Traffic Control at Flagger-Operated Work Zones on Two-Lane Roads

Abstract

To clarify the traffic flow characteristics and the signal timings at work zones controlled by flaggers, traffic flows at some work zones were measured. Using the measurement data a computer simulation program based on the microscopic traffic flow model was developed. The simulation results were in accordance with the measured results. Using the simulation program traffic behavior was analyzed for various work-zone conditions under the assumption that no heavy vehicles were mixed with the traffic. First, the delay characteristics at short work zones less than 200 m long were investigated. The summed delay of the acceleration delay and the speed-decrease delay was between 35 and 40 percent of the total delay. This suggests that those delays cannot be ignored in estimates of delay at short work zones. Next, three methods for estimating the green intervals under flaggers' control were presented: nomograph, regression equation, and analytical optimization. The first two methods were obtained directly from the simulation results, whereas the third was derived by describing both the queuing and the acceleration delays with a regression equation and minimizing the total delay. The analytically optimized green intervals diverged from the simulated ones as the traffic became heavier. The signal timings produced by a nomograph and a regression equation can be installed in pretimed traffic lights as a substitute for flaggers, and the optimized ones can be installed in actuated lights combined with traffic detectors.