This paper describes the implementation and the evaluation of a link aggregation system using Network Mobility (NEMO). The link aggregation system, called NEMO SHAKE, constructs a temporal network (called an alliance) between multiple mobile routers (MRs) carried by vehicles and aggregates external links between multiple MRs and the Internet to provide a fast and reliable transmission with mobile devices in vehicles carrying MRs. We also designed a system for controlling alliances. By estimating the distance and the link condition between MRs, it can achieve a high throughput and the stability of the aggregated paths between vehicles and the Internet. We evaluated the usefulness of NEMO SHAKE and its alliance-control mechanism in real vehicular networks. We confirmed that the alliance-control mechanism can achieve a high throughput by changing the member of the alliance dynamically.