AASHO The American Assosiation of State Highway Officials. An American body carrying out road research.
Aggregate Graded stone added to cement and water to form concrete.
Asphalt Binder used in road construction. A combination of naturaly occuring bitumen and mineral matter.
Auger A tubular tool with opposed cutting edges used for drilling in cohesive soils.
AADF Average Annual Daily Flow. The total number of vehicles using a road in one year, divided by 365.
Axle The horizontal bar supporting wheels on a vehicle.

Basecourse Lower of the surfacing materials in a flexible pavement.
Bitumen A derivative of crude oil, bitumen is used as a binder to stabilise and strengthen roadstone.
Boreholes Holes drilled into the ground to allow an assessment of the soil.
Bulking Factor A soil parameter that is used in earthworks design to compemsate or the cahnge in volume during excavation.
Bulldozer Machine used to push earth from one location to another by means of a large plough.

Capping Part of the pavement foundation, providing a temporary haul road, protection of the soil from frost and support for the upper road layers.
CBM Cement Bound Material. A mixture of cement and soil or aggregate, weaker than pavement material they are often used in the roadbase.
CBR California Bearing Ratio. A test used to estimate the supporting value of the subgrade or soil.
Cement Constituent part of concrete. A calciferous material that acts as a binder.
Compaction The process of reducing the thickness of the soil, thus improving it's strength.
Composite A pavement type that is a combination of both flexible and rigid.
Concrete A mixture of cement, aggregate and water that bonds together to form an engineering material.
Contraction Joints Joints in a reinforced pavement that act as crack inducers when the pavement contracts.
CRC Continuously reinforced concrete. Concrete with reinforcement of approximately 0.6% of the cross sectional area.
C40, C20 etc. A measure of the strength of concrete. The number being the cube strength in N/mm² after 28 days.
cv/day Commercial Vehicles per day. A measure of the total flow of commercial vehicles per day, used in traffic analysis.

DBM Dense Bitumen Macadam. A continuously graded material of a relatively low binder content (100 penetration). It has less resistance to fatigue cracking than other materials.
DBM50 is DBM with a 50 penetration binder. It is marginally inferior to HDM but is superior to ordinary DBM.
Dense Tar Macadam is similar to DBM but uses a tar binder. This improves performance but is more temperature susceptible.
Diggability A measure of the ease with which a soil can be excavated.
DoT Department of Transport. The UK Government deprtment responsible for public Highways.
Drag Line This vehicle allows excavation below it's own level. It is essentially a bucket on the end of a jib and is used solely for bulk excavation as it is relatively uncontrolled.
Dump Truck Earthwork plant used for transportationof soil across large distances.
d₉₀ A measure of average soil particle size.

E The Young's Modulus of a material. Also called elastic modulus.
Eartworks The process of preparing the natural land to a suitable level for road construction to begin.
Excavators Vehicles used in earthworks to excavate the land. Many different types.
Expansion joints Jonts in a concrete or rigid pavement that are filled with a flexible material to allow eaxpansion.

Failure Criteria A method of judging when a road is no longer usable. Can vary between countries.
Flexible Pavement A pavement made of different levels of bituminous material.

Geological maps Maps showing the geological layout of an area, used in the dsk study phase of a site investigation.
Granular A description of soil type.
Growth Factor A factor used in traffic assesment to predict future loadings.

HDM High Density Macadam is a continuously graded material with a greater percentage of finer material than DBM. It is less easy to lay but has high resistance to cracking and deformation and has the highest stiffness of the road materials.
Highway A word for roads, coming from the Roman habit of building elevated roads to avoid ambush.
HRAHot Rolled Asphalt is a gap graded surfacing material with a high binder concentration (50 Penetration). It is easy to lay and has good fatigue resistance but is susceptible to slow moving heavy traffic (eg uphill).

JCP Jointed Concreted Pavement. Concrete pavement that requires joints to allow for expansion and contraction
Joints Breaks in a concrete or rigid pavement to allow fo the pavement to deform without cracking. See Contraction, Expansion and Warping.

Kerbs Raised pavement at side of main pavement. Used to separate carriageways.

Mass Haul Diagram A method of determining the location and voulme of waste in an earthworks calculation.
MCV Moisture Condition Value. A measure of the suitability of soils for use as engineering materials
Motorway A general term for roads with greater than two lanes.
msa Millions of standard axles. A measure of the ammount of vehicles using a road in a given period.

'N' Value A soil property related to the Standard Penetration Test.
Non-standard method The traffic analysis method that incorporates growth and wear factors in the calculation.
NRTF National Road Traffic Forecast. A national prediction of traffic growth, used when no relevant data is available.

OGV1 Commercial vehicles over 1.5 tonnes with three axles or less.
OGV2 Commercial vehicles over 1.5 tonnes with four axles or more.
Overlay The layer on the surface of a composite pavement.

PA Porous Asphalt is an open graded surfacing material designed to facilitate rapid drainage of surface water from the road, reducing spray. It also has the added bonus of reducing traffic noise.
Pavement The name given to the whole construction. General term for the whole road.
pcu Passenger car unit. The standard unit used to asses the volume of traffic on a proposed road. Not used in pavement design.
Percussive drilling The process of boring that uses repetaed impacts to break up the ground.
pfa Pulverised fuel ash. Used to stabilise weak soils. A byproduct of power generation.
PI Plasticity Index. A soil property, the difference between the liquid and plastic limits, as a percentage.
PSV Public Service Vehicle. The classification of vehicle that includes buses and coaches. Used in Traffic Analysis.

Reinforcement Steel added to a rigid pavement to reduce the slab size necessary to prevent failure.
Rigid Pavement The type of pavement where the road surface is a concrete slab.
Roadbase The middle layer on a flexible pavement design.
Roman Roads Earliest form of road building.

Shrinkage Factor A soil parameter that is used in earthworks design to compemsate or the cahnge in volume during excavation.
Site investigation The process of data gathering to allow a road design to take place.
SPT Standard PenetrationTest. A measure of soil properties, it's use comes not directly but from other properties it allows us to estimate.
Standard Method The method of traffic assesment where the design loading comes straight from the traffic flow at opening and the percentage OGV2.
Sub-base The lowest level of the pavement, placed diractly onto the soil.
Subgrade The soil or ground on which the road is to be built.

TRL Transport Research Laboratory. A major UK research centre into road design.
Trial Pits Small excavations that allow the soil properties near the surface to be analysed.

VDF Vehicle Damaging Factor. A conversion factor for the msa standard.

Warping JointsJoints in rigid pavements that restrict horizontal movements and 'tie' the slabs together.
Wear Factor A factor used in traffic assesment to differentiate between the different types of commercial vehicle.
Wearing Course The uppermost layer of a flexible pavement.