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control study design. They found, "..the risk of involvement in a casualty crash increased more than exponentially with increasing free travelling speed above the mean traffic speed and that travelling speeds below the mean traffic speed were associated with a lower risk of being involved in a casualty crash." Outlining past research in this area, they suggest that, in the
Solomon research, "Both the numerator (number of crashes in a particular speed band) and the denominator (number of vehicle-miles travelled in that same speed band) may have been quite inaccurate for relatively low speeds."
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roadway, driver, and vehicle characteristics affect the probability of being involved in a crash. He found that the probability of being involved in a crash per vehicle-mile as a function of on-road vehicle speeds follows a U-shaped curve with speed values around the median speed having the lowest probability of being in a crash. Although typically called the
Solomon curve, the U-shaped curve has also been referred to as the Crash Risk Curve.
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negotiate a turn from vehicles moving slowly in the flow of traffic. Reporting on these results in 1971, academics West and Dunn confirmed the findings of
Solomon and Cirillo, but found that crashes involving turning vehicles accounted for 44 percent of all crashes observed in the study and that excluding these crashes from the analysis greatly attenuated the factors that created the U-shape of the Solomon curve.
20:
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that control of absolute driver speed, and not variability, should be the primary focus of traffic safety regulation. Both views support the fact that the seminal research underlying the
Solomon curve shows that the greater the difference between a driver’s speed and the average speed of traffic—both
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conducted a study in 1970 where data was collected on 114 crashes involving 216 vehicles on a state highway in
Indiana to address these concerns by (1) combining automated, embedded speed-monitoring stations with trained on-scene crash investigators, and (2) distinguishing data on vehicles slowing to
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and plotted the results. While others have attempted to quantify the relationship between average speed and collision rates, Solomon's work was both "the earliest and best known". Solomon conducted a comprehensive study of more than 10,000 collision-involved drivers and their vehicles and how other
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While
Solomon’s research focused on speed deviation, and not speed per se, some commentators have cited Solomon’s research to support the conclusion that raw speed and crash risk are not directly related. On the other hand, while recognizing Solomon's research reveals the importance to safety of
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In July 2001, Kloeden CN, Ponte G and McLean AJ of the Road
Accident Research Unit, Adelaide University quantified the relationship, "... between free travelling speed and the risk of involvement in a casualty crash in 80 km/h or greater speed limit zones in rural South Australia" using a case
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In 1991, Fildes, Rumbold, and
Leening collected self-reported crash data from 707 motorists in Australia with fewer than 200 reporting that they had been in a collision but, unlike Solomon and Cirillo, the researchers found no relationship between slower speeds and increased crash involvement.
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Notwithstanding the many studies over the years, in testimony before the Ohio Senate
Highways and Transportation Committee on June 10, 2003, Julie Cirillo, Former Assistant Administrator and Chief Safety Officer for the Federal Motor Carrier Safety Administration (
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In 1968, Julie
Cirillo conducted a similar study of 2,000 vehicles on interstate highways that addressed speed variation’s impact on crashes that involved two or more vehicles. The Cirillo data produced a U-shaped curve similar to the Solomon curve. The
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Solomon, David (July 1964). "Accidents on main rural highways related to speed, driver, and vehicle". Technical report, U.S. Department of Commerce/Bureau of Public Roads (precursor to Federal Highway Administration).
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above and below that average speed—the greater the likelihood of involvement in a crash. Consequently, many states and safety organizations advise drivers to “drive with the flow of traffic”.
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conducted by David Solomon in the late 1950s and published in 1964. Subsequent research suggests significant biases in the Solomon study, which may cast doubt on its findings.
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of the collision rate of automobiles as a function of their speed compared to the average vehicle speed on the same road. The curve was based on
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of the pack is 60 mph, how many cars will pass me in an hour and hence have a chance to collide with me?”—that showed that the theoretical
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Research Triangle Institute, "Speed and Accident, Volume II," Report No. FH-11-6965, National Highway Safety Bureau, June 1970.
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West, L. B., Jr. and Dunn, J. W. (1971). "Accidents, Speed Deviation and Speed Limits." Traffic Engineering. 41 (10), 52-55
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Hauer provided a theoretical foundation for the Solomon curve in 1971—“for example, if I drive at 45 mph, while the
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Monsere, C. M., Newgard, C., Dill, J. Rufolo, A., Wemple, E., Bertini, R. L., and Milliken, C. (September 2004).
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402:"Cost-Benefit Evaluation of Large Truck- Automobile Speed Limit Differentials on Rural Interstate Highways"
294:"Cost-Benefit Evaluation of Large Truck- Automobile Speed Limit Differentials on Rural Interstate Highways"
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Transportation Research Board, Committee for Guidance on Setting and Enforcing Speed Limits (1998).
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Meyer, John Robert; José A. Gómez-Ibáñez; William B. Tye; Clifford Winston (February 1999).
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John Robert Meyer; José A. Gómez-Ibáñez; William B. Tye; Clifford Winston (February 1999).
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327:"A CASE STUDY IN VEHICLE EMISSIONS REGULATIONS TO ACHIEVE AMBIENT AIR QUALITY STANDARDS"
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Interstate System Accident Research Study II, Interim Report II, Public Roads, 35 (3)
444:"Impacts and Issues Related to Proposed Changes in Oregon's Interstate Speed Limits"
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501:. Monash University Accident Research Centre, Victoria Australia. Archived from
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571:. Road Accident Research Unit, Adelaide University. July 2001. Archived from
214:. Road Accident Research Unit, Adelaide University. July 2001. Archived from
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25:"Accidents on main rural highways related to speed, driver, and vehicle"
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Chan, Kuei-Yuan; Steven J. Skerlos; Panos Y. Papalambros (2006-09-10).
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365:
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566:"Travelling Speed and the Risk of Crash Involvement on Rural Roads"
209:"Travelling Speed and the Risk of Crash Involvement on Rural Roads"
533:. OOIDA. 2003-06-10. Archived from the original on August 16, 2004
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635:. New York, New York: Van Nostrand Reinhold. pp. 155–56.
336:. Philadelphia, Pennsylvania: ASME. p. 8. Archived from
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variability around average speed, Leonard Evans concludes in
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Graphical representation of the collision rate of automobiles
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University of Arkansas, Department of Industrial Engineering
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University of Arkansas, Department of Industrial Engineering
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Kloeden CN, McLean AJ, Moore VM, Ponte G (November 1997).
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Society for Safety by Education Not Speed Enforcement.
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In 1964, Solomon researched the relationship between
268:"Travelling Speed and the Risk of Crash Involvement"
499:"Speed Behaviour and Drivers' Attitude to Speeding"
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400:Johnson, Steven L.; Naveen Pawar (November 2005).
292:Johnson, Steven L.; Naveen Pawar (November 2005).
662:. National Research Council (U.S.). p. 46.
599:Essays in Transportation Economics and Policy
497:Fildes BN, Rumbold G, Leening A (June 1991).
242:Essays in Transportation Economics and Policy
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602:. Brookings Institution Press. p. 276.
473:: CS1 maint: multiple names: authors list (
245:. Brookings Institution Press. p. 275.
111:was nearly identical to the Solomon curve.
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270:. pp. Section 2.1. Archived from
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173:Traffic engineering (transportation)
23:The Solomon curve as published in
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527:"Testimony of Julie Anna Cirillo"
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632:Traffic Safety and the Driver
334:Proceedings of IDETC/CIE 2006
123:Traffic Safety and the Driver
138:Assured Clear Distance Ahead
80:Research Triangle Institute
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550:: CS1 maint: unfit URL (
36:graphical representation
629:Evans, Leonard (1991).
385:Cirillo, J. A. (1968).
366:"Is speed killing us?"
115:Practical implications
99:Theoretical foundation
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46:The original research
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408:: 25. Archived from
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158:Road-traffic safety
73:Subsequent research
699:Traffic collisions
531:Land Line Magazine
178:Traffic psychology
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694:Automotive safety
609:978-0-8157-3181-8
389:. pp. 71–75.
252:978-0-8157-3181-8
168:Traffic collision
143:Automobile safety
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32:Solomon curve
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148:Design speed
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109:distribution
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704:Road safety
163:Speed limit
66:automobiles
683:Categories
615:2009-03-01
582:2014-12-27
537:2009-03-02
509:2009-03-02
460:2009-03-01
419:2009-03-01
371:2009-03-01
347:2009-03-01
311:2009-03-01
278:2009-03-01
225:2014-12-27
185:References
689:Accidents
546:cite news
413:(MS Word)
305:(MS Word)
59:collision
469:cite web
131:See also
57:and the
40:research
52:average
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105:median
576:(PDF)
569:(PDF)
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341:(PDF)
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89:FMCSA
62:rates
55:speed
34:is a
664:ISBN
637:ISBN
604:ISBN
552:link
475:link
247:ISBN
30:The
64:of
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