public function getReleaseDirs() {
        $dirs = array();
        foreach ($this->roadMap as $road) {
            /* @var $road SourceRoad */
            $release_dir = $road->getReleaseDir();
            if (empty($release_dir)) {
                continue;
            }
            if (!$release_dir->exists()) {
                if (!$release_dir->mkdirs()) {
                    continue;
                }
            }
            array_push($dirs, $release_dir);
        }
        return $dirs;
    }