Northern, eastern, southern, and westernmost points on a state's highway system

[thspfc]

Only state maintained highways count. (Yes, I know there are some oddities like the Illinois tollways not being state maintained, but please just use good judgement and don't ask questions you know the answer to.)
WI:
Northern is WI-13 at the Sand River in Bayfield County
Eastern is WI-42 at the Washington Island ferry dock
Southern is a tie between several if you aren't being picky, but if you factor in the curve of the earth, WI-32 at the Illinois border is the winner.
Western is the US-10 bridge over the St. Croix River at Prescott.

[JoePCool14]

I appreciate you making it easy for me to figure out Illinois' northern most.

The northern most would be IL-137 (Sheridan Road) which becomes WI-32 going into Wisconsin.
The real northern most would be IL-35 in East Dubuque. (Thanks Brandon!)
The eastern most could possibly be IL-33 or US-50 down by Vincennes, Indiana.
The southern most would have to be US-62 south of Cairo.
The western most looks like it is US-24 through Quincy.

[ozarkman417]

MO:

North: Tie, because most of the northern border lies on a single latitude. Taking in to account the Earth's curvature, it becomes Atchison County V.

South: Tie. Southern end of the Bootheel is at Lat 36 N. Candidates: I-55, US 61, MO 108, Supplemental Routes F, DD, TT, and NN. 

East: US Routes 60 & 62.

West: Once again Atchison County V.

[US 89]

Southern is a tie between several if you aren't being picky, but if you factor in the curve of the earth, WI-32 at the Illinois border is the winner.

North: Tie, because most of the northern border lies on a single latitude. Taking in to account the Earth's curvature, it becomes Atchison County V.

How are these at all related to the curvature of the earth? Theoretically, the state lines are supposed to follow an exact parallel of latitude - the only reason they don't necessarily run perfectly east-west is because 19th century surveyors could only be so accurate.

[Thing 342]

(excluding secondary routes)

N: US-522 at the VA/WV border.
S: A bunch along the VA/NC border, but I think that due to surveying errors, US-258 may be the furthest south.
E: Eastern end of VA-175 on Chincoteauge Island.
W: US-58 at the VA/TN Border.

[Flint1979]

The northern most highway in Michigan is M-26, slightly further north of US-41 between the Brockway Mountain Drive ends.

The southern most highway in Michigan is M-49, slightly south of every state maintained highway east of it.

The eastern most highway in Michigan is a tie with I-69 and I-94 at the Bluewater Bridge.

The western most highway in Michigan is US-2.

[froggie]

The following are approximate for Vermont:

Northern:  due to surveying errors and the Canadian border not exactly following an exact straight parallel, it's potentially one of three crossings:  I-89, VT 108, or VT 253.

Eastern:  VT 253's border crossing to Quebec.

Southern:  Same as before...surveying errors put it at VT 142 in Vernon.

Western:  The VT 17/NY 185 "Champlain Bridge".

[WNYroadgeek]

New York:

North: 4-way tie (NY 30, NY 189, NY 276, NY 374)
South: NY 440
East: NY 27
West: 4-way tie (NY 5, NY 17, NY 426, NY 430)

[Occidental Tourist]

Eastern CA is CA 62 at Parker Dam.
Southern CA is I-5 at the San Ysidro Border Crossing.
Western CA is CA 211 at Ferndale.
Northern CA is US 101, US 199, I-5, US 97, CA 161, CA 139, and US 395, all across the 42nd parallel.

edited.

[Bruce]

For Washington:

Westernmost - SR 110 at La Push, a small coastal village surrounded by Olympic NP
Easternmost - US 12 between Clarkston and Lewiston, ID as it crosses the Snake River, which is slightly east of the Idaho straightline at 117 degrees east
Southernmost - SR 14, as it runs along the Columbia River; the southernmost point seems to be southeast of Washougal
Northernmost - Any Canadian border crossing (I-5, SR 543, SR 539, SR 9, SR 9 Spur, US 97, SR 21, US 395, SR 25, SR 31)

[TheHighwayMan3561]

MN

Northern: several routes crossing the 49th parallel border with Canada
Southern: all routes crossing into Iowa
Eastern: MN 61 crossing the Canadian border at Grand Portage
Western: MN 28 crossing the South Dakota border at Browns Valley, in the little jut formed by the Minnesota River and Lake Traverse

[DandyDan]

MO:

North: Tie, because most of the northern border lies on a single latitude. Taking in to account the Earth's curvature, it becomes Atchison County V.

South: Tie. Southern end of the Bootheel is at Lat 36 N. Candidates: I-55, US 61, MO 108, Supplemental Routes F, DD, TT, and NN. 

East: US Routes 60 & 62.

West: Once again Atchison County V.

Something I didn't know until I read it on Jeff Morrison's Iowa Highway Ends website is that the southern Iowa border (the northern Missouri border) is not straight East-West west of the Des Moines River. He wrote an article about Sullivan's Line and the Honey War at http://iowahighwayends.net/maps/sullivanline.html . Basically, the border creeps further and further north the farther east you go. That said, the most northerly point in Missouri's highway system is probably where MO 81 enters Iowa north of Kahoka.

For Iowa:
North: Everything that goes into Minnesota plus IA 9, which enters South Dakota on its short East-West border northwest of Larchwood
South: US 61/136 crossing the Des Moines River west of Keokuk
East: US 52/IA 64 as they cross the Mississippi River at Sabula
West: IA 3 as it crosses the Big Sioux River west of Westfield

[Bickendan]

Oregon:
North: US 101
East: OR 86
South: US 95, OR 140, US 395, OR 39, US 97, I-5, US 199, and US 101
West: OR 250

[Crown Victoria]

PA:

Northern: PA 5 at the PA/NY border in Erie County
Eastern: Interstate 84 while crossing the Delaware river to enter NY in Matamoras, Pike County
Southern: Due to surveying errors, the southernmost point of PA is south of Hanover, York County. There is no state-maintained road that crosses at this point. As PA's southern border is rather long, there could be several candidates for southernmost road, including a few that run directly on the border (including PA 163 and PA 851).
Western: There are several candidates for westernmost state-maintained route in PA. Again, surveying errors could cause slight deviations from true north-south.

Florida:

Northern: Several routes along the FL/AL border, exactly which one depends on surveying errors.
Eastern: FL A1A in Riviera Beach
Southern: Although US 1 is very close to being the winner, it's FL A1A in Key West (unless the roads at the Southenmost Point marker are state-maintained).
Western: FL 292 along the beach at the FL/AL border

[CardInLex]

KY (looking at Apple Maps on my phone):

Eastern: KY 194
Southern: KY 94
Western: KY 971 (unless there are any state routes in Kentucky Bend–but I don't think there are)
Northern: KY 8

[tdindy88]

For Indiana:

Northern: the most boring of the four extremes, it's whatever highway crosses from Indiana into Michigan. Several state, U.S. and interstate highways do that.

Eastern: Surprisingly more easy to do, it's SR 156 in rural Switzerland County along the Ohio River. The bend of the river juts it further east than the Indiana-Ohio border

Southern: I had originally guessed it would be in Posey County, but nope. Southernmost state highway is SR 161 in Spencer County at the beginning of the the Glover Cary Bridge into Owensboro, Kentucky

Western:Alright, this one is definitely in Posey County. It's SR 62 at the Wabash Memorial Bridge over the Wabash River.

[SectorZ]

Massachusetts:
N: MA 150 in Amesbury entering South Hampton, NH
E: MA 28 in Chatham
S: MA 88 southern terminus in Westport
W: MA 23 in Egremont entering Hillsdale, NY

New Hampshire:
N: US 3 in Pittsburg entering Quebec
E: NH 1B in New Castle
S: NH 38 in Pelham entering Dracut, MA (the border there does go ESE from the CT River ever so slightly - confirmed latitude)
W: NH 119 in Hinsdale entering Brattleboro, VT (NH 9 to north almost as close - but longitude confirms 119)

[thspfc]

Southern is a tie between several if you aren't being picky, but if you factor in the curve of the earth, WI-32 at the Illinois border is the winner.

North: Tie, because most of the northern border lies on a single latitude. Taking in to account the Earth's curvature, it becomes Atchison County V.

How are these at all related to the curvature of the earth? Theoretically, the state lines are supposed to follow an exact parallel of latitude - the only reason they don't necessarily run perfectly east-west is because 19th century surveyors could only be so accurate.

All I did was click on the location on Maps, and the spot where WI-32 crosses into Illinois was at a lower latitude than the spot where WI-35 crosses into Illinois. So I may have been wrong, but I don't feel like checking every single place it could posibly be.

[jeffandnicole]

NJ appears to have 3 easy answers, and 1 vague...

N: NJ 23 in Montague
S: NJ 109 in Cape May.
E: NJ 67 in Fort Lee. Other routes exist though, including 9W and the Palisades. (NJ 36 is close when you factor in Latitude, but still west of NJ 67's eastern-most point.)
W: NJ 49 in Pennsville.

[Jim]

New York:

North: 4-way tie (NY 30, NY 189, NY 276, NY 374)
South: NY 440
East: NY 27
West: 4-way tie (NY 5, NY 17, NY 426, NY 430)

As seen graphically with a METAL vertex extremes search result based on TM data in New York:

[tigerwings]

Ohio
Northern -  Where Ohio 7 and Ohio 531 end at each other in Conneaut.
East -  Several along the PA border.
South - US 52 West of Burlington
West - Several along IN border.

[I-55]

Since Indiana has been done I'll do Mississippi

North - any highway that crosses into Tennessee (US-45, US-61, I-55, I-269, MS-301, MS-309, MS-15 to name a few)

East - US-72 at the Alabama State line east of Iuka

South - US-90 at the Louisiana State line in Pearlington

West - MS-24 western terminus at Fort Adams

[jmacswimmer]

Maryland:

West: 4-way tie between US 219, US 50, MD 39 & I-68 at the WV border in Garrett County
North: Any of the countless routes that touch the Mason-Dixon Line
East: MD 528 in Ocean City
South: MD 380 in Somerset County

[Kulerage]

North Carolina:

Northernmost: Hard to say, but based on surveying errors, my guess is the northern terminus of NC 194
Easternmost: Along NC 12 near Rodanthe
Southernmost: Eastern terminus of NC 904
Westernmost: western end of US 64/74 west of Murphy

[vdeane]

New York:

North: 4-way tie (NY 30, NY 189, NY 276, NY 374)
South: NY 440
East: NY 27
West: 4-way tie (NY 5, NY 17, NY 426, NY 430)

As seen graphically with a METAL vertex extremes search result based on TM data in New York:

Yeah, a combination of surveying errors and an adjustment made to put Fort Blunder on the US side means that the NY/QC crossings are NOT all at the same latitude.  Looking at Google Maps, it appears the NY/PA border is better about staying on the same longitude, though I didn't look THAT closely.

The following are approximate for Vermont:

Northern:  due to surveying errors and the Canadian border not exactly following an exact straight parallel, it's potentially one of three crossings:  I-89, VT 108, or VT 253.

Eastern:  VT 253's border crossing to Quebec.

Southern:  Same as before...surveying errors put it at VT 142 in Vernon.

Western:  The VT 17/NY 185 "Champlain Bridge".

Looking at Google Maps, the northernmost would be VT 108.