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Institute of Traffic Engineers.

Traffic engineering handbook online

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Street, Surface. A street at grade and with unlimited access.
Street, Through. Same as Through Highway.

Strip, Center. Unpaved strip of land lying within the roadway limits. Center strips
may form divisional islands and may be planted with trees, grass or shrubbery.

Strip, Side. Unpaved strip of land paralleling the roadway, often planted with
trees, grass, or shrubbery. Side strips often flank sidewalks.

Super-Elevation. The rate of rise in cross section of the finished surface of a road-
way on a curve, measured from the lowest or inside edge to the highest or outside

Super-Highway. A highway of major cross sectional and longitudinal dimensions,
especially designed to accommodate very large traffic movements at a high rate of
speed and which may also have provisions for rapid transit in a medial or side strip.
Trafficway. The entire width between property lines (or other boundary lines) of
every way or place on which any part is open to the use of the public for purposes
of vehicular traffic as a matter of right or custom. A trafficway and a public way
are synonymous terms.

Viaduct. A bridge for carrying a road over a valley, road or other way.
Way. A way as applied to traffic is that upon which traffic passes. The term "way"
shall be considered generic to all places upon which traffic may move. It includes
highway, parkway, limited way, freeway, road, path, route, street, avenue, boule-
vard, lane, alley, arcade, drive, etc.
Way, Limited. See Freeway.


C. fntersect/ons, Approaches and Ramps

Approaches (At a grade separation). The portions of the intersecting roads on
each side of the structure that lie within the intersection area or that are utilized
in grade line rolls or dips to provide the difference in levels at the structure

Approach, Intersection. That portion of an intersection leg which is used by traffic
approaching the intersection.

Circle, Traffic. A type of intersection having a single circular rotary island with
or without supplementary channelizing islands.

Cloverleaf. A grade separation with ramps for both directions of travel in each of
the quadrants. All left turns are made without direct crossing of traffic by means of
exits to the right, a curve around to the right, and entrance to the right of the
through traffic. Also referred to as a 4-ramp design (from above the intersection
looks like a cloverleaf).

Cloverleaf, Partial (Also referred to as 1-, 2-, or 3-Ratnp Designs). A grade
separation with ramps in less than all four quadrants.

Connection, Direct. A form of one-way ramp which does not deviate much from
the intended direction of travel.

Connection, Outer. A ramp used by traffic destined for a right-turn movement from
one of the through roadways separated by a structure to the second through road-

Crossroad, Intercepted. A crossroad at an intersection where a median strip on the
major trafficway continues through the intersection, thus barring direct crossing
by vehicles on the crossroad.

Exit, Intersection. That portion of an intersection leg which is used by traffic
leaving the intersection.

Interchange. Point of access for vehicles to enter and leave a freeway. Also a
system of interconnecting roadways in conjunction with a grade separation or grade
separations providing for the interchange of traffic between two streets or highways
on different levels.

Intersection. The area embraced within the prolongation or connection of the
lateral curb lines, or, if none, then the lateral boundary lines of the roadways of two
trafficway s which join one another at or approximately at right angles, or the area
within which vehicles travelling upon different highways joining at any other angle
may come into conflict. (Note: Divided highways with more than a 30-foot separa-
tion strip are considered to make two intersections with a crossing roadway.)

Intersection, Bridged Rotary. An intersection with grade separation of intersecting
highways and rotary channelized connections.

Intersection, Compound (Also called Multiple or Multi-way Intersection). An in-
tersection with five or more legs. Compound intersections are referred to frequently
as five-way, six-way, etc.

Intersection, Flared. An intersection in which the number of traffic lanes or the
pavement width exceeds the normal number of lanes or the normal width of the
intersecting highway.


Intersection, Four-Way. A roadway junction with four intersecting legs. If two
of the intersection legs are approximate prolongations of the directions of approach
of the other two, and the angle of the intersection of these two prolongations is less
than 75 degrees or more than 105 degrees, it is classed as a four- way oblique inter-
section. If two of the intersecting legs are approximate prolongations of the other
two legs and the angle of intersection of these prolongations is 75 degrees or more,
but not greater than 105 degrees, it is classed as a four-way right angled intersection.

Intersection, Multiple-Bridge or Braided. An intersection involving more than one
grade separation structure or more than two levels of traffic, with direct connections
between roads. Essentially these are combinations of individual grade separations
and ramps.

Intersection, Multiway. A junction having five or more legs.

Intersection, Offset. A simple intersection where the medial line of one of the
intersecting ways is broken or offset at right angles at the crossing of the second

Intersection, Rotary. An intersection of two or more roads where vehicles move
one way only around a central area or island approximately 150 feet in diameter
or greater.

Intersection, Simple. An intersection of two traffic ways, with four legs or ap-

Intersection, Skew. A simple intersection where the ways meet and cross so as to
form acute and obtuse angles.

Intersection, "T." An intersection with three legs (shaped like the letter "T")
where one of the intersecting ways meets at approximately right angles, but does
not cross the other way. See following term.

Intersection, Three-Way. A roadway intersection with three legs. If one of the legs
is an approximate prolongation of the direction of approach of another, and if the
third leg intersects this prolongation at an angle between 75 and 105 degrees, the
three-way intersection is classed as a "T" intersection. If one leg is a prolongation of
the approach of another and the third leg intersects this prolongation at an angle
less than 75 degrees or greater than 105 degrees, it is classed as a "Y" intersection.

Intersection, Turbine-Type Rotary. A rotary intersection where most of the
change in direction is made on entering and a near tangent path is used on leaving.

Intersection, "Y". An intersection with three legs (shaped like the letter "Y")
where one of the intersecting ways meets, but does not cross, the other way so as
to form an acute or an obtuse angle. See Three- Way Intersection.

Leg, Intersection. That part of any one of the roadways radiating from an inter-
section which is outside of the area of the intersection proper.

Loop, Inner. A ramp used by traffic destined for a left-turn movement from one
highway to a second when such movement is accomplished by making a right-exit
turn followed by a three-quarter round right-turn maneuver and a right entrance

Ramp. An inclined section of way over which traffic passes for the primary purpose
of ascending or descending so as to make connections with other ways. Also, an
interconnecting roadway of a traffic interchange, or any connection between high-


way facilities of different levels, on which vehicles may enter or leave a designated

Road, Preference (at an intersection). One of two or more roads upon which road
it is clearly indicated that traffic is permitted to proceed through the intersection
without interruption.

Rotor. A rotary intersection.

Roundabout. An intersection of trafficways having one or more rotary islands,
with or without supplementary channelizing islands, together with peripheral

Separation, Grade. A junction of ways such that one passes over the other and
connections between the ways may or may not be made by ramps or other special

Separation, "T" Grade (or "Trumpet"). A grade separation at a "T" intersection,
generally with 3 direct connections and one inner loop.

Separation, "Y" Grade. A "Y" intersection where two of the left-turning move-
ments are separated.

Turn, Entrance. A turn where traffic turns from a ramp and enters a through

Turn, Exit. A turn where traffic leaves a through roadway and enters a ramp.

0. Parking and Terminals

Garage, Private Parking. A garage, use of which is restricted to the owner, tenants,
employees or other special persons.

Garage, Public Parking. A facility, open to the general public. The words "pay"
or "free" are sometimes added to distinguish whether or not a parking fee is

Lot, Parking. An open area, off the street, used for parking. It may be enclosed by
a fence or wall, but is not considered a building.

Terminal. A special area, including buildings, structures, and equipment at the end
of a transportation facility, for the storage, transfer, handling, delivery and recep-
tion of vehicles, passengers and materials.

Terminal, Stub. A terminal where the entering carrier must retrace on departure
the same way it came into the terminal or loading platform.

Terminal, Through. A terminal where the carrier continues progressively on de-
parture along untraced sections of the same way it came into the terminal or load-
ing platform.

Track, Truck (Also called Team Track). A track where freight is transferred
directly between freight cars and trucks or wagons.

A. Composition I Vehicles, Drivers, Pedestrians)

Automobile. A private passenger motor vehicle with seating capacity of 7 or less.


Bicycle. A device propelled by human power upon which any person may ride,
having two tandem wheels either or both of which are usually over 20 inches in
diameter, and including any device generally recognized as a bicycle though
equipped with two front or two rear w r heels.

Bus (or Motor Bus or Coach). A motor vehicle designed to carry more than 7
passengers without auxiliary folding seats, usually engaged as a common carrier
in the transportation of persons.

Bus, Trolley (or Trackless Trolley). A public conveyance similar to a bus, pro-
pelled by electric power supplied from overhead conductors and designed to travel
on the roadway for the primary purpose of transporting persons but not materials
within a metropolitan area.

Car, Cable. A street car that is mechanically drawn by a moving cable.

Car, Passenger. A passenger motor vehicle with seating capacity of 7 or less.
Includes taxicabs and automobiles.

Car, Private Passenger. Same as Automobile.

Car, Street. A public conveyance designed to travel exclusively upon rails usually
laid in the street or highway, for the primary purpose of transporting persons but
not materials, within a metropolitan area.

Chauffeur. A motor vehicle operator employed for the principal purpose of operat-
ing the vehicle, or who drives the vehicle while in use as a public or common
carrier of persons and materials.

Coach, Trolley. Same as Trolley Bus.

Driver. A person who drives or is in actual physical control of a motor vehicle.

Motorcycle. A motor vehicle having a saddle for the use of the rider and designed
to travel on not more than 3 wheels in contact with the ground. Tractors are not

Operator. A Driver.

Passenger. Any person in or upon a conveyance, other than the operator, with the
knowledge and consent of the operator. Any person in or upon the conveyance
without knowledge and consent of the operator is termed a trespasser.

Pedestrian. Any person afoot. For purpose of accident classification, this shall be
interpreted to include any person riding in or upon a device moved or designed for
movement by human power or the force of gravity except bicycles, including stilts,
skates, skis, sleds, toy wagons, scooters, scooter-bikes (having wheels less than 24
inches in diameter), tricycles, baby carriages, etc., while upon or adjacent to the

Platoon (or Wave). Closely grouped elemental components of traffic moving or
standing ready to move over a roadway, with clear spaces ahead and behind.

Railroad. A carrier of persons or property upon cars, other than street cars, oper-
ated upon stationary rails. Does not include elevators.

Semi-Trailer. A vehicle of the trailer type so designed and used in conjunction
with a motor vehicle that some part of its own weight and that of its load rests
upon or is carried by another vehicle.


Taxicab. A motor vehicle similar to an automobile, generally of the sedan or im-
perial sedan type, usually with a partition between the rear seat and operator's
compartment and used as a public carrier in a commercial business for gain.

Traffic. Pedestrians, ridden or herded animals, vehicles, street cars, and other con-
veyances, either singly or together while using any street for purposes of travel.

Traffic, Converted. Induced traffic representing trips made by persons converting
from some other mode of transportation ; e.g. automobile passengers who change
to bus riders because of improved bus transportation facilities.

Traffic, Diverted. Induced traffic representing units of traffic transferred from some
other trafficway; e.g., traffic diverted from a surface street to a new freeway, or
diverted from one street to another because of a detour.

Traffic, Generated. Induced traffic representing units of traffic which had not
existed before ; e.g. more frequent trips taken by previous users of existing facilities,
or trips made by those who had not travelled previously, but now travel because of
installation of an attractive facility. Includes converted traffic.

Traffic, Induced. Increased number of trips by persons or vehicles on or over a
trafficway or public transit facility, not attributable to normal growth, but caused
solely by improvement or change in the trafficway or facility, or by installation of
the trafficway or facility where none existed before. Includes generated and-or
diverted traffic and-or converted traffic.

Traffic, Through. Traffic proceeding through a district, not originating in or des-
tined to the district.

Traffic, Weighted Average. Total vehicle miles of travel on a route divided by
length of route in miles.

Trailer. A vehicle without motive power designed for carrying materials (or
persons) wholly on its own structure and for being drawn by a motor vehicle,
usually a truck.

Transit, Local. Low speed rail or bus lines serving local needs with frequent stops.
This service usually operates on the surface streets.

Transit, Mass. Transportation of large groups of persons.

Transit, Public. The public passenger carrying service afforded by vehicles follow-
ing regular routes and making specified stops. Such vehicles are usually buses, street
cars, trolley buses and railroad trains, but may include air-borne and water-borne

Transit, Rapid. High speed rail or bus line service operating over long distances
and with few stops. This service often operates at a grade separated from other
traffic, such as in a subway or private right-of-way.

Transportation, Private. Carrying of passengers by private passenger cars.
Trip. One way travel between origin and destination.

Trip, Through. A trip proceeding through a district, not originating in or destined
to the district.

Truck. A motor vehicle with body designed for the primary purpose of transporta-
tion of materials or freight.


Truck-Tractor. A truck designed and used primarily for pulling trailers and semi-
trailers and not so constructed as to carry a load other than a part of the weight of
the trailer (with load).

Vehicle, Commercial. A free-wheeled vehicle designed for the transportation of
cargo other than passengers, and broadly referred to as a "truck" may be further
classified as light, medium, heavy, etc., and includes tractor-trucks, trailers, and
semi-trailers when used in combination.

Vehicle, Free-Wheeled. A vehicle not limited in operation by rails or tracks.

Vehicle, Motor. Any mechanically or electrically powered device (except one
moved by human power), not operated on rails, upon which or by which any person
or property may be transported upon a land highway. The load on a motor vehicle
is considered as part of the vehicle. Included in this category are such vehicles as
motor trucks, automobiles, motor buses, trolley buses, motorcycles, motorized bicycle
or scooter, tractors, army tanks, highway graders, trailers and semi-trailers.

B. Movements {Distances, Capacity and Studies!

Area, Cordon. The district bounded by the Cordon Line and included in a Cordon

Capacity, Basic. The maximum number of passenger cars that can pass a given
point on a lane or roadway during one hour under the most nearly ideal roadway
and traffic conditions which can possibly be obtained.

Capacity, Lane. The maximum traffic volume per lane which will permit vehicles
to travel at the assumed speed without appreciable delay.

Capacity, Possible. The maximum number of vehicles that can pass a given point
on a lane or roadway during one hour, under the prevailing roadway and traffic

Capacity, Practical. The maximum number of vehicles that can pass a given point
on a roadway or in a designated lane during one hour without the traffic density
being so great as to cause unreasonable delay, hazard or restriction to the drivers'
freedom of maneuver under the prevailing roadway and traffic conditions.

Conflict, Point of. The point or limited area where elemental movements of traffic
intersect or join a common path.

Count, Cordon. A count of all vehicles and persons entering and leaving a district
(cordon area) during a typical day.

Count, Ground. Actual counts of all types of motor vehicles made at control points,
roadside interview stations, and screen line stations, in an O and D study.

Count, Long Time. A traffic count extending over 8 or more successive hours on
one day.

Count, Pedestrian. A physical count of the number of pedestrians passing a point
during a specific period of time.

Count, Short. A traffic count extending over a short period, usually several hours
or less.

Deceleration, Chronotropic. Deceleration that occurs in situations where motion
beyond a specified point cannot be continued until a definite instant of time (such
as approaching a traffic signal red light).


Deceleration, Functional. Deceleration that occurs in a situation where forward
motion may be resumed as soon as the specific stopping function is fulfilled.

Delay. Time lost by traffic due to traffic frictions. Also, the time consumed while
traffic or a specified component of traffic is impeded in its movement by some
element over which it has no control.

Delay, Fixed. Delays caused by such things as Stop signs or signals, to which
traffic is subjected regardless of the amount of traffic volume and interference.

Delay, Operational. Delay caused by mutual interference between vehicles. The
difference between travel times over a route during extremely low and during high
traffic volumes, or the time consumed while waiting at a Stop sign for cross traffic
to clear, are operational delays. Time losses resulting from congestion, from inter-
ference with parking vehicles, and from turning vehicles are also examples of oper-
ational delays.

Density, Critical. The density of traffic when the volume is at the possible capacity
on a given roadway. At a density either greater or less than the critical density the
volume of traffic will be decreased. Critical density occurs when all vehicles are
moving at or about the optimum speed.

Density, Traffic. The number of vehicles occupying a unit length of roadway at a
given instant, usually expressed in vehicles per mile.

Distance, Brake Lag. The distance travelled (by a vehicle being braked to a stop)
between the time the driver contacts the brake controls and the point at which the
brake lining contacts the brake drum.

Distance, Braking. The distance travelled between the point at which the brake
lining contacts the brake drum and the point at which the vehicle comes to rest.

Distance, Driver Perception-Reaction. The distance covered by a moving vehicle
during the time the driver sees and reacts to a situation, and before he can affect
the vehicle's motion in any way.

Distance, Driver Reaction. The distance travelled between the point at which the
driver perceives that braking is required and the point at which he contacts the
braking controls.

Distance, Driver Stopping. The distance travelled between the point at which the
driver perceives that braking is required and the point at which the vehicle comes
to rest.

Distance, Minimum Non-Passing Sight. The distance required for a vehicle to be
stopped from the instant a stationary object in the vehicle's lane becomes visible to
the driver. A height of 4 inches is assumed in determining non-passing sight

Distance, Minimum Passing Sight. This distance is used in conjunction with a
situation where vehicle no. 1 is passing vehicle no. 2 proceeding in the same direc-
tion on a 2-lane or 3-lane high\vay and a 3rd vehicle is approaching from the oppo-
site direction. It is the minimum distance between no. 1 and no. 3 when each driver
can see the other's vehicle, when no. 1 can safely pass no. 2 before meeting no. 3


Distance, Non-Passing Sight. The longest distance at which a driver whose eye
is assumed to be 4.5 feet above the pavement surface can see the top of an object
4 inches high on the road.

Distance, Passing Sight. The longest distance at which a driver whose eye is
assumed to be 4.5 feet above the pavement surface can see the top of an object 4.5
feet high on the road. Also, the minimum sight distance that must be available to
enable the driver of one vehicle to pass another vehicle safely and comfortably
without interfering with the speed of an oncoming vehicle travelling at the design
speed should it come into view after the maneuver is started.

Distance, Restrictive Sight. A sight distance which, by reason of its inadequate
length, causes a reduction in the operating speed and otherwise restrains the free
movement of traffic under the prevailing conditions.

Distance, Sight (at an intersection). The distance from the driver's eye (his
vehicle approaching the intersection) to the point of intersection of the paths of his
vehicle and another approaching vehicle on a cross road, measured from the. point
where as both vehicles approach the intersection each driver is first able to see the
other's vehicle. Where no sight obstruction exists on the intersection approach for
several hundred feet, the sight distance is, for all practical purposes, unlimited.

Distance, Stopping Sight. See Non-Passing Sight Distance.

Distance, Vehicle Stopping. The distance travelled between the point at which the
driver contacts the braking controls and the point at which the vehicle comes to
rest. This equals the brake lag distance plus the braking distance.

Effort, Braking. The net effective retarding force exerted by the brakes, expressed
as a percent of the vehicle's weight component normal to the road surface.

Friction, Intersectional. The retarding effect on traffic movement caused by poten-
tial and actual traffic movement conflicts at an intersection of two moving streams
of traffic. This friction is due solely to the effect of one stream of traffic crossing
the other stream.

Friction, Marginal. The retarding effect on the free flow of traffic caused by
interference of any sort at the margin of the trafficway. This does not include con-
flicts at intersections or medial friction.

Friction, Medial. The retarding effect on the free flow of traffic caused by inter-
ference between traffic units proceeding in opposite directions on a trafficway. Turn-
ing conflicts are classed as intersectional conflicts.

Friction, Stream. The retarding effect on the free flow of traffic caused by mutual
interferences between traffic units proceeding in the same direction. This does not
include turning conflicts. Conflicts are caused primarily by differences in sizes and

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