From WFAA:

The crane was en route from the Houston area when it was involved in an accident with an 18-wheeler at I-45 and Linfield road, just south of downtown Dallas around 8:15 p.m.

Why the rush to tear down statues?

To prevent BLM enthusiasts from massacring more Dallas cops by conceding them their demands quickly. From the Dallas News:

As Mayor Pro Tem Dwaine Caraway (right) arrived to bask in the result of this hastened action, I asked about the basis for the rush to judgment.

Q. Why couldn’t we wait the 90 days for the task force? Why did this have to happen in such a rush?

A. Well, number one, it’s not really a rush, but it is a rush, and it is an emergency for all of the citizens of Dallas.

Q. Emergency? Defined how?

A. When the police in the last rally were out protecting us, the citizens of Dallas, our police were at risk. What was not reported was the fact that they had bottles being thrown at them, and they were armed, of course, and we did not need to revisit something that occurred a year ago on the 7th.

Q. Right. The horrible July 7th massacre. What does that have to do with this?

A. Because there were going to be more rallies. And with more rallies, that would mean that folks in our police would have been at risk at every single rally, every single weekend.