minor leg of a three-arm junction.
If a movement has CANSHARELEFT = T coded, then there must be a movement to this movement’s left and the movement to this movement’s left must have CANSHARERIGHT = T coded.
If SINGLELANE = T then CANSHARELEFT should not be coded.
This keyword specifies that there is a shared lane to the right of the exclusive lanes for this movement (that is, the movement can share with the movement to its right). Note that this keyword does not mean "can share with right turners" unless either the movement is THROUGH or the movement is on the minor leg of a three-arm junction.
If a movement has CANSHARERIGHT = T coded, then there must be a movement to this movement’s right, and the movement to this movement’s right must have CANSHARELEFT = T coded.
If SINGLELANE = T then CANSHARERIGHT should not be coded.
This real-valued keyword is required for all signals. Its value is the length of the signal cycle in seconds.
The cycle time must be strictly greater than the sum of all the coded green times.
At actuated signals, the CYCLETIME value is taken to be part of the example feasible solution and the subkeywords MAXIMUM and MINIMUM may be used to supply constraints. For example:
Actual Cycle = 120, Minimum = 60, Maximimum=180,
If no constraints are placed on the cycle time at an adaptively modeled signal, the constraints will be deduced from the constraints on the individual green times.
This integer-valued keyword gives the number of lanes, on the specified approach, which are reserved for the exclusive use of vehicles making the specified movement.
If SINGLELANE = T, then EXCLUSIVELANES should not be coded.
Set LANEADJUST to Y at a signal to invoke the HCM2000 capacity calculations.
Set LANEADJUST to N at a signal if you are supplying saturation flows.
These keywords occur in pairs; every occurrence of the integer- valued keyword, PHASE must be followed by a single occurrence of the real-valued keyword ACTUALGREEN. There should be one such pair for each phase of the signals during which vehicles move (that is, all-red and/or pedestrian phases should not be coded).
The values of the PHASE keyword should form a continuous sequence, starting at one and increasing, without gaps, until the number of phases is reached. Every phase must be mentioned in a PHASE keyword for some movement at the intersection.
The value of the ACTUALGREEN keyword is the duration, in seconds, of the effective green-time associated with the phase. The effective green time is the period during which vehicles move across the stop line. It starts shortly after the signals change to green (because the vehicle drivers must react to the change in signal aspect) and continues through the following red/yellow. The CYCLETIME must greater than the summation of the ACTUALGREEN.
If the signal is being modeled adaptively, then the keywords maximum (required) and minimum (optional) may be used to specify constraints, and the coded value of ACTUALGREEN is taken to be part of the example feasible solution. If no minimum is applied, CUBE Voyager may remove the phase altogether (that is, set green-time to zero).
The keyword PHASES is integer-valued but, conceptually, it consist of either one phase number (that is, digit) or of two phase numbers (that is, two digits). The vehicles making the movement see a green signal aspect when the specified phase(s) is/are running and red otherwise.
Note that the (node-level) keyword PHASE is used to define phases and the (movement-level) keyword PHASES associates movements with the defined phases.
At geometrically specified signals, then any two-digit phase specifications must specify contiguous phases. No such restriction is required when saturation flows are coded.
This real-valued keyword allows the specification of saturation flows in pcu (vehicles) per hour per lane.
Saturation flows at signals are the flows that would be observed if the movement had a continuous green all other movements had no flow and no green.
Saturation flow at a priority junction (two-way yield-controlled intersection) is defined similarly, except that no signal aspects are involved. SATFLOWPERLANE is only applicable to Saturation flow model. The suggested value is 1700 pcu/h for THROUGH and UNOPPOSED movements and 1279 pcu/h for OPPOSED movements.
The logical-valued keyword is used to indicate that an approach consists of a single lane. It is applicable to many junction types:
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Signal-controlled intersection:
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All-way stop-controlled intersection: SINGLELANE may not be coded; code NUMBEROFLANES = 1.
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Two-way stop-controlled intersection:
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Priority intersection (two-way yield- controlled intersection):
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Roundabout:
Coding SINGLELANE=Y for an approach precludes the use of EXCLUSIVELANES, CANSHARERIGHT, or CANSHARELEFT on that approach.
At two-way stop-controlled intersections and priority junctions, a minor arm that does not have SINGLELANE=Y explicitly coded, has two lanes.
This section describes geometric keywords:
Note: Keywords are case insensitive. For example, capitalizing as AverageLaneWidth might improve readability.
This real-valued keyword describes the mean lane width, in meters or feet, of an approach to a geometrically modeled signalized junction. If no value is provided, a default of 3.6m is used.
The average lane width must be in the range from 2.4m to 4.8m. If the value falls outside this range, the approach should be recoded to have more or fewer lanes, as appropriate.
The flow of bicycles in from the curb-side lane in units of bicycles per hour. Bicycle traffic which weaves with turning traffic in advance of the stop line should be excluded from this value, because these bicycles do not interact with the other vehicles while they are still within the intersection.
The diagram below illustrates the relevant bicycle flow for right hand rule of the road. In the diagram, the crossed box is the bicycle conflict zone where right turning traffic may be impeded by any bicycles crossing the intersection. The CONFLICTINGBIKE is the flow of bicycles through this region.
The real values supplied to this keyword are number of buses stopping per hour. The first element refers to the normal curb side of the road; the second refers to the other side of the road (for example, if there is a tram line in the center of the road or there is a bus stop on the offside of a one-way street). Only buses stopping within 75 meters (246 feet) of the stop line (either upstream or downstream) should be included.
This keyword is only applicable at geometrically modeled signals.
CENTRALBUSINESSDISTRICT is a logical-valued keyword which may be applied at geometrically-modeled fixed-time signals. Coding CENTRALBUSINESSDISTRICT=Y causes all calculated capacities to be 90% of the value that would be obtained otherwise.
Selects the delay modeling methodology applied to the capacities calculated by the HCM2000 signal capacity modeling methodology. The keyword accepts the values "HCM" or "Catling" (case-insensitive). By default, The HCM delay equations are invoked.
The number of lanes traveling away from the modeled intersection. This key may occur on the same arm as the EXITONLY keyword but is invalid for a one-way link that travels towards the intersection.
CUBE Voyager only uses this value for pedestrian and bicycle modeling.
Note: If exit lanes are omitted from an arm that pedestrians cross, the capacity of movements entering the arm may be reduced significantly.
This keyword defines the length in the entry leg measured from the stop line to the earliest point when a free turn vehicle can enter the free turn pocket or channel in the current unit (meter or feet. See Data file settings). If this value is greater than zero and the turn is coded as exclusive, then it is considered a free turn. Default to 0 for not a free turn. The Intersection Data Editor only takes values with 2 decimal places. If provided with more than 2 decimal places, the values will be rounded up with 2 decimal places.
This keyword defines the length in the exit leg measured from the earliest point to the latest point a free turn vehicle can merge into the main flow of traffic in the current unit (meter or feet). It only becomes effective when calculating the statistics for free right-turn movements. It can be 0 for no merging lane, similar to a yield situation and it is default to 0. The Intersection Data Editor only takes values with 2 decimal places. If provided with more than 2 decimal places, the values will be rounded up with 2 decimal places. If this value is equal to or greater than the Free Turn Exit Lane Max Length value in the Intersection File Settings screen (See Data file settings), then it is assumed that no merging is needed or no impact on the free turn capacity.
Free turn followup time in seconds. It only becomes effective when calculating the statistics for free right-turn movements. It will default to the Intersection File Setting. If not specified in file setting, default to 2.5 seconds. The Intersection Data Editor only takes values with 2 decimal places. If provided with more than 2 decimal places, the values will be rounded up with 2 decimal places.
This keyword defines free turn critical gap in seconds. It only becomes effective when calculating the statistics for free right-turn movements. It will default to the Intersection File Setting (See Data file settings). If not specified in file setting, default to 4 seconds. The Intersection Data Editor only takes values with 2 decimal places. If provided with more than 2 decimal places, the values will be rounded up with 2 decimal places.
The real-valued keyword GRADE describes the grade, expressed as a percentage, of an approach to a geometrically modeled signals or a two-way stop-controlled intersection. It is a signed value; negative values indicate that the approach is downhill and positive values indicate that the approach is uphill.
By default the approach is assumed to be flat (GRADE = 0).
The models have been calibrated for grades the range -6% to +11%, but more extreme grades do occur. For example the maximum grade in San Francisco is about 31%.
Option to stop the de-facto exclusive turn lane check on the unopposed turning movement (right turn on right drive and left turn on left drive). This is a boolean keyword. Setting this option to True will disable the check for exclusive turn lane modeling when volumes exceed threshold. This setting is used to control the lane grouping for turn movements.
Option to stop the de-facto exclusive turn lane check on the opposed turning movement (left turn on right drive and right turn on left drive). This is a boolean keyword. Setting this option to True will disable the check for exclusive turn lane modeling when volumes exceed threshold. This setting is used to control the lane grouping for turn movements.
The real values supplied to this keyword are number of maneuvers per hour. The first element refers to the normal curb side of the road; the second refers to the other side of the road (that is, if there is parking in a central reservation or on the offside of a one way street). Only parking within 80 meters of the stop line should be included
By default, parking is not allowed. Coding PARKINGMANUEVERS=0 means that parking is allowed, but it is extremely rare.
This keyword is only applicable at geometrically modeled signals.
The number of pedestrians crossing the approach per hour. Note that this is a two-way flow.
The keyword PEDESTRIANPHASE is integer-valued but, conceptually, it consist of either one phase number (that is, digit) or of two phase numbers (that is, two digits). In this respect, it is like the keyword PHASES. The phases mentioned are the phases when pedestrians crossing the approach are given permission to use the crosswalk. The symbols displayed to the pedestrians vary by country, for example in the U.S. the word WALK or an icon of a man walking is displayed in white whereas in the U.K. an icon of a man walking is displayed in green.
If using a two-digit number, the two phases must be adjacent.
The keyword PHASES is integer-valued but, conceptually, it consist of either one phase number (that is, one digit) or of two phase numbers (that is, two digits). The vehicles making the movement see a green signal aspect when the specified phase(s) is/are running and red otherwise.
Note that the (node-level) keyword PHASE is used to define phases and the (movement-level) keyword PHASES associates movements with the defined phases.
At geometrically specified signals, any two-digit phase specifications must specify contiguous phases. No such restriction is required when coding saturation flows.
The minimum gap, in seconds, between successive vehicles moving on a traffic-actuated approach to a signalized intersection that will cause the signal controller to terminate the green display.
This keyword defines queued vehicle spacing on the adjacent through lane in meter or feet depending on the unit setting of the file. It only becomes effective when calculating the statistics for free right-turn movements. It will default to the Intersection File Setting (See Data file settings). If not specified in file setting, default to 6 meters. The Intersection Data Editor only takes values with 2 decimal places. If provided with more than 2 decimal places, the values will be rounded up with 2 decimal places.
CUBE Voyager does not contain a model for right turn on red. The right filter phase coded below might be used as a proxy for RTOR when the right turns are heavy.
Junction,
Node = 276,
laneadjust=t,
Type = FixedTimeSignal,
Approach1 = 291,
CycleTime = 90,
Phase = 1,
ActualGreen = 59,
Phase = 2,
ActualGreen = 5,
Phase = 3,
ActualGreen = 11,
Approach = 291,
AverageLaneWidth = 3.6,
minimumcapacity=50,
Movement = Left,
ExclusiveLanes = 1,
EstimatedDelay = 0.1,
Phases = 1,
Movement = Through,
EstimatedDelay = 0.1,
ExclusiveLanes = 1,
Phases = 1,
Movement = Right,
ExclusiveLanes = 1,
EstimatedDelay = 0.1,
Phases = 12,
Approach = 264,
AverageLaneWidth = 3.6,
minimumcapacity=50,
Movement = Left,
EstimatedDelay = 0.3,
ExclusiveLanes = 1,
Phases = 3,
Movement = Through,
EstimatedDelay = 0.3,
Phases = 3,
ExclusiveLanes = 1,
Movement = Right,
EstimatedDelay = 0.3,
ExclusiveLanes = 1,
Phases = 32,
Approach = 267,
AverageLaneWidth = 3.6,
minimumcapacity=50,
Movement = Left,
ExclusiveLanes = 1,
EstimatedDelay = 0.1,
Phases = 1,
Movement = Through,
EstimatedDelay = 0.1,
ExclusiveLanes = 1,
Phases = 1,
Movement = Right,
ExclusiveLanes = 1,
EstimatedDelay
Phases = 12,
Approach = 306,
AverageLaneWidth = 3.6
Movement = Left,
EstimatedDelay = 0.2,
ExclusiveLanes = 1,
Phases = 3,
Movement = Through,
EstimatedDelay = 0.2,
Phases = 3,
ExclusiveLanes = 1,
Movement = Right,
EstimatedDelay = 0.2,
ExclusiveLanes = 1,
Phases = 32
Saturation flow signals e
Saturation flow signals example
This example illustrates the coding of fixed-time signals:
Junction,
Node = 276,
Type = FixedTimeSignal,
Approach1 = 291,
CycleTime = 90,
Phase = 1,
ActualGreen = 59,
Phase = 2,
ActualGreen = 5,
Phase = 3,
ActualGreen = 11,
Approach = 291,
Movement = Left,
CanShareRight=y,
EstimatedDelay = 0.1,
Phases = 1,
Movement = Through,
CanShareLeft=y,
EstimatedDelay = 0.1,
ExclusiveLanes = 1,
Phases = 1,
Movement = Right,
ExclusiveLanes = 1,
EstimatedDelay = 0.1,
Phases = 2,
Approach = 264,
Movement = Left,
EstimatedDelay = 0.3,
CanShareRight=y,
Phases = 3,
Movement = Through,
EstimatedDelay = 0.3,
CanShareLeft=y,
Phases = 3,
ExclusiveLanes = 1,
Movement = Right,
EstimatedDelay = 0.3,
ExclusiveLanes = 1,
Phases = 23,
Approach = 267,
Movement = Left,
CanShareRight=y,
EstimatedDelay = 0.1,
Phases = 1,
Movement = Through,
CanShareLeft=y,
EstimatedDelay = 0.1,
ExclusiveLanes = 1,
Phases = 1,
Movement = Right,
ExclusiveLanes = 1,
EstimatedDelay = 0.2,
Phases = 2,
Approach = 306,
Movement = Left,
EstimatedDelay = 0.2,
CanShareRight=y,
Phases = 3,
Movement = Through,
EstimatedDelay = 0.2,
CanShareLeft=y,
Phases = 3,
ExclusiveLanes = 1,
Movement = Right,
EstimatedDelay = 0.2,
ExclusiveLanes = 1,
Phases = 23