Argentina has one of the world's worst records for traffic accidents, and the busy highways of Buenos Aires Province are often where they happen. January and February are the worst times, when drivers anxious to get to and from their holiday destination speed, tailgate, and exercise illegal maneuvers even more alarmingly than usual. If you're driving, do so very defensively and avoid traveling on Friday and Sunday, when traffic is worst.
Expressways and interprovincial routes tend to be atrociously signposted, so take a map. Getting a GPS-equipped rental car costs an extra 35 pesos or so per day: devices usually work well in cities, but the calibration is often a couple of hundred yards off in rural areas. Major routes are usually privately owned, which means frequent tolls. There are sometimes alternative roads to use, but they're generally smaller, slower, and in poor condition. On main roads the speed limit is 80 kph (50 mph), while on highways it's 130 kph (80 mph), though Argentinean drivers rarely pay heed to this.