Technical details on the measurements performed for the present study can be found in "Effet dièdre sur plan réflecteur et sur surface absorbante - Descriptif des mesures", report LTE n°0414 (Fr), by J-M. Clairet and F-X. Bécot. The present work deals with the influence of the road absorption on the prediction of pass-by noise levels using hybrid methods. First, the context of the present work is recalled. Objectives and milestones are given. In a second part, the determination of the acoustic properties of some material is tackled. Two complementary methods are used for this: tube measurements and level difference measurements. Results using the two techniques are compared and discussed. In a third part, the sound amplification due to the horn effect is characterized experimentally. Situations with a long cylinder and with a single tyre placed over a rigid or an absorbing surface are examined. Measurement results are compared to predictions using two-dimensional models for the tyre radiation. Finally, the horn effect for twin wheels over a rigid surface is measured and discussed. SILVIA code: SILVIA-INRETS-014-00-WP2-3/9/2004