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| Sr. | Term | Definition |
| 1 | Ramp | (1) A steeply sloping road or floor. (2) A connecting roadway between two intersecting highways at a highway separation (3) A short length of drain laid much more steeply than the usual gradient. |
| 2 | Random Sample | A sample selected without bias so that each part has an equal chance of inclusion. |
| 3 | Rankine Theory | For dry, cohesionless backfill soil behind retaining walls, the Rankine theory is used to find the vertical and the horizontal (lateral) pressure at any depth, H. The horizontal pressure depends on the coefficient of earth pressure at rest, ko, which varies from 0.4 to 0.5 for untamped sand. |
| 4 | Rapid-Hardening Or Higl-Early-Strength Cement | A portland cement which hardens more quickly than ordinary Portland cement and is more costly because it is more finely ground. |
| 5 | Ravelling Or Fretting | Progressive disintegration of a pavement surface through the loss (Breaking away) of aggregate particles from a road surface. |
| 6 | Ravine | Deep, narrow cliff or gorge in the earth surface. |
| 7 | Recycling (Pavement) | The re-use of existing pavement materials in a new pavement structure. |
| 8 | Rehabilitation | The improvement of an existing roadway surface by improving the existing surface or by removing (milling) a specified thickness of the existing pavement and placement of additional pavement layers. |
| 9 | Release Agent Or P Arting Agent Or Parting Compound | A general term that includes any greases, mould oils or sealants, laid over forms or form linings either to ensure a good finish to the concrete, to prevent concrete bonding to forms or to improve the durability of the form or for both. |
| 10 | Reinforced Concrete | Concrete containing more than 0.6% by volume of reinforcement consisting of steel rods or mesh. The steel takes all the tensile stresses (theoretically). In good design the reinforcement is sufficiently distributed so that the cracks are not conspicuous. |
| 11 | Resistivity | A measure of a substance’s resistance to the flow of electricity through it, expressed in ohm-centimeters. Used on soils to determine coating requirements for new pipe and used to determine the extent of corrosion of existing metal pipes. |
| 12 | Retarder Or Retarder Of Set | An admixture which slows up the setting rate of concrete. |
| 13 | Rigid Pavement | A pavement having sufficiently high bending resistance to distribute loads over a comparatively large area (Portland Cement Concrete Pavement). |
| 14 | Right-Of-Way | A general term denoting land, property of interest therein, usually in a strip, acquired for or devoted to transportation purposes. |
| 15 | Ridge | A long narrow elevation of land. |
| 16 | Rigidity | Resistance to twisting or shearing. |
| 17 | Riprap | Rock used for the protection of embankments, cut slopes, etc., against agents of erosion, primarily water |
| 18 | Roadbed | The roadbed is that area between the intersection of the upper surface of the roadway and the side slopes or curb lines. The roadbed rises in elevation as each increment or layer of subbase, base, surfacing or pavement is placed. Where the medians are so wide as to include areas of undisturbed land, a divided highway is considered as including two separate roadbeds. |
| 19 | Roadside | A general term denoting the area adjoining the outer edge of the roadway. Extensive areas between the roadways of a divided highway may also be considered roadside. |
| 20 | Roadway | That portion of the highway included between the outside lines of sidewalks, or curbs, slopes, ditches, channels, waterways and including all the appertaining structures and other features necessary to proper drainage and protection. |
| 21 | Rumble Strip, Serrated Strip Or Jiggle Bar | A slightly raisedor lowered strip of asphalt, plastic, etc., across the highway traffic lane or along the shoulder lane. Rumple strips are placed together at a spacing (usually one foot) to warn the driver, through an audible warning of the approaching hazard. |
| 22 | Run-Off | The amount of water from rain, snow, etc., which flows from a catchment area past a given point over a certain period. It is the rainfall less infiltration and evaporation. It can be increased by springs of goundwater or reduced by loss to the ground. |
| 23 | Rustication | Having the surface rough or irregular, or the joints deeply sunk or chamfered. |
| 24 | Rutting | Formation of longitudinal depressions by the displacement of soils or surfaces under traffic. |
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