going to the neil young show a couple years back, i went 175 to 29 and used the South Entrance and drove right into the parking lot.
taking 175 until it turns into Little Patuxent Parkway will get one next to the mall.
if you can into Columbia before the gates open the traffic around the venue is light. this summer i've been getting there around 45 mintues before gates. kill time in the mall if you have too... i believe the parking lot opens before the gates do.
the worst part of the trip is getting out of DC but 95N usually gets moving by the time you get to Laurel.
getting out is alot easier than Nissan that is for sure.
Merriweather got a bad rep because of the Radiohead show, where tons of people all showed up at the same time clogging 29, etc.