## 5 Discussion  
The goal of this study was to understand the relationship between traffic density and the number of collisions. Moreover, the paper aimed to look at the concept of higher traffic density serving to suppress collisions by regulating driver speed, especially if drivers were not adhering to prescribed speed limits. Previous studies indicate that higher levels of congestion can result in fewer road accidents. This theory was the case for a single highway segment in Detroit [70]. Similarly, the authors in [71] found this to be the case on two to three-lane motorways in France. However, this is not true at intersections [72], or on urban roads in London [51; 71], where the number of accidents was found to increase linearly at low to mid-levels of traffic and nonlinearly at high levels of traffic. This study found that higher levels of traffic density do not reduce the frequency of collisions. Furthermore, higher traffic levels do not suppress the increased collision rates caused by non-adherence to speed limits. Empirical findings found that traffic congestion  
Figure 6: Distribution of number of additional vehicles involved in simulated collisions based on number of vehicles in system and proportion of vehicles adhering to speed limits. has little or no impact on the frequency of road accidents; however, it should be noted that the results are constrained to the M25 London motorway [52]. The author in [42] found that an increase in collision rates resulted from the road network design of urban roads, which consisted of higher lengths of road and high traffic density. This study aims to contribute to the ongoing debate as to whether traffic congestion impacts the frequency of road accidents [55]. This study found that high-density systems are affected to the same degree as low-density systems and provide no protective effect. This would suggest that the traffic management goals of congestion-reduction and accident-reduction are not in conflict for urban road networks. This study also suggests that lower traffic density on average leads to fewer collisions regardless of adherence levels, as was observed in [72]. However, as adherence decreases, this leads to increased collisions relative to the number of vehicles in the urban environment. These findings were also observed in [73]. Empirical evidence from UK government sources in 2019 shows that, on average, 55% of vehicles in 2019 exceeded the speed limit on urban roads. During this time, 63% of all collisions occurred on these urban roads [1; 2]. This study also shows that increases in collisions are more likely as more vehicles break speed limit rules. This study's results do not reflect the same linear-to-nonlinear relationship between accidents and traffic levels as [71; 72]. At low to mid traffic densities, collisions increase disproportionately as traffic density increases. Collisions begin to increase proportionately at a critical point in density, so an individual vehicle's risk of colliding does not increase as traffic increases. However, the results reflect the global number of collisions against an urban road network's global traffic density rather than studying micro-level intersections or specific urban roads. The study also attempted to provide a micro-level analysis to supplement the findings of the research. The analysis observed the distribution of the number of additional vehicles involved in collisions based on the global number of vehicles and the proportion of vehicles adhering to speed limits. We found that higher global traffic density resulted in higher local traffic density near collision sites. Furthermore, we found that lower adherence results in higher local traffic densities near collision sites for 100 to 200 vehicles; this is not the case for 50 vehicles. This indicates that local traffic density may contribute to collisions when combined with low adherence to speed limits, a higher average speed, or greater speed variance.