Transportation - Kampong Chhnang, Cambodia
Your best bet if you don't have your own transportation is to take the Hoh Wah renting bus. To and from Phnom Penh costs just 5,000 riel on the air-con bus.
Kampong Chhnang to Phnom Penh
departs 6:30 am, 9:30 am, 11:00 am, 12:00 pm, 1:15 pm, 2:00 pm, 3:30 pm, 4:30 pm.
Phnom Penh to Kampong Chhnang departs (from Central Market Terminal) 6:40 am, 8:00 am, 9:00 am, 10:00 am, 11:30 am, 1:00 pm, 2:00 pm, 3:30 pm, and 4:30 pm. If you like, you can get off at Udong and see the old ruins and its newest additions (just grab a moto-taxi next to the entrance road), then go back out to the highway and grab the next bus heading your way to Kampong Chhnang.
Highway No 5 from Kampong Chhnang to Pursat is slowly getting some resurfacing work and while not good by any stretch of the imagination, it's not as bad as it used to be. As mentioned, the Kampong Chhnang to Phnom Penh stretch qualifies a dream road in Cambodia. Security is not a problem.