# Road Safety Management of Uncontrolled Access Points:
## 3 Results and Discussion
### The Relationship between Traffic Accidents and the Radius and Width of the Access  
The literature overview suggested that the safety conditions of access points are affected by the variability of some geometry-related parameters. In particular, according to several studies, the width (\(\mathrm{L_{a}}\)) and the entry radius (\(\mathrm{R_{i}}\)) of an access point are the most relevant variables that affect the safety and operational level [5; 12; 17]. In this section of the study these variables are considered through the synthesis parameter \(\mathrm{L_{a}}/\mathrm{R_{i}}\) with the following main purposes:  
* quantitative analysis of the relationship between safety and the concomitant variability of the entry radius and the width of the access point;
* definition of a variation domain of \(\mathrm{L_{a}}/\mathrm{R_{i}}\) aimed at minimizing/mitigating accident phenomena. The following hypotheses were taken into account:  
* the ratio \(\mathrm{L_{a}}/\mathrm{R_{i}}\) was evaluated for each uncontrolled access point; except for \(\mathrm{T_{3,j}}\) entry class accesses (not curved edge);
* the value \(\mathrm{R_{i}}\) = 0.2 m was established for \(\mathrm{T_{2,j}}\) entry class accesses (the presence of curbs or hedges does not allow to measure of a physical curved edge);
* a value for \(\mathrm{R_{i}}\) was estimated for \(\mathrm{T_{4,j}}\) entry class accesses simulating the potential trajectory of the entry vehicle;
* access points with the implementation of the following access management measures were included in the analysis: AM_3 (frontage or service roads/shared access), AM_4 (left-turn acceleration lane), and their combination; access points with right-turn acceleration/deceleration lane (AM_1) or channelizing island (AM_2) were excluded from the analysis: AM_1 does not imply an entry manoeuvre in the access interfering with the main traffic flow as there is a dedicated lane; furthermore, the presence of the channelizing island (AM_2) does not allow to establish a direct relationship between the width and the radius of the access point. Twelve classes of variation were identified relating to the values of \(\mathrm{L_{a}}/\mathrm{R_{i}}\). Classes distinction is based on previous studies [5; 17; 39; 44; 45]; more specifically, the lower threshold (\(\mathrm{L_{a}}/\mathrm{R_{i}}\) = 4.89) was obtained from the ratio between \(\mathrm{L_{a,max}}\) = 7.34 m (obtained averaging the maximum values found in the literature) and \(\mathrm{R_{i,min}}\) = 1.5 m (obtained averaging the minimum values found in the literature). This choice is motivated by previous research, which reports that a large width should compensate for the presence of a small radius. An additional class was added to better investigate the variation of the dependent variable  
Figure 8: Pedestrians involved in driveway-related accidents for each access connection transition shape. in the range 0.23-4.89 ((\(\rm{L_{a}/R_{i}}\))\({}_{\rm{min}}\) = 0.23 in this study) since the sample size within this range is very large. In light of the above, the first class includes values lower than 2.45 (the midpoint of the range 0.23-4.89). As regards the accident rate, TIG (Global Accident Rate) was used. TIG for the i-th section is defined as follows [46]:  
\[\rm{(TIG)_{i}=\frac{10^{8}\cdot N_{i}}{M_{i}}} \tag{5}\]  
where \(\rm{N_{i}}\) is the number of traffic accidents in sections i-th; \(\rm{M_{i}}\) is estimated for a period of x years in this way:  
\[\rm{M_{i}=365\cdot L_{i}\cdot\sum\limits_{j=1}^{x}(AADT)_{j}} \tag{6}\]  
where \(\rm{L_{i}}\) is the length of the section (in kilometres), (\(\rm{AADT}\))\({}_{\rm{i}}\) is the annual average daily traffic (for the jth year). In this study \(\sum\limits_{j=1}^{5}(AADT)_{j}=58,235\) veh/day [47]. The Global Accident Rate was estimated for each section with an access point; the length of section \(\rm{L_{i}}\) was assumed to be equal to the functional area \(\rm{L(AF)_{i}}\); \(\rm{N_{i}}\) is the number of accidents recorded in the functional area of the access.