Multi-level traffic control at large four-leg roundabouts.

Yield control and full signalization are typical traffic control solutions that can be used at large roundabouts. In the face of increasing congestion issues, it is preferred to use yield control during off-peak periods and full signalization during peak periods. To automatically accommodate time-varying vehicular demands, a multi-level traffic control (MTC) is developed to implement hybrid yield control and fully actuated control at large four-leg roundabouts. With new application of traffic control devices and traffic detection system, the right-of-way can be assigned to entering and circulating vehicles in three modes. The 'all entering' mode is equivalent to a yield control. The 'no entering' and 'concurrent entering' modes are equivalent to a fully actuated control. On the basis of time headways and occupancy times that are detected on the entry and circulatory roadways, the mode of right-of-way assignment can be changed in response to actual traffic conditions. For a specific mode of right-of-way assignment, traffic signal operation is managed by some detectable traffic events that are happening. The results of the simulation experiments conducted by VISSIM indicated that: (i) MTC was stabilized at the 'all entering' mode during off-peak periods and at the 'concurrent entering' mode during peak periods; (ii) MTC would typically change the mode of right-of-way assignment according to actual traffic conditions as vehicular demands increased from off-peak to peak or decreased from peak to off-peak; and (iii) statistically speaking, MTC inherited the operational advantages of yield control and fully actuated control, and could be effective in improving the operational performance of large four-leg roundabouts for all hours of the day, regardless of the level of left-turn ratios. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]