Two-lane Highway Work Zone Capacity Model and Control Analysis
Lane closure is a common practice for two-lane highway work zones. To effectively control the open lane to serve both travel directions, it is necessary to implement a traffic control strategy. Due to lane closure, the roadway capacity will drop significantly. The remaining capacity will depend on work zone configurations, traffic parameters and traffic control strategy. This study develops a mathematical model calculating capacity and vehicle delay specifically for two-lane highway work zones with pre-timed signal control strategy. A VISSIM simulation model is developed and calibrated using field observed data to validate the mathematical model. After fine tuning the parameters, the mathematical model is able to make reasonably accurate delay estimates for both saturated and under-saturated traffic demands, with mean absolute prediction errors between 1% ~ 3%. Flagger control is incorporated in the VISSIM simulation model using a gap-out distance method. Field observations are used to validate the model outputs. The study then compared flagger control with fixed time signal control under multiple traffic conditions. Results show that at low traffic demands flagger control performs better than fixed time signal control. For the specific work zone site studied, flagger control is able to achieve approximately 10% ~ 20% lower vehicle delay. The developed models and simulation results can be applied to optimize two-lane highway lane-closure work zone management by reducing overall user delay while maintaining adequate roadway capacity. The optimized pre-timed signal control plan can reduce the user delay to a similar level as that of the actuated or flagger control method and thus can be used to avoid the human operation cost. Sensitivity analysis shows that traffic operators can increase the roadway capacity by reducing work zone length, increasing vehicle travel speed, and making unbalanced signal allocation based on actual traffic demands.
- Civil engineering