State comparison · Updated October 2026
Iowa vs. South Dakota Driving Laws (2026)
Iowa and South Dakota part ways on 6 of 9 topics we track: max speed limit, phone law, car insurance, car sales tax, new resident deadline and helmet law.
On a trip from Des Moines to Sioux Falls takes you across the border, and 6 of the laws switch at the line. Main routes include I-80 on the Iowa side and I-90 in South Dakota; the capitals, Des Moines and Pierre, write the laws for their side.
What changes most: newcomers get 30 days in Iowa versus 90 days in South Dakota ahead of the first deadline. People who live in Cedar Rapids who travel to Rapid City, and back, follow both rulebooks: Iowa's on I-35 and South Dakota's after the border on I-29. Read the Iowa vs South Dakota guide if you shop for a car between Des Moines to Sioux Falls.
On a weekend drive from Des Moines to Pierre, keep your documents if you ride, set navigation ahead of time, and watch for the limit to change from 70 to 80 mph at the line.
| Topic | Iowa | South Dakota |
|---|---|---|
| Max speed limit | 70 mph | 80 mph |
| Phone law | Hands-free law | Texting ban only |
| Learner's permit age | Permit at 14 | Permit at 14 |
| Car insurance | 20/40/15 | 25/50/25 |
| Car sales tax | 5% | 4% |
| Car inspection | No regular inspection | No regular inspection |
| New resident deadline | 30 days | 90 days |
| Helmet law | No helmet law | Under 18 |
| Lane splitting | Not allowed | Not allowed |
Driving laws compared: Iowa vs South Dakota
Iowa vs South Dakota: South Dakota and Iowa have the same rule for learner's permit age: Permit at 14.
Max speed limit: Iowa vs South Dakota
South Dakota is faster on max speed limit, with Iowa at 70 mph and South Dakota at 80 mph. Open-road interstates reach 70 mph in Iowa and 80 mph in South Dakota. Driving out of Des Moines toward Sioux Falls, watch the signs at the state line.
Cell phone and texting laws: Iowa vs South Dakota
Iowa is stricter on phone law: Iowa at hands-free law and South Dakota with texting ban only. Phone use that is fine in Des Moines can be illegal near Sioux Falls once you cross.
Owning a car compared: Iowa vs South Dakota
Iowa vs South Dakota: Iowa and South Dakota agree on car inspection (No regular inspection).
Car insurance: Iowa vs South Dakota
The law is higher in South Dakota on car insurance, with Iowa with 20/40/15 and South Dakota at 25/50/25. Iowa is at-fault and South Dakota is at-fault. A policy written in Des Moines must be updated if you relocate to Sioux Falls.
Car sales tax: Iowa vs South Dakota
The law is higher in Iowa on car sales tax: Iowa at 5% and South Dakota at 4%. For a $30,000 purchase, state tax comes to roughly $1,500 in Iowa and $1,200 in South Dakota. Shoppers in Cedar Rapids and Rapid City owe the tax of the state where they register, wherever they buy.
Moving deadlines: Iowa vs South Dakota
South Dakota is longer on new resident deadline: Iowa at 30 days and South Dakota at 90 days. Families moving from Cedar Rapids into Rapid City ought to book DMV appointments early.
Motorcycle side by side: Iowa vs South Dakota
Iowa vs South Dakota: South Dakota and Iowa agree on lane splitting: Not permitted.
Helmet law: Iowa vs South Dakota
South Dakota is stricter on helmet law: Iowa with no helmet law and South Dakota at under 18. Riders crossing from Des Moines to Sioux Falls must follow South Dakota's helmet law on arrival.
Crossing the line for good
- Iowa vs South Dakota: moving from Iowa to South Dakota means 90 days to register the car and 90 days for a license.
- Going from South Dakota to Iowa: 30 days to register and no fixed license deadline.
Iowa vs South Dakota: common questions
Which has the higher speed limit, Iowa or South Dakota?
South Dakota (80 mph vs. 70 mph).
Is car tax lower, Iowa or South Dakota?
South Dakota costs less at the state level (5% vs. 4%).
Do I need a helmet in both Iowa and South Dakota?
Iowa: No helmet law; South Dakota: Under 18.