The Romans were doing the executing factory style. Jesus was not the first ever and it was not as if their method was just invented that day. They had a system. It was a regular event. The poles and such would get reused over and over.
The condemned were subjected to all kinds of brutality prior to the actual lifting up. They would be exhausted. Jesus all the more so. There’s no way a person who was beaten and abused as was Jesus, could drag a pole, without even a way to grip it, the distance.
In fact, Simon from Cyrene was impressed into carrying whatever Jesus crucifiction required, Jesus was beat that bad.
I am not going to say that I know exactly how it was done, but certain things shine through. According to the Gospels, Jesus was nailed hand and foot. He would not have been nailed until he was on site at Golgotha. So, the idea that he was tied with ropes to a crosspiece and then later untied and nailed does not add up to an efficient Roman system.
The timbers used would have been brought into town as part of the system. It was part of the whole action to first force the condemned to carry their timber the distance through town, a public humiliation and torture meant for all to see, such that people learned to fear the Romans. It was for effect. It was terrorism.
Jesus was abused beyond the norm, such that even the Romans could see it was not business as usual. Hence Simon was employed.
Yes, a condemned prisoner could drag a pole, with a crosspiece to grab on to, through town and up to Golgotha. It would have been difficult, for sure. But that was the point, as the condemned was going to be killed. And it was a painful spectacle.
But a single pole, with no means to grip it, would be ridiculous. And it would be historically inconsistent.
If Jesus was tied to a crosspiece first, and that is all He had to manage, did they then unite him from it and tie Simon to it? I think not.
The Roman system needed to be simple and uncomplicated and able to be reused efficiently. And the site at Golgotha would certainly have had prepared and fortified holes for the timbers to drop into. It was, after all, a public torture and execution chamber. They didn’t dig the holes that day.
To have the condemned using every ounce of energy trying to grasp the straight pole would mean they would tire long before getting to the site. I’d like to see it tried.