Glossary

active traffic management.

The practice of dynamically managing recurrent and nonrecurrent congestion based on prevailing traffic conditions. Focusing on trip reliability, it maximizes the effectiveness and efficiency of the facility, and increases throughput and safety through the use of integrated systems with new technology, including the automation of dynamic deployment to optimize performance quickly and without the delay that occurs when operators must deploy operational strategies manually.

dynamic rerouting.

The provision of route information on overhead sign gantries along a roadway in response to recurrent and nonrecurrent congestion. The signs provide en route guidance information to motorists on queues, major incidents, and appropriate routes.

dynamic message sign.

A permanently installed or portable electronic traffic sign used on roadways to give travelers information about roadway conditions, including traffic congestion, crashes, incidents, work zones, speed limits, alternative routes, or special events on a specific highway segment. It can be changed or switched on or off as required and can be used to provide roadway lane control, speed control, and operational restrictions. Also known as a changeable message sign or a variable message sign.

merge control.

A variation of the temporary shoulder used in Germany. Typically, it is applied at entrance ramps or merge points where the number of downstream lanes is fewer than the number of upstream lanes. Lane control signals are installed over both upstream approaches before a merge. They provide priority to the facility with the higher volume and give a lane drop to the lesser volume roadway or approach. Also known as junction control or mainline merging control.

managed lanes.

Highway facilities or a set of lanes in which operational strategies are implemented and managed (in real time) in response to changing conditions to preserve unimpeded flow. They are distinguished from traditional lane management strategies in that they are proactively implemented and managed and may involve using more than one operational strategy with the goal of achieving unimpeded flow.

plus lane.

The practice of opening up the shoulder next to the inside lane of traffic for temporary use to address capacity bottlenecks on the freeway network during times of congestion and reduced travel speeds. Travel on the shoulder is permitted only when speed harmonization is active and speed limits are reduced. Signs indicate when travel on the shoulder is permitted.

queue warning.

The display of warning signs and flashing lights along a roadway to alert that congestion and queues are ahead.

ramp metering.

Procedures used to reduce congestion by managing vehicle flow from local-access on-ramps. The entrance ramp is equipped with a traffic signal that allows vehicles to enter the freeway at predetermined intervals.

speed harmonization.

The practice of using an expert system to monitor data coming from field-deployed sensors on a roadway and automatically adjust speed limits when congestion thresholds are exceeded and congestion and queue formation are impending. Sign gantries that span the facility provide speed limits and additional information, depending on roadway conditions. Also known as line control.

symbology.

The use of graphic symbols to represent information pertinent to roadway users. The European practice of using symbology follows the Vienna Convention.

temporary shoulder use.

The practice of opening up the shoulder next to the outside lane of traffic for temporary use to address capacity bottlenecks on the freeway network during times of congestion and reduced travel speeds. Travel on the shoulder is permitted only when speed harmonization is active and speed limits are reduced. Signs indicate when travel on the shoulder is permitted. Also known as hard-shoulder running or a rush-hour lane.

truck restrictions.

Any restrictions along a roadway on the operation of trucks or heavy goods vehicles. Examples include restricting trucks to specific lanes, prohibiting them from using particular lanes, limiting their operating speed, or prohibiting their use of the entire facility during specific periods of the day.

variable speed limits.

Speed limits that change based on road, traffic, and weather conditions. Also known as dynamic speed limits.