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.
Critical length of grade
The maximum length of a specific upgrade on which a loaded truck can operate without an unreasonable reduction in speed. Very often, a speed reduction of 15 km/h or more is considered “unreasonable”.
Cross fall
See camber. In the case of cross fall, the high point is at the roadway edge.
Cross-over crownline
The line across which an instantaneous change of camber takes place. In the case of a normally cambered road, the centreline is a special case of the cross-over crownline. The cross-over crownline can be located anywhere on the road surface and need not even be parallel to the road centreline.
Crosswalk
A demarcated area or lane designated for the use of pedestrians across a road or street.
Crown runoff
(Also referred to as tangent runout) The rotation of the outer lane of a twolane road from zero cross fall to normal camber (NC).
Culvert
A structure, usually for conveying water under a roadway but can also be used as a pedestrian or stock crossing, with a clear span of less than six metres.
Cut
Section of highway or road below natural ground level. Sometimes referred to in other documents as a cutting or excavation.
Cycle lane
A portion of the roadway which has been designated by road markings, striping and signing as being exclusively for the use of cyclists.
Cycle path
Also known as a bike way. A path physically separated from motorised traffic by an open space or barrier and located either within the road reserve or an independent reserve.
Decision sight distance
Sometimes referred to as anticipatory sight distance, allows for circumstances where complex decisions are required or unusual manoeuvres have to be carried out. As such, it is significantly longer than Stopping Sight Distance.
Density
The number of vehicles occupying a given length of road. Usually averaged over time and expressed as vehicles per kilometre.
Depressed median
A median lower in elevation than the travelled way and so designed to carry portion of the storm water falling on the road.
Design domain
The range of values of a design criterion that are applicable to a given design, e.g. lane widths of more than 3,3 metres.
Design hour
The hour in which the condition being designed for, typically the anticipated flow, is expected to occur. This is often the thirtieth highest hour of flow in the design year.
Design speed
The speed selected as the basis for establishing appropriate geometric elements for a section of road.
Design vehicle
A compilation of the 85th percentile values of the various parameters of the vehicle type being designed for, e.g. length, width, wheelbase, overhang, height, ground clearance, etc.
Design year
The last year of the design life of the road or any other facility, often taken as twenty years although, for costly structures such as major bridges, a longer period is usually adopted.
Directional distribution (split)
The percentages of the total flow moving in opposing directions, e.g. 50:50, 70:30, with the direction of interest being quoted first.
Divided highway
A highway with separate carriageways for traffic moving in opposite directions.
Driveway
A road providing access from a public road to a street or road usually located on an abutting property.
Eighty-fifth percentile speed
The speed below which 85 per cent of the vehicles travel on a given road or highway.
Footway
The rural equivalent of the urban sidewalk.
Freeway
Highest level of arterial characterised by full control of access and high design speeds.
Frontage road
A road adjacent and parallel to but separated from the highway for service to abutting properties and for control of access. Sometimes also referred to as a service road.
