Transportation Research Record 1027 9. J.S. Smyth. The Brightness and Legibility at Night of Road Traffic Signs. Transactions of the Illuminating Engineering Society. Vol. 12, No. 4, 1947, pp. 71-94. 10. T.W. Forbes, B.B. Saari, W.H. Greenwood, J.G. Goldblatt, and T.E. Hill. Luminance and con- trast Requirements for Legibility and Visibil- ity of Highway Signs. In Transportation Research Record 562, TRB, National Research Council, Washington, D.C., 1976, pp. 59-72. 11. B.L. Hills and K.D. Freeman. An Evaluation of the Luminance Contrast Requirements in Fully Reflectorized Signs. Proc., 5th Australia Road Research Board Conference. Nunawading, Vic- toria, Australia, Vol. 5, No. 3, 1970, pp. 67-94. 12. M. Sivak, P.L. Olson, and L.A. Pastalan. Effect of Driver's Age on Nighttime Legibility of Highway Signs. Human Factors. Vol. 23, 1981, pp. 59-64. 13. M. Sivak and P.L. Olson. Nighttime Legibility of Traffic Signs: Conditions Eliminating the Effects of Driver Age and Disability Glare. Ac- cident Analysis and Prevention. Vol. 14, 1982, pp. 87-93. 14. B.L. Cole. Visual Aspects of Road Engineering. Proc., Australian Road Research Board, Nunawad- ing, Victoria, Australia, Vol. 6, No. 1, 1972, pp. 102-148. 15. A. Burg. Visual Acuity as Measured by Dynamic and Static Tests: A Comparative Evaluation. Journal of Applied Psychology. Vol. 50, 1966, pp. 460-466. 16. T.M. Allen. Night Legibility Distances of High- way Signs. Bull. 191. Highway Research Board, 57 National Research Council, Washington, D.C., 1958, pp. 33-40. 17. w.c. Richardson. Comparison of Legibility Po- tential of Reflective Sign Components. Ohio Department of Transportation, Columbus, July 1976. 18. H.L. Woltman and W.P. Youngblood. An Assessment of Indirect Factors Affecting Reflective Sign Brightness. Paper presented at the 1976 Annual Meeting of the Transportation Research Board, Washington, D.C., Jan. 19. P.L. Olson and M. Sivak. Improved Low-Beam Photometrics. Interim Report UM-HSRI-81-4. Highway Safety Research Institute. University of Michigan, Ann Arbor, Feb. 1981. 20. J.A. Hicks, III. An Evaluation of the Effect of Sign Brightness on the Sign Reading Behavior of Alcohol Impaired Drivers. Human Factors. Vol. 18, 1976, pp. 45-52. 21. J .w. Anderson and G.C. Carlson. Vehicle Spray Pattern Study. Investigation 338, Minnesota Highway Department, St. Paul, Aug. 1966. 22. N.T. Cox. The Effect of Dirt on Vehicle Head- lamp Performance. RRL Report LR 240. Road Research Laboratory, Crowthorne, Berkshire, England, 1968. 23. P.L. Olson and R.G. Mortimer. Analysis of Sources of Error in Headlamp Aim. SAE Report 740312. Highway Safety Research Institute, Uni- versity of Michigan, Ann Arbor, 1974. Publication of this paper sponsored by Cammi ttee on Visibility. Freeway Lighting and Traffic Safety-A Long-Term Investigation RUEDIGER LAMM, JUERGEN H. KLOECKNER, and ELIAS M. CHOUEIRI ABSTRACT The objective of this study was to assess the effectiveness of freeway light- ing. To achieve this, a case study on traffic accident characteristics was con- ducted that utilized a suburban freeway area west of Frankfurt, Federal Repub- lic of Germany, between 1972 and 1981. The study revealed that (a) the effects of lighting on suburban freeway accident rates was positive--there was a reduc- tion in accidents, and (b) these positive results of continuous freeway light- ing were lost in the case of partial lighting, especially after switching off lights at night between 10:00 p.m. and 5:30 a.m. for the purpose of saving energy.