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3+ Carpool Lane – A carpool lane requiring three or more passengers to travel toll-free.  


Auxiliary Lane An outer lane on the right side of a freeway that begins at an on-ramp and ends and the following off-ramp. The lane is a transition zone for cars entering the freeway and merging into the through-lanes.


Audible (Accessible) Pedestrian Signal -  Creates a sound signal advising visually impaired pedestrians that it is safe to cross and intersection.









Bicycle Lane Class IVClass IV Bikeways includes a barrier that separates cyclists or other users from motorized traffic. Types of barriers include grade separation, flexible posts, inflexible physical barriers, or on-street parking. The objective is to foster bicycling as a means of transportation, in a manner that improves safety for all users, including motorists, transit users, and pedestrians, including persons with disabilities.”


Bridge Scour - A process where rapidly flowing water strikes a bridge column resulting in whirlpools that erode the sediment supporting the bridge column, which can compromise the strength of the bridge. 

Bridge Scour Diagram 


Cast in Drilled Holes Piles (CIDH) - Piles serve as a foundation for bridges and other structures. They can be driving into the ground by hammer (pile driving), vibrated into place, or cast in drilled holes. In the latter case, a cylindrical hole is bored into the ground.  Next, a steel cages is inserted into the hole, and finally the hole is filled with concrete. 

Cast in Drilled Holes Piles




Changeable (Electronic) Message Sign (CMS) - An electronic informational sign facing traffic that displays messages which can be changed according to circumstances. There are permanent overhead CMSs and portable ones. Also known as electronic message board or sign.  Shown below:  A fixed changeable message sign and a portable changeable message sign. 


  Overhead Changeable Message Sign                Portable Changeable Message Sign


Concurrency (Route) -  A combination of at least two routes that share the same physical roadway. Such combinations occurs for geographic, economic or environmental reasons.  Routes are often combined along rivers or through mountain passes.  In less populated area routes are sometimes combined due to a decrease in traffic. 


Crosswalk -  A place designed for pedestrian to cross a road indicated with striping on the road.  Typical state highway crosswalks come in three forms of striping, rectangular, continental and ladder.  Below: a continental type crosswalk. 

  Continental style crosswalk


Curb Ramp, ADA Compliant -  A place, typically at an intersection, where the sidewalk has been modified to slope down to the street to allow access for wheelchairs and covered with a yellow mat with bumps for the visually impaired.  Compliant with the Americans with Disabilities Act of 1990.

ADA Compliant Curb Ramp \














Express Lane - A carpool lane that permits use by a single-occupancy vehicle upon payment of a toll. Also known as a HOT Lane, a high-occupancy toll lane.


Gabion wall - A retaining wall made of rock-filled steel cages. Gabion walls work well along streambeds and other aquatic locations but can be used elsewhere, too. 

Gabion Wall












HOV Lane High occupancy lane, also known as a carpool lane.


Leading Pedestrian IntervalGives pedestrians the walk signal 3-7 seconds before vehicles are given the green light. It allows pedestrians a head start over right or left-turning traffic, establishing their presence – and visibility – in the crosswalk. 


Managed Lane  A general term for either a carpool lane or an express lane. The term is often used during the project planning stage before deciding whether a lane would be a carpool lane or an express lane.

Lane Drop -  A lane drop is a location on a highway where the number of lanes decreases. Lane drops can be categorized into three classes: lane exits, lane splits, and lane terminations.  Reducing the number of lanes on a multi-lane roadway can reduce pedestrian crossing distances and slow vehicle speeds. Below is a merge signs indicating a forthcoming lane drop. 

Merge Ahead or Lane Drop


One-Way Traffic Control  -  A method of moving bi-direction traffic through a single lane by permittinga single direction of traffic toproceed while the opposing traffic waits. At some point the process is reversed, allowing the waiting traffic to proceed while traffic opposing traffic waits. Traffic is controlled by flaggers or traffic signals.  Typically used in construction zones or roadways narrowed by landslides or flooding. 


Pedestrian Hybrid Beacon -  An electronic traffic signal operated by push button that stops vehicular traffic to allow pedestrian to cross a road.  Often the signals are used at locations where there is a long distance between intersections where pedestrians typically cross the street. 

Pedestrian Beacon

















Permissive and Protected Left Turns - When a motorist makes a left turn at a signalized intersection which lacks a left turn arrow, they are making a permissive left turn, in other words, making a turn when cross traffic is permits it.  A motorist making left turn made at a signalized intersection with an illuminated green arrow is making a protected left turn, the green arrow means that cross traffic is stopped, meaning the motorist is protects by the traffic signal.


Rectangular Rapidly Flashing Beacon (RRFB) A traffic control device installed at crosswalks to alert motorists of the presence of pedestrians, consisting of a pole, a sign, and flashing rectangular beacons activated by a push button.  (See also Pedestrian Hybrid Beacon.)
A pedestrian crossing sign with a rectangular rapidly flashing beacon beneath the sign.


Roundabouts - A roundabout is an intersection where traffic travels around a central island in a counterclockwise direction. Vehicles entering or exiting the roundabout must yield to vehicles, bicyclists, and pedestrians.

roundRoundabouts can have many advantages over traffic signals when constructed in the right location, including:

  • They provide traffic calming, resulting in reduced speeds.
  • They require less maintenance, have lower yearly operational costs, and have a longer service life.
  • They reduce greenhouse gas emissions by reducing vehicle idling time.
  • The median islands provide refuge for pedestrians, allowing them to cross one direction of traffic at a time.
  • They provide additional opportunities for landscaping in the community.



Rumble StripsRumble strips are a road safety feature designed to alert drivers of potential hazards or changes in road conditions. They are raised or grooved Rumbles Stripssections of pavement placed along the edges of roads or in the centerline. When a vehicle's tires travel over rumble strips, they produce a tactile and audible vibration or rumbling noise inside the vehicle, hence the name "rumble strips."






Sheet Piles - Unlike structural piles which are typically cylindrical in shape, sheet piles are usually elongated sheets of steel, which can be connected together by flanges, creating a wall. Sheet piles are often used to hold back earth, as in a retaining wall, or water, as in a coffer dam or seawall. 

sheetpile wall













Speed Feedback Sign -  A speed feedback sign, also known as a radar speed sign or dynamic speed display, is a traffic calming device used to alert drivers of their current speed and encourage them to adhere to the posted speed limit. These signs typically consist of a radar unit that detects the speed of approaching vehicles and a digital display that shows the detected speed to the driver.

Speed Feedback Sign


Split Phase Traffic SignalsSplit phasing describes an operation where all movements on one approach are served prior to all movements on the opposing approach. This is typically used if the geometry of the intersection, traffic volumes and/or crash history creates a conflict with normally non-conflicting movements.


Stormwater Pollution Prevention Plans (SWPPP) - Stormwater runoff is water produced by rain or snowmelt that does not soak into the ground. Instead, it flows over land or impervious surfaces, such as paved streets and parking lots, picking up pollutants like trash, chemicals, oil, and dirt/sediment that harm rivers, streams, lakes, and coastal waters. To prevent such pollution, agencies develop plans called Stormwater Pollution Prevention Plans. Such plans are often known by the nickname "Sweet Pea."


Turn Pockets - A special traffic lane used for making right or left turns.


Throughput The number of vehicles or persons passing through a lane or road over a specific period, usually an hour or a day. Vehicle throughput is the number of vehicles traveling through a location. Person throughput is the number of people traveling through a location. 


Traffic Bulb-outs  – An extension of the sidewalk and curb at an intersection that shortens pedestrians' crossing distance and slows down turning vehicles. Also known as a curb extension.

Bulb Out