The paper proposes an approach for real time control of freeways by route guidance, an emerging technique for efficient freeway management. A first order fluid approximation is employed to model in a modular framework the vehicle flows by first order hybrid Petri nets. The hybrid Petri nets formalism enables the network designer to choose suitable splitting rates to off-ramps to minimize congestion. The increased freeway operation is performed based on the state knowledge of the obtained linear discrete-time, time-varying state variable model of the freeway to react to unpredictable events such as the blocking of a lane due to an accident or to work in progress. The proposed route guidance approach is applied to a case study to show its effectiveness.