Showing papers by "Margaret Bell published in 1983"

Plan Change Algorithms for Traffic Control Systems

Abstract: Several algorithms exist to implement a change between fixed-time signal plans. These are reviewed and the constraints influencing the process of change are examined. A comparison of actual networks reveals the daily and cyclical variations in flow which prevail in practice and within which the plan-changing process must be seen. Studies using TRANSYT are reported and finally 5 plan-change algorithms are assessed against an "ideal" plan-change, using Monte Carlo simulation techniques. The results suggest that significantly less delay (at the 5% level) and fewer stops are incurred when plan-changes are implemented at off-peak rather than at peak flows. The MODIFIED ABRUPT algorithm (commonly called CRASH), which is in common use, is found to generate no statistically significant (at the 5% level) additional stops or vehicular delay on main roads, irrespective of the level of flow at which the plan-change is made and whether the change is from off-peak to peak or vice versa. The variation in delay caused by implementing a plan-change with the MODIFIED ABRUPT method is found to be less than 2%. It is concluded that plan-changes should always be implemented during off-peak flow conditions and that the commonly used MODIFIED ABRUPT algorithm is the most satisfactory method under prevailing constraints. (Author)