Steven M. Rock [18] studied the effect of 65 mph speed in Illinois and also support the general notion that increase in speed limit to 65 mph increased the crash frequency. The method he adopted was ARIMA method (Autoregressive Integrated Moving Average Method). Rock [18] assumes that the increase in 65 mph roads could be also attributed to the increase in vehicle miles travel due to higher …show more content…
The study was conducted in Utah region. The authors studied different road classifications such as urban interstates, rural interstates and concluded that there was significant change in crash rates in both road classification [19. This study have also used the ARIMA method where the before trends in time series is used to estimate the future response. Like Steven M. Rock, Vernon et al. [19] are of the opinion that ARIMA method is the best method to analyze the data. The authors have not noted a significant increase in crash rates when the speed limit was increased in both interstates and non-interstates and was unable to explain the exact cause of sudden increase in crash rates and crash fatality. The authors point that they have many limitations in the study, hence the results could not be justified by reasons. The study concludes by pointing that big data and similar datasets is required to draw conclusive evidence and many confounding variables can affect the outcome of speed vs crash study [19]
Najjar et al. [20] studied the impact of increased speed limit in Kansas by conducting a before and after study and concluded there is no significant increase in the crash rates or fatality rates in urban interstates and rural interstates. …show more content…
[22] studied the effect of 65 mph speed enforcement in 40 states. Garber et al. also supported earlier works which stated that the crash rate and fatality rate increased with increase in speed limits but the increase in speed limits varied across different states. The authors came up with a valuable observation that the variation in crashes could also occur due to difference in enforcement in different states. The authors state that the variance among different vehicles increase when the speed limit is increased because certain vehicles do not abide by the new speed limit. The authors also mentioned that “speed spillover” effect also increases the crash rate. Also some drivers may drive in higher speeds in highways and when the exit the highways to continue their travel in lower classification roads, they might continue to drive in higher speed limits [22]. “Speed spillover” effect can create variance and more the variance result in higher number of crashes. The spillover effect was noticed by earlier studies such as …..The authors also stated that crash variations may be attributed to seasonal variations, type of trip (business or recreational) or day of travel. The method of analysis was multiple regression with the independent variables as 65 mph speed limit, unemployment rate, seatbelt use, day of the week. Garber et al. [22] stated that “serial correlation” is present in rural interstates but they are absent in non- rural interstates. The conclusion of