One of the sources of Bangkok's traffic jam is "soi." Soi is a narrow street that feeds the main roads of Bangkok and it was created as a byproduct of poor city planning in the past. It's usually so narrow that public transportation (such as buses) cannot reach, and people living in those "soi" will require effort in order to get to the main road where public transportation options are available. Therefore, millions of people in the "soi" of Bangkok prefer to use personal vehicle over public transportation and subsequently create traffic problem that we have today.