On foot.
Without a solid double bass case to carry the instrument on my back like a backpack, I would have to figure out something else. But even an old canvas case is manageable on foot. Let\’s put the double bass in front of you. One hand on the neck, the other on the side. Lift the instrument so that the head is down and the spikes are up. Place it on your shoulder and keep it balanced so that it does not fall over.
When I was walking around town with the instrument in this way, I was told that it looked like Jesus was carrying a cross on his back. I imagine that they may have compared me to him, since I had long hair at the time.
With a modern case, you can carry your instrument like a backpack, but you must be careful to keep the spikes tucked away. Otherwise, they will get stuck in the heels.
By car 
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I have carried these instruments in various vehicles. I have even heard of a double bass fitting into a Trabant; on a 300-kilometer trip, I secured two double basses to the roof of a car, carried two double basses in the car, and experienced a record number of instruments and passengers. In addition to the driver, there were two other passengers, including myself.
By train
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I often traveled with my instrument on Czech trains. At first I tried different ways of placing my instruments, such as placing them in the bathroom, or placing my double bass in a bag holder. When the train was full, I even put my instruments on the extended aisle of the family car. But in the end, I found it best to place the instruments in the cargo hold. At first I worried that I might not be able to control them, but in the end I had to admit that it was much safer.
No matter how one travels, one should always consider the safety of one\’s equipment. In the past, when traveling by train, if a compartment was available, I would practice directly on my instrument while traveling. Now I don\’t dare to do that.
Since the double bass is a rather large and expensive instrument, it is often worth arranging for a different instrument at the concert venue. But it takes skill to play instruments that are so vastly different from one another.
— 16 November 2022