Transportation of the goods along Danube river makes important part in the local economy. It is more cheaper then road transportation and therefore of course more convinient for the companies. Before the war of 1991, Vukovar was a very important port on the Danube River.
You can easily reach Vukovar by car, bus or train.
If you're arriving by car then leave the A3 highway at Zupanja exit and just take the road to Vukovar via Vinkovci.
Croatian automobile club: www.hak.hr
Croatian highways: www.hac.hr
There are direct buses to Vukovar from Zagreb, as well as from Osijek or Vinkovci.
Local bus company: www.panturist.hr
Zagreb bus station: www.akz.hr
Trains to Vukovar are not very frequent, and there are only local trains from Osijek or from Vinkovci. As the train station in Vukovar is still destroyed trains stop in Vukovar-Borovo naselje station.
However, train to Vinkovci combined with a local bus to Vukovar might be a quick, cheap and comfortable option.
Croatian railways: www.hznet.hr