Changes in the Flow-density Relation Due to Environmental, Vehicle, and Driver Characteristics

This research explores the idea that weather conditions and driverand vehiclepopulation characteristics affect a homogenous roadway segment’s flow-versus-density relationship. Third-order-polynomial regressions of flow on powers of density interacted with a variety of explanatory variables suggest that driver, vehicle, and environmental attributes significantly influence the flow-density relation and conform in substantial part with intuitive expectations. For example, higher flows are predicted across most densities for more mature and more male traveler groups, as well as for non-rainy conditions with fewer long vehicles and trucks. Moreover, under highly congested conditions, braking is associated with slightly higher flows than those predicted for accelerating vehicles.