Research Trends and Results

Reliability index
transportation

onRoad Department Traffic Engineering Division

travelingtimeinroad

Research Coordinator : Mr. Kenji MOROTA
Senior Researcher : Mr. Hirotaka SEKIYAHead (Doctor of Academy) : Dr. Susumu TAKAMIYA（Key word）Road transportation, Travelling time reliability, Probe data
[In case departuretime 7:00 in week day]
【平日7：00出発の場合】

90%
累積確率分布50%

50% tile
90% tile
50%タイル
90%タイル
Traveling time Traveling
旅行時間（中央値）
旅行時間time(medium55min.
30分value)
55分

Travelingtime
旅行時間30 min.

Figure 1. Distribution of traveling time and 90% tile traveling time90%[Criteria]【判定基準】
Satisfy median of sample data and 90% tile
サンプルデータの中央値及び90%タイ
value satisfy condition A and B
ル値がA及びBの条件を満たす
A: Within + 2.5% or -2.5% of true value
真値の中央値±2.5%以内
B:AWithin+ 2.5% or -2.5% of 90% tile value
B 真値の90%タイル値±2.5%以内

80%
70%
60%

外れ率

Fringe ratio

2. What is travelling time reliability index?
Travelling time reliability is intending to indicate
reliability of the travelling time of variability to the samezone. 「90% tile traveling time」is frequently used astraveling time reliability index.
This travelling index「90% tile traveling time」indicatesthat 90% of days (9 days out of 10 days) can be traveledwithin 55 minutes and remaining 10% (1 day out of 10days ) is required more than 55 minutes when 90% tile
traveling time is 55 minutes and reliability in the sametime zone is targeted for example as shown in Figure 1..

100%

Accumulated probability

1. Preface
Recently, large number of data can be available bydevelopment
ofinformation
technology
andunderstanding of travelling time for running vehicle ingiven zone is also becoming possible.
Road Laboratory Room is conducting concerning
calculating method of travelling time reliability index byusing this probe data.

50%[Numberof days less than 10% fringe ratio obtained]【外れ率10%を下回るデータ取得日数】
Missingzone length ratio 0% ----morethan 28 days
欠測区間長割合0%
28日以上
Missingzone length ratio 0% ----morethan 32 days
欠測区間長割合10%
32日以上
Missing zone length ratio 0% ----more than 33 days

40%
30%

欠測区間長割合20%

33日以上

20%
10%
2
4681012141618202224
26
2830
32
3436
38
40
42
44
46
48
5052
5456
58
60

0%

3. Relation analysis between data missing state andcalculation accuracy
To execute accurate analysis, correct data acquisition isrequired. Not always proof data can be adequately
available during analysis targeted time zone. It is
assumed that required accuracy for travel time reliability
index could not be secured when data missing are many.
So analysis is executed targeting at relation between data
missing state and accuracy of traveling time reliability
index. As an analysis example of targeted 30km zone thatdata acquisition at 7 in the morning was made for 60 days
was analyzed and introduced in this report. Following areprocedure of analysis.
(1) Medium value and 90% tile value during travelingtime are calculated based on acquired all the data.
(These values are assumed as true values.)(2) For all the calculated values in procedure (1) areassumed acquired data temporary setting missingzone and acquired date.
(3) Calculate medium value and 90% tile value using
obtained data in procedure (2) and assess if the datasatisfy the criteria shown in Figure2.

Data obtained days
データ取得日数
欠測区間長割合0%Data missing zone ratio: 0%

欠測区間長割合10%
Data missing zone ratio: 10%欠測区間長割合20%
Data missing zone ratio: 20%

Figure 2. Relationship between the situation of
missing data and calculation accuracy(4) Every data missing zone length ratio (0%, 10%, and20%) and data acquired days (from 2 days to 60 days)
repeat procedure (2) 1,000 times in random mannerthen calculate fringe ratio (ratio that the value is notsatisfied the criteria in process (3).
Analyzed result is shown in Figure 2. Naturally themore missing ratio is improved the more accuracy isimproved. Figure 2 indicates that more than 33 dataacquired days out of 60 days are required to obtain 10%
fringe ratio when data missing zone length ratio is 20%.
By using this method accuracy can be presented fromindex value obtained from acquired data.
In future we are going to summarize calculation
method of travel time reliability index as manual
including knowledge obtained from this study adding
further analysis.