Investigation of discrepancies between posted speed limits and operating speeds with particular reference to turkish drivers and road geometry

Due to a number of reasons, considerable discrepancies between legal speed limits and actual operating speeds occur in certain places. As a result, lack of compliance and respect to the posted speed limits become a common practice. The gap between the legal limits and the "felt speed" as a function of the road geometry has been the motive of the present research. Within the scope of this thesis, speed histograms are produced to be able to demonstrate and measure this gap. Ten different roads were selected in Antalya to collect spot speed data around free flow conditions and, except the 24th Street and Ataturk Boulevard, at all eight locations, drivers well exceeded the speed limits. Then, the pin point locations of speed signs were geocoded using a hand-held GPS device along 97.4 km of various classes of urban roads in Antalya. Their frequencies and functionalities were also studied. It has been discovered that no clear standards exist in Turkey in relation to the good practice of these signs in urban areas. To be able to ascertain the reasons behind the above-mentioned discrepancies, a questionnaire survey was conducted among 150 drivers at three petrol stations on 100. Yıl, Ataturk and Bulent Ecevit Boulevards, which contained 10 questions under four headings. The survey results revealed that drivers have very little respect to the posted speed limits and adjust their speed according to actual traffic densities rather than the statutory limits. If geometric design related mistakes in Turkish roads are handled professionally so that roads give the correct "felt speed" impression which is in agreement with the posted limits, then the problem of speed related accidents can only be dealt with at a satisfactory level.