PTOE key terms

A letter grade from A to F describing how well a roadway facility serves its users, based on measures such as delay, density, speed, or volume-to-capacity ratio, with A being free-flowing and F being congested.

The ratio of demand flow rate to the maximum rate the facility can serve under prevailing conditions; values near or above 1.0 indicate oversaturation and queuing.

The maximum hourly rate at which persons or vehicles can reasonably be expected to traverse a point or uniform segment of a lane or roadway under prevailing traffic and control conditions.

The maximum hourly flow, typically expressed per lane, that a signalized approach can discharge during effective green if the green were available continuously, often estimated near 1,900 passenger cars per hour per lane.

The portion of a signal cycle during which a movement is considered to discharge at saturation flow rate, accounting for startup lost time and yellow/red clearance usage.

Time within a signal cycle not usable for discharging traffic, including startup lost time at green onset and clearance lost time at the end of the interval.

The yellow plus all-red portion of a signal cycle that provides transition between conflicting green phases, sized using perception-reaction time, approach speed, deceleration, and intersection width.

The all-red time following a yellow interval during which no conflicting movements are released, allowing vehicles that entered on yellow to clear the intersection.

The approach region where a driver neither can stop comfortably before the stop line nor clear the intersection before conflicting traffic is released, often addressed with dilemma zone detection.

Delay experienced by a vehicle due to traffic signal control, including deceleration, stopped time, and acceleration back to desired speed; it is the primary measure for intersection level of service.

The delay component in signalized intersection analysis that results from the cyclic pattern of red and green when demand is below capacity, assuming uniform arrivals.

The additional delay experienced when demand exceeds capacity, caused by residual queues that carry over from one cycle to the next.

A signal operating strategy in which phase durations and sometimes sequence are adjusted in real time in response to detector calls from arriving vehicles or pedestrians.

In actuated control, the time a detector call remains registered after a vehicle leaves the detection zone, used with minimum green to extend the green for approaching vehicles.

Termination of a green phase in actuated control when no vehicle call occurs within the passage time, indicating the arrival stream has a gap large enough to end the phase.

Coordination of adjacent signalized intersections so that platoons of vehicles receive successive green indications along a corridor, often described by bandwidth and offset.

The time difference, usually measured from a reference point in one signal's cycle to the same point in the next signal's cycle, used to coordinate progression along a corridor.

The amount of green time in a coordinated signal timing plan during which a vehicle traveling at a given speed can pass through all signals in a corridor without stopping.

The total time required for a signal to complete one full sequence of all phase indications, from the start of a green to the start of the next occurrence of that same green.

A left-turn movement allowed to proceed during a green ball after yielding to opposing through traffic and pedestrians, as opposed to a protected turn with a green arrow.

A left-turn movement given the exclusive right of way with a green arrow while conflicting through and pedestrian movements are stopped.

An intersection with a circular central island where entering traffic yields to circulating traffic, typically characterized by lower speeds, fewer conflict points, and reduced severe crashes.

The speed of traffic on a facility when volumes are low enough that vehicles are unaffected by other vehicles or control devices, used as an input to many capacity analyses.

The number of vehicles occupying a given length of lane or roadway, usually expressed as passenger cars per mile per lane; it is the primary level-of-service measure for freeway and multilane highway segments.

The ratio of the peak-hour volume to four times the peak 15-minute volume, used to adjust hourly volumes to reflect the busiest sub-hourly flow within the hour.

A factor converting the effect of a heavy vehicle or other nonstandard vehicle into an equivalent number of passenger cars for capacity and flow-rate analysis.

A multiplier applied to traffic volumes to account for the greater space and headway consumed by trucks, buses, and recreational vehicles in a traffic stream.

The coordinated detection, response, and clearance of crashes, breakdowns, and other roadway incidents to restore capacity and reduce secondary crashes and delay.

A freeway management technique that uses signals on entrance ramps to regulate the rate at which vehicles merge onto the mainline, reducing congestion and improving flow stability.

The set of strategies, including ramp metering, variable speed limits, traveler information, and incident response, used to operate freeways efficiently and safely.

Physical or operational measures such as speed humps, chicanes, and narrowed lanes that reduce vehicle speeds and volumes on local streets to improve safety and livability.

A reconfiguration that reduces the number of through lanes on a roadway, often converting a four-lane undivided road to three lanes with a center turn lane, to improve safety and accommodate other users.

The planned control of the location, spacing, design, and operation of driveways, median openings, and street connections to preserve roadway capacity and safety.

The temporary signs, markings, barriers, and channelizing devices used to guide road users safely through or around a construction or maintenance area while protecting workers.

The overall planning and design of traffic flow through and around work zones, including lane closures, detours, and flagging operations, typically following a manual of uniform devices.