Glossary of Road & Traffic Terms

This page last updated May 23, 2021

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 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 other states.

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 a downstream (usually 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.

bent - technical term for a bridge column.

Botts' Dots - colloquial term for raised pavement markers, also known as "traffic buttons" and "turtles". Named for the traffic engineer who invented them.

braided ramp - a ramp configuration where an entrance ramp passes over an exit ramp, or vice-versa. 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 reasons.

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 should only be used for the specific type of interchange with circular ramps. Compare with directional interchange.

collector - a street that provides connectivity between an arterial and local streets. The main street into and through a subdivision is typically a collector.

collector/distributor - a roadway that runs parallel to but is separate from the freeway mainlanes and from the frontage road and provides connectivity between the mainlanes and another roadway. These are often used in interchanges where traffic exits the freeway onto the collector/distributor, then exits again from the collector/distributor onto an exit ramp. Some people mistakenly conflate collector/distributors and frontage 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. See also light rail.

concurrency - when a single physical roadway shares two or more route numbers, for example, if a single road is both I-10 and US 87. Sometimes called "multiplexing".

connector - a ramp, often elevated, that connects two highways. These are commonly just referred to as a "ramp" or, if elevated, a "flyover".

controlled-access - a type of roadway whereby traffic can only enter and exit at specific designated locations (i.e. 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 with turnaround.

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 Texas in general, deceleration lanes are not as common as in other states.

diamond interchange - an interchange between a freeway and surface street where the entrance and exit ramps form a diamond shape as viewed from above. In most places outside of Texas, 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 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 ("flyovers"), 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" or "spaghetti bowls". Compare with cloverleaf.

displaced left turn (DLT) - an intersection where one or both left turn movements of one or both intersecting roadways is shifted to cross over the opposing traffic lanes prior to reaching the main intersection. This allows two or more normally conflicting movements to travel simultaneously, thus increasing the efficiency and capacity of the intersection. Also known as a "Continuous Flow Intersection".

diverging diamond interchange (DDI) - an intersection-- typically where an arterial crosses a freeway-- where the opposing traffic on the arterial crosses over to the left side while traversing the interchange, then crosses back to the right side. This allows for left turns to be made without crossing opposing traffic and for two or more normally conflicting movements to travel simultaneously, thus increasing the efficiency and capacity of the intersection.

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.

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 Texas, 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. Compare with freeway, highway, and parkway.

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.

feeder road - the common term in Houston and southeast Texas for a frontage road.

flyover - a colloquial term for an overpass, especially an overpass that is an interchange 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 necessarily 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 they are referred to colloquially as access roads in San Antonio, feeder roads in Houston, gateways in El Paso, and service roads in Dallas, "frontage road" is the official term and is also the common term in the Austin area.

gateway - the common term in El Paso for a frontage road.

grade-separated - an 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.

heavy rail - a type of public rail transportation/rapid transit that utilizes subway-type trains running in a dedicated exclusive right-of-way. Compare with light rail and commuter rail.

High Occupancy Toll (HOT) lane - a dedicated lane that can be used for free by vehicles that have a minimum number of occupants, typically 2 or more, and can also be used for a fee (toll) by single-occupant vehicles.

High Occupancy Vehicle (HOV) lane - a dedicated lane for vehicles that have a minimum number of occupants, typically 2 or more. HOV lanes are used extensively in the Houston area and are also found in the Dallas and San Antonio areas. Many HOV lanes in Texas and elsewhere have been converted to HOT lanes or tolled managed lanes.

highway - as defined by law, 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 many places, the term is often used colloquially to refer to a freeway.

Intelligent Transportation System (ITS) - a system that uses various technologies to monitor and manage traffic on a roadway or network of roadways such as TransGuide in San Antonio and TransStar in Houston.

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 often the term is primarily used to refer to freeway-to-freeway intersections.

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 typically used in urban areas.

interconnect - a system whereby traffic signals communicate with each other and/or a central controller, usually as part of a coordinated progression system. This can be done by means of a cable, dedicated radio, or cellular modems. 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.

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. 

lane drop - a place on a freeway or other roadway where a lane terminates by either becoming an an exit-only lane or by way of simply ending and merging into the adjacent lane. Also see trap 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 heavy stop-and-go congestion.

light rail - a type of public rail transportation that utilizes streetcar-like vehicles either on streets with shared right-of-way and/or on exclusive right-of-way. The term "light tail" is sometimes incorrectly used interchangeably with "commuter rail". Compare with commuter rail and heavy rail.

limited-access - another term for controlled access.

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.  Perhaps the best-known non-circular "loop" in Texas is Loop 1, or MoPac Expressway, in Austin.

mainlanes - the main or primary travel lanes or through lanes on a freeway or other highway, as opposed to the frontage road lanes. See also acceleration lane, deceleration lane, auxiliary lane, and collector/distributor.

major thoroughfare plan - a plan by a municipality, county, 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 lay out a comprehensive road network so as to preserve the locations for possible future roads.

managed lane - a lane or set of lanes on a road, typically on a freeway, that are separated from the general-purpose mainlanes by barriers, to which access is regulated by some criteria (for example payment of a toll, occupancy requirements, or vehicle type) to maintain a desired level of service.

Manual of Uniform Traffic Control Devices (MUTCD) - the standard guide that defines and regulates all traffic signs, signals, and markings in the United States. Some states adopt the federal MUTCD directly with or without an addendum, while other states have their own MUTCD based on the federal version.

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 federal and state transportation funding among all agencies that receive such funding in a metropolitan area.

mill and overlay - See overlay.

multiplex - another term for concurrency.

parkway - a roadway that typically runs through a park-like setting. In the Northeast, parkways are generally freeways where commercial vehicles are prohibited. In Texas and many other places, the term is used somewhat arbitrarily on roads that might otherwise be called a boulevard or avenue. In San Antonio, the term "parkway" has also been used in another context, that being a roadway that is essentially a minor expressway or "super-arterial", namely the Wurzbach Parkway. 

pedestrian scramble - an intersection where signals stop all motor traffic to allow pedestrians to cross in all directions simultaneously. Also known as a "Barnes Dance" (named for the traffic engineer who reportedly invented it.)

pre-emption - a system whereby specific vehicles can interrupt the normal traffic signal cycle to gain priority. In many cities, signal pre-emption is used by emergency vehicles. Some public transit buses also have pre-emption capabilities along some or all of their routes. Railroads crossings near signalized intersections also have pre-emption capabilties; in those cases, pre-emption usually takes the form of sending the traffic signals into flash mode while a train is present, followed by a special sequence to help clear traffic after the train has passed.

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 "synchronization". See also interconnect.

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 and connector.

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. Houston, Dallas, San Antonio, and Austin all had ramp metering in the '60s, '70s, and '80s that was removed in subsequent expansions. Ramp metering, branded as "flow signals", was reintroduced in Houston in the mid '90s, although many have again been subsequently removed during expansion projects.

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. The term "Ranch-to-Market" is more often used west of US 281. 

RCUT - abbreviation for Restricted Crossing U-Turn intersection.

Restricted Crossing U-Turn intersection - see Superstreet

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 priority over another at an intersection.

riprap - pavement or other treatment along a slope or around a post or column to prevent erosion.

roundabout - a roadway intersection that utilizes a circular roadway to connect the intersecting roads. Roundabouts, sometimes incorrectly referred to as "traffic circles" (which are larger), 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 pass.

signal pre-emption - See pre-emption.

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 was 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 frontage road.

spaghetti bowl - a colloquial term for a stack interchange. 

spur - a short state highway that branches-off from another highway.

stack interchange - a multi-level, fully-directional interchange between two freeways, so-called because the roadways and flyovers are "stacked" one atop the other. Also see directional interchange.

State highway - 1. any roadway built and maintained by the state. 2. in Texas, a specific class of roadway-- typically a trunk road-- that is part of the state highway system and are marked with a black and white square sign with the route number and the word "Texas". These route numbers are prefixed with "SH" in TxDOT nomenclature. 

superstreet - 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. These intersections are more technically called "Restricted Crossing U-Turn" (RCUT) intersections. The first superstreet in Texas was built on US 281 north of Loop 1604 in San Antonio, but has since been replaced by a freeway. Superstreets are sometimes incorrectly called "Michigan Lefts", which are similar but have a different traffic pattern.

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 a fee 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 freeway.

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.

trap lane - A lane that terminates in a forced turn or exit (i.e. a turn-only or exit-only lane.) See also lane drop.

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. 

turtle - 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 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. 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 a specific year.

X-interchange - 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 above. 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". Compare with diamond interchange.