## 6 Discussion  
Discussion on the Comparative Analysis of Selected \"Speed-Density\" Models Fitted to Empirical Data Collected under Continuous and Interrupted Traffic Stream Conditions  
Based on the results obtained, it is evident that, for most of the models considered, the highest comparative difference among the mean traffic flow speeds representative of continuous and interrupted traffic stream conditions occurs in a free-flow regime. This difference is steadily reduced with the increase in traffic flow density, and it reaches its minimum in a congested traffic stream regime. The difference among traffic flow speeds for continuous and interrupted traffic stream conditions computed by [PERSON] model ranges between 19.2 kph at free-flow speed (\(v_{max}\)) and 9.6 kph at critical (saturation) speed (\(v_{c}\)). In a saturated traffic stream regime, this difference is further reduced, and it becomes zero at jam density (\(g_{max}\)). The differences in predicted traffic flow speed obtained by [PERSON]'s model calibrated to empirical data collected in continuous and interrupted traffic stream conditions range from 18.9 kph at free flow to 3.7 kph at saturation density. In a congested regime, this difference continues to decrease, and it reaches zero at jam density. The regression functions obtained by fitting the [PERSON] and [PERSON] models suggest that the maximum comparative difference in the mean speed of continuous and interrupted traffic flow appears in the region between unsaturated and saturated traffic stream regime, i.e., when the traffic flow reaches practical road capacity. According to [PERSON]'s model, the difference between continuous and interrupted traffic flow speed is equal to 4.3 kph in free-flow conditions, reaches its maximum of 12 kph at traffic density of 64 veh/km and then reduces back to 7.8 kph in a congested traffic flow regime. Even smaller differences are obtained using [PERSON]'s model, according to which the absolute speed difference predicted for continuous and interrupted traffic stream conditions is equal to 0 both at free-flow speed and at jam density, while the largest speed difference of 8.3 kph is reached at 57 veh/km. According to the modified [PERSON] logistic model, the differences between continuous and interrupted traffic flow speeds are reduced from 21.1 kph at free flow to 10.6 kph at critical density. In a congested traffic flow regime, the difference between these two speeds is further reduced to 5.9 kph. [PERSON]'s three-parameter sigmoid model generates significantly different traffic flow speeds for continuous and interrupted traffic stream in free-flow conditions and approximately equal speed values in a saturated traffic flow regime, whereby the difference in the traffic flow speeds produced for continuous and interrupted traffic flow varies from 19.9 kph at free flow to 3.6 kph at saturation density. In a congested traffic flow regime, this difference is further reduced, and it reaches zero at jam density. [PERSON]'s five-parameter sigmoid model produces very similar results to [PERSON]'s three-parameter model over the entire range of possible density values, whereby the maximum difference between continuous and interrupted traffic stream speed does not exceed 1.5 kph. [PERSON] and [PERSON]'s model shows similar differences between continuous and interrupted traffic flow speeds to [PERSON]'s three-parameter and five-parameter models in free-flow and normal traffic flow regimes and slightly larger differences in the saturated and congested traffic flow regime. The five-parameter model developed by [PERSON] and [PERSON] produces somewhat unexpected results for the saturated and congested traffic stream regime. The difference in traffic flow speeds for continuous and interrupted traffic stream conditions computed by [PERSON] and [PERSON]'s five-parameter model ranges between 18.2 kph at free-flow speed and approximately 0 kph at critical (saturation) speed.