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Table 1 Descriptive statistics of potential crash predictors for segments and intersections

From: The variability of urban safety performance functions for different road elements: an Italian case study

Variables [for segments] Modalities Homogeneous Segments
(n = 320a)
One-way homogeneous segments
(n = 190)
Two-way homogeneous segments
(n = 130)
Mean (st. dev.)/ Counts Min-max/ Percentages Mean (st. dev.)/ Counts Min-max/ Percentages Mean (st. dev.)/ Counts Min-max/ Percentages
Fatal+Injury (F + I) crashes Numerical 689 283 406
F + I crashes/segment/year Numerical 0.43 (0.86) 0–6 0.30 (0.68) 0–5 0.63 (1.03) 0–6
One-way 0 – No (two-way) 0–130 0–0.41 0–0 0–0.00 0–130 0–1.00
1 – Yes 1–190 1–0.59 1–190 1–1.00 1–0 1–0.00
One-lane 0 –No (multilane) 0–226 0–0.71 0–96 0–0.51 0–130 0–1.00
1 – Yes 1–94 1–0.29 1–94 1–0.49 1–0 1–0.00
AADT Numerical 8637.2 (5889.3) 300.0–29,960.0 6228.8 (4569.5) 300.0–22,600.0 12,157.1 (5843.5) 1160.0–29,960.0
Length (m) Numerical 138.3 (183.3) 30.0–1510.0 124.1 (175.4) 30.0–1510.0 159.1 (193.0) 30.0–1415.0
Speed Limit = 50 km/h 0 – Yes 0–309 0–0.97 0–190 0–1.00 0–119 0–0.92
1 – No (>  50 km/h) 1–11 1–0.03 1–0 1–0.00 1–11 1–0.08
Road width (m) Numerical 10.5 (3.0) 4.1–28.0 9.9 (2.6) 5.5–20.0 11.3 (3.5) 4.1–28.0
Type of lanes 0–1 lane 0–116 0–0.36 0–116 0–0.61 0–0 0–0.00
1 – >  1 lane (up to 3) 1–74 1–0.23 1–74 1–0.39 1–0 1–0.00
2–1 + 1 lane 2–89 2–0.28 2–0 2–0.00 2–89 2–0.68
3 – >  1 + 1 lanes (up to 3 + 3) 3–41 3–0.13 3–0 3–0.00 3–41 3–0.32
Density of minor roads/ driveways per km Numerical 26.9 (26.0) 0.0–143.0 22.4 (22.8) 0.0–142.9 33.3 (28.9) 0.0–143.0
Vertical signs on minor roads/ driveways 0 – No 0–256 0–0.80 0–158 0–0.84 0–98 0–0.75
1 – Yes 1–64 1–0.20 1–32 1–0.16 1–32 1–0.25
Poor maintenance of pavements 0 – No 0–71 0–0.22 0–49 0–0.26 0–22 0–0.17
1 – Yes 1–249 1–0.78 1–141 1–0.74 1–108 1–0.83
Road markings 0 – No/Partially absent or illegible 0–60 0–0.19 0–24 0–0.13 0–36 0–0.28
1 – Illegible 1–124 1–0.39 1–82 1–0.43 1–42 1–0.32
2 – Yes 2–136 2–0.42 2–84 2–0.44 2–52 2–0.40
Parking type 0 – Prohibited 0–85 0–0.27 0–26 0–0.14 0–59 0–0.45
1 – One side 1–109 1–0.34 1–74 1–0.39 1–35 1–0.27
2 – Both sides 2–119 2–0.37 2–87 2–0.46 2–32 2–0.25
3 – Mixed 3–7 3–0.02 3–3 3–0.02 3–4 3–0.03
Cycle paths 0 – No 0–291 0–0.91 0–163 0–0.86 0–128 0–0.98
1 – Yes 1–29 1–0.09 1–27 1–0.14 1–2 1–0.02
Sidewalks 0 – No 0–31 0–0.10 0–4 0–0.02 0–27 0–0.21
1 – Yes 1–289 1–0.90 1–186 1–0.98 1–103 1–0.79
Median 0 – No 0–244 0–0.76 0–114 0–0.60 0–130 0–1.00
1 – Yes 1–76 1–0.24 1–76 1–0.40 1–0 1–0.00
Bus stop 0 – No 0–227 0–0.71 0–143 0–0.75 0–84 0–0.65
1 – Yes 1–93 1–0.29 1–47 1–0.25 1–46 1–0.35
Bus/taxi lane 0 – No 0–284 0–0.89 0–154 0–0.81 0–130 0–1.00
1 – Yes 1–36 1–0.11 1–36 1–0.19 1–0 1–0.00
Land use 0 – Residential 0–115 0–0.36 0–71 0–0.37 0–44 0–0.34
1 – Mainly commercial 1–150 1–0.47 1–110 1–0.58 1–40 1–0.31
2 – Other 2–55 2–0.17 2–9 2–0.05 2–46 2–0.35
Variables [for intersections] Modalities Intersections
(n = 120a)
Three-legged intersections
(n = 48)
Four-legged intersections
(n = 72b)
Mean (st. dev.)/ Counts Min-max/ Percentages Mean (st. dev.)/ Counts Min-max/ Percentages Mean (st. dev.)/
Counts
Min-max/ Percentages
Fatal+Injury (F + I) crashes Numerical 906 232 674
F + I crashes/intersection/year Numerical 1.51 (1.84) 0–15 0.97 (1.41) 0–15 1.87 (1.99) 0–12
Traffic lights 0 – No 0–59 0–0.49 0–38 0–0.79 0–21 0–0.29
1 – Yes 1–61 1–0.51 1–10 1–0.21 1–51 1–0.71
Type = 4 legs 0 – No 0–48 0–0.40 0–48 0–1.00 0–0 0–0.00
1 – Yes 1–72 1–0.60 1–0 1–0.00 1–72 1–1.00
Main AADT Numerical 12,192.4 (5313.2) 2475.0–23,680.0 12,588.4 (5350.8) 3550.0–22,340.0 11,928.4 (5309.1) 2475.0–23,680.0
Secondary AADT Numerical 5084.1 (4271.5) 300.0–17,880.0 4008.3 (3897.4) 300.0–18,520.0 5801.4 (4384.2) 345.0–17,880.0
Total AADT Numerical 17,276.5 (7981.8) 4175.0–41,560.0 16,596.6 (7018.3) 5420.0–32,300.0 17,729.7 (8582.2) 4175.0–41,560.0
Main AADT/ Total AADT Numerical 0.53 (0.03) 0.50–0.62 0.55 (0.03) 0.50–0.62 0.53 (0.02) 0.50–0.61
Lane balance 0 – No 0–81 0–0.67 0–38 0–0.79 0–43 0–0.60
1 – Yes 1–39 1–0.33 1–10 1–0.21 1–29 1–0.40
Median on the main road 0 – No 0–100 0–0.83 0–48 0–1.00 0–52 0–0.72
1 – Yes 1–20 1–0.17 1–0 1–0.00 1–20 1–0.28
Median on the secondary road 0 – No 0–107 0–0.89 0–43 0–0.90 0–64 0–0.89
1 – Yes 1–13 1–0.11 1–5 1–0.10 1–8 1–0.11
Entering lanes on the main road Numerical 1.5 (1.1) 0.0–5.0 1.1 (1.0) 0.0–4.0 1.8 (1.1) 0.0–5.0
Mean lane width at intersections (m) Numerical 4.5 (1.1) 2.8 (8.7) 4.3 (1.0) 2.8–6.6 4.6 (1.2) 2.8–8.7
Critical sight distance (m) Numerical 31.2 (26.0) 0.0–139.5 30.0 (28.1) 0.0–139.5 32.0 (24.6) 1.6–100.0
One-way legs Numerical 1.7 (1.5) 0.0–4.0 1.4 (1.1) 0.0–3.0 2.0 (1.6) 0.0–4.0
Specialized turning lane 0 – No 0–88 0–0.73 0–43 0–0.90 0–45 0–0.63
1 – Yes 1–32 1–0.27 1–5 1–0.10 1–27 1–0.37
Traffic control 0 – No 0–22 0–0.18 0–16 0–0.33 0–6 0–0.08
1 – Give-way/Stop 1–37 1–0.31 1–22 1–0.46 1–15 1–0.21
2 – Traffic lights 2–35 2–0.29 2–7 2–0.15 2–28 2–0.39
3 – Traffic lights with dedicated turning 3–26 3–0.22 3–3 3–0.06 3–23 3–0.32
Poor maintenance of pavements 0 – No 0–18 0–0.15 0–9 0–0.19 0–9 0–0.13
1 – Yes 1–102 1–0.85 1–39 1–0.81 1–63 1–0.87
Cycle path crossing 0 – No 0–103 0–0.86 0–36 0–0.75 0–67 0–0.93
1 – Yes 1–17 1–0.14 1–12 1–0.25 1–5 1–0.07
Sidewalks 0 – No 0–8 0–0.07 0–3 0–0.06 0–5 0–0.07
1 – Yes (both sides) 1–112 1–0.93 1–45 1–0.94 1–67 1–0.93
Bus stops 0 – No 0–111 0–0.93 0–46 0–0.96 0–65 0–0.90
1 – Yes 1–9 1–0.07 1–2 1–0.04 1–7 1–0.10
Bus/taxi lanes on intersecting roads 0 – No 0–92 0–0.77 0–43 0–0.90 0–49 0–0.68
1 – Yes 1–28 1–0.23 1–5 1–0.10 1–23 1–0.32
  1. aNote: Five segments were discharged from the initial dataset due to segment length minor than 30 m, which were deemed as irrelevant for safety modelling purposes. Two intersections were discharged from the initial dataset due to possible errors in the counts of traffic volumes, leading to unrealistic data
  2. bThese intersections include one five-legs intersection