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Pavement instrumentation with embeddable in-situ sensors has been a feasible approach to determine pavement deteriorations. Determining pavement deflections during the passage of the load is a promising strategy to determine the overall performance of the pavement. There are different devices that apply loads to the pavements and measure the deflection basin, these include static, vibratory or impulse loadings. Most commonly used are the static loading like Benkelman beam and impulse loading like the Falling Weight Deflectometer (FWD). However, these techniques are costly and the measurements are recorded infrequently i.e. once per year or two years. This study focuses on the use of geophones and accelerometers to measure the surface deflections under traffic loading. To develop a method to measure pavement deflections, the sensors have been submitted first to laboratory tests, and then tested in situ, in a full scale accelerated pavement test. In the laboratory, the sensors have been submitted to different types of loading using a vibrating table. These tests were used to determine the noise and sensitivity of the sensors, and then to evaluate their response to signals simulating pavement deflections under heavy vehicles. The sensor response has been compared with measurements of a reference displacement sensor. Different processing techniques have been proposed to correct the measurements from geophones and accelerometers, in order to obtain reliable deflection values. Then, the sensors have been evaluated in a full scale accelerated test, under real heavy axle loads. Tests have been performed at different loads and speeds, and the deflection measurements have been compared with a reference anchored deflection sensor. The main advantage of using accelerometers or geophones embedded in the pavement is to enable continuous pavement monitoring, under real traffic. The sensor measurements could also be used to determine the type of vehicles and their corresponding speeds. The study describes in detail the signal analysis needed to measure the pavement deflections accurately. The measurements of pavement deflection can be then used to analyze the pavement behaviour in the field, and its evolution with time, and to back calculate pavement layer properties.