Here are a couple of websites discussing state to state legality of DUI checkpoints. It seems Iowa is one of the handful of states where these are not permitted.
Sobriety checkpoints
"Not permitted because statute authorizing roadblocks controls and does not authorize sobriety checkpoints. 321K.1. DUI arrests may be made at roadblocks authorized by statute.
State v. Day, 528 N.W.2d 100 (Iowa 1995). Absent statutory impediments, Iowa courts have upheld the constitutionality of checkpoints.
State v. Loyd, 530 N.W. 2d 708);
State v. Riley, 377 N.W.2d 242 (Iowa App. 1985). Se also
State v. Hillesheim, 291 N.W.2d. 314 (Iowa 1980).
State v. Heminover, 2000 WL 564049 (Iowa App.), held avoidance does not justify stop. It also found the roadblock did not comply with guidelines."
Here is an article from just a few days ago discussing the legality of what Iowa is wanting to do.
: vehicle checkpoint : Iowa Law Blog