Roads Flashcards
Acceleration lane
An auxiliary lane used by an entering vehicle to accelerate before entering the travelled way.
Access control
The condition whereby the road agency either partially or fully controls the right of abutting landowners to direct access to and from a public highway or road.
Access interchange
An interchange providing access to a freeway from the adjacent non-freeway road network.
Arterial
Highway designed to move relatively large volumes of traffic at high speeds over long distances. Typically, arterials offer little or no access to abutting properties.
Auxiliary lane
Short lane located immediately adjacent to the basic or through lane to accommodate some or other special circumstance such as a turning movement to right or to left, acceleration to or deceleration from the speeds prevailing on the travelled way or heavy vehicles reduced to crawl speeds on a steep upgrade.
Average Daily Traffic (ADT)
The number of vehicles per day passing a point on the highway during a defined period. If this period extends from 1 January to 31 December, reference is to Annual Average Daily Traffic (AADT)
Average running speed
The distance summation for all vehicles divided by the running time summation for all vehicles. Also referred to as space mean speed whereas time mean speed is simply the average of all recorded speeds.
Axis of rotation
The line about which the pavement is rotated to superelevate the roadway. This line normally maintains the highway profile
Barrier sight distance
The limiting sight distance below which overtaking is legally prohibited.
Boulevard
The area separating sidewalks from the through lanes.
Bridge
A structure erected with a deck for carrying traffic over or under an obstruction and with a clear span of six metres or more. Where the clear span is less than six metres, reference is to a culvert.
Broken-back curve
Two curves in the same direction with a tangent shorter than 500 metres long connecting them.
Camber
The slope from a high point (typically at the centre line of the highway) across the lanes of a highway. Negative camber refers to a central low point, usually with a view to drainage of a small urban street or alley.
Capacity
The maximum number of vehicles that can pass a point on a highway or in a designated lane in one hour without the density being so great as to cause unreasonable delay or restrict the driver’s freedom to manoeuvre under prevailing roadway and traffic conditions.
Carriageway
Roadway forming part of a divided highway and intended for movement in one direction only – hence dual carriageway as an alternative name for divided highway.
Catchwater drain
Located above a cut face to ensure that storm water does not flow down the cut face causing erosion and deposition of silt on the roadway.
Channel grading
Where side channels are designed to gradients that differ from those of the road centreline, typically on either side of the highest points on crest curves and the lowest points on sag curves where the centreline gradient is less than 0,5 per cent.
Channelisation
The use of pavement markings or islands to direct traffic through an intersection.
Clearance profile
Describes the space that is exclusively reserved for provision of the road or highway. It defines the minimum height of the soffit of any structure passing over the road and the closest approach of any lateral obstacle to the cross-section.
Cloverleaf interchange
An interchange with loop ramps in all quadrants to accommodate right turns and outer connectors for the left turns.
Collector
A road characterised by a roughly even distribution of its access and mobility functions.
Collector-Distributor road
A road used at an interchange to remove weaving from the through lanes and to reduce the number of entrances to and exits from the through lanes.
Compound curve
A combination of two or more curves in the same direction without intervening tangents between them.
Criterion
A yardstick according to which some or other quality of the road can be measured. Guideline values are specific numerical values of the criterion. For example, delay is a criterion of congestion.