Revelations from 1 Year of Traffic Cameras – V – Speeding in the Turnpike School Zone 8-11-10.doc
Revelations from 1 Year of Traffic Cameras
This is the fifth in a series of articles examining the trends in Oak Ridge traffic camera statistics to
determine successes and failures in modifying driving habits. The data are from the official monthly
reports issued by the City of Oak Ridge.
V. Speeding in the Turnpike School Zone
In the previous article from this series, we analyzed the speeding citations in the school zone on
Robertsville Road near the Willowbrook Elementary School. For tickets issued when the school-zone
lights were not flashing, the data showed an abrupt drop in violations by a factor of 3 after the first
month. Then, the citations wandered around the average of 283/month for the remaining 11 months,
except for an unexplained anomaly spiking to 908 in October 2009. When the yellow lights were
flashing, the citations averaged 98/month over the 7 months. But, the number of citations showed
large fluctuations, and no evidence of improving compliance. Will the pattern for the school zone on
the Oak Ridge Turnpike near the High School be the same or different?
3500
35 mph Zone Camera Speeding Tickets: O. R. Turnpike @ ORHS
3000
2500
2000
Eastbound 35 mph Zone
1500
Westbound 35 mph Zone
1000
Total 35 mph Zone
500
0
The first chart shows the monthly citations for the school zone on the Oak Ridge Turnpike in the vicinity
of the Oak Ridge High School, when the yellow lights are not flashing, and the normal 35-mph speed
limit applies. Starting with the totals of the eastbound and westbound directions, the citations start out
at 3025 in the first month, and gradually decline to 1130 in the last month. The expected 1-sigma
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fluctuations from Poisson Statistics should be less than 3% for these totals. Consequently, systematic
trends and cycles are discernable in the graph. For the westbound direction, the monthly numbers do
not demonstrate that same distinct downward trend. Instead they vary up and down around an average
of 705, with only a slight hint of a downward relaxation. Most of the downward trend is derived from
the eastbound numbers, which start out much higher than the westbound data in the first three
months. Nevertheless, one can derive satisfaction from the fact that the totals have decreased by a
factor of 2.7 from the beginning to the end of the 12-month period. From the pattern of the last 6
months, it is not clear whether the trend has reached a plateau, or will continue downward in the next
12 months.
The second chart presents the monthly citation data when the yellow school-zone lights are flashing,
and the speed limit is reduced from the normal 35 mph to 20 mph. For the months of September 2009
through May 2010, the totals for both directions range from 240 to 825. That means we should expect
the minimum random fluctuations from Poisson Statistics to be no more than 6.5%. The seemingly
random fluctuations in the chart are much larger than 6.5%. Consequently, it is reasonable to conclude
that something else is driving those variations. Clearly, the violations before September 2009 and after
June 2010 must be zero, because school is not in session, and the flashing lights remain off. The low
number in June marks the transition into summer vacation. January is low, because of the holidays at
the turn of the year. It is not certain why October is low. Could it be due to a Fall break?
If those low months caused by vacation or breaks are removed from the calculation, the remaining
seven months average 725 citations/month. Within those 7 full months there is no evidence of a
downward or upward trend. Within the limitations of the data, one must conclude that there is no
conclusive evidence of improved compliance for the 20-mph school zone when the yellow lights are
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flashing. However, the 7-month average rate of monthly violations for the 20-mph limit is still a factor
of 1.6 lower than the June 2010 violations for the 35-mph limit in the same location. Are drivers paying
closer attention when the yellow lights are flashing, or is the traffic volume more than a factor of 1.6
lower during the 20-mph periods? RedFlex and the City need to report the pertinent traffic volumes so
that the difference can be understood. By comparing the number of citations to the number of vehicles
moving through the school zone during the two different speed limits, one could determine whether the
percent of the drivers violating the speed limit is similar or significantly different for the two speed
limits.
Although the relevant traffic-volume information is normally retrievable from the cameras, it has not
been reported by the City of Oak Ridge. However, one can calculate an approximate violation rate for
the 35-mph zone by using the several-year-old estimate by the City Engineer, Steve Byrd, of circa 20,000
vehicles per day travelling on the Turnpike. On that basis, the 1130 citations for exceeding 35 mph
during June 2010 amounts to circa 0.19% of the drivers cited for violating the speed limit.
The bottom line is the cameras in the ORHS school zone seem to have gradually reduced the 35-mph
speed violations by a factor of 2.7 over the 12 months. But, long-term improvement in compliance for
the 20-mph school zone is not discernable in the data.
Councilwoman Anne Garcia Garland has suggested an alternative to the speeding cameras for improving
safety in the Turnpike school zone. She proposed installing a pedestrian, on-demand, stop-light at the
school zone cross-walk. The traffic light would remain green for vehicles on the Turnpike until a
pedestrian desiring to cross the street pushed the button. The resulting red light would be timed to
allow the pedestrian to safely cross all 5 lanes. A white, flashing strobe light on the circumference of
the red light (like in the eastbound Turnpike and Nebraska traffic light) is desirable to catch the attention
of drivers who were not expecting a red light. This solution would improve safety both during school
hours and for pedestrians crossing during major events outside of school hours.
Who pays for the camera tickets, and how much money has gone to which beneficiaries? The answers
to those questions are in the next article in this series.
Dr. Dale Gedcke is a Marketing and Technical Consultant. He can be contacted at
gedcked@bellsouth.net.
Dale Gedcke, B.Eng., M.Sc., Ph.D.
Marketing & Technical Consultant
1033 W. Outer Drive
Oak Ridge, TN 37830
USA
Phone: 865-483-6615
Mobile: 865-805-0355
E-mail: gedcked@bellsouth.net
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