Red-Light Cameras

Red-Light CamerasRed-Light CamerasThe GoodThe Good

The Bad &The Bad &

The UncertainThe Uncertain

Dale Gedcke, B.Eng., M.Sc., Ph.D.

Marketing & Technical ConsultantOak Ridge, TN

OR RLC Presentation 5-18-08.ppt

How RLCs WorkHow RLCs Work

Sensor

Traffic Light

Camera

Car

Crossing sensor on redcaptures ±6 sec of video

If you cross thesensor on red, about 2 weeks latera citation like thisarrives in the mailfor the owner of thevehicle.

The black bars include thetime, place, speed limit,your speed, and amount of time the light was red whenyour crossed the sensor.

Where to view thevideo on-line.

Red-Light Violation Response OptionsRed-Light Violation Response Options View video on-line, then chose one of 3 options:View video on-line, then chose one of 3 options:

1) Pay $501) Pay $50 No points on licenseNo points on license No notification to insurance companyNo notification to insurance company No notification to TN Dept. of SafetyNo notification to TN Dept. of Safety

2) Name the actual driver2) Name the actual driver AffidavitAffidavit Vehicle owner is liable if actual driver fails to respondVehicle owner is liable if actual driver fails to respond No notification to Insurance Company, nor TN Dept. of SafetyNo notification to Insurance Company, nor TN Dept. of Safety

3) Contest the ticket in court. 3) Contest the ticket in court. If you loseIf you lose:: Additional $8 scheduling fee, plus $60 court fee Additional $8 scheduling fee, plus $60 court fee Judgement becomes a public record available to data mining companiesJudgement becomes a public record available to data mining companies

Knoxville, TN / Redflex Citations in 2007Knoxville, TN / Redflex Citations in 2007

• Revenue Sharing Formula:< $4500 per camera per month: 15% to City, 85% to Redflex> $4500 per camera per month: 50% to City, 50% to Redflex

• 15 Intersections with cameras

• 60,299 Red-light violations

• $955,014 to City revenue

• $1,644,719 to Redflex revenue

• Net = $43.11 per initial citation. (Compare to $50 ticket.)

RLC Safety PremiseRLC Safety Premise

Drivers running a red light risk a collision with cross-Drivers running a red light risk a collision with cross-traffic operating on greentraffic operating on green

Red-Light Cameras catch Red-Light Cameras catch ALLALL red-light violations red-light violations Drivers soon learn to stop on Drivers soon learn to stop on redred to avoid a ticket to avoid a ticket

Installing Red-Light Cameras should improve safety because:

Why Do Drivers Run Red Lights?Why Do Drivers Run Red Lights?

In a rush. Tried to beat the red.In a rush. Tried to beat the red. (Sensitive to RLC)(Sensitive to RLC) Misjudged time versus distanceMisjudged time versus distance (Minor sensitivity to RLC)(Minor sensitivity to RLC)

Thought there was time to make it on yellowThought there was time to make it on yellow Distracted when it changed to yellowDistracted when it changed to yellow

Did not see the signalDid not see the signal (Not sensitive to RLC)(Not sensitive to RLC) Visibility problemVisibility problem

Could not stop in timeCould not stop in time (Not sensitive to RLC)(Not sensitive to RLC) Dilemma Zone (yellow too short for speed limit)Dilemma Zone (yellow too short for speed limit)

CONCLUSION: RLC will not suppress all CONCLUSION: RLC will not suppress all red-light running.red-light running.

Proving/Disproving the RLC Safety PremiseProving/Disproving the RLC Safety Premise Simple analyses are almost always misleadingSimple analyses are almost always misleading Requires a comprehensive and sound statistical analysis because:Requires a comprehensive and sound statistical analysis because:

Many confounding variables Many confounding variables (traffic rate, traffic patterns, weather, (traffic rate, traffic patterns, weather, intersection characteristics, speed, time of day, day of week, changes in intersection characteristics, speed, time of day, day of week, changes in vehicle safety features, driver characteristics, truck traffic, yellow duration, vehicle safety features, driver characteristics, truck traffic, yellow duration, all-red duration, etc.)all-red duration, etc.)

Must correct for changes in traffic volumeMust correct for changes in traffic volume Must compare the before and after accident rates to similar intersections Must compare the before and after accident rates to similar intersections

without RLCs (to determine what changes were due to the RLCs)without RLCs (to determine what changes were due to the RLCs) Important to test for spill-over effects at nearby intersections without RLCsImportant to test for spill-over effects at nearby intersections without RLCs Paucity of data and poor quality of dataPaucity of data and poor quality of data Dealing with low numbers of random accidents: Statistical uncertainty is Dealing with low numbers of random accidents: Statistical uncertainty is

large. large. To detect a 10% difference with 95% confidence requires >800 accidents To detect a 10% difference with 95% confidence requires >800 accidents

Before/After RLC installation and >1600 Before/After at non-RLC control sites.Before/After RLC installation and >1600 Before/After at non-RLC control sites.

Must use tests for statistical significance of trendsMust use tests for statistical significance of trends t-test, Chi-squared test, F-test, variance analysis, regression analysis, t-test, Chi-squared test, F-test, variance analysis, regression analysis,

empirical Bayes analysisempirical Bayes analysis If an analysis does not use any of these tests, its conclusions are worthless.If an analysis does not use any of these tests, its conclusions are worthless.

Several Sound Statistical Studies are AvailableSeveral Sound Statistical Studies are Available

Barbara Langland-Orban Barbara Langland-Orban et al.,et al., Red Light Running Cameras: Would Crashes, Red Light Running Cameras: Would Crashes, Injuries and Automobile Insurance Rates Increase If They Are Used in Florida? Injuries and Automobile Insurance Rates Increase If They Are Used in Florida? Florida Public Health Review, 2008; 5:1-7, and 5: 47-52.Florida Public Health Review, 2008; 5:1-7, and 5: 47-52.

Nattaporn Yaungyai, Nattaporn Yaungyai, Evaluation Update of Red Light Camera Programming in Evaluation Update of Red Light Camera Programming in Fairfax County, VirginiaFairfax County, Virginia; Master’s Thesis, Virginia Polytechnic Institute and State ; Master’s Thesis, Virginia Polytechnic Institute and State University, April 2004.University, April 2004.

Mark Burkey and Kofi Obeng, Mark Burkey and Kofi Obeng, A Detailed Investigation of Crash Risk Reduction A Detailed Investigation of Crash Risk Reduction Resulting from Red Light Cameras in Small Urban Areas, Resulting from Red Light Cameras in Small Urban Areas, North Carolina North Carolina Agricultural & Technical State University, Greensboro, NC, July 2004.Agricultural & Technical State University, Greensboro, NC, July 2004.

Nicholas J. Garber Nicholas J. Garber et alet al., ., The Impact of Red Light Cameras (Photo-Red The Impact of Red Light Cameras (Photo-Red Enforcement) on Crashes in Virginia, Enforcement) on Crashes in Virginia, Virginia Transportation Research Council, Virginia Transportation Research Council, Charlottesville, VA, June 2007.Charlottesville, VA, June 2007.

Barbara Langland-Orban Barbara Langland-Orban et al.,et al., Florida, 2008 Florida, 2008

Excellent review and critique of all statistical studies Excellent review and critique of all statistical studies performed on RLC installations to date.performed on RLC installations to date.

Easy to read for the non-statistician.Easy to read for the non-statistician.

A good place to start!A good place to start!

Nattaporn Yaungyai, Thesis, Virginia Polytechnic Institute Nattaporn Yaungyai, Thesis, Virginia Polytechnic Institute and State University, April 2004.and State University, April 2004.

Excellent introduction to the RLC technology, history, laws and Excellent introduction to the RLC technology, history, laws and statistical testing processstatistical testing process

Summarizes laws in all USA States extant up to April 2004.Summarizes laws in all USA States extant up to April 2004. Summarizes experience in several countriesSummarizes experience in several countries Reviews public opinion surveys on RLCs in various cities.Reviews public opinion surveys on RLCs in various cities. Analyzes RLC impact in Fairfax County, VAAnalyzes RLC impact in Fairfax County, VA 13 camera intersections; 12 to 82 accidents per year per intersection 13 camera intersections; 12 to 82 accidents per year per intersection

category (RLC, comparison, spill-over); only 2 comparison category (RLC, comparison, spill-over); only 2 comparison intersections; 4453 to 887 total RLC violations per monthintersections; 4453 to 887 total RLC violations per month

Inadequate number of accidents and too few comparison Inadequate number of accidents and too few comparison intersections for determining significant accident trends.intersections for determining significant accident trends.

Enough RLC violations to determine RLC violation trend.Enough RLC violations to determine RLC violation trend. RLCs reduced red-light violations as much as RLCs reduced red-light violations as much as 58%58% in 22nd - in 22nd -

27th month after installation27th month after installation Lengthening yellow light duration reduced red-light violations Lengthening yellow light duration reduced red-light violations

as much as as much as 70%70% Statistically Statistically non-significantnon-significant reduction in accident rate. reduction in accident rate.

Burkey and Obeng, Greensboro, NC, July 2004.Burkey and Obeng, Greensboro, NC, July 2004.

Large data base yields good statistical accuracy:Large data base yields good statistical accuracy: 303 intersections 303 intersections 18 RLC sites: 840 accidents before & 777 accidents after RLC installation 18 RLC sites: 840 accidents before & 777 accidents after RLC installation 285 non-RLC sites: 4827 accidents before, 4211 after285 non-RLC sites: 4827 accidents before, 4211 after

Analyzed correlation with weatherAnalyzed correlation with weather RLC installation associated with a statistically significantRLC installation associated with a statistically significant 40% 40%

increaseincrease in accident rates compared to non-RLC intersections.in accident rates compared to non-RLC intersections. No change in angle accident rates, and No change in angle accident rates, and large increases in rear-end large increases in rear-end

crash rates crash rates and other types of crashesand other types of crashes relative to non-RCL relative to non-RCL intersectionsintersections

StatisticallyStatistically non-significant increase in fatal accident rate non-significant increase in fatal accident rate Decrease in left-turn accident rate with cross traffic at RLC sitesDecrease in left-turn accident rate with cross traffic at RLC sites Longer yellow light durationLonger yellow light duration decreases accident ratedecreases accident rate

Garber Garber et alet al., VA Trans. Res. Council, 2007., VA Trans. Res. Council, 2007

Large data set yields good statistical accuracy in the aggregate:Large data set yields good statistical accuracy in the aggregate: More than 3500 crashes over 7 yearsMore than 3500 crashes over 7 years 28 RLC intersections and 44 non-RCL intersections28 RLC intersections and 44 non-RCL intersections 6 jurisdictions (VA): Alexandria, Arlington, Fairfax City, Fairfax County, Falls 6 jurisdictions (VA): Alexandria, Arlington, Fairfax City, Fairfax County, Falls

Church & ViennaChurch & Vienna Analyzes aggregate versus individual jurisdictions and intersection Analyzes aggregate versus individual jurisdictions and intersection

types for differing trends. types for differing trends. (Statistical accuracy suffers when subdivided by (Statistical accuracy suffers when subdivided by jurisdiction or intersection.)jurisdiction or intersection.)

Offers guide for selecting successful accident-reduction RLC sitesOffers guide for selecting successful accident-reduction RLC sites Attempts cost vs. benefit analysis: Inconclusive +/- resultAttempts cost vs. benefit analysis: Inconclusive +/- result Aggregate total accident rates Aggregate total accident rates increased 29% with RLCincreased 29% with RLC Aggregate Rear-end crash rates Aggregate Rear-end crash rates increased 42% with RLCincreased 42% with RLC Aggregate red-light running crash rates Aggregate red-light running crash rates decreased a statistically decreased a statistically

non-significant 8% with RLCnon-significant 8% with RLC 4 of RLC intersections experienced increased angle crash rates4 of RLC intersections experienced increased angle crash rates 2 of RLC intersections showed decreased rear-end collision rates.2 of RLC intersections showed decreased rear-end collision rates.

Dilemma ZoneDilemma Zone

Sensor

Traffic Light

Camera

Dilemma Zone:If light turns yellow, it is impossible to enter the intersection before red, and impossible to stop

safely before the intersection.

dc

ds

You can get trapped by adilemma zone, if the yellow duration is tooshort for the speed limit.

Dilemma ZoneDilemma Zone

Approach speed = v = 40 mph = 58.7 ft/sYellow light duration = tY = 4.0 secondsDecision time = tD = 1.00 secondsReaction time = tR = 0.50 secondsMaximum safe deceleration rate = a = 10 ft/s/sPercent Grade (+ve uphill, -ve downhill) = G% = 0

Maximum distance to make it on yellow:fttvd Yc 235

Minimum distance to stop safely (avoiding rear-end collision):

ftGa

vttvd RDs 260

32.02 %

2

Dilemma Zone exists from 235 to 260 ft from intersection.If the light turns yellow when you are in this zone you can neither continue safelynor stop safely.

Minimum Yellow to Eliminate Dilemma ZoneMinimum Yellow to Eliminate Dilemma Zone

From 2003 TN Traffic Design Manual, recommended yellow light durations for level intersections are:

Approach Speed (mph): 25 30 35 40 45 50 55 60 65Yellow Duration (sec.): 4.0 4.0 4.0 4.5 4.5 5.0 5.0 5.5 6.0

NOTE: Descending grades require longer delays.

Using values from the previous slide, the minimum yellow duration at 40 mph is computed as:

.sec4.432.02 %

min

Ga

vttt RDY

For more realistic 85th percentile reaction times (tD + tR), see: 1) APPENDIX B and 2) Thomas J. Triggs and Walter G. Harris, Reaction Time of Drivers to Road Stimuli, Human Factors Report No. HFR-12, ISBN 0 86746 147 0. Human Factors Group, Department of Psychology, Monash University, Victoria 3800,

Australia, June 1982.

ConclusionsConclusions The most important and most effective safety solution:The most important and most effective safety solution: Increase Increase

yellow duration according to approach speed and grade to eliminate yellow duration according to approach speed and grade to eliminate unsafe Dilemma Zones.unsafe Dilemma Zones.

Statistically sound studies show that Red-Light Cameras are Statistically sound studies show that Red-Light Cameras are NOT NOT a reliably effective solution for improving safety.a reliably effective solution for improving safety.

The RLC effect on angle collision rates varies from positive to negativeThe RLC effect on angle collision rates varies from positive to negative RLCs usually significantly increase the rate of rear-end collisionsRLCs usually significantly increase the rate of rear-end collisions RLCs tend to increase RLCs tend to increase totaltotal accident rates accident rates However, RLC citation rates do decline in the first two years of operationHowever, RLC citation rates do decline in the first two years of operation

Red-Light Cameras generate addictively large revenuesRed-Light Cameras generate addictively large revenues Conflict of InterestConflict of Interest: Safety can easily become less important than : Safety can easily become less important than

revenuerevenue Analyze the operating costs carefully.Analyze the operating costs carefully. Some municipalities have lost Some municipalities have lost

money because of increased direct labor, overhead, and court costs. money because of increased direct labor, overhead, and court costs. Some have discontinued RLCs due to declining revenue.Some have discontinued RLCs due to declining revenue.

See Appendices A through D for more details.See Appendices A through D for more details.

Appendix A: Useful ReferencesAppendix A: Useful References

US DOTUS DOT Federal Highway Administration Manual on Uniform Traffic Control Devices Federal Highway Administration Manual on Uniform Traffic Control Devices ((MUTCDMUTCD): http://mutcd.fhwa.dot.gov/): http://mutcd.fhwa.dot.gov/

Tennessee MUTCDTennessee MUTCD Traffic Design Manual: Traffic Design Manual: http://mutcd.fhwa.dot.gov/resources/state_info/tennessee/tn.htmhttp://mutcd.fhwa.dot.gov/resources/state_info/tennessee/tn.htm

Making Intersections Safer:Making Intersections Safer: A Toolbox of Engineering Countermeasures to Reduce A Toolbox of Engineering Countermeasures to Reduce Red Light RunningRed Light Running, FHWA and Institute of Transportation Engineers, Pub. No. IR-, FHWA and Institute of Transportation Engineers, Pub. No. IR-115, ISBN: 0-935403-76-0 (2003):115, ISBN: 0-935403-76-0 (2003): http://safety.fhwa.dot.gov/intersections/rlr_report/index.htm (http://safety.fhwa.dot.gov/intersections/rlr_report/index.htm (published before the published before the 2004 and 2007 studies on RLCs2004 and 2007 studies on RLCs))

Dr. Peter T. Martin, Vikram C. Kalyani and Aleksander Stefanovic, Dr. Peter T. Martin, Vikram C. Kalyani and Aleksander Stefanovic, Evaluation of Evaluation of Advanced Warning Signals on High Speed Signalized Intersections, Advanced Warning Signals on High Speed Signalized Intersections, Univ. of Utah, Univ. of Utah, Nov. 2003.: http://www.mountain-plains.org/pubs/html/mpc-03-155/index.php Nov. 2003.: http://www.mountain-plains.org/pubs/html/mpc-03-155/index.php ((Dilemma ZonesDilemma Zones))

Philip R. Bevington and D. Keith Robinson, Philip R. Bevington and D. Keith Robinson, Data Reduction and Error Analysis for the Data Reduction and Error Analysis for the Physical SciencesPhysical Sciences, WCB/McGraw-Hill, ISBN 0-07-911243-9, 1992. (, WCB/McGraw-Hill, ISBN 0-07-911243-9, 1992. (Excellent Excellent introductory book on statistical analysisintroductory book on statistical analysis))

Appendix B: Driver Reaction TimesAppendix B: Driver Reaction Times

Dependent on several factors:Dependent on several factors:

DistractionsDistractions Anticipation of, or focus on a particular warning or hazard Anticipation of, or focus on a particular warning or hazard Difficulty of interpreting the significance of the hazard or warningDifficulty of interpreting the significance of the hazard or warning Difficulty of figuring out the best solutionDifficulty of figuring out the best solution Physical motion required to implement the solutionPhysical motion required to implement the solution Mechanical delay in vehicle actuationMechanical delay in vehicle actuation

What is the Right Reaction Time?What is the Right Reaction Time? MUTCD documents use a 1-second reaction time with a yellow light.MUTCD documents use a 1-second reaction time with a yellow light. Dilemma Zone example used 1.5 seconds.Dilemma Zone example used 1.5 seconds. Studies showed a longer yellow reduces accidents and red-light violations.Studies showed a longer yellow reduces accidents and red-light violations.

Appendix B (cont’d.): Driver Reaction Times.Appendix B (cont’d.): Driver Reaction Times.1.5 sec. is a reasonable minimum1.5 sec. is a reasonable minimum

Driver Reaction Time to Surprise Encounter: Triggs and Harris 1982 Around a blind curve, past the crest of a hill, or triggered ON at the last moment

Field Test

Mean Reaction Time (s)

Standard Deviation

(s)

85th Percentile

(s)

Car Following (response to lead car brake light) 0.92 0.28 1.26Protruding Vehicle with Tyre Change 0.97 0.45 1.50Lit Vehicle Under Repair at Night 1.02 0.36 1.50Flashing Railway Crossing - Night (Rally Drivers) 1.14 0.34 1.50Flashing Railway Crossing - Night (General Population) 1.18 0.36 1.50Flashing Railway Crossing - Day 1.77 0.84 2.53Speed Trap: Tynong 1.75 0.7 2.54Parked Police Vehicle (just past crest in hill) 2.37 0.69 2.80C.R.B. "Roadworks Ahead" Sign 1.64 1.26 3.00Speed Trap: Beaconsfield 2.46 1.04 3.40Speed Trap: Dandenong North 2.45 0.92 3.60Speed Trap: Gisborne 2.54 0.66 3.60

From: Thomas J. Triggs and Walter G. Harris, Reaction Time of Drivers to Road Stimuli, Human Factors Report No. HFR-12, ISBN 0 86746 147 0. Human Factors Group, Department of Psychology, Monash University, Victoria 3800, Australia, June 1982.

Traffic Engineers typically use the 85th Percentile for design: i.e., 85% of drivers have a lower reaction time.

Appendix C: Required Yellow Duration and Green DelayAppendix C: Required Yellow Duration and Green Delayto Eliminate Dilemma Zone and Clear the Intersectionto Eliminate Dilemma Zone and Clear the Intersection

Maximum Deceleration Measurement & Basic Parameters: Enter Measured Red Values

Initial Speed (mph)

Minimum Time to Stop, after

applying brake (sec.)

Minimum Stopping

Distance (ft.)

Effective Deceleration

Constant (ft/sec/sec)

Time to recognize change from Green to Yellow light and decide whether or not to stop (sec.)

Time to Move foot from Accelerator to Brake pedal

(sec.)

Duration of Yellow Light (sec.)

40 5.86 171.9 -10.0 1.0 0.5 4

Minimum Yellow Duration to Eliminate Dilemma Zone Required Green Delay vs. Intersection Width

Initial Speed (mph)

Initial Speed (ft/sec)

Distance Travelled (ft.)

while deciding to

stop

Distance travelled (ft.) while moving foot to brake

Distance Travelled while Decelerating

(ft.)Total Distance to

Stop (ft.)

Minimum Required Yellow

Duration (sec)

40-ft Width: Green Delay (sec)





5 7.3 7.3 3.7 2.69 13.7 1.9 5.5 8.2 10.9 13.6 16.410 14.7 14.7 7.3 10.74 32.7 2.2 2.7 4.1 5.5 6.8 8.2

15 22.0 22.0 11.0 24.17 57.2 2.6 1.8 2.7 3.6 4.5 5.5

20 29.3 29.3 14.7 42.97 87.0 3.0 1.4 2.0 2.7 3.4 4.125 36.7 36.7 18.3 67.15 122.1 3.3 1.1 1.6 2.2 2.7 3.3

30 44.0 44.0 22.0 96.69 162.7 3.7 0.9 1.4 1.8 2.3 2.7

35 51.3 51.3 25.7 131.61 208.6 4.1 0.8 1.2 1.6 1.9 2.340 58.7 58.7 29.3 171.89 259.9 4.4 0.7 1.0 1.4 1.7 2.045 66.0 66.0 33.0 217.55 316.6 4.8 0.6 0.9 1.2 1.5 1.850 73.3 73.3 36.7 268.58 378.6 5.2 0.5 0.8 1.1 1.4 1.655 80.7 80.7 40.3 324.99 446.0 5.5 0.5 0.7 1.0 1.2 1.560 88.0 88.0 44.0 386.76 518.8 5.9 0.5 0.7 0.9 1.1 1.465 95.3 95.3 47.7 453.91 596.9 6.3 0.4 0.6 0.8 1.0 1.370 102.7 102.7 51.3 526.42 680.4 6.6 0.4 0.6 0.8 1.0 1.275 110.0 110.0 55.0 604.31 769.3 7.0 0.4 0.5 0.7 0.9 1.1

Green Delay is also called the “All-Red”phase (red for all directions).

Appendix D: Poisson Statistics.Appendix D: Poisson Statistics.Why the Sample Size Must Be LargeWhy the Sample Size Must Be Large

Poisson Probability Distribution for Mean = 9

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0 5 10 15 20 25

N

P(N

)

Mean

ss

• Accidents have a low probability: typically < 50 per 1 million cars thru the intersection.• Poisson Statistics apply: the probability of observing N accidents in a time period t is:

!)(

N

eNP

NN

= the mean or average of the distribution.

A measure of the width or dispersion of the distribution about the mean is the standard deviation, s

s

Appendix D (cont’d.): Poisson Statistics.Appendix D (cont’d.): Poisson Statistics.Why the Sample Size Must Be LargeWhy the Sample Size Must Be Large

For a single sample of N accidents observed in a time t, the best estimate of the mean of the underlying probability distribution is

N

The best estimate of the standard deviation of the underlying probability distribution is

N s

The dispersion, expressed as a percent of the mean value is

NN

%100%100%

ss

s% represents the percent uncertainty in estimating the true, mean number of accidents from a single measurement, N.

Appendix D (cont’d.): Poisson Statistics.Appendix D (cont’d.): Poisson Statistics.Why the Sample Size Must Be LargeWhy the Sample Size Must Be Large

Percent Uncertainty in the Number of Accidents N : 1 10 100 1,000 10,000 100,000 1,000,000s% : 100 32 10 3.2 1 0.32 0.1

• To detect changes of the order of a few percent, one must have a sample of more than 10,000 accidents.

• When comparing accident rates at RLC intersections to similar, non-RLC intersections, one needs more than twice as many non-RLC intersections to keep from degrading the statistical uncertainty.

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