Except for a few kilometers from the border crossing to the outskirts of Trieste, you'll drive all the time on motorways.

The coastal road from Piran to Koper is a bit narrow, but easy. In Koper you find a short stretch of free motorway up to the border crossing (BTW if you come down from Ljubljana it's all motorway now), then a few kilometers of slow road because of extensive roadworks which will be completed not before 2008. You then turn right for the ramp leading to the ring (well, half-ring, as there's the sea on the other half) road navigating around Trieste and after about 40 km you hit the toll station of A4 motorway, which will take you to Venice after about 115 km. The toll should be around 6 euros for a car.

If you wish to pay a visit to Trieste on the way, at the ring road ramp you turn left towards the city center and you'll pass along the seafront of neoclassical buildings, the big square open on the sea, running at the foot of the steep hills just off the rocky beaches with wonderful views of the town and the gulf. This route is shorter but slower because of traffic.

Have a nice trip.

Paolo Trieste, Italy