Ruohan Zheng

The %days of cogestion

Los Angeles faces significant traffic congestion, with approximately 7.5 million cars in the city compared to around 2 million in New York City. Despite the difference in total vehicles, both cities experience severe traffic issues. While high traffic volume is often cited as a major contributor to congestion, I argue that in downtown Los Angeles, the freeway layout plays a more critical role in influencing traffic flow. Buffer analysis provides a valuable method for assessing the spatial impact of specific locations on surrounding areas. This research focuses on the intersection of Freeways 101 and 110, examining how their design affects traffic conditions.

annual daily average volume data

As shown on the map, the graduated symbology represents the Annual Average Daily Traffic (AADT) for specific freeway segments. While Freeways 101 and 110 exhibit similar traffic volumes, congestion on the 101 appears significantly worse. One potential factor contributing to this disparity is the layout of freeway entrances and exits. To explore this, the approximate locations of entrances and exits were identified on the map for further analysis.

the approximate locations of entrances

The eastern section of Freeway 101 experiences severe congestion, leading to the assumption that this may be influenced by the density of freeway entrances and exits. The placement of these access points can significantly impact traffic flow, potentially causing slowdowns and increased merging conflicts. According to the Federal Highway Administration (2007)[1], the recommended distance between freeway ramps is approximately one mile. When ramps are placed too closely together, they can contribute to higher crash rates and reduced traffic speeds.

buffers of entrances

To assess the spacing of freeway entrances, buffer analysis is applied to visualize a one-mile boundary around each entrance. The concept is straightforward: if another entrance falls within this buffer zone, the spacing is considered too short. The intersections of these buffer zones indicate locations where freeway entrances are within one mile of each other, highlighting potential areas of congestion and traffic flow disruption.

spatial join of entrances and buffers

To further validate this analysis, a spatial join is used to determine whether freeway entrances fall within another entrance’s buffer zone. The results indicate that all identified entrances are within one mile of at least one other entrance. This suggests that the density of entrances and exits might be one of the reasons of congestion, as higher density may lead to increased traffic slowdowns and merging conflicts. However, due to data limitations, this conclusion requires further verification through additional analysis and supporting datasets.

conclusion

This StoryMap examines traffic congestion by utilizing data from Caltrans PeMS[2] and traffic volume records from Caltrans[3] for the intersection of Freeways 110 and 101. By identifying the locations of freeway entrances and exits, the analysis explores their impact on congestion using buffer analysis and spatial join techniques.

The relationship between freeway entrances and traffic congestion may exhibit some correlation; however, due to limited traffic data, there is insufficient evidence to fully support this theory. Nonetheless, for future planning and analysis of freeway entrances and exits, buffer analysis and spatial join can serve as valuable tools. Additionally, with more comprehensive data, network analysis could further aid in optimizing the layout and improving traffic flow.

The %days of cogestion