South Dakota speed limits and key traffic laws

By the end of this topic you can

• You can state South Dakota's default speed limits for interstates, highways, towns and school areas.
• You can explain when you must drive below the posted limit.
• You can describe what to do for stopped emergency and warning-light vehicles.
• You can apply the school bus and snowplow rules.

What you need to know and understand

• The interstate maximum is 80 mph unless a lower limit is posted, and the interstate minimum is 40 mph.
• Other streets and highways have a 65 mph maximum unless a different limit is set and posted.
• Urban areas with no posted limit have a 25 mph limit.
• Passing a school during recess or while children arrive or leave, the limit is 15 mph.
• Within 50 feet of a railroad crossing or intersection where your view is blocked, the limit is 15 mph.
• On roads posted 35 mph or more, stay at least 200 feet behind a snowplow with its red or amber lights on.
• Fines for speeding in a work zone may be doubled.

Default limits in state law

These limits apply when no other limit is posted. The Transportation Commission and local authorities can set and post different limits, and the sign always wins.

• Interstate highways: 80 mph maximum, 40 mph minimum.
• Other streets and highways: 65 mph. Some divided four-lane rural highways are posted up to 70 mph.
• Township roads: 55 mph unless the township sets another limit.
• Urban areas without a posted limit: 25 mph.
• Passing a school at recess or arrival and dismissal times: 15 mph.
• Within 50 feet of a railroad crossing or intersection with a blocked view: 15 mph.

Slower than the sign

State law requires a speed that is reasonable and prudent for the conditions, so you can be ticketed below the posted limit. The manual points out that limits are set for summer months on dry pavement. Slow down at the first sign of rain, snow, sleet or ice, on gravel and in fog. Driving far below the flow of traffic is also an offense, so if you are holding up a line of cars, pull over safely and let them pass.

Move over, school buses and snowplows

1. Emergency vehicle stopped with red lights: come to a complete stop before reaching it, then go on with caution only when it is safe.
2. Any stopped vehicle with amber, yellow or blue lights on a road with two or more lanes your way: move to the lane farthest from it at least 300 feet before you reach it.
3. Same situation on a two-lane road: slow to at least 20 mph below the posted limit (or to 5 mph where the limit is 20 mph or less) starting at least 300 feet before it.
4. School bus with red lights flashing or stop arm out: stop, unless the road is separated by a physical barrier. Go on slowly once the lights stop and the arm is in.
5. Snowplow with red or amber lights on a road posted 35 mph or more: stay at least 200 feet behind it.

Common mistakes

• Driving at 80 mph in snow because the sign allows it. Limits are for ideal conditions.
• Forgetting the 25 mph default in towns where no limit is posted.
• Passing a stopped trooper at full speed on a two-lane road. Slow to at least 20 mph under the limit.
• Following a plow closely to get through faster. The law requires at least 200 feet on roads posted 35 mph or more.

Test yourself: South Dakota speed limits and key traffic laws

Answer each question, then read the explanation. Questions come in a random order each time.

Go deeper

• Learning to Drive in South Dakota
• South Dakota 50-Hour Practice Log
• South Dakota Driving Test and When Driver’s Ed Waives It