The Commercial Vehicle Safety Alliance (CVSA) is an association of industry representatives, and state, territorial, provincial, and federal government officials in the United States, Canada, and Mexico. The CVSA's goal is to improve commercial vehicle safety. The CVSA concentrates its safety focus on three areas; driver, vehicle, and hazardous materials. Since 1981, the CVSA has developed a set of criteria for each of the three areas that define conditions which are so unsafe that a truck and/or driver should not be allowed to operate. These criteria are known as out of service (OOS) criteria. To check the compliance of motor carriers with the CVSA criteria, a series of road side inspections is conducted by state and local governments. If the driver and/or vehicle are found in violation of the CVSA OOS criteria, they are placed "out of service" until the conditions are completely remedied. Due to criteria growth, the CVSA wanted to examine the OOS criteria in the vehicle and hazardous materials areas. This study, focused on the vehicle portion of the OOS criteria, attempted to correlate commercial vehicle defects to commercial vehicle accidents. For a major portion of this project, actual accident reports from six states of the United States were evaluated. The states and reports were selected via a stratified two stage cluster sampling system. The results were used to form estimates of the proportion and number of commercial vehicle accidents in the United States with a mechanical defect as a contributing factor. In addition to the accident report sampling, other sources were used to establish a correlation between vehicle defects and commercial vehicle accidents. They include literature, national databases, and post-crash inspections. Results from this study show that approximately 4.6% of all commercial vehicle accidents have a mechanical defect as a factor contributing to the accident. Of these, brakes (1.66%), tires (0.45%), couplings (0.38%), load securement (0.37%), and wheels (0.33%) accounted for the majority. A comparison was also made between the OSU study results and the information gathered from other sources. A cost factor was also used to rank the accidents. The sampled accidents accrued $22.7 million in damage to people and property. The underlying assumption is vehicle defects that are strongly represented in accidents and accident damage estimates should have a strong representation in the out-of-service criteria. / Graduation date: 1997

Traffic safety has been considered one of the most important issues in the transportation field. Crashes have caused extensive human and economic losses. With the objective of reducing crash occurrence and alleviating crash injury severity, major efforts have been dedicated to reveal the hazardous factors that affect crash occurrence. With these consistent efforts, both fatalities and fatality rates from road traffic crashes in many countries have been steadily declining over the last ten years. Nevertheless, according to the World Health Organization, the world still lost 1.24 million lives from road traffic crashes in the year of 2013. And without action, traffic crashes on the roads network are predicted to result in deaths of around 1.9 million people, and up to 50 million more people suffer non-fatal injuries annually, with many incurring a disability as a result of their injury by the year 2020. To meet the transportation needs, the use of expressways (toll roads) has risen dramatically in many countries in the past decade. In fact, freeways and expressways are considered an important part of any successful transportation system. These facilities carry the majority of daily trips on the transportation network. Although expressways offer high level of service, and are considered the safest among other types of roads, traditional toll collection systems may have both safety and operational challenges. The traditional toll plazas still experience many crashes, many of which are severe. Therefore, it becomes more important to evaluate the traffic safety impacts of using different tolling systems. The main focus of the research in this dissertation is to provide an up-to-date safety impact of using different toll collection systems, as well as providing safety guidelines for these facilities to promote safety and enhance mobility on expressways. In this study, an extensive data collection was conducted that included one hundred mainline toll plazas located on approximately 750 miles of expressways in Florida. Multiple sources of data available online maintained by Florida Department of Transportation were utilized to identify traffic, geometric and geographic characteristics of the locations as well as investigating and determination of the most complete and accurate data. Different methods of observational before-after and Cross-Sectional techniques were used to evaluate the safety effectiveness of applying different treatments on expressways. The Before-After method includes Naive Before-After, Before-After with Comparison Group, and Before-After with Empirical Bayesian. A set of Safety Performance Functions (SPFs) which predict crash frequency as a function of explanatory variables were developed at the aggregate level using crash data and the corresponding exposure and risk factors. Results of the aggregate traffic safety analysis can be used to identify the hazardous locations (hot spots) such as traditional toll plazas, and also to predict crash frequency for untreated sites in the after period in the Before-After with EB method or derive Crash Modification Factors (CMF) for the treatment using the Cross-Sectional method. This type of analysis is usually used to improve geometric characteristics and mainly focus on discovering the risk factors that are related to the total crash frequency, specific crash type, and/or different crash severity levels. Both simple SPFs (with traffic volume only as an explanatory variable) and full SPFs (with traffic volume and additional explanatory variable(s)) were used to estimate the CMFs and only CMFs with lower standard error were recommended. The results of this study proved that safety effectiveness was significantly improved across all locations that were upgraded from Traditional Mainline Toll Plazas (TMTP) to the Hybrid Mainline Toll Plazas (HMTP) system. This treatment significantly reduced total, Fatal-and-Injury (F+I), and Rear-End crashes by 47, 46 and 65 percent, respectively. Moreover, this study examined the traffic safety impact of using different designs, and diverge-and-merge areas of the HMTP. This design combines either express Open Road Tolling (ORT) lanes on the mainline and separate traditional toll collection to the side (design-1), or traditional toll collection on the mainline and separate ORT lanes to the side (design-2). It was also proven that there is a significant difference between these designs, and there is an indication that design-1 is safer and the majority of crashes occurred at diverge-and-merge areas before and after these facilities. However, design-2 could be a good temporary design at locations that have low prepaid transponder (Electronic Toll Collection (ETC)) users. In other words, it is dependent upon the percentage of the ETC users. As this percentage increases, more traffic will need to diverge and merge; thus, this design becomes riskier. In addition, the results indicated significant relationships between the crash frequency and toll plaza types, annual average daily traffic, and drivers* age. The analysis showed that the conversion from TMTP to the All-Electronic Toll Collection (AETC) system resulted in an average reduction of 77, 76, and 67 percent for total, F+I, and Property Damage Only (PDO) crashes, respectively; for rear end and Lane Change Related (LCR) crashes the average reductions were 81 and 75 percent, respectively. The conversion from HMTP to AETC system enhanced traffic safety by reducing crashes by an average of 23, 29 and 19 percent for total, F+I, and PDO crashes; also, for rear end and LCR crashes, the average reductions were 15 and 21 percent, respectively. Based on these results, the use of AETC system changed toll plazas from the highest risk sections on Expressways to be similar to regular segments. Therefore, it can be concluded that the use of AETC system was proven to be an excellent solution to several traffic operations as well as environmental and economic problems. For those agencies that cannot adopt the HMTP and the AETC systems, improving traffic safety at traditional toll plazas should take a priority. This study also evaluates the safety effectiveness of the implementation of High-Occupancy Toll lanes (HOT Lanes) as well as adding roadway lighting to expressways. The results showed that there were no significant impact of the implementation of HOT lanes on the roadway segment as a whole (HOT and Regular Lanes combined). But there was a significant difference between the regular lanes and the HOT lanes at the same roadway segment; the crash count increased at the regular lanes and decreased at the HOT lanes. It was found that the total and F+I crashes were reduced at the HOT lanes by an average of 25 and 45 percent, respectively. This may be attributable to the fact that the HOT lanes became a highway within a highway. Moreover adding roadway lighting has significantly improved traffic safety on the expressways by reducing the night crashes by approximately 35 percent. Overall, the proposed analyses of the safety effectiveness of using different toll collection systems are useful in providing expressway authorities with detailed information on where countermeasures must be implemented. This study provided for the first time an up-to-date safety impact of using different toll collection systems, also developed safety guidelines for these systems which would be useful for practitioners and roadway users.