Traffic Glossary
Traffic Volume Measurements:
Average Daily Traffic (ADT): The average traffic volume over a 24-hour period at a given location
during a specific count period; typically 7 days.
Annual Average Daily Traffic (AADT): The average traffic volume over a 24-hour period at a
given location averaged over the course of one year. Often estimated from seasonal adjustment
factors
Peak Hour Traffic Volume: The highest traffic volume over a one-hour period at a given location
occurring at a peak time of day; typically during the morning and afternoon commuter peak
periods.
Peak Hour Factor (PHF): A factor that represents the distribution of the traffic volumes over the
course of the peak hour. . The variability of the peak hour traffic is typically based on the
comparison of each of the four 15-minute count periods, and can range from 0.25 to 1.0, with
PHFs closer to 1.0 representing traffic that is more evenly distributed throughout the hour.
Vehicle Miles Traveled (VMT): The product of traffic volume and the length of the road
segment(s) within a limited network during the period of interest. For the Casey Arborway
project, CTPS calculated VMT for the study area network in the peak period under the future
no-build and build alternatives to determine whether the build alternatives induced or diverted
traffic to the project area.
Vehicle Hours Traveled (VHT): The product of traffic volume and travel time on a roadway(s)
within a limited network during a period of interest. For the Casey Arborway project, CTPS
calculated VHT for the study area network in the peak period under the future no-build and
build alternatives to determine whether the build alternatives increased or decreased travel
time within the study area.
Traffic Operations:
Level of Service (LOS): A qualitative measure describing operational conditions within a traffic
system and their perception by users that represents a service measure. LOS can be applied to
various modes of transportation. Vehicular LOS can be applied to various components of a
roadway system including intersections, roadway corridors, signal systems, and freeway lanes,
merges, diverges, and weave segments. For intersections, the level of service is based solely on
average vehicle delay. For roadway segments and ramps, the level of service is based on
vehicle density.
Pedestrian LOS is based upon walking space, walking experience, travel time and distance and
includes factors for pedestrian volume, sidewalk width, distance to adjacent traffic and objects,
and motorized traffic volumes and speeds.
The bicycle LOS score model includes bicyclists’ comfort and perceived exposure to traffic and
is a function of separation from traffic, traffic speeds, heavy-vehicle usage, presence of parking,
and pavement quality.
Transit LOS is based upon transit rider’s perception accounting for the passenger’s experience
walking to the transit stop, wait time and travel time on the transit vehicle, service reliability,
and the presence of shelters and benches.
Specific delay thresholds for vehicular LOS can be found in the tables below for both
unsignalized and signalized intersections.
Level of Service Criteria for Unsignalized Intersections
Level of Service
Control Delay Per Vehicle (seconds)
A
< 10.0
B
10.1 to 15.0
C
15.1 to 25.0
D
25.1 to 35.0
E
35.1 to 50.0
F
> 50.0
Level of Service Criteria for Signalized Intersections
Level of Service
Control Delay Per Vehicle (seconds)
A
< 10.0
B
10.1 to 20.0
C
20.1 to 35.0
D
35.1 to 55.0
E
55.1 to 80.0
F
> 80.0
Queue: The line of vehicles stopped at a given location, measured in feet. The 50th percentile
queue represents the median length of this queue. The 95th percentile represents approximately
the longest queue length as it will only be exceeded during 5% or less of the peak period.
Delay: A measurement of the amount of time in seconds a vehicle is stopped on average for a
given movement.
Volumes to Capacity Ratio (v/c): A ratio of traffic volume to capacity. A v/c ratio can be applied to
a number of items, such as a travel lane, an intersection approach, or a transit route. A v/c ratio
approaching one indicates that item is reaching capacity and soon will not be able to process the
volume arriving in the given time.
Traffic Signals:
Exclusive Pedestrian Phase: A signal phase that serves pedestrians exclusively while all vehicular
traffic is stopped.
Concurrent Pedestrian Phase: A pedestrian phase that allows pedestrians to cross at the same time
as the vehicles running parallel to the pedestrian crosswalk location. Conflicting turn
movements must yield to pedestrians in this scenario.
Protected Signal Phase: A signal phase that permits movements without conflict. For example, a
left turn under protective phasing moves without conflicts from opposing thru traffic.
Permitted Signal Phase: A signal phase that allows movements to occur at the same time as
conflicting traffic. For example, a left turn under permissive phasing must yield to opposing
thru traffic.
Bus Queue Jump Lane: Exclusive lane for bus usage that allows busses to move to the front of a
traffic queue.
Bus Signal Priority: Detection system that allows buses to send a message to the signal controller
prompting the controller to switch to the signal phase which will serve the desired bus
movement.
Signal Coordination: The phasing and timings of closely spaced signals are coordinated to
optimize the throughput along a roadway corridor in balance with the efficiency of the system.
When signals are coordinated, the occasions when a vehicle that passes through a green signal
will encounter a red signal downstream are minimized.