Why must car drivers always be alert for motorcycles and mopeds?

• Because motorcycles and mopeds usually ignore traffic signals
• Because their small size makes them difficult to see
  Explanation:

  "Drivers of cars must always be alert for motorcycles, mopeds and scooters, as their size makes them very difficult to see."
• Because motorcycles and mopeds can move faster than cars
• Because they take up more space on the road than cars