deletions | additions       diff --git a/subsection_Merging_Zone_The_reasoning__.tex b/subsection_Merging_Zone_The_reasoning__.tex  index 109d47b..a5b29e3 100644  --- a/subsection_Merging_Zone_The_reasoning__.tex  +++ b/subsection_Merging_Zone_The_reasoning__.tex 
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While the sites are selected to control for as many factors as possible, inevitably, some variation between sites still exists, especially regarding traffic volumes and patterns; these are identified such that they may be controlled during analysis. Table~\ref{tab:analysis_zones} lists a summary of the merging zones at each roundabout studied and any remaining variable geometric and land use characteristics, as well as a summary of historical accident data at each roundabout. Quality of the available historical accident data is relatively poor, with sampling periods ranging between 2 and 15 years (average of 7) and data missing entirely at one roundabout. Furthermore, this historical accident data is representative of the entire roundabout instead of the merging zone exclusively since accident geolocation is often not fine enough to distinguish roundabout merging zones (this is especially true for the Québec data). These problems justify using surrogate safety measures for this study, and more generally. In any case, the pattern in this data is consistent with regional trends in accidents cited earlier: accidents are twice as likely in Québec than in Sweden, even at comparable sites, suggesting that unexplained effects can be found between the sites selected.    \begin{table}  \caption{Merging Zones Zone  Inventory} \label{tab:analysis_zones}  \begin{tabular}{llllllllll}  \hline 
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Ruben Rausings gata/Borgs väg-2 & Mixed & Low & 22.0 & 121.4 & 0.568 & 2010 & 1.5 \\  Svenshögs/Norra Gränsvägen-1 & Residential & Low & 16.5 & 191.0 & -0.417 & 1995 & 1.4 \\  Svenshögs/Norra Gränsvägen-2 & Residential & Low & 16.5 & 142.9 & 0.054 & 1995 & 1.4 \\  \textbf{MEAN} \textbf{MEAN (Sweden)}  & & & \textbf{21.5} & \textbf{239.9} & \textbf{0.270} & \textbf{1995} & \textbf{1.8} \\ \hline   des Soeurs/du Golf & Residential & Medium & 25.0 & 315.1 & -0.327 & 2004 & 7.0 \\ %Québec Accident data is over a 4-7 year period  des Soeurs/Rene-Levesque & Residential & Low & 22.5 & 178.8 & 0.421 & 2003 & 1.4 \\  
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St-Emilie/St-Denis & Residential & Low & 18.5 & 46.6 & 0.112 & 2005 & 1.0 \\   Talbot/Jacques-Cartier-1 & Mixed & Medium & 18.0 & 150.8 & 0.608 & 2004 & 7.7 \\   Talbot/Jacques-Cartier-2 & Mixed & Medium & 18.0 & 238.6 & 0.534 & 2004 & 7.7 \\   \textbf{MEAN} \textbf{MEAN (Québec)}  & & & \textbf{19.5} & \textbf{152.3} & \textbf{0.186} & \textbf{2004} & \textbf{4.19} \\ \hline  \end{tabular}  * No construction date available. Date is estimated from historical aerial footage and carries an uncertainty of $\pm~2$ years. $\pm~2$~years.  \end{table} %flows last updated Sept-10  In addition to the flow rate, the flow ratio governs how many interactions occur across the merging zone, and of what nature they tend to be since expected behaviour is asymetric between approaching road users and conflicting (within the roundabout) road users. The flow ratio is defined as  \begin{equation} \label{eqn:flow_ratio} Flow ratio=\frac{Q_{app}-Q_{conf}}{Q_{app}+Q_{conf}} \end{equation} 
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Speed is widely regarded in the literature as a predictor of collision severity \citep[e.g.][]{Fildes_1993, elvik2004speed}. Meanwhile, TTC is one of the most popular surrogate safety measures intended as a predictor of collision probability (as it models near-misses). yPET is of interest as a model of yielding behaviour and merging aggressivity (it is related to gap time and gap acceptance).  In addition to the surrogate safety measures outlined above, additional measures of behaviour describing instantanteous collision-course conditions are stored alongside each collision-course (and TTC measure). These include 15-second exposure, a micro-mesure of exposure, which counts the number of road users present within the merging zone 7.5~seconds before and after the collision course is modeled, and intersection angle, which measures the angle of approach of the road users at the instant of the collision course in degrees. This angle is $0^{\circ}$ when the road users are following each other and $180^{\circ}$ when approaching other head on.