ROUNDABOUT CONTROL IS SIGNAL SUCCESS

The first signal controlled roundabout in the West Midlands is now operational on a four-armed layout on the Wolverhampton ring road carrying between 4000 and 5000 vehicles per hour at peak periods. A computer simulation of the network, treating the roundabout as four t junctions linked together showed that a modified TRANSYT system could reduce delays at peak periods. Because delays could increase outside the peaks, the signals were operated on a part-time basis. An additional lane was provided on one of the approaches and the radii on the roundabout inside was increased slightly to provide greater width at the stop lines. A microprocessor controller uses parallel-stage streaming allowing the junction to operate as a four independent two-stage installation. Green times and offsets calculated using TRANSYT have proved very effective but improvements could be gained by having different control plans for different days of the week. Eventually the junction will be linked with others within the utc area as part of the country SCOOT system. (TRRL)