3. Data collection

The crash data used involved 104 intersections belonging to two-lane rural roads in Southern Italy located in a flat area with a vertical grade of less than 5%, that is, 97 non-circular intersections before the Italian Road Design Standard [20] became law and seven single-lane roundabouts were built.

The road surface of the intersection area is paved, and neither space for pedestrian and bicycle use nor space to park vehicles exists by the roadside. In particular, 10% of the typical intersections have exclusive left-turn lanes, a sufficient sight distance for drivers at a stop-controlled or yield-controlled approaches, an acceptable entry and exit edge radius, and a median-refuge island along the legs. Almost all intersections have right-turn lanes on major-road approaches. The mean value of the approaching lane width and departing lane width is 2.70 m, and the average value of the entry and exit radius is 8 m; the average speed on the road segments belonging to the major roads approaching the intersections is around 70 km/h on a road Section 150 m from the intersection area, while on the minor road, it is approximately 45 km/h at the control section and 150 m from the intersection area.

All the single-lane roundabouts analyzed here are of the modern type. There are three conventional roundabouts with an inscribed circle diameter of between 40 and 50 m, three compact roundabouts with an inscribed circle diameter of between 25 and 40 m, and one mini-roundabout with an inscribed circle diameter of between 14 and 25 m. All the roundabouts have one entry lane for each approach as well as for the exit lanes of all the departures with an average entry and exit width of 3.00 m; the circulatory roadway has no lane markings, and the average width is 6.00 m. The circular central island is not practicable, and the average width is 4.00 m. The length of the splitter islands is almost 3.50 m, and the average width is 1.50 m. The average entry radius is 15 m with an exit radius of 25 m. The distance between an entry lane and the first exit lane for the next leg is at least 10 m. Analytical Assessment of Effective Maintenance Operations on At-Grade Unsignalized… DOI: http://dx.doi.org/10.5772/intechopen.86435

The main features of each crash as identified by analyzing the crash reports were as follows: the location where the crashes happened, the number of crashes, injuries, and fatalities, type of crash, type, and number of vehicles involved, road surface conditions, lighting conditions, marking conditions, the number of legs and lanes, lane width, AADTmaj, that is, the AADT on major roads in terms of vehicles per day, and AADTmin, that is, the AADT on minor roads in terms of vehicles per day, the presence of left-turn lanes, median-refuge islands, right-turn lanes, and the diameter of the roundabouts.

A total of 827 crashes were recorded in 5 years. The geometric features of each investigated intersection (see Table 1) were established from documents made available by the Regional Administrative Offices. A total of 770 crashes were observed at non-circular intersections, 623 of which were injury crashes, and 147 involved property damage only (PDO) crashes; a total of 1025 injuries were recorded at non-circular intersections, and 12 fatalities occurred. A total of 57 crashes were observed at single-lane roundabouts, of which 36 were injury crashes and 21 PDO crashes; a total of 57 injuries were recorded at single-lane roundabouts, and no fatalities occurred.

The crash value for each intersection shows the number of crashes over a 5-year study period, while the frequency of injury crashes refers to the number of injury crashes per year at each intersection during the study period. Figure 2a shows that


Note: Min—minimum value; Mean—average value; Max—maximum value; C.V.—coefficient of variation, equal to the standard deviation divided by the mean value.

#### Table 1.

• Modifying the configuration into a roundabout to achieve benefits in terms of a reduction of conflict points, vehicle speed reduction around the

f. Assessing the effectiveness of risk management: comparing before and after configurations of the hotspots by calculating the expected LoS and the

In greater detail, the expected LoS effects were calculated following HCM2016 procedure, but revising, in the light of measurements obtained at study sites; on the other hand, the expected computation of safety effects was performed by adopting the Safety Performance Function (SPF) introduced in [16] according to Highway Safety Manual (HSM) 2010 [17] procedure but revised in the light of study carried out in Southern Italy to which the intersections investigated here belong. Calculation of the expected safety effects obtained from converting the intersections to roundabouts was performed by (a) adopting the analytical models proposed in Rodegerdts et al. [18, 19], whose calibration conditions fit the study context presented here and (b) by using EB analysis to quantify the positive advance of

This book chapter is organized as follows: Section 2 focuses on data collection, while Section 3 focuses on data analysis for evaluating measures that reflect the exposure of sites to crash risk; the results of the case study are displayed and

The crash data used involved 104 intersections belonging to two-lane rural roads in Southern Italy located in a flat area with a vertical grade of less than 5%, that is, 97 non-circular intersections before the Italian Road Design Standard [20] became

The road surface of the intersection area is paved, and neither space for pedestrian and bicycle use nor space to park vehicles exists by the roadside. In particular, 10% of the typical intersections have exclusive left-turn lanes, a sufficient sight distance for drivers at a stop-controlled or yield-controlled approaches, an acceptable entry and exit edge radius, and a median-refuge island along the legs. Almost all intersections have right-turn lanes on major-road approaches. The mean value of the approaching lane width and departing lane width is 2.70 m, and the average value of the entry and exit radius is 8 m; the average speed on the road segments belonging to the major roads approaching the intersections is around 70 km/h on a road Section 150 m from the intersection area, while on the minor road, it is approximately 45 km/h at the control section and 150 m from the intersection area. All the single-lane roundabouts analyzed here are of the modern type. There are three conventional roundabouts with an inscribed circle diameter of between 40 and 50 m, three compact roundabouts with an inscribed circle diameter of between

25 and 40 m, and one mini-roundabout with an inscribed circle diameter of between 14 and 25 m. All the roundabouts have one entry lane for each approach as well as for the exit lanes of all the departures with an average entry and exit width of 3.00 m; the circulatory roadway has no lane markings, and the average width is 6.00 m. The circular central island is not practicable, and the average width is 4.00 m. The length of the splitter islands is almost 3.50 m, and the average width is 1.50 m. The average entry radius is 15 m with an exit radius of 25 m. The distance between an entry lane and the first exit lane for the next leg is at least 10 m.

central island, and pedestrian safety [5, 17, 18].

intervention, a common statistical practice in the scientific literature.

law and seven single-lane roundabouts were built.

discussed in Section 4.

3. Data collection

166

expected safety effects in terms of crash frequency.

Transportation Systems Analysis and Assessment

Overview of the main statistical features of the crashes and the intersection type.

#### Figure 2.

Hazard maps of injury crash frequency. (a) Crashes vs geometric properties of lanes. (b) Crashes vs traffic and geometric properties.
