ITE Journal - March 2021 - 26

Safety
The safety analysis from this study included 343 sites, which
consisted of 186 PHB crossings, 56 signalized intersections, and
101 unsignalized intersections. The variables considered in the
safety analyses are listed in Table 3. There were 52 PHBs installed
between 2011 and 2015 that were identified for use in the before-after empirical Bayes (EB) analysis. PHB installation dates were
Table 3. Roadway Variables Considered in Safety Analyses.
Variable
C_Lanes
Legs
M_Bike_01
M_Lanes
M_LTL
M_LTL_A
M_MT
M_MT_R
M_PK_01
Ped or
PB_Vol_MC
PSL
PSL_group
Sig_Dist
Veh

Description
Cross: total number of lanes on the cross street
Number of legs at the intersection (2, 3, or 4), 2-legs =
midblock crossing
Major: is a bike lane present? (1=bike lane on one or both
sides, 0=none)
Major: number of through lanes
Major: is a left-turn lane present on the major street
(0=neither approach has a left-turn lane, 1=at least one of
the approaches has a left-turn lane)
Major: number of approaches with an exclusive left-turn
lane (0, 1, or 2)
Major: median type (raised, TWLTL, none, flush)
Major: median type (Raised (0) = raised, Not Raised (1) = all
others e.g., flush, TWLTL, none)
Major: is a parking lane present? (1=parking lane on one or
both sides, 0=none)
Daily number of pedestrians at the intersection, sum of the
pedestrian volume on the major and on the cross street
Major: posted speed limit (mph)
Major: the posted speed limit for the main street grouped
into either 35 mph and below or 40 mph and higher
Major: distance between the PHB and the nearest traffic
signal in feet
Major: daily number of vehicles on the major street, also
called average daily traffic (ADT)

obtained from the various government agencies. Reference groups
consisting of signalized and unsignalized intersections were chosen
from intersections in close proximity to the 52 before-after PHB
sites and were used in the EB before-after analysis. In all cases, no
other major roadway or geometric changes were made other than
PHB installation at the PHB sites during the study period. Table 4
summarizes the descriptive statistics for these sites.

Each reference group has potential limitations; therefore, the
research team considered three different reference groups:
ƒ	 Unsignalized intersections
ƒ	 Signalized intersections
ƒ	 Both unsignalized and signalized intersections combined

For the signalized and combined unsignalized and signalized
intersection groups, all crash types considered showed statistically significant reductions in crash frequency (e.g., total crashes,
fatal and injury crashes, rear-end crashes, fatal and injury
rear-end crashes, angle crashes, fatal and injury angle crashes,
pedestrian-related crashes, and fatal and injury pedestrian-related crashes) as shown in Table 5. Previous studies have also
Table 5. Results of EB before-after safety evaluations based on 52 PHB
sites using unsignalized intersections and signalized intersections as a
reference group.
Crash Type
Total
Fatal and injury
Pedestrian related
Fatal and injury pedestrian related
Rear end
Fatal and injury rear end
Angle
Fatal and injury angle

Percent Crash
Reduction at PHBs
18.2**
25.2**
45.7**
45.0**
20.5**
28.6**
22.6**
24.5*

Statistical level indications:
* Statistically significant results with 90 percent confidence level
** Statistically significant results with 95 percent confidence level

Table 4. Descriptive Statistics for PHB sites used in EB Before-After Evaluations.
Variablea
Legs
M_Lanes
M_LTL
M_PK_01
M_Bike_01
C_Lanes
Veh (Period AADT)
PB_Vol_MC
M_MT_R, Value (# of sites)

PHB (52 sites)
Min
Max
Avg
2
4
3.3
2
7
5.0
0
2
0.9
0
1
0.1
0
1
0.6
0
3
1.3
5,400
47,627
23,959
10
1,670
297
Not Raised (33), Raised (19)

Note: a See Table 3 for description of roadway variables.

26

Ma rch 2021

ite j o u rn al

Unsignalized intersections (101 sites)
Min
Max
Avg
2
4
3.6
2
9
5.3
0
2
1.5
0
1
0.1
0
1
0.6
0
6
1.6
4,937
47,627
24,377
10
480
99
Not Raised (69), Raised (32)

Signalized intersections (56 sites)
Min
Max
Avg
3
4
3.9
2
10
5.5
0
2
1.9
0
1
0.1
0
1
0.6
2
12
6.0
5,400
48,512
24,421
30
1,520
308
Not Raised (35), Raised (21)



ITE Journal - March 2021

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