#road[class=1][zoom>=10] {

  line-color: #678;

  [zoom=10] { line-width: 1.4; }
  [zoom=11] { line-width: 1.8; }
  [zoom=12] { line-width: 2.2; }
  [zoom=13] { line-width: 2.4; }
  [zoom=14] { line-width: 2.8; }
  [zoom=15] { line-width: 4; }
  [zoom=16] { line-width: 8; }

}

#road[class=2][zoom>=10] {

  line-color: #889;

  [zoom=10] { line-width: 0.8; }
  [zoom=11] { line-width: 1.0; }
  [zoom=12] { line-width: 1.4; }
  [zoom=13] { line-width: 1.8; }
  [zoom=14] { line-width: 2.0; }
  [zoom=15] { line-width: 3; }
  [zoom=16] { line-width: 6; }

}

#road[class=3][zoom>=11] {

  line-color: #889;

  [zoom=11] { line-width: 0.4; }
  [zoom=12] { line-width: 0.6; }
  [zoom=13] { line-width: 1.0; }
  [zoom=14] { line-width: 1.2; }
  [zoom=15] { line-width: 2; }
  [zoom=16] { line-width: 4; }

}

#road[class=4][zoom>=13] {

  line-color: #889;

  [zoom=13] { line-width: 0.4; }
  [zoom=14] { line-width: 0.8; }
  [zoom=15] { line-width: 1.4; }
  [zoom=16] { line-width: 2; }

}
