Title
Accident Rate and Population in the City of Roseville

Author

Josh Little
American River College, Geography 350: Data Acquisition in GIS, Fall 2009
Email: josuextg@gmail.com
Abstract

This report will discuss whether or not accident rates in the form of Accidents per Million Vehicle Miles are directly related to population growth within the City of Roseville. Data was collected from several sources within the City of Roseville Engineering Department and then analyzed.

Introduction

The purpose of this project is to track accident data over time in order to determine if population growth has an effect on the number of vehicle collisions at key intersections within the City of Roseville. I will be comparing accident data from 10 years ago to data from 5 years ago and to current accident data. This data will then be compared to their respective roadway volumes in order to calculate “accidents per million vehicle miles”. This is a standard measurement for accident rate. With this data I will then be able to determine if there is any correlation between population growth and number of vehicle collisions. I will also be able to determine if there are any intersections more susceptible to collisions due to increased volume.

Background

Despite the many advances in roadway design, traffic engineering, car manufacturing, and police enforcement technologies, many places still suffer from a growing problem of traffic collisions. During 2007, California alone had a total of 501,908 traffic collisions. (2007 California Quick Collision Facts, 2009). These collisions can lead to death, 3,557 fatalities in California in 2007, and disability as well as significant financial costs to both society and the individual. In an effort to help curb these costs, accident data research is performed by many agencies around the world to hopefully discover trends that could lead to changes in conditions which will in turn lead to a safer driving environment.

I previously worked for the City of Roseville Traffic Studies Section of the Engineering Department. While there, I noticed that the residents of the City held the perception that as urban areas have become more populated, thus placing more vehicles on the roadway, a greater number of collisions have occurred as a direct result. I am also currently a resident of Roseville and am curious to see what intersections are at higher risk where I drive the most.

Methods

In order to calculate Accidents per Million Vehicle Miles I needed several pieces of information for each intersection for each year. I also needed the population from each year I was to look at.

I decided to look at 10 intersections that spanned across the geography of the City. I also wanted to make sure that each intersection was signalized and had information available from each of the time periods. This was accomplished with the help of the City of Roseville Engineering Department, Traffic Studies Section. I gave them the list I had produced and with a little bit of research, they confirmed that each intersection I had chosen had sufficient data. The intersections chosen are as follows:

1) Eureka Rd. & N. Sunrise Ave. 2) E. Roseville Pkwy. & Sierra College Bl. 3) Douglas Bl. & Sierra College Bl. 4) Roseville Pkwy. & Pleasant Grove Bl. 5) Pleasant Grove & Woodcreek Oaks Bl. 6) Foothills Blvd. & Vineyard Rd. 7) Foothills Blvd. & Junction Bl. 8) Fairway Dr. & Stanford Ranch Rd. 9) Fiddyment Rd. & Blue Oaks Bl. 10) Vernon St. & Cirby Way

Now that I knew the intersections I had chosen were sufficient, it was time to gather the data. I retrieved Traffic Collision Reports, again with the help of the Traffic Studies Section. Each report contained a complete year’s collision information for each intersection. So I had 10 intersections and 3 years for a total of 30 reports. This is an example of one of the reports:
I also gathered Average Daily Traffic (ADT) volume information for each intersection from the Engineering Dept. and from the City of Roseville website. I then input these data into Microsoft Excel in order to organize the information into the separate years and to calculate Accidents per Million Vehicle Miles (MVM).

The calculation for MVM is as follows:

# of Accidents/((ADT * 365)/1,000,000)

I input this calculation using each intersection’s respective cell numbers into Excel. I then averaged all of the intersection’s MVMs for each year in order to get an Accidents per Million Vehicle Miles number for the 3 years.

Results
The table I created in Excel shows most of my finalized data in raw form:

Being able to visualize the intersections within the City is a bit better though!

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Each map shows all 10 intersections in the 3 different years. Each map is symbolized with proportional symbols (classified by natural breaks) showing each intersection’s Accidents per Million Vehicle Miles.

As you can see when looking at the maps, there are several intersections each year that stand out. However, there is not one intersection that stands out for all 3 years.

Also, in the above table you can see that the Average MVM for the years are 0.34 for 1999, 0.47 for 2004 and 0.34 for 2009. The populations for these years are 71,599 for 1999, 96,600 for 2004 and 112,343 for 2009 (Population, 2009).

Analysis
I feel that this report could have been more comprehensive in the sense that it could contain information from more years. Gathering the information for this report was relatively easy on my part. The City of Roseville Engineering Department was very cooperative and spent quite a bit of time gathering information on my behalf. Without their help I would not have been able to access the data I needed. However, when I pressed to get data from other years to get a larger sample size, I hit a roadblock. Any data that they have before the year 1998 is not as complete as the information I was able to obtain. I also found that the City has a backlog of information that is in the process of being digitized for easier use. I probably could have found suitable information from earlier years, but it would have taken up much more of the Traffic Studies Department’s time. Therefore I stayed with the 30 samples I had already obtained.
Conclusions
Looking at the maps showed that there is not one intersection that stands out in all 3 years. This shows that none of these intersections are constant problem areas year after year. It does mean, however, that one must be careful all the time and at all intersections when driving.

Despite a constant increase in population over the ten year period, the Average MVM rate has not increased in the same proportion. In fact, it rose from 1999 to 2004, but then dropped to the same level as 1999 in 2009. This shows that accidents are not a direct result of growing population. I also noticed that between 2004 and 2009 intersection volumes did not rise that much, meaning that accidents are not directly linked to volume either. I believe that this can be partially explained by a study conducted by the Federal Highway Administration which shows that the number of miles people are driving each month starting in late 2007 up to the third quarter of 2008 had drastically declined. With this finding, traffic experts believe that the higher prices of fuel, though not favorable to the economy, may be good in reducing the numbers collisions (Despuez, 2008).

References

CHP, State of California, 2007. “2007 California Quick Collision Facts”. (PDF) Web. Retrieved 2009-12-2.
< http://www.chp.ca.gov/switrs/>

Despuez, Nemilou. 2008-08-20. “Traffic Collision And Fatalities In California”. Web. Retrieved 2009-12-2.
< http://www.articlesnatch.com/Article/Traffic-Collision-And-Fatalities-In-California-/85878>

Economic Development Department, 2009 “Population”. Web. Retrieved 2009-12-2.
< http://www.roseville.ca.us/ed/demographics/population/default.asp>