Driving from Vienna to Hallstatt

I'm curious about this too. We're also traveling from Vienna to Hallstatt in September and wondering if we should drive or take the train.

You would take he A1 highway--as Googlemaps.com says. It'd be a long day trip from Vienna. You're so close to Salzburg that it'd be a shame not to visit that great city.

We are planning to go to Hallstatt for one night then on to Salzburg for two nights. Any other thoughts?

From Vienna highway A1 to exit 224, roads 145 and 166 to Hallstatt.

If you do not intend to explore the area around lake Hallstatt by car, trains are a reasonable alternative.
The train ride, icluding one change, is 3:30 hours. It will be difficult to beat that time using a car.

When you arrive at Hallstatt, you'll have to park at Lahn and then walk to your hotel. If you're only spending one night there, you won't have time to see much since you probably won't arrive until late in the afternoon. You may find this website to be helpful.....

http://www.hallstatt.net/parking-in-hallstatt/

Parking will likely be expensive in Salzburg. This website should provide the information you need.....

https://www.salzburg.info/en/travel-info/arrival-traffic/car/parking

I've done the more southern drive through Leoben and also the highway drive through Linz. The highway is busy and cars go fast, often accidents or construction. The Leoben route is less of a major highway and slightly more scenic. I'd pack a picnic and plan to stop at one of the roadside picnic areas for lunch.

All of this said, a car really does you no good in Hallstatt or Salzburg- and can be a hindrance. Trains to both of these locations is fine and possibly faster.

The highway is busy and cars go fast,

Driving habits in Austria (and most other European countries) are considerably different to what you are used in US.
Once you are acquainted you should be fine, but you have to pay a lot of attention to the traffic.