You know, Kaliningrad is a trade city, and there are many people who use cars to move with goods to resell, so sometimes there are a lot of cars going through the border station.
From other side, the old border station in Mamononvo is not very big, which causes additional problems during crossing the border.
Also, Kaliningrad has many strategic places nearby, so sometimes the security aspect can cause the problem (even if it is not your car, you still have to wait).
But I think that Wikitravel containss kind of old information - nearly a year ago a new border station was opened in Mamonovo-2/Grzechotki, after that the federal autobahn Berlinka was continued, and the traffic situation became easier.
Still, during holidays you can meet traffic at the border stations. You can check the situation at the border online. The left column is to Kaliningrad, the right one is to Poland.
Also, I want add information about the visa - even if you don't have one, you can get a Kaliningrad 72 hours visa (maximum staying period is 4 days 3 nights), if you are citizen of Shengen countries, UK or Japan.