I can travel you can travel he can travel we can travel you can travel they can travel
V-ing form
I can be travelling you can be travelling he can be travelling we can be travelling you can be travelling they can be travelling
Perfect
I can have travelled you can have travelled he can have travelled we can have travelled you can have travelled they can have travelled
V-ing perfect
I can have been travelling you can have been travelling he can have been travelling we can have been travelling you can have been travelling they can have been travelling
Negation
Simple form
I can't travel you can't travel he can't travel we can't travel you can't travel they can't travel
V-ing form
I can't be travelling you can't be travelling he can't be travelling we can't be travelling you can't be travelling they can't be travelling
Perfect
I can't have travelled you can't have travelled he can't have travelled we can't have travelled you can't have travelled they can't have travelled
V-ing perfect
I can't have been travelling you can't have been travelling he can't have been travelling we can't have been travelling you can't have been travelling they can't have been travelling
Interrogative form
Simple form
can I travel? can you travel? can he travel? can we travel? can you travel? can they travel?
V-ing form
can I be travelling? can you be travelling? can he be travelling? can we be travelling? can you be travelling? can they be travelling?
Perfect
can I have travelled? can you have travelled? can he have travelled? can we have travelled? can you have travelled? can they have travelled?
V-ing perfect
can I have been travelling? can you have been travelling? can he have been travelling? can we have been travelling? can you have been travelling? can they have been travelling?
Interro-negative form
Simple form
can't I travel? can't you travel? can't he travel? can't we travel? can't you travel? can't they travel?
V-ing form
can't I be travelling? can't you be travelling? can't he be travelling? can't we be travelling? can't you be travelling? can't they be travelling?
Perfect
can't I have travelled? can't you have travelled? can't he have travelled? can't we have travelled? can't you have travelled? can't they have travelled?
V-ing perfect
can't I have been travelling? can't you have been travelling? can't he have been travelling? can't we have been travelling? can't you have been travelling? can't they have been travelling?