Information Technology Reference
In-Depth Information
Table 1.
Input and output variables and their corresponding modified name in fuzzy logic
Variable category
Variable name
Denoted in FLM
Length
Length
Number of access points/intersecting links
IntLnks
Number of pedestrian crossings
PedCros
Input variables
Volume to capacity (V/C) ratio
VCRat
Hourly pedestrian volume
PedVol
Posted speed limit
PostSp
85
th
percentile speed
Output variable
SpEF
3.1
Development of Initial Fuzzy Logic Model
The development of initial models involves three major steps- fuzzification (convert-
ing numeric variables into linguistic terms), fuzzy inference (knowledge base- 'IF-
THEN' logics) and de-fuzzification (converting linguistic terms into numeric output
values).
3
.
1.1 Fuzzification
The input and output variables are numeric in nature. The drivers mostly perceive
these as linguistic terms. For example, the traffic volume may be perceived as high or
medium or low rather than its actual numeric values. As such, the numeric values of
each input variables were converted into three linguistic terms and the values of the
output variable has been converted into five linguistic terms (Table 2). The minimum
and maximum values of each variable were determined from the survey results. It is
to be noted that the variability of data for the output variable is high and grouping
these data into more linguistic terms might result in more accurate estimation of the
output variable. On the other hand, three terms have been selected for the input va-
riables due to low variability of the data. It will also reduce the number of rule bases
and neuro-fuzzy training time.
Table 2.
The proposed FLM variables term definitions
Variable name
Day of the Week
Min
Max
Linguistic terms
Length
Weekday, Weekend
0.46
2.94
Low, medium, high
IntLnks
Weekday, Weekend
4
11
Low, medium, high
PedCros
Weekday, Weekend
0
3
Low, medium, high
Weekday
0.08
1.03
VCRat
Low, medium, high
Weekend
0.07
1.13
Weekday
0
184
PedVol
Low, medium, high
Weekend
0
156
PostSp
Weekday, Weekend
40
80
Low, medium, high
Weekday
13.9
109.9
Very low, low, medium, high, very
high
SpEF
Weekend
22.36
124.89
