Is it permissible to combine two prayers or to pray in a vehicle due to the unavailability of a place to pray?

It is inconceivable that there would be no place for prayer, for the entire earth is a mosque except for graveyards and bathrooms. A worshipper can carry his prayer rug and pray on it anywhere. It is not permissible to combine two prayers except for the sick, the traveler, and others who have a legitimate excuse according to Islamic law.