Fixed the character thing.
Also, about the ghouls. It's true that the standard ghoul is about as fast as an average person. However, I'm diabolical you see, which is why I gave you runners. Even if we assumed we killed all of the initial runners, there would be others in the city. Likely, even, in areas that the convoy had already passed, hiding from the daylight.
Now, if we also consider that in today's reality, the drive from Brown's Point to Federal Way (the destination) is supposedly 20ish minutes. The route I had envisioned in my head was more around 30 - In today's world.
Add in an overgrown jungle, dangers around every corner, rough and unstable terrain, and the need to drive about as fast as the jurassic park automated observation jeeps (slow). We have a trip that takes a good amount of hours. Now, in all of those hours of trying not to kill yourself driving through other dangers, on top of the millions of ghouls in the city -- The ghouls coming at Refuge can be implied to be a different set of baddies.
However, there is an unknown variable. The weird phenomena, the girl, the sounds, and why all the ghouls that had been in Eli's area are gone. So perhaps, maybe it's not the truck's fault? Perhaps there are darker forces at work here, or perhaps the runners (who could keep up with the trucks trying to plow their way through uncertain paths) notified their brethren, and thus a horde began to amass behind them.
If we ascertain that each pack of ghouls has a good number of runners, as seen by the skirmish at the rubble pile, which we can assume were probably between 10-30 in number, than attracting a wide swathe of ghouls from sections of the city could potentially bring hundreds of runners. Thus, the need to get in the gate quickly.
Yes, I did say hundreds of runners, which I would say is about equal to as Sergeant Docker put it "a tide of ghouls".
Speculate on that.
You don't even see the rest of the ghouls.
Yet.
Was this explanation satisfactory?