Anh Hong Nguyen, Thi, Chikaraishi, Makoto, Seya, Hajime, Fujiwara, Akimasa, AND Zhang, Junyi. " Elderly’s heterogeneous responses to topographical factors in travel mode choice within a hilly neighborhood: An analysis based on combined GPS and paper-based surveys" European Journal of Transport and Infrastructure Research [Online], Volume 17 Number 3 (1 June 2017)