This is officially called a "precast concrete temporary barrier" but is usually called a "jersey barrier" since they are used extensively on highways in New Jersey. This one was designed by a friend of mine who is a civil engineer, John Mastronardi. It is scaled to 1/87 of full size for use with HO scale models. It also can be scaled down 54% for use with N scale models.

John Mastronardi designed this in AutoCad. I printed it on a MakerBot Replicator2 using MakerWare 2.4 with the following settings and no raft:

Infill = 10%
Layer Height = 0.200
Shells = 1
Feedrate = 40
Travel Feed = 55
Temperature = 220

It took 17 minutes to print.