## 3 Results
### Descriptive Analysis: Publication Development
#### 3.1.3 Contributions and Collaborations of Countries and Affiliations  
Forty-nine countries or territories contributed to the digitization of transportation literature in the WoS and Scopus databases. The collaboration of countries is illustrated in Figure 5.  
The sizes and colors of the countries are based on their numbers of publications and their collaborating groups. Those with the highest numbers of publications are China (63), the United States (59), Italy (32), and Germany (29). Moreover, we also find in first place China, where the inter-country (MCP) publications numbered 53, followed in second and third place by the United Kingdom (18) and Australia (10). They have published 18 papers and 10 papers, respectively. They both have nine international co-publications. In the fourth position is the United States, with 59 papers and eight foreign collaborations. Comparatively, Germany (29) and Russia (13) have many scientific publications but less external collaboration. In terms of cooperation between countries, United States-China (8), China-Singapore (7), Australia-China (7), and Canada-China (6) are the top-ranked combinations. International collaborative research is well regarded in China.  
Figure 5: Collaboration of Countries. Intra-country (SCP) and Inter-country (MCP) Collaboration of Top 20 Countries or Territories.  
\begin{table}
\begin{tabular}{l l l l l l l l} \hline \hline
**No.** & **Author** & **h\_index** & **g\_index** & **m\_index** & **TC** & **NP** & **PY\_start** \\ \hline
1 & [PERSON] & 5 & 7 & 1 & 64 & 7 & 2018 \\
2 & [PERSON] & 4 & 5 & 1.333 & 31 & 5 & 2020 \\
3 & [PERSON] & 4 & 5 & 1.333 & 31 & 5 & 2020 \\
4 & [PERSON] & 4 & 5 & 1.333 & 31 & 5 & 2020 \\
5 & [PERSON] & 4 & 5 & 1.333 & 39 & 5 & 2020 \\
6 & [PERSON] & 4 & 4 & 0.5 & 292 & 4 & 2015 \\
7 & [PERSON] & 2 & 2 & 0.667 & 5 & 3 & 2020 \\
8 & [PERSON] & 2 & 3 & 0.667 & 9 & 3 & 2020 \\
9 & [PERSON] & 2 & 3 & 0.667 & 9 & 3 & 2020 \\
10 & [PERSON] & 2 & 2 & 0.333 & 5 & 3 & 2020 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Top 10 Specialists’ Local Impact in the WoS and Scopus.  
Table 6 shows the total number of citations in selected papers by countries or territories. We found that Pakistan, Egypt, and Germany's publications received high numbers of citations and had the greatest impact. In addition, as part of North America, Canada and the United States excel in total citations, while their average paper citations need to be improved. Publications in China and Hong Kong, China, need to gain more influence as well.  
In addition, it is worth noting that in the 493 related publications, case studies of mega infrastructure projects are also concentrated in the high-citation countries. In Germany, this category includes the Frankfurt Airport Terminal 3 Construction Project and the Stuttgart 21 Project [34]. In China, the Sichuan-Tibet railway and the Hong Kong-Zhuhai-Macao railway [35] are the most representative projects. As for other countries, the HS2 and the Thames Tideway Tunnel in the United Kingdom [36] and California High-Speed Rail [37] in the United States are also widely mentioned.  
Table 7 shows the classification of scientific publications by author affiliation. The following are the top five affiliations: University of Naples Federico II (Italy), Cornell University (United States), The Hong Kong Polytechnic University (China), Jiangsu University (China), and Beijing Jiaotong University (China). A total of 15% of publications were attributed to the top five affiliations. Half of the most relevant affiliations are from China, while the United States and Italy each have two universities in top 10.