State comparison · Updated October 2026
Idaho vs. Washington Driving Laws (2026)
Idaho and Washington differ on 5 of 9 topics we track: max speed limit, learner's permit age, car insurance, car sales tax and helmet law.
Heading from Boise to Seattle takes you across the border, and 5 of the laws change on the way. Key roads include I-84 on the Idaho side and I-5 in Washington; the capitals, Boise and Olympia, set the rules for each side.
What changes most: the highest posted limits are 10 mph different. Residents of Meridian heading to Spokane, and back, live under both rulebooks: Idaho's on I-15 and Washington's following the state line on I-90. Use the Idaho vs Washington guide if you shop for a car between Boise or Seattle.
On a weekend drive from Boise to Olympia, pack a helmet and proof of insurance, set navigation before leaving, and expect a change from 80 to 70 mph at the border.
| Topic | Idaho | Washington |
|---|---|---|
| Max speed limit | 80 mph | 70 mph |
| Phone law | Hands-free law | Hands-free law |
| Learner's permit age | Permit at 14 | Permit at 15 |
| Car insurance | 25/50/15 | 25/50/10 |
| Car sales tax | 6% | 6.8% |
| Car inspection | No regular inspection | No regular inspection |
| New resident deadline | 30 days | 30 days |
| Helmet law | Under 18 | All riders |
| Lane splitting | Not allowed | Not allowed |
Driving laws compared: Idaho vs Washington
Idaho vs Washington: Idaho and Washington match on Hands-free law for phone law.
Speed limits: Idaho vs Washington
Washington is slower on max speed limit, with Idaho at 80 mph and Washington at 70 mph. Open-road interstates reach 75 mph in Idaho and 70 mph in Washington. Driving out of Boise toward Seattle, expect the limit to change at the border.
Learner's permit age: Idaho vs Washington
The law is earlier in Idaho on learner's permit age, with Idaho at permit at 14 and Washington with permit at 15. Teens in Boise driving to Seattle must follow Washington's teen restrictions while in the state.
Owning a car compared: Idaho vs Washington
Idaho vs Washington: Idaho and Washington match on No regular inspection for car inspection and 30 days for new resident deadline.
Car insurance: Idaho vs Washington
The law is higher in Idaho on car insurance, with Idaho at 25/50/15 and Washington with 25/50/10. Idaho is at-fault while Washington is at-fault. An insurance policy from Boise must be updated when you settle in Seattle.
Car sales tax: Idaho vs Washington
Idaho is lower on car sales tax: Idaho at 6% and Washington at 6.8%. On a $30,000 car, state tax comes to roughly $1,800 in Idaho versus $2,040 in Washington. Buyers from Meridian or Spokane owe car tax where the car is registered, not the dealer's.
Motorcycle compared: Idaho vs Washington
Idaho vs Washington: Idaho and Washington match on lane splitting (Not allowed).
Motorcycle helmet laws: Idaho vs Washington
The rule is stricter in Washington on helmet law, with Idaho at under 18 and Washington at all motorcyclists. Motorcyclists riding from Boise into Seattle switch to Washington's helmet law at the line.
Moving or buying across the border
- Idaho vs Washington: moving from Idaho to Washington means 30 days to register the car and 30 days for a license.
- Moving from Washington to Idaho: 30 days to register and 30 days for a license.
Idaho vs Washington: FAQ
Which has the higher speed limit, Idaho or Washington?
Idaho (80 mph vs. 70 mph).
Is it cheaper to buy a car — Idaho or Washington?
Idaho costs less at the state level (6% vs. 6.8%).
Do I need a helmet in both Idaho and Washington?
Idaho: Under 18; Washington: All motorcyclists.