Coming to a dead stop in the middle of an ambush is a really bad idea. It’s the worst possible thing you can do in fact. US military doctrine is pretty consistent on this.
There are two responses to ambush: retreat/break-contact and charge. If the ambush is “close” you charge through and counterattack, if the ambush is not “close” then you break contact and maneuver around the ambush — the difficult thing is determining whether you’re in a “close” situation or not.
In a ‘barricade’ situation for civilian vehicles on roads it’s very likely that the retreat (aka avoid) option is restricted — the traffic behind you for one, the buildings and structures to the sides for another, and possibly the oncoming traffic. — Cut off all avenues of escape and only fight is left.