Ah. The car is a souped-up Range Rover. The woods are no match for that.
Silas's bound and gagged in the trunk. Teabing has his gun. Rémy's the getaway driver, and he's doing a great job heading towards the forest without any lights to give them away.
They safely make the woods.
Robert wishes they'd left Silas behind, but Teabing wisely points out that he may be Langdon's ticket to freedom. After all, they need to find out how he found them and with whom he's working.
Teabing summons his private plane with a single telephone call. They'll head to England (where Teabing's research makes him pretty sure the Grail will be located) and avoid all the normal security they'd face if they went commercially. Teabing has some well-placed bribes in play that lets him go back and forth pretty freely.
When Silas makes a choking sound from the back of the car, Teabing removes the duct-tape from his mouth and begins questioning him, to no avail.
Silas just silently prays for a miracle.
Suddenly a light bulb goes on above Langdon's head. (Metaphorically, that is.)
He's just realized something, but needs to make a phone call to the States to confirm. Hmm.