Outcome

TRAFFIC LIGHTS AND CRASH ACCIDENTS AT STREET INTERSECTION

INTENTION

Taken Squirrel Hill as an example, can setting up more traffic lights reduce the crash accidents? Two data sets were chosen to explore this question – Allegheny County Crash Data and Pittsburgh Traffic Signals Data. Allegheny County Crash Data contains all the crush accidents reported in 2014 (only 2014 data is operatable on Carto). The meta data includes time, location and injured number. It also identifies the type and possible reason of the crash but it doesn’t have a clear definition of what each number represents. Thus, the missing of the field actually leaves a room for this analysis.

PROCESS

After importing these 2 data sets into Carto and processing the map a little bit, the figure above shows the traffic signals and crashes in Squirrel Hill. It's obvious that many of the locations of crashes overlap with the locations of the traffic signs. However, for the crashes are not at the same location with traffic signals, is there a correlation between the missing of the traffic lights and the crashes?  Here I introduced another color for the crashes happened at the intersections. There are 32 accidents in one year in this single neighborhood that were located at the intersections without traffic signals. If not taking consideration of the crashes on the highway. The number is 26 out of 121 crashes in total. One-fifth of the crashes are at the street intersections without the traffic light. So far, it looks persuasive that the city should add more traffic lights to prevent the crashes. However, another question comes to me. What about the number of the crashes at the intersections with traffic lights? It's 40! This definitely provides the counter-evidence to verify my assumption. 

Now, since the original story I'm going to tell failed. I decide to continue to explore what if these 26 crashes could be prevented if there are more traffic lights? This leads to the question how can we improve the transportation infrastructure to reduce crashes. If taken 250 meters as a minimum distance that two traffic lights can be set up next to each other (because too many traffic lights will cause problems to the mobility of automobiles), we can see which spots are available to set up more traffic lights (figure below).

However, after I highlighted the crashes at the intersections again within these non-traffic light areas, there are only 9 crashes left, let alone the causes of these crashes may be the bad weather, the road condition etc. In conclusion, setting up more traffic lights won't help to reduce the crash accidents in Squirrel Hill.

REFLECTION

I would say this is a wrong hypothesis to analyze on but also, I learned the lesson that the analysis process actually made me gain a deeper understanding of the data sets and the questions I asked. By visually exaggerating the crashes at the intersections, the comparison is more clear and easier to identify the problem with the analysis. I think the caricature doesn't need to be so distorted that affects the accurancy of the data but definitely represents the data in a way that the main story is catchy to the readers.

SOURCE

[1] Allegheny County Crash Data. https://data.wprdc.org/dataset/allegheny-county-crash-data

[2] Pittsburgh Traffic Signals. https://data.wprdc.org/dataset/pittsburgh-traffic-signals

[3] Pedtro Cruz and Penousal Macado. City Portraits and Caricatures. https://cdv.dei.uc.pt/wp-content/uploads/2015/08/cruz-2014tz.pdf