Three-Dimensional Models
Figure 11 shows the field observations collected at one of the stations used for the development of the model.
In a recent study, Acha-Daza and Hall (1993) showed that speed estimation by the cusp catastrophe model is significantly more reliable than speeds obtained by previously developed models (Greenshields'; Greenberg's; Edie's; and the double linear regime model). In addition, the advantages of this model is that it can show graphically that freeway operations do not have to stay on the (e.g. speed-flow) curve; jumps are possible from one branch to the other, and when they occur, there will be sudden changes in speeds. Also it allows for the fact that at some locations the data will go around the discontinuity in the surface, while at others the data will cross directly over the discontinuity.
Figure 11: Speed-density-flow observations (Hall 1989)
