Travel and route guidance services are widely available. Social navigation services that provide travelers with advice aimed at minimizing driver travel time, while also taking into account the effect on travel times of other travelers, are relatively new. Theoretically, social navigation has been shown to reduce total travel time by 10% to 30%. This paper presents the evaluation results of a largescale field trial for pretrip and ontrip route advice with load balancing, in which about 20,000 participants were active. The evaluation provided insight into the potential effects of incar information services, such as effects on user behavior, traffic flow effects, and technical aspects. Participants used mostly the pretrip advisories. Compliance with the ontrip route advice was 50%, which was considered high (compared with compliance with route advice on variable message signs). An effect on traffic flow could not be measured, as penetration rates were (despite thousands of users) still too low. An offline study using measured travel times combined with a traffic model, however, showed that substantial delay reductions can be achieved for the Amsterdam, Netherlands, region. Participants’ appreciation of the service resulted in a mixed picture with positive and negative ratings. The main practical contribution of this paper is that the results can be used to develop social navigation services. Empirical insights about route advice compliance can be seen as the main scientific contribution.@en