If the guy who had the OE and crash had to keep working, there weren't enough people in the tower.
We know there weren't enough controllers in the tower. They were not there, because they do not exist. It is the same situation in every FAA tower in the country, along with every TRACON and ever ARTCC. Most "ATC Delays" are either due to, or worsened by, staffing.
One of them yes, but not necessarily both. PF is going to be eyes outside, but the PM may have a lot of other stuff going on.
That's not how it works. Under those conditions, night, in rain, and with an approach speed around 140kts, the PF will be on the instruments until relatively close to minimums with only occasional scans out the window. His goal is to keep a stable approach, on speed, until the DA. At some point near DA, it changes to primarily visual with frequent cross-checks of the instruments and that continues until the initiation of the flare. You pay very little attention to aircraft or vehicles holding short of the runway because there frequently are airplanes and vehicles holding short of the runway.
I am not aware of any other accidents where the controller wasn't pulled immediately, though one could presume Comair 5191 was the same.
With only two controllers in the cab, if you pull one of them then you have only one controller left to do everything which, at that point, involved spending a lot of time on phones and land lines coordinating with all of the stake holders in the emergency response. With the airport now closed, it was the Local controller position that had the lower workload.
At the angle they were crossing, the plane was coming from the blind side of a traditional truck, and the plane may have been still in the air when they looked and thus above the roofline of the truck.
In that truck, the driver sits in the middle so there was no blind side (or there were two, depending on how you look at it). The problem is that the airplane would have been well behind his shoulder, due to the angle of the taxiway, and he might not have turned far enough to see it. Particularly true since he had just been cleared to cross and did not expect to see an airplane at less than 100' above the ground. Confirmation bias is a real threat and likely also contributed with him missing the red RWSL.
If the plane was in the landing roll when the call was made, there may have been in-cockpit callouts that drowned out the radio.
The airplane was one second away from descending through 100' RA when the trucks were cleared to cross. That was when the pilots had a chance to recognize the controller's error and initiate a go-around. Their opportunity was short-lived as the ability to complete a go-around, and climb above the crossing trucks, lasted only a few seconds. At 100' RA, the pilots were focused on their task of landing the airplane on a short, wet runway, which made it less likely that they'd process a radio call, that wasn't directed to them, quickly enough to understand the threat.
While I agree that would be cutting it close and likely a mistake, 10 seconds should be enough time for a fire truck to cross a runway.
No, the clearance for the trucks to cross was most certainly a mistake--the mistake that started the accident sequence. It was given as the CRJ was reaching the 100' RA point and, to be legal, the trucks would have to have been clear of the runway by the time the CRJ reached the runway threshold (TCH 54')--about 5 seconds.
