We looked at the available options train, bus and car.
If you have a car available, then driving yourself is the fastest option. If you don't have your own car, there are a number of rental companies available in Zadar where you can rent a car and return the car back to the rental company in Split. Besides it being the fastest option, driving you have the freedom to take a more scenic route or wander off the main road and find yourself a nice spot to have a rest with a picnic.
The estimated travel time from Zadar to Split will be around 1 hour 45 minutes. The distance is about 160 kilometres. Leaving Zadar you would take road 424 to the main highway E65 which you would follow most of the way South. Google Maps route
A second option is a bus, buses leave daily every hour from the Zadar Central Bus Station to Split Bus Station. The travel time is around 3 hours and 15 minutes. Depending on which bus line you take, it could be possible that you would need to make a change at Šibenik Central Bus Station. Bus tickets vary around the12 euros which we think is a pretty good price. A popular bus company is 'Arriva' and 'Autotrans', the buses are comfortable and all airconditioned.
Check this website for bus tickets: https://getbybus.com/en/bus-zadar-to-split
The last option is by train. However, due to the long travel time, it is not a very good option. The log ride is around the 7 hours with a change over at Knin. Ticket prices are around 16 euros. The plus-side is that you can enjoy beautiful views on the journey.
Website to buy train tickets: http://www.hzpp.hr/en
If you want to travel fast, then the car is the way to go, if you want to sit back and relax and travel cheap we highly recommend the bus. Due to the long travel time by train, we don't recommend this.