The road condition from Sihanoukville to Siem Reap is good and the drive is pretty smooth all of the way.Travel by busThe Mekong Express bus leaves Siem Reap at 7:00am, then you change bus in Phnom Penh to another Mekong Express bus, which takes you to Sihanoukville. The price of the Mekong Express bus ticket from Siem Reap to Sihanoukville is around US$19 and you will arrive in Sihanouville around 5:00pm. The Sorya bus makes the same trip, but the connection in Phnom Penh is longer and therefore you will not arrive into Sihanoukville until around 7:00pm. Sorya charge around US$10 for this trip, but it is not as nice a bus as the Mekong Express. From Sihanoukville to Siem Reap, you can take any bus that leaves before 8:30am and then you will be able to get any connecting bus to Siem Reap. There is also an overnight bus from Siem Reap to Sihanoukville. The bus leaves Siem Reap at 8:00pm and arrives in Sihanoukville at 6:00am the following morning. It also stops in Phnom Penh around 1:00pm for anyone wanting to go to Phnom Penh.