A planning methodology is introduced to ensure that workers on construction sites remain at a safe distance from each other. The methodology is based on the assumption that hazardous conditions, which occur on sites due to the proximity of different workers, depend on the interaction between both reinforcing and counteracting characteristics of the workers. The methodology includes a matrix-based method for the definition of minimum safe distances between workers, and the use of 3D time-space diagrams to represent and analyze the dynamic movements of workers on site. The methodology is implemented in a real case study in order to verify its feasibility. (C) 2014 Elsevier B.V. All rights reserved.