Glossary of Road &
This page last updated
January 01, 2010
Below is a list of common
highway-related words and terms, both the technical jargon as well as
layman's terms, and their definitions, especially as they apply here in
San Antonio and/or Texas.
acceleration lane - a short lane
at the end of an entrance ramp that allows entering traffic to build-up
speed before merging into the main travel lanes. In San Antonio,
and in Texas in general, acceleration lanes are not as common as in
access road - the common term in
San Antonio for a frontage road.
arterial - a main road or
thoroughfare. Arterials are typically divided into "major
arterials" and "minor arterials".
auxiliary lane - a lane that is
added to a freeway at an entrance ramp and then is subsequently dropped
at the next exit ramp. Compare with acceleration lane,
deceleration lane, mainlanes, and collector/distributor.
average annual daily traffic (AADT) -
a traffic count that counts the number of vehicles that pass a given
point on a road during a 24-hour period, averaged over several counts
taken during a 12 month period.
Barnes Dance - a colloquial term
for a pedestrian scramble crossing. See pedestrian scramble.
bent - technical term for a bridge
pier. Commonly referred to as a "bridge column".
Botts' Dots - colloquial term for
raised pavement markers, also known as "traffic buttons" and
braided ramp - a slip ramp
configuration where an entrance ramp passes over an exit ramp, or
vice-versa. There are numerous examples in San Antonio, such as
the ramps along both sides of Loop 410 between Vance Jackson and
Jackson-Keller. Braided ramps eliminate weaving in areas with
limited room for conventional slip ramps. See also slip ramp.
cat's eyes - colloquial term for
reflectorized raised pavement markers.
centerline mile - technical term
for one mile of a roadway, regardless of the number of lanes.
Compare with lane mile.
changeable message sign (CMS) -
another term for a variable message sign.
clearway - the area adjacent to a
roadway that, by design, is kept clear of immovable objects for safety
cloverleaf - an interchange that
has four circular ramps that turn at 270 degrees to provide for left turn
movements (which, when viewed from above, resembles a four-leaf clover) and four
outer 45-degree ramps for right-turn movements.
Many people refer to any freeway-to-freeway interchange as a
"cloverleaf", but the term is reserved for the specific type of
interchange with circular ramps. Compare with directional
collector - a street that provides
connectivity between an arterial and local streets. The main
street into and through subdivision is typically a collector.
collector/distributor - a roadway
that runs parallel to but is separate from the mainlanes on a freeway
that provides connectivity between the freeway mainlanes and another
roadway, typically the ramps to another freeway. For instance,
when you exit from I-10 near La Cantera to get onto Loop 1604, you first use a
collector/distributor road, then the ramp to 1604, then another
collector/distributor road before you actually enter the Loop 1604 mainlanes.
A similar arrangement exists on I-35 and Loop 1604 in Live Oak. Some people mistakenly refer to collector/distributors
as access roads.
commuter rail - a type of public
rail transportation that connects a central city with its outlying
suburbs, satellite towns, or another city. Many people interchange
the terms "commuter rail" and "light rail", but this is incorrect.
Commuter rail differs from light rail in that is
uses larger, heavier trains (such as subway or Amtrak style trains) that
run entirely on exclusive rights-of-way. Commuter rail
also specifically differs from light rail in that it connects a central city
with its outlying areas and has far fewer stations and less-frequent
schedules (headways) than a typical light rail system.
concurrency - when a single
physical roadway shares two or more route numbers. An example in
San Antonio is the freeway on the western edge of downtown, which is
I-10, I-35, and US-87.
connector - a ramp, often
elevated, that connects two highways. These are commonly just
referred to as a "ramp".
controlled-access - a type of
roadway whereby traffic can only enter and exit at specific designated
locations (typically entrance and exit ramps). Controlled access
roads are generally referred to as freeways or expressways.
crossover - a paved area in a
median of a divided highway where traffic is allowed to cross over to
the other side of the highway or to an intersecting road. Compare
deceleration lane - a short lane
just prior to an exit ramp that allows exiting traffic to reduce speed
before leaving the main travel lanes. In San Antonio, and in Texas
in general, deceleration lanes are not as common as in other locales.
diamond interchange - an
interchange between a freeway and surface street where the entrance and
exit ramps form a diamond shape as viewed from the air. In most
places, the ramps connect directly from the freeway to the surface
street, and so the diamond pattern is obvious. In Texas, however,
the ramps usually connect to a frontage road, so the diamond may be
"elongated". In San Antonio, an example of a typical diamond
interchange without frontage roads is the US 281 exit to Hildebrand or
the I-37 exit to Hot Wells. A couple of examples of a diamond
interchange with frontage roads are Loop 1604 at Blanco and I-35 at
Eisenhauer. In congested areas with frontage roads, diamond
interchanges are oftentimes replaced with X-interchanges to reduce
weaving on the mainlanes. Compare with X-interchange.
directional interchange - an
interchange, usually a freeway-to-freeway interchange, where connectors,
typically elevated, provide direct connections to the intersecting
roadway by turning in the direction of travel. In other words, the
connector for the left turn movement actually bends to the left rather
than making a 270-degree right turn as it does in a cloverleaf
interchange. Most fully-directional interchanges
are known colloquially as "stacks". Compare with
divided highway - a roadway that
has a median or some other physical barrier separating the two opposing
sides of traffic. Some people automatically assume that any
divided highway is a freeway or expressway, but this is an incorrect
assumption. While nearly all freeways are divided highways, not
all divided highways are freeways. In San Antonio, Bandera Rd. outside Loop 410
and US 281 outside Loop 1604 are examples of standard surface-level
divided highways that are not an expressway or freeway.
dynamic message sign (DMS) -
another term for a variable message sign.
easement - the use of a part of
private property for a public purpose. Typically, easements are
used for utility lines. Owners of property with an easement are
required to provide access to the easement and are typically not
compensated for the use. Compare with right-of-way.
expressway - a road that has
controlled-access. In most parts of the country, including San
Antonio, the term "expressway" and "freeway" are essentially
interchangeable. However, the technical term "expressway" differs
from "freeway" in that expressways can have at-grade intersections,
whereas freeways cannot. In San Antonio, an example of a true
expressway is Spur 422 near Palo Alto College. Compare with freeway, highway, and
Farm-to-Market (FM) road - the
network of rural roads in Texas that connect farming and ranching areas
with nearby towns. The FM system also contains Ranch-to-Market (RM)
roads. In metropolitan areas, many FM roads no
longer serve that purpose and instead are simply state-maintained
arterials. For funding purposes, TxDOT officially classifies these
types of FM roads as "Urban Roads", but they are still signed as
feeder road - the common term in
Houston and southeast Texas for a frontage road.
flyover - a general term for an
overpass, especially an overpass that is a ramp or connector.
freeway - a road designed for
high-speed traffic with controlled-access and grade-separated
intersections. Contrary to popular belief, a freeway is not a road
free from tolls, but rather a road that is free from signals and
intersections; a "free-flowing" road. Indeed, when one uses the
term freeway, it conjures images of a certain type of road based on its
functional capabilities, and, in fact, most tollways are
functionally-classified as freeways. Compare to expressway,
highway, and parkway.
frontage road - a road that runs
parallel to a freeway or expressway for the purpose of providing access
to adjacent properties and intersecting surface streets.
Typically, there will be a frontage road on each side of a freeway.
In urban areas, frontage roads are one-way, while they are usually
two-way in rural areas. While referred to colloquially as access
roads, feeder roads, gateways, and service roads in various areas of the
state, "frontage road" is the official term and is the common term in
the Austin area.
grade-separated - a intersection
of two roads where one roadway passes over the other. In other
words, the roads do not intersect at-grade. Every intersection
along a freeway is grade-separated. See also interchange.
High Occupancy Vehicle (HOV) lane -
a dedicated lane for vehicles that have a certain number of
occupants, typically 2 or more. HOV lanes are used extensively in
the Houston area.
highway - technically, a highway
is any public roadway. Typically, the term highway is generally
used to refer to a major roadway, usually maintained by the state.
In San Antonio and other places, the term highway is often used colloquially to refer to
Intelligent Transportation System
(ITS) - a system that uses technology to monitor and manage traffic
on a roadway or network of roadways. In San Antonio, TransGuide is
interchange - a grade-separated
junction of two roadways with full or partial access between them.
Technically, the term "interchange" can refer to a junction between a
freeway and a surface street, but typically the term is reserved for
interchange sequence series sign -
a road sign that lists the next three (sometimes two) exits and the
distance to each. Interchange sequence series signs are used
sporadically and inconsistently in the San Antonio area.
interconnect - a system whereby
traffic signals communicate with each other and/or a central controller,
usually as part of a coordinated progression system. Most traffic
signals along San Antonio's major arterials are interconnected, either by
means of a cable or via radio. See also progression.
Interstate - a freeway that is
part of the federally-designated Interstate Highway System. This
term is often used colloquially (although technically incorrectly) to
refer to any freeway.
Jersey barrier - the ubiquitous
concrete barrier used to separate opposing traffic flows on freeways as
well as protective barriers in construction zones and as bridge rails.
The term "Jersey barrier" technically refers to a specific type of
barrier, but is commonly used to refer to all sloped concrete barriers.
Newer concrete barriers that are not technically "Jersey barriers" are
generally "constant slope" barriers. Jersey barriers are known as
"K-rails" in some areas.
jughandle - a type of ramp,
typically at ground level, that is essentially an elongated
version of a cloverleaf ramp with a sharper turn, so-named because
it resembles a jug handle when viewed from above. In San Antonio, some examples of jughandles are at I-35 and Olympia Parkway, US 281 at Sonterra Blvd.,
and US 90 at Hunt Lane.
lane control signal (LCS) - a
signal above a lane that shows a red, green, or yellow arrow or "X"
symbol to denote whether the lane is open or closed. In San
Antonio, LCSs are used on most TransGuide-equipped freeways as well as
the reversible lanes around the AT&T Center.
lane drop - a place on a freeway
where a mainlane terminates by either becoming an an exit-only lane or
by way of simply ending and merging into the adjacent lane.
lane mile - one mile of one lane
of road. One mile of a roadway with four lanes is four lane miles.
Contrast with centerline mile.
level of service (LOS) - a
mostly subjective measurement of the performance of a roadway or intersection
based on the traffic conditions. LOS is graded on a scale of A-F
(including E), where LOS-A is free-flowing traffic and LOS-F is
light rail - a type of public rail
transportation that utilizes streetcar-like vehicles on streets with
shared right-of-way or on exclusive right-of-way. The term "light
tail" is oftentimes incorrectly used interchangeably with "commuter
rail". Compare with commuter rail for differences between
limited-access - another term for
loop - in Texas, a loop is a state
highway that connects two or more other state highways. Usually, a
loop is circular in nature, but frequently is not. For example, in
San Antonio, while Loops 410 and 1604 ring the city, several other state
highways are also designated as Loops: Fredericksburg Rd. (Loop 345) and
Austin Hwy. (Loop 368) are two prime examples.
mainlanes - the main or primary
travel lanes on a freeway or other highway, typically as opposed to
the frontage road lanes. See also acceleration
lane, deceleration lane, auxiliary lane, and
major thoroughfare plan - a plan
by a municipality or other transportation planning agency that
classifies existing arterial roadways and designates corridors for
possible future arterials. The primary purpose of such a plan is
twofold-- to designate roadways for funding purposes and
to reserve the location for possible future roads but
not necessarily to indicate that such roads will be built.
managed lane - a lane or set of
lanes on a road, typically on a freeway, that is separated from the
general-purpose mainlanes by barriers, to which access is regulated by
some means or criteria (typically tolls) to maintain a certain level of
Manual of Uniform Traffic Control
Devices (MUTCD) - the standard guide that defines and regulates all
traffic signs, signals, and markings in the United States. Most
states have their own MUTCD as well.
median - an unpaved area that
separates two parallel roadways. Sometimes mispronounced or
misspelled as "medium".
Metropolitan Planning Organization (MPO)
- a state-designated agency that is required under Federal law to
coordinate and manage federal transportation funding among all agencies
that receive such funding in a metropolitan area.
multiplex - another term for
parkway - a roadway
that typically runs through a park-like setting. In the Northeast,
parkways are generally freeways where commercial vehicles are prohibited. In San
Antonio, the term "parkway" has started to acquire a slightly different meaning,
that being a roadway that is essentially a minor expressway or
"super-arterial", such as the Wurzbach Parkway or planned Kelly Parkway.
However, the term has also been used arbitrarily on roads that typically
would otherwise be referred to as a boulevard or avenue, such as Stone
Oak Parkway and AT&T Center Parkway.
pedestrian scramble - an intersection
where signals stop all motor traffic to allow pedestrians to cross in all
directions simultaneously. In San Antonio, pedestrian scramble systems
have been installed at several downtown intersections. Also known as a
pre-emption - a system whereby
specific vehicles can interrupt the normal traffic signal cycle and
obtain a green signal for their direction of travel. In San
Antonio and many cities, signal pre-emption is used by emergency vehicles. Pre-emption for VIA buses is being planned as
part of the Bus Rapid Transit corridor along Fredericksburg Rd.
progression - a system whereby
traffic signals are coordinated along a given corridor to provide for
all green signals as a group of vehicles (known as a "platoon") makes
its way through the corridor at a set speed. Known colloquially as
"signal synchronization". See also
raised pavement marker - a device,
usually made of ceramic or plastic, that is used as a lane marker.
These are known colloquially as "Botts' Dots", "turtles", or "traffic
buttons". Oftentimes, raised pavement markers will be
reflectorized; these are sometimes known as "cat's eyes".
ramp - a short road that provides
a connection between two other roads. See also slip-ramp,
connector and jughandle.
ramp metering - a system that uses
traffic signals on a freeway entrance ramp to regulate (meter) the
number of vehicles that can enter the freeway, typically during peak
periods. Ramp metering was fairly widespread on I-35 and I-10 in
downtown San Antonio in the '60s, '70s, and early '80s, but was removed
during the double-decking of those roads in the mid and late '80s.
Ramp metering was reintroduced in Houston in the mid '90s and is now
commonplace there, with the metering signals known as "flow signals."
Ranch Road - another term for a
Ranch-to-Market road, although there is one official "Ranch Road" (RR1)
that serves the LBJ Ranch. See Ranch-to-Market road.
Ranch-to-Market road - another
name for a Farm-to-Market road, typically used west of US 281. See
right-of-way - 1. a strip of land
owned by a public entity for use by transportation, utility, and/or
communication purposes. Compare with easement. 2. the
legal authority of one vehicle to have precedence over another at an
riprap - pavement or other
treatment along a slope to prevent erosion.
roundabout - a roadway
intersection that utilizes a circular roadway to connect the
intersecting roads. Roundabouts, sometimes referred to as "traffic
circles", are a form of traffic calming.
service road - the common term in
Dallas-Ft. Worth for a frontage road.
shoulder - a paved area adjacent
to a travel lane, typically on the right-hand edge of the road, that is
not intended for use as a main travel lane, but rather as an area for
vehicles to slow or stop in an emergency or to turn right. In
Texas, an improved shoulder (one that is paved and of similar width to a
normal travel lane) can also be used to pass someone who is slowing or
stopped to turn left on the main travel lane or can be driven on by slow
vehicles to allow faster traffic to
signal pre-emption - See
Single Point Urban Interchange (SPUI)
- a type of diamond interchange whereby the left turn movements are
curved in such as way as to provide a single intersection for them
centered under or above the freeway instead of two distinct
intersections on each side of the freeway. The first SPUI in Texas
is at US 75 and Parker Rd. in Plano.
slip ramp - a short ramp between
two adjacent, parallel roads, such as the entrance and exit ramps
between a freeway's mainlanes and its frontage road.
spur - a short state highway that
branches-off from another highway.
stack - a multi-level,
fully-directional interchange between two freeways, so-called because
the roadways and connectors are "stacked" one atop the other. In
San Antonio, older stacks are located downtown at I-10/I-37 and I-35/US 90,
I-37/Loop 410, with newer stacks at I-10/Loop
410 (NW) and US 281/Loop 410.
State highway - 1. any roadway
built and maintained by the state. 2. a specifically numbered
roadway that is part of the state highway system. State highways
are prefixed with "SH". In San Antonio, two examples are SH 16 and
super-street - a roadway with one or more
intersections where the straight-through and left-turn movements of the cross
street have been eliminated and replaced by right-turns coupled with downstream
turnarounds. The first super-street in Texas will be built on US 281 north
of Loop 1604 in San Antonio.
surface street - a standard road
that runs at ground level. This term is generally used to
differentiate a particular road from a freeway.
tollway - a road where motorists
are charged to use the road. Because of the inherent need to
control access to a tollway for the purposes of toll collection, nearly
all tollways are also freeways. Sometimes, tollways are built as
managed lanes on an otherwise toll-free freeway. See also
traffic button -
colloquial term for raised pavement
markers, also known as "Bott's dots" and "turtles".
traffic calming - techniques used
to slow traffic. Such techniques include roundabouts, speed humps,
chicanes, and bottlenecking. See also roundabout.
TransGuide - the Intelligent
Transportation System in San Antonio. TransGuide monitors area
freeways using cameras and speed sensors, then notifies motorists of
incidents or congestion using variable message signs and lane control
signals. TransGuide is also known as a type of advanced "traffic
turnaround - a ramp that allows
traffic to make a U-turn across a divided highway. In Texas,
turnarounds are used predominately to allow traffic to go from a one-way
frontage road on one side of a freeway to the opposing one-way frontage
road on the other side of the freeway without having to traverse the
intersections for the cross street. In most places, turnarounds
are marked with a simple U-turn sign, but in San Antonio, signs for
turnarounds actually use the term "turnaround".
colloquial term for raised pavement
markers, also known as "traffic buttons" and "Botts' Dots".
US highway - a highway that is
part of the nationally-coordinated system of highways that bear the same
name. Contrary to popular belief, US highways are not "federal
highways" per se. US highways are not under any federal
jurisdiction, but rather are state highways that use a coordinated
national numbering system to provide for easier interstate travel.
The numbering system is administered by the American Association of State
highway and Transportation Officials (AASHTO).
variable message sign (VMS) -
electronic signs along or above freeways and other highways that provide
dynamic messages to alert the motoring public of incidents, congestion,
construction, or other information. In San Antonio, permanent VMSs
are operated by TransGuide along most area freeways and include mainlane
and entrance ramp VMSs. VMSs are also known-as changeable message
signs and dynamic message signs.
vehicle miles traveled (VMT) - the
total number of miles driven by all vehicles on a specific road, class
of roads, or in a geographical area during a specific time period.
For instance, the total number of miles driven by all vehicles in Texas during 2009.
an interchange between a freeway and a
surface street where the entrance and exit ramps connect to a frontage
road and form an "X" shape relative to the cross street as viewed from
the air. In a standard frontage-road "diamond" interchange, the
entrance ramp from one cross street typically precedes the exit ramp for
the next cross street. However, in an X-ramp configuration, those
ramps are reversed. This reduces weaving on the mainlanes.
The process of converting a diamond interchange to an X-interchange is
known as "ramp reversal". In San Antonio, a couple of examples of
X-interchanges are I-10 at DeZavala and I-35 at FM 3009. Compare
with diamond interchange.