## 3 Results and Discussion
### Bibliometric Analysis of Research on Pavement Management (2000-2013)
#### 3.1.3 Distribution of Output in Journals and Conferences  
The distribution of research subjects can be observed in Table 5, where the 10 most popular categories were compiled. Once again, the categories are non-exclusive, and a document can be related to more than one category, due to interdisciplinary research. The ranking indicated that Engineering was the clear dominant category, with a contribution percentage as high as 82.5%. Social Sciences and Computer Science occupied the 2 nd and 3 rd positions, respectively. Out of these categories, none of the other subjects represented more than 5% contribution. The distribution of outputs in top 13 journals is shown in Table 6, with some data about those journals, like impact factors. The journal that appeared most frequently was _Transportation Research Record_, as more than 150 documents were published in this journal, which represented 20.9% of the total amount of papers. _Journal of Transportation Engineering_ and _Journal of Infrastructure Systems_ completed \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Ranking** & **Author** & **Affiliation** & **Documents** & **Percentage (\%)** \\ \hline
1 & [PERSON] & University of Waterloo & 22 & 3.1 \\
2 & [PERSON]. & Universidade de Coimbra & 20 & 2.8 \\
3 & [PERSON] & University of Waterloo & 11 & 1.5 \\
4 & [PERSON] & National Central University Taiwan & 11 & 1.5 \\
5 & [PERSON] & University of Texas at Austin & 10 & 1.4 \\
6 & [PERSON] & University of South Florida Tampa & 10 & 1.4 \\
7 & [PERSON] & Purdue University & 10 & 1.4 \\
8 & [PERSON] & Michigan State University & 10 & 1.4 \\
9 & [PERSON] & UC Berkeley & 10 & 1.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The top nine most prolific authors. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Ranking** & **Institutions** & **Country** & **Documents** & **Percentage (\%)** \\ \hline
1 & University of Waterloo & Canada & 25 & 3.4 \\
2 & Universidade de Coimbra & Portugal & 22 & 3.0 \\
3 & Texas A and M University & USA & 19 & 2.6 \\
4 & University of Texas at Austin & USA & 17 & 2.3 \\
5 & Tongli University & China & 17 & 2.3 \\
6 & Applied Research Associates Inc. & USA & 14 & 1.9 \\
7 & National Central University Taiwan & Taiwan & 13 & 1.8 \\
8 & Purdue University & USA & 12 & 1.7 \\
9 & Michigan State University & USA & 12 & 1.7 \\
10 & Stantec Inc. & Canada & 12 & 1.7 \\
11 & UC Berkeley & USA & 11 & 1.5 \\
12 & Virginia Polytechnic Inst. and State University & USA & 11 & 1.5 \\
13 & California Department of Transportation & USA & 11 & 1.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The top productive institutions (with more than 10 publications). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Ranking** & **Research Areas** & **Documents** & **Percentage (\%)** \\ \hline
1 & Engineering & 600 & 82.5 \\
2 & Social Sciences & 132 & 18.2 \\
3 & Computer Science & 70 & 9.6 \\
4 & Earth and Planetary Sciences & 28 & 3.9 \\
5 & Environmental Science & 23 & 3.2 \\
6 & Materials Science & 20 & 2.8 \\
7 & Decision Sciences & 16 & 2.2 \\
8 & Mathematics & 14 & 1.9 \\
9 & Physics and Astronomy & 14 & 1.9 \\
10 & Business, Management and Accounting & 12 & 1.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The top 10 most popular subject categories. the podium of the top journals, and two specific journals about pavement, _International Journal of Pavement Engineering_ and _International Journal of Pavement Research and Technology_, were situated in 4 th and 5 th positions, respectively. In addition to the commented journals, several proceedings, corresponding to congresses and conferences celebrated during the analyzed time interval, contributed with more than 5 documents (Table 1). Their total contribution achieved was 11.0%, while the contribution of the journals in Table 5 was 46.8%.