TRANSPORTATION_ENGINEEERING_TERMS_CHAPTER2-Traffic Capacity

Density

It is defined as the number of vehicles per unit distance occupying a section of roadway at a given instant time and is usually measured in vehicles per mile or per km.

Traffic volume

The number of vehicles moving in a specified direction on a given lane or roadway that pass a given point during specified unit time and is usually expressed as vehicles per hour or vehicles per day.

Traffic capacity

The ability of a roadway to accommodate traffic volume. It is expressed as the maximum number of vehicle in a lane or a road that can pass a given point in unit time, usually an hour, that is vehicles per hour per lane or roadway.

Basic capacity

The max. number of passenger cars that can pass a given point on a lane of roadway during one hour under the most nearly ideal roadway and traffic conditions which can possibly be attained.

Possible capacity

The max. number of passenger cars that can pass a given point on a lane of roadway during one hour under prevailing roadway and traffic conditions.

Practical capacity

The max. number of vehicles that can pass a given point on a lane or roadway during one hour without traffic density being so great as to cause unreasonable delay, hazard, or restrictions to the driver's freedom to maneuver under the prevailing roadway and traffic conditions.

Weaving

The crossing of two or more traffic streams traveling in the same general direction along a significant path of highway without the aid of traffic signals.

spot speed

The instantaneous speed of a vehicle at a specified section or location.

average speed

The average of the spot speeds of all vehicles passing a given point in the highway.

space mean speed

The average speed of vehicles in a certain road length at any time.

time-mean speed

The speed distribution of vehicles at a point on the roadway and it is the average of instantaneous speeds of observed vehicles at the spot.

running speed

The average speed maintained by a vehicle over a particular stretch of road, while the vehicle is in motion. This is obtained by dividing the distance covered by the time during which the vehicle is in motion.

Time headway

The time interval between the passage of successive vehicles moving in the same lane and measured from head to head as they pass a point on the road.

space-headway

The distance between successive vehicles moving in the same lane measured from head to head at any instance

passing sight distance

The distance ahead that must be clear to permit safe passing is called

Expressway

Divided arterial highway for through traffic with full or partial control of access and generally with grade separations at major intersections.

Expressway

An expressway with full control of access.

Parkway

An arterial highway for non-commercial traffic with full or partial control of access and usually located within a park.

stopping sight distance

Minimum sight distance required for a driver to stop a vehicle after seeing an object in the vehicle’s path without hitting that object. This distance is the sum of the distance traveled during perception-reaction time and the distance traveled during braking.

passing sight distance

Minimum sight distance required on a two-lane, two-way highway that will permit a driver to complete a passing maneuver without colliding with an opposing vehicle and without cutting off the passed vehicle.

Super elevation run off

The length of super elevation development from zero cross slope to full design super elevation in a circular curve alignment.

Tangent run out

The length of super elevation development from the normal cross slope to the zero cross slope point on the tangent.

Vertical Alignment

The longitudinal profile along the centerline of the road. It is made up of a series of grades and vertical curves.