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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.


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 


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.


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.


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
















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