By ship
Bangkok and its traffic-congested commercial districts, including Ramkhamhaeng Road, are hard to navigate by car. Thus, the best way to get into the area is by boat. The Saen Saep Express Boat service runs on the canal of the same name, and you don't have to worry about getting stuck in traffic! The service runs about every 5 to 10 minutes and as the canal is exactly parallel to Ramkhamhaeng Road wit many stops along that road.
It is a fast and inexpensive way of transport as a single trip costs about 9 to 19 baht, depending on the distance travelled. The most important stops are The Mall Ram in Hua Mak and The Mall Bangkapi, both of which are served by the NIDA Line that starts in Pratunam and goes all the way northeast to Wat Sriboonreung. The route is served by 100 boats of 40-50 seats, and operates from 05:30 to 20:30 daily. Most piers have English signs up, but be wary, as The Mall Ram does not have any sign at all, and from the boat it is not clear that you have reached the mall!
Be wary of sitting at the outer sides of the boat as polluted water from the canal sometimes spills over on-board. Also be careful when entering and exiting the boats as "safety first" does not seem to apply for the crew here. During rush hour, you might have to fight your way in the boat as too many people are trying to get on. Another minor annoyance is the noisy atmosphere during the ride, don't expect a sensual experience.
By bus
Getting to Ramkhamhaeng by bus is very troublesome, but at least its a cheap way of doing some exploring. Expect a long ride though, and ask a local where to get off as you easily get lost in traffic. An important route is bus 40, that starts at Hualamphong Train Station and then passes Rama IV Road, Phaya Thai Road, Siam Square, Sukhumvit, Pridi Phanomyong Road and Ramkhamhaeng Road with The Mall Ramkhamhaeng as its final destination.
By Public Transit
Opened in August 2010, the Airport Rail Link is an alternative way of getting in. The City Line of that service has a stop at Ramkhamhaeng, which is at the utter southwest of the district at the beginning of Ramkhamhaeng Road. There is a direct service from Suvarnabhumi Airport in the east, as well as from Phaya Thai, Ratchaprarop and Makkasan stations in the west. Do not take the Express Line as it skips Ramkhamhaeng completely.