Porcupine, SD to Watertown, SD is 420.6 miles and takes about 7h 50m via I 90 and SD Highway 25, with a fuel budget near $64 and enough daylight to finish in a day. This drive stays within the Great Plains region, offering a familiar landscape throughout. Given its mostly highway profile and single-day recommendation, it's a straightforward trip for those looking to cover ground efficiently. You'll spend the majority of your time on interstates before transitioning to state highways. Plan this trip for a day when you want a direct connection between these two South Dakota points.
Trip Pace
Same-day drive is realistic
A same-day return is possible, but it will make for a full day on the road.
Break Rhythm
2 planned breaks
Plan on a short reset every 3 to 4 hours to stay fresh behind the wheel.
Midpoint
210.3 miles from Porcupine, SD
A natural place for your longest stop of the day
, about 4h 2m into the drive
.
Main Roads
Road
Distance
Duration
I 90
199.1 mi
3h 6m
SD Highway 25
83.8 mi
1h 38m
US 18
48.1 mi
57m
State Highway 73
44.6 mi
51m
Big Foot Trail
14.6 mi
35m
US Highway 212
14.5 mi
18m
9th Avenue Southwest
6.4 mi
8m
SD Highway 34
6 mi
7m
Longest stretch:
I 90
— 199.1 mi, about 3h 6m
Traffic on I-90
Hour-of-day weekday pattern from 19 FHWA count stations on your route.
Peak
2 PM
~335 veh/hr typical
· worst 583
Quietest
2 AM
~22 veh/hr
Peak-to-quiet ratio
15.2×
busier at peak than in the quiet hours
12a6anoon6p11p
Averaged across 52 weeks of 2023 FHWA Travel Monitoring Analysis System data. Weekday hours only (Mon–Fri).
Turn-by-Turn Driving Directions
Step-by-step road directions between Porcupine, SD and Watertown, SD.
1
Start on Eagle Drive
29 ft·2 sec·Eagle Drive
2
Turn right onto Main Street
124 ft·10 sec·Main Street
3
Turn left onto BIA 27
15 mi·35 min·Big Foot Trail
4
At end of road, turn left onto US 18
48 mi·57 min·US 18
5
Turn left onto SD 73
45 mi·51 min·State Highway 73
6
Continue on SD 73
1.0 mi·2 min·SD Highway 73
7
Take the ramp
0.4 mi·48 sec
Toward I 90 East
8
Merge onto I 90
199 mi·3 hr 6 min·I 90
9
Take the exit
0.3 mi·47 sec
Toward SD 25: Emery, Farmer
10
Turn left onto SD 25
24 mi·27 min·SD Highway 25
11
Turn right onto SD 25; SD 34
6.0 mi·7 min·SD Highway 34
12
Turn left onto SD 25
60 mi·1 hr 10 min·SD Highway 25
13
At end of road, turn right onto US 212; SD 25
3.9 mi·5 min·US Highway 212
14
Continue on US 212
1.0 mi·1 min·4th Street
15
Continue on US 212
11 mi·12 min·US Highway 212
16
Continue on US 212
6.4 mi·8 min·9th Avenue Southwest
17
Turn left onto South Broadway
0.7 mi·1 min·South Broadway
18
Arrive at destination
South Broadway
Trip Plan
Aim for an early start to comfortably complete this 7h 50m drive within daylight hours. With a recommended one-day trip, you can be flexible with your timing. There are 2 planned stops, so factor those into your schedule for fuel, food, or a quick stretch. The longest stretch without services is 199.1 miles on I 90, so ensure you have adequate fuel before embarking on that segment. Keep an eye on your fuel gauge as you approach the transition from I 90 to SD Highway 25, as services might become less frequent.
Morning Departure
Start early — leave by 6-7 AM to arrive at a reasonable hour.
Evening Departure
This is a long drive — plan for a morning departure or consider splitting it into two days.
You can normally do this drive in one day.
Plan roughly 2 meaningful breaks for fuel, food, and rest.
The halfway point lands around 210.3 miles from Porcupine, SD, or about 4h 2m into the drive.
The longest continuous stretch on this route runs about 199.1 miles.
This is a comfortable same-day trip.
Departure
Before you leave
Start with fuel, water, and navigation already sorted so the first hour feels easy.
First stop
Around 93 miles or 2h 7m in
Use this first pause for coffee, a restroom break, and a quick traffic check ahead.
Halfway reset
Around 210.3 miles or 4h 2m in
This is the best place for your longest stop, a real meal, and a full fuel check.
Final approach
Final hour starts around 6h 36m
Traffic, exits, and arrival timing usually matter more near Watertown, SD than in the middle of the route.
Before You Leave
+
Open the route before leaving Porcupine, SD so your first major turns are already loaded.
+
Leave with enough water and a charging cable within reach, not packed away.
+
Check your fuel range against the first long segment, especially if you are starting outside city service areas.
+
Pick one backup stop option before the midpoint in case traffic changes your pacing.
Day 1
Settle into the route from Porcupine, SD
This is one driving day of about 420.6 miles and 7h 50m.
Your first comfortable stop window is around 93 miles from Porcupine, SD.
This route can stay practical as a one-day drive if traffic stays reasonable.
Plan about 2 real breaks rather than only quick fuel stops.
The longest stretch is on I 90 for about 199.1 miles.
Where to Stop
Rest stops, refuel points, and overnight suggestions along this route.
Place data sourced from public business listings. Hours and availability may vary.
Heads-up: tricky spots
5 of 12
5 decision points cluster between mile 0 and 398 — GPS handles the exact turns, but know they're coming. Your lane choice matters more than the turn itself.
4
0 mi into trip|~0m in|Main Street
Turn right onto Main Street
Navigation decision point
4
0 mi into trip|~0m in|BIA 27 / Big Foot Trail
Turn left onto BIA 27 / Big Foot Trail
Navigation decision point
5
14.7 mi into trip|~35m in|US 18
At end of road, turn left onto US 18
Navigation decision point
5
307.9 mi into trip|~5h 34m in
Take the exit toward SD 25: Emery, Farmer
Exit ramp - move to the correct lane early. Multiple destination signs - pick the right one
Toward SD 25: Emery, Farmer
5
398 mi into trip|~7h 20m in|US 212; SD 25 / US Highway 212
At end of road, turn right onto US 212; SD 25 / US Highway 212
Navigation decision point
Fuel & Cost
Regular Gas
$62.11 one way
$124.23 round trip
$3.75/gal25.4 MPG avg147 kg CO2
Fuel Type
$/gal
One Way
Round Trip
midgrade
$4.14
$68.57
$137.14
premium
$4.72
$78.09
$156.19
diesel
$4.80
$79.42
$158.83
No toll roads detected on this route.
Estimated Trip Cost (one way, 1 person)
Fuel
$62
Meals
$25–$50
Total
$87–$112
Rough estimate based on US averages. Hotel $80–$140/night, meals $25–$50/day.
Estimated CO2 emission: 147.2 kg one way.
Prices: EIA weekly data, 2026-07-13.
Driving Electric?
About $44 in charging
· 1 stop
· 67% less CO2
Vehicle Type
kWh
Stops
DC Fast
Home Charge
Average EV
126.2
1
$44.16
$20.19
Efficient EV
105.2
1
$36.80
$16.82
EV Truck/SUV
168.2
2
$58.88
$26.92
Gas CO2
147 kg
EV CO2
49 kg (67% less)
Plan for 1 charging stop. A 30-minute DC fast charge mid-route should be enough to complete the trip comfortably.
DC fast charging avg $0.35/kWh. Home charging avg $0.16/kWh. US grid CO2: 0.39 kg/kWh.
Travel Intel
Current conditions at both ends of the drive.
Forecast as of Jul 17, 2026
Origin
Porcupine, SD
Evening
in Porcupine on Saturday
Local time
7:14 PM
MDT
Current temp
68°F
Mostly Clear
S 9 to 14 mph2% chanceLive forecast
Heat Advisory
Heat Advisory issued July 16 at 7:09PM MDT until July 19 at 9:00PM MDT by NWS Rapid City SD
Heat Advisory
Heat Advisory issued July 16 at 11:50AM CDT until July 16 at 10:00PM CDT by NWS Aberdeen SD
Destination
Watertown, SD
Evening
in Watertown on Saturday
Local time
8:14 PM
CDT
Current temp
72°F
Mostly Clear
SSE 10 mph0% chanceLive forecast
Heat Advisory
Heat Advisory issued July 16 at 7:09PM MDT until July 19 at 9:00PM MDT by NWS Rapid City SD
Heat Advisory
Heat Advisory issued July 16 at 11:50AM CDT until July 16 at 10:00PM CDT by NWS Aberdeen SD
Seasonal Notes
Summer travel usually means heavier construction, hotter rest stops, and busier weekend traffic around major cities.
Winter travel shortens daylight, so a route that looks manageable on paper can feel much longer after dark.
Holiday weekends tend to make both departure and arrival windows slower than the raw route time suggests.
Time zone
1 hour later
The destination clock does not match departure time, so double-check hotel check-in windows and late arrival plans.
Temperature spread
4 degrees warmer at arrival
A meaningful temperature swing is a good cue to rethink layers, water, and how soon you want to arrive.
Road read
7h 50m on the road
Start early — leave by 6-7 AM to arrive at a reasonable hour.
Weather data from the National Weather Service. Conditions may change; check closer to your travel date.
More Details
What kind of drive is this?
With 94% of this route on highways, expect consistent cruising. The longest uninterrupted stretch is 199.1 miles on I 90. You'll transition from interstate speeds to surface roads around mile 395, as SD Highway 25 and US 18 make up the latter part of the drive. The abundance of highway miles means you'll encounter a steady stream of exits for services and potential breaks.
94% highway — fuel and pacing are the main things to plan.
18 navigation steps total — most of the decisions cluster near the start and finish.
Longest single stretch: 199.1 mi on I 90.
How Hard Is This Drive?
4/10
This is a straightforward highway drive that stays mostly on I 90 and SD Highway 25. There are only a few real navigation decisions along the way. The trickiest moment comes early in the drive near Main Street.
Driving Effort4/10
Easy - simple navigation with a manageable amount of wheel time
Balances navigation complexity with total wheel time.
The route itself is not hard, but at 7h 50m, endurance matters. Plan breaks every 2-3 hours. The 12 decision points are all manageable with basic attention.
Where does it get tricky?
The main spots that need attention: near the start (Main Street): Navigation decision point; near the start (BIA 27 / Big Foot Trail): Navigation decision point; at 14.7 miles (US 18): Navigation decision point.
Elevation Profile
Gently rolling terrain
3,404 ft1,339 ft
Total Climb
683 ft
Total Descent
2,140 ft
Highest Point
3,404 ft
~30 mi in
Elevation Range
2,065 ft
Towns Mentioned on Route Signs
Based on OSRM destination-sign hints, not a full list of every settlement the road passes.
On the drive from Porcupine, SD to Watertown, SD, road signs begin pointing toward Farmer along the way.
The longest stretch is about 199.1 miles on I 90. The full list of main roads is in the Roads section above.
Yes — we found about 12 rest areas or service plazas within a short detour of the route (from OpenStreetMap). See the Rest Stops tab under Nearby Places for locations and mile markers. Plan to stretch, use the bathroom, and top off fluids every 2–3 hours on longer drives.
It helps. This is a long drive, so arriving tired and in the dark compounds. If the last hour of the trip is on surface roads or mountain grades, aim to arrive at Watertown, SD before sunset when you can. Check the Trip Plan for departure windows that land you in daylight.
Only with planning. This is a long drive for kids — consider splitting it into two days rather than pushing through. Plan at least 2 meaningful breaks. There are 12 rest areas along the route for bathroom stops.
Mostly yes along the main roads, but rural stretches through SD can have sparse or no coverage. Before you leave, download offline Google Maps or Apple Maps for the route, and consider downloading music or podcasts instead of streaming. If you depend on data for navigation, keep a paper backup of the turn-by-turn directions.
The main spots that need attention: near the start (Main Street): Navigation decision point; near the start (BIA 27 / Big Foot Trail): Navigation decision point; at 14.7 miles (US 18): Navigation decision point.
Not recommended in a single day. At 7.8 hours each way, a round trip means 15.7 hours of driving — that is an unsafe level of fatigue for most drivers. Plan at least one night at Watertown, SD before the return drive.
