LESSON 4: VOLUME/CAPACITY AND LEVEL OF SERVICE

UNINTERRUPTED FLOW

Flow occurs at long sections of road where vehicles are not required to stop by any cause external to the traffic stream.

INTERRUPTED FLOW

Flow occurs at intersections or driveways where vehicles are required to stop by any cause outside the traffic stream, such as traffic signs, traffic lights, etc

Flow rate

number of vehicles passing a point during a specified period of time. It is often referred to as volume when measured over an hour

Speed

rate of motion in distance per unit of time

Time mean speed

called spot speed, simply the arithmetic mean of the speeds of vehicles passing a point within a given interval of time

trap length in spot speed studies.

Space mean speed

rate of movement of a traffic stream within a given section of road

It is also called the harmonic speed

Density

number of vehicles in a given length of road at an instant point in time

Level of Service (LOS)

represents a qualitative ranking of the traffic operational conditions experienced by the users of the facility under specified roadway, traffic, and traffic control conditions

Capacity

maximum number of vehicles or people that can reasonably and safely pass through a specific section of a roadway within a given period under prevailing conditions

passenger car equivalent factors (PCEF)

passenger car unit per hour (pcu/hr) and would depend on