Information Points and Optimal Discharging Speed: Effects on the Saturation Flow at Signalized Intersections

An information point was defined in this study as any object, structure, or activity located outside of a traveling vehicle that could potentially attract the visual attention of the driver. Saturation flow rates were studied for three pairs of signalized intersections in Toledo, Ohio. Each pair of intersections consisted of one intersection with a high number of information points and one intersection with a low number of information points. The study results revealed that the intersection with high information points had a lower saturation flow rate than the one with low information points for each pair of intersections. Statistical analysis found that the differences were significant. Information point effect regression models were developed based on the collected and derived saturation flow data.;In academic research regarding the intersection saturation headway, there are various and sometimes seemingly conflicting findings in terms of how the discharge headway (time between discharging vehicles) or saturation flow rate changes as green time elapses. Some research found the discharge headways remain constant; some found the discharge headways have a compression trend. Others found the discharge headways get longer after a certain point of time as the discharge continued. This study introduced an optimal discharge speed concept to explain the different trends found in saturation headway research. For a queue of traffic to discharge from an intersection, if the discharge speed quickly reached the maximum discharge speed which was at or below the optimal discharge speed, the discharge headways would remain constant; if the discharge speeds continued to increase but never exceeded the optimal speed in the whole discharge process, the headway would show a compression trend; if the discharge speeds at a certain point exceeded the optimal discharge speed, the headway would show an elongation trend. The queue discharge characteristics at two signalized intersections located in Toledo, Ohio were studied. The discharge headways of through lane traffic at both intersections demonstrated an elongation trend. The optimal discharge speeds that were associated with the lowest average headways were 27 mph for one intersection and 20-23 mph for the other.