In the last thirty years, determined travelers have developed a new method of travel that allows them to receive the benefits of traveling on the HOV lane without forming traditional carpools. This new mode is known as casual carpooling (also known as ??slugging??). Casual carpools are impromptu carpools formed among strangers in order to meet the occupancy requirements of HOV lanes. In this research, survey respondent data from Houston, Texas were used to evaluate the behavior of casual carpool passengers. At the time of this research, there were approximately 500 casual carpool passengers in Houston each day during the morning peak period. These passengers gained time savings of up to 13 minutes over the alternative of driving alone on the main lanes. Statistical models were used to evaluate the factors that influence travelers to choose casual carpooling. The results of the analyses indicated that travelers on commute trips were more likely to casual carpool. The results also indicated that casual carpoolers in Houston made more trips per week, were between the ages of 25 and 34, and hadoccupations that were either professional/managerial or administrative/clerical. Additionally, Houston travelers that had incomes between $25,000 and $35,000 and were between the ages of 55 and 64 were significantly less likely to casual carpool. The research results provided insight into some of the factors that influenced the decision to casual carpool. It is important to understand the types of travelers that casual carpooled, and the information learned in these analyses can be used to better evaluate HOV and HOT lane use and performance. Casual carpool passengers can comprise a significant portion of HOV/HOT lane person movement and should be considered when considering HOV or HOT lane implementation. However, further research in this area is necessary to better understand these travelers.

High-Occupancy toll (HOT) lanes allow lower-occupant vehicles (LOVs) to use a HOV lane for a fee, while maintaining free travel to qualifying HOVs. HOT lanes are gaining interest throughout the country as a strategy for meeting multiple performance objectives in congested urban freeway corridors. Currently there are ten fully operational HOT lanes around the country in seven different states and this research examined the nine of them (excluding I-35 W). Even with only a handful of operational HOT lane projects, there is great diversity in terms of HOT lane design and operations. With HOT lane implementation there are many issues, including: toll rates, vehicle occupancy requirement, number of access points, and safety. This research examined (i) the different factors which lead to the development of the HOT lanes in their respective corridors (ii) the objectives of the HOT lanes (iii) changes made in the corridor due to HOT lane implementation (iv) the different impacts of the HOT lanes and (v) the extent to which the objectives of the HOT lanes were achieved. Using three pairs of HOT lanes with similar design and operational characteristics, comparisons were made to examine the impacts of the similar HOT lanes in two different corridors. With the strict registration requirement for HOV3+ on the I-95 Express Lanes there were indications that some carpoolers broke up in to lower occupancy vehicles. Tolled access for HOV2s on I-95 as well as the SR 91 Express Lanes resulted in lower usage of the Express Lanes by the HOV2s (fewer than 30 percent of the total corridor HOV2s) as compared to a conventional HOV lane (60 percent) where HOV2 access is free. The effect of availability of transit on the HOT lanes can also be seen from SR 91 as compared to I-95. On SR 91, the Express bus does not use the Express Lanes and there was almost no change in its ridership after the Express Lanes were implemented. However, on I-95, the Express bus uses the Express Lanes and travel time of buses decreased by 17 minutes due to Express Lanes implementation. The Express bus ridership also increased by 30 percent. On the SR167 and I-25 HOT lanes, the exogenous factors like gas prices and economic recession seemed to influence the usage of the HOT lanes. In both the HOT Lanes, carpool usage was positively correlated to the gasoline prices. On I-25, the increasing unemployment rate coincided with the decreasing toll paying travelers. On SR 167 there were also indications of mode shifts among the transit, carpool and toll paying SOVs due to fluctuating gas prices. With declining gas prices, the transit and carpool usage went down while toll paying users increased. An inverse relationship between the convenience of access points and the safety perceived by the HOT lane users was found. For example, I-15 Express Lanes in Salt Lake City reduced the access points from unrestricted with the previous HOV lanes to limited with the Express Lanes. As a result, more predictable merging led to an increase in the perceived safety of the Express lanes as well as the speed of the corridor. On the other hand, some carpoolers mentioned not using the Express Lanes anymore because of access inconvenience. The access inconvenience was also mentioned by previous carpoolers in HOV lanes on I-95 as one of the reasons for not using the Express Lanes. These findings underscore the importance of outreach programs during the planning process of the HOT lanes to minimize the confusion among the previous users of the HOV lanes and spreading awareness among them regarding the increased safety benefits.

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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.