WORST location for a traffic incident/road closure?

[webny99]

I'm back to share a long-form of sorts.

The I-95 closure in Philly and subsequent discussion got me thinking, there really shouldn't be that much long-distance traffic on that section of I-95 since NJ has a parallel freeway (I-295) and anyone with endpoints beyond the Philly area should already be using the NJ Turnpike (not to mention I-95 wasn't even continuous until five years ago); US 1 serves as a potential alternate for short-to-medium distance traffic, and the local street network offers several alternatives, none appealing for long-haul traffic but likely serviceable for local traffic. Thus, the impacts of the closure will tend to be dispersed across several alternative roadways depending on origin/destination rather than concentrated on a single alternate route. The overall impact is still notable, but it's mostly manifest as a shift in traffic patterns everywhere rather than a second route becoming completely overwhelmed. This contrasts with the concentric effect often seen with routes in suburban or rural areas (or areas with a fixed street grid) where an incident/closure on route A causes congestion on route B which causes congestion on route C, and so on.

That got me thinking: what is the worst possible location for a roadway incident or closure, in terms of the immediate impact and ripple effects on traffic within a region? It's a surprisingly interesting thought experiment, and I think there's potential for an interesting discussion for each metro area/region across the country.


Interestingly, I happened across the potential answer for the Rochester area on my commute home just a few weeks ago. Prior to leaving, I had checked traffic on Google Maps and identified an incident on NY 104 EB just east of the Bay Bridge. My normal commute doesn't take me that way, but it's a serviceable alternate which I decided to take out of curiosity. The lack of EB traffic was very noticeable for several miles approaching the incident, and it was almost completely empty beyond Bay Rd, beyond which the accident came into view, and it was a bad one. Emergency vehicles dotted the width of the EB carriageway; at least two lanes were fully blocked and if a third lane was open, it was only barely, with traffic getting through one at a time sporadically (and with plenty of rubbernecking, no doubt).

The length of the Bay Bridge gleamed with three lanes of stopped traffic, a rarity caused only by an incident of this severity. I was very thankful to be safe and moving along at speed, but that was short-lived, as traffic ground to a halt as I continued onto 590 SB. That's when I realized the scope of the situation: everyone wanting to avoid the Bay Bridge would be forced south to an alternate through the Irondequoit Bay valley. That meant that when NY 104 EB backed up as far as the NY 590 interchange, traffic had been pouring onto NY 590 SB to access NY 404. Sure enough, I stuck to the left lane and soon found out that the line to turn left onto NY 404 had backed up onto the 590 mainline and slowed mainline traffic all the way to NY 104. Once past that bottleneck, I had clear sailing, but NB traffic was at a crawl. I correctly surmised that both NY 286 and Blossom Rd would be backed up as well (primarily due to NB traffic, with some added SB traffic continuing beyond NY 404 adding to things as well), so I continued down to Penfield Rd to complete an unusual commute home in almost double the normal time.

It was only then that I had a chance to dive back into Google Maps for a closer analysis of the traffic impacts of the accident. These impacts can be applied to any similar incident, and are summarized in part as follows:

Immediate Impacts
1. Traffic on NY 104 EB backs up 1.5 miles to the NY 590 interchange
2. NY 590 NB mainline backs up to NY 404 from the ramp to NY 104 EB (common at rush hour due to the single lane ramp, but it's usually just slow, not stopped)
3. NY 104 EB traffic begins seeking alternates via NY 590 SB

Secondary Impacts
1. NY 590 NB backup extends south to I-490
     a. NB traffic begins seeking alternates via NY 404, NY 286, and Blossom Rd
     b. NB, EB, and WB approaches to I-490/590 interchange become congested (common at rush hour, but it's usually just slow, not crawling/stopped)
2. NY 404 EB exceeds signal capacity at Winton Rd, ensuring a WB green arrow every cycle
     a. NY 404 backs up to NY 590
     b. SB traffic exiting at NY 404 backs on to NY 590 mainline
     c. NB traffic exiting at NY 404 backs on to NY 590 mainline, slowing it further
     d. EB traffic on NY 404 backs up to Culver Rd, local traffic seeks alternates
3. Plank Rd EB exceeds signal capacity at Creek St, backs up to NY 404
4. NY 404 EB exceeds signal capacity at Creek St/Bay Rd, backs up and interferes with local traffic
5. NY 286 EB exceeds left turn capacity at Blossom Rd/Creek St and backs up, eventually as far as N Landing Rd
6. Blossom Rd NB exceeds signal capacity at NY 286 (note lack of right turn lane) and backs up, eventually as far as N Landing Rd


Tertiary Impacts
1. NY 590 NB traffic already north of NY 404 seeks alternatives, including U-turn via Exit 9 (Norton St) and Exit 11 (Ridge Rd), adding to congestion on NY 590 SB and local streets such as Culver Rd and Helendale Rd
2. Winton Rd becomes the primary alternate to NY 590 NB west of the bay
     a. Winton Rd becomes gridlocked in both directions between I-490 and Atlantic Ave
     b. Browncroft Blvd and Blossom Rd become gridlocked between NY 590 and Winton Rd
3.   Creek St NB to Bay Rd NB becomes the primary alternate to NY 590 NB east of the bay
     a. Creek St NB exceeds signal capacity at Plank Rd and NY 404
          i. Creek St SB left turn at Plank Rd backs up (note absence of green arrow)
          ii. Creek St backs up in both directions between NY 404 and Plank Rd
          iii. Traffic seeks local alternates, including Yorktown Dr and unnamed cut through to NY 404
     b. Bay Rd NB exceeds signal capacity at Ridge Rd
     c. Creek St SB left turn at NY 286 backs up (note absence of green arrow)
4.   Traffic on NY 286 seeks alternates to avoid left turn onto Creek St.
     a. NY 286 exceeds signal capacity at Panorama Trail and Qualtrough Rd
     b. NY 286 backs up at lane merge beyond Qualtrough Rd
     c. Traffic seeks local alternates, including Qualtrough Rd, Clark Rd, and Scribner Rd
5. NY 404 exceeds signal capacity at Five Mile Line Rd and backs up to where it joins/splits from Ridge Rd (a common occurrence, but usually mid-day or early afternoon, not in the evening)
6. Five Mile Line Rd becomes primary alternate to Creek St/Bay Rd and backs up at Plank Rd and NY 404
7. This is the approximate shortest route around the bay with no backups directly resulting from the incident.

That concludes my case that any incident occurring on or near the Bay Bridge has potential to cause greater traffic disruption than an equivalent incident at any other location in the Rochester region.




Secondly, what if instead of looking at an entire region, we look at a single long-distance corridor? That's exactly what I decided to do with I-90 between Buffalo and Syracuse. When I noticed an incident near Montezuma the other day, I started looking at the impact and noticing how much worse it was on that segment than it might be on another segment, and eventually landed on the following "power rankings" , from best to worst segment for an incident or closure to occur. I-290 and I-690 were my endpoints for this analysis.


12. [Exit 50] I-290 to [Exit 49] NY 78
At first glance, this seems like an odd choice for location best able to accommodate an incident or closure — after all, it is the second-busiest section on the list and serves Buffalo area commuter traffic as well as long-haul traffic. But there were two factors that tipped the scales: first, the relative length of the segment; at just over 3 miles in length, it's the shortest segment on the list, so any pain points are confined to a short distance. Second, the availability of four-lane alternates; NY 33 is a decent four-lane alternate that runs parallel just a mile to the south, and while part of it has signals, they're usually timed favorably, and traffic is usually light east of the airport. There's also NY 5, and while that has its own share of traffic woes, it is four lanes as far as NY 78 and can function as a reasonable alternate, and Wehrle Dr can serve as an alternate to NY 5. All told, I wouldn't panic if forced to find an alternate around this section of the Thruway.


11. [Exit 47] I-490 to [Exit 46] I-390
If it wasn't clear already, I weighted the availability of a four-lane alternate very heavily in this exercise, and I-490 is a great high speed one with low traffic for much of the length that would be needed to bypass this segment of the Thruway. Using the entire length of I-490 to bypass both this segment and the next one on the list adds about 10-12 minutes to a LeRoy to Victor trip. It's not perfect, but it is more than serviceable as a long-distance alternative. Traffic would be encouraged to use I-390 to get to/from I-490, as the eastern half of I-490 is more congestion-prone, while Scottsville and West Henrietta loom as obstacles for traffic attempting to stay further south. Meanwhile, I-490 to NY 252 (via NY 259 and NY 33A) saves some mileage and looks good on paper, but the "last mile"  from NY 383 to I-390 may have you wishing you just stuck to the interstates.


10. [Exit 46] I-390 to [Exit 45] I-490
Despite the eastern I-390-to-I-490 segment being almost five miles shorter than its counterpart above, it's easy to identify why an incident here would be more problematic. First, if you're heading east and already passed LeRoy, you're stuck with one of the gnarlier Thruway-adjacent areas to navigate, even without congestion. And second, that shorter distance and the relative circularity of the interstate alternative(s) via I-490 may encourage traffic to find a more localized alternate closer to the Thruway, but, as alluded to above, there is an extreme dearth of good ones parallel to this segment. NY 252 and anything in the village of Pittsford are best avoided even at the best of times, and anything else north of the Thruway requires upwards of a dozen turns through Mendon, Pittsford and Perinton exurbia. NY 251 is serviceable, but not well-suited to long-haul traffic with numerous speed zones, plus Mendon and Fishers to deal with on the eastern half of the trek. In short, it's I-490 or bust, which could be both a blessing and a curse, but at least having that option available saves this segment from falling down the list.

(Side note: I kind of want to see the Thruway closed between the ends of I-490 at least once in my lifetime. The traffic impacts on I-490 and throughout the Rochester area, which is usually almost entirely free of long-distance traffic, would be a subject of incredible fascination.)


9. [Exit 42] NY 14 to [Exit 43] NY 414
This was one of the simpler segments to rank since it's relatively short and the alternative is so obvious. It's the NY 318 show, and that means it's actually pretty bearable by the standards of Thruway alternates. Most of it is 55 mph, you can go straight from the Exit 42 ramp to NY 318 and vice versa, and there's only one stoplight (the one at the outlets) between NY 14 and NY 414. The short connection to/from the Thruway via NY 414 is no fun and would greatly benefit from a widening, but at least there's turn lanes and arrows at both the Thruway and NY 318. NY 96 is also a decent alternative from Waterloo/Seneca Falls and points south, with an overbuilt junction at NY 14 that can handle plenty of extra volume.


8. [Exit 44] NY 332 to [Exit 44] NY 21
NY 96 is the primary alternative to this segment, as the road network to the north between the Thruway and NY 31 is not suitable for long-distance traffic. Shortsville Rd is a second serviceable alternate just south of NY 96, while Collett Rd and Kyte Rd combine to form a third alternate north of NY 96. The area is essentially exurban, so NY 96 is already fairly busy on this stretch, with a stoplight at CR 28 and surprising lack of one at CR 8. Manchester and Farmington have potential to become congested, but the availability of options south of the Thruway and the relatively short distance figure to keep this segment manageable.


7. [Exit 48A] NY 77 to [Exit 48] NY 98
We've reached the Batavia section of the list, also known as the "grin and bear it"  section. Batavia suffers from sub-optimal connectivity between the various approaching state routes and the Thruway interchange on NY 98, as traffic tends to converge on the overburdened NY 5/NY 33/NY 63/NY 98 intersection on the west side of the city. There are a few local shortcuts to get between NY 5 and the Thruway interchange, namely Union St and Park Rd, and add in River St if you want to get to NY 33 instead of NY 5. Fortunately, NY 5 is four lanes between Batavia and Bushville, allowing traffic to break up before/after the remaining two lane stretch to NY 77, and NY 33 is just a mile south if NY 5 becomes overburdened. There are even some serviceable options north of the Thruway that avoid Batavia entirely if you're prepared for sub-state route levels of maintenance.


6. [Exit 48] NY 98 to [Exit 47] I-490
The drawbacks of Batavia's spoke-like road network are even more evident on the east side of the city. Getting from the Thruway to NY 33 requires navigating a maze of local and residential streets, or slogging it out through a sea of stoplights on NY 33's overlap with NY 5. Once you get to NY 33 and get out of Batavia, though, it's clear sailing on perhaps one of the best two-lane alternates on the list. Even better, traffic can split up partway, with those bound for I-490 staying on NY 33, while those returning to the Thruway can take Griswold Rd to NY 19. As an alternate to NY 33, NY 5 offers several miles of four-lane road enroute to LeRoy, where traffic can use NY 19 to return to the Thruway.


5. [Exit 40] NY 34 to [Exit 39] I-690
Things start to get interesting in the top five. The final stretch west of Syracuse is a long one, at nearly 15 miles. Fortunately, NY 31 covers most of that distance and is reasonably well-equipped to do so, even S-curving to avoid the village of Jordan. Getting from Ionia to the Thruway, however, requires the use of NY 173 and Brickyard Road (the latter of which is well signed as the primary route to the Thruway despite not being a state route). From there, traffic can get directly on I-690 or return to the Thruway, reducing the burden on I-690 Exit 2. Remaining on NY 173 to Herman Rd is a secondary option that goes through the hamlet of Warners.


4. [Exit 43] NY 21 to [Exit 42] NY 14
The primary alternate to this segment is NY 96, which is in many respects an "average"  alternate to the Thruway, but the distance of over 13 miles is a factor, as is the fact that it goes right through the heart of Phelps. The roughly two-mile 30 mph zone through Phelps is often slow even without any additional traffic. Notably, it also serves as the primary route from Newark (pop. 9k) to/from the Thruway and points east, adding another layer of through traffic. The junction of NY 96 and NY 88 lacks turn arrows and right turn lanes, which makes it prone to backups, especially EB. Fortunately, NY 96 takes an S-curve to avoid Clifton Springs, and largely avoids Manchester, although the lack of a traffic signal on NY 21 at the Thruway ramps is problematic. At the other end of the segment, the junction with NY 14 is overbuilt and can easily handle extra traffic volume, but unfortunately, that just shifts the bottleneck back to Phelps.


3. [Exit 45] I-490 to [Exit 44] NY 332
At less than four miles in length, this should be an easy segment to detour around, right? Not so fast. That overlooks a multitude of complicating factors, starting with the fact that this is the busiest segment on the list, and the only one with six lanes. Then factor in the village of Victor located just south of the Thruway and the lack of alternates north of the Thruway, and things start to go downhill fast. The Thruway's transition to AET in 2020 has been marvelous overall, but one large problem left unresolved is the bottleneck at the end of EB I-490 created by the toll booth removal. It's almost never possible to navigate at speed, and regularly backs up beyond Exit 29 on summer Fridays. Adding to this problem, the only alternate is Exit 29, which lacks access to NY 96 NB and instead dumps more traffic onto the already overburdened NY 96 SB heading into the village of Victor, which regularly backs up to NY 251 without any additional traffic. As such, Cork Rd to Dryer Rd to School Rd to Boughton Hill Rd has become the unofficial bypass of Victor, but that ends up at a brutal four-way stop with NY 444 that has desperately needed a traffic signal for over a decade, and would be a non-starter with any extra traffic. On the other hand, going south of Boughton Hill Rd isn't viable either, so you're pretty much stuck dealing with one or more major chokepoints. To make things worse, anything north of the Thruway is hard to access (either backtracking on NY 96 to High St or using the one-lane Willowbrook Rd) and is prone to becoming overwhelmed quickly due to the exurban nature of the area and lack of traffic control (i.e. signals) at intersections. On the NY 332 end of things, NY 96 is a total slog east of Victor, and Farmington has become a full-blown suburb itself in recent years, so getting to/from the Thruway interchange at NY 332 is not fun to deal with either.


2. [Exit 49] NY 78 to [Exit 48A] NY 77
If Clarence is Buffalo's equivalent of Victor, I would take it traffic-wise any day of the week, and that's even despite the slog that is NY 5. The problem is that Clarence is sorely lacking in access to the Thruway, as evidenced by the nearly 16-mile segment from Bowmansville to Pembroke. With NY 5 venturing through sub- and exurbia on much of this stretch, NY 33 serves as the primary alternate for long-distance traffic, but it's plenty busy even without extra traffic. It also meets NY 77 in the village of Corfu, where heavy truck traffic making turn movements creates problems, and EB traffic also has a left turn that can snag traffic, not to mention confuse drivers. US 20 is too far south for most traffic and also passes right through the hamlet of Town Line and village of Alden. Some local alternates exist for portions of the route, but the distance is so considerable that traffic will likely stick to a main route or end up on one of them anyways, and that inevitably means a very long slog, primarily on two-lane roads.


1. [Exit 41] NY 414 to [Exit 40] NY 34
It's never a good sign when 30 minutes is your starting point to get between Thruway exits via an alternate route — and that's with no traffic whatsoever. Then add interstate through traffic to an already overburdened stretch of NY 414, very busy sections of NY 318 and US 20/NY 5 complicated by a gnarly five-point junction with NY 89, a National Wildlife Refuge with limited road crossings, the hamlet of Montezuma, the quaint village of Port Byron, and a slog through Weedsport, and you're looking at something pretty close to a nightmare to bypass this 16.5-mile segment of the Thruway no matter how you cut it. I would recommend taking NY 31 to NY 89 to avoid US 20/NY 5, but that still leaves NY 318 or various alternates using local roads to get back to NY 414. At one point during the incident last week, Google Maps started recommending NY 370 to NY 104 between Syracuse and Rochester (which is mostly two lanes and normally at least 10 minutes longer) and that's when I knew this was the clear-cut choice for number one on the list.


Thanks for reading! Thoughts and commentary specific to your own region or to these two case studies are welcome.

[Max Rockatansky]

Any accident or weather closure on I-5 along the Ridge Route corridor between Castaic and Grapevine Village causes apocalyptic levels cascading traffic problems.  There is close to zero redundancy and what little there is tends to be two lane/remote mountain roads like San Francisquito Canyon Road. 

[LilianaUwU]

Anywhere on the Alaska Highway west of BC 37 cuts Alaska off from the rest of the world.

There's also ON 17 west of Kenora, which cuts off Canada in two in the event of a closure (and it happened before).

[kalvado]

Anywhere on the Alaska Highway west of BC 37 cuts Alaska off from the rest of the world.

There's also ON 17 west of Kenora, which cuts off Canada in two in the event of a closure (and it happened before).

How much through traffic is actually on that road compared to southern routings through US?

[Brandon]

Around Metro Chicago, it's anything on the Borman/Kingery Expressway (I-80/94).  The Toll Road (I-90) is difficult to reach from I-80/294, and the other alternates are all surface streets through the area with US-30 fairly far to the south.  Unfortunately, incidents are all too common on the Borman/Kingery.

[VTGoose]

A wreck just about anywhere on I-81 in Virginia will tie up traffic for hours/miles due to the volume of traffic on the highway. While there are some places that have parallel U.S. 11 or other roads as an alternative, other locations have no easy outlet for traffic. A typically bad section is the 10 miles northbound between exit 118 at Christiansburg and the Ironto exit. Two lanes, up and down profile, lots of trucks, and no way out once past the exit ramp at Christiansburg.

I-95 in South Carolina is another bad location for an incident -- two lanes and not many alternatives. What alternatives there are are also two lanes and can get just as congested as the interstate.

[1995hoo]

....

I-95 in South Carolina is another bad location for an incident -- two lanes and not many alternatives. What alternatives there are are also two lanes and can get just as congested as the interstate.

Heh. Some years back for our drive to Florida I had taken US-29 south through Greensboro and we stopped for the night near Charlotte. Heading south on I-26 the next day, we encountered a long line in the right lane waiting to exit to I-95 south. A check of Waze revealed a big wreck that had I-95 backed up as well. I wound up continuing on I-26 all the way down to Charleston and taking US-17 back to the Interstate. At the time, US-17 was two lanes (widening is now complete). The detour added 56 miles to the trip, so it probably didn't save us all that much time in the end, but I'm much happier when I'm moving (and, in that case, using roads that were new to me).

If that happened again, I'd consider trying US-15 south to Walterboro instead of going all the way to Charleston, although my wife tends to be happier on Interstates or four-lane highways. She seems not to like it when I pass people on two-lane roads. Plus, as you note, US-15 is likely to get congested because it's the obvious alternate when you look at a map.

[GaryV]

A long time ago, our family was coming home from Florida after New Year's. I-75 hadn't been completed in GA. A semi hauling fruit had tipped over on the exit ramp at the end of the completed freeway. That caused quite the backup. Motor homes were pulling off to the side of the highway to cook and eat meals. My dad found an off-ramp and we, pre any GPS, found our way northward through small towns. Several times we crossed under the freeway or saw it off to the side and it was still clogged up.

[WillWeaverRVA]

A wreck just about anywhere on I-81 in Virginia will tie up traffic for hours/miles due to the volume of traffic on the highway. While there are some places that have parallel U.S. 11 or other roads as an alternative, other locations have no easy outlet for traffic. A typically bad section is the 10 miles northbound between exit 118 at Christiansburg and the Ironto exit. Two lanes, up and down profile, lots of trucks, and no way out once past the exit ramp at Christiansburg.

I-95 in South Carolina is another bad location for an incident -- two lanes and not many alternatives. What alternatives there are are also two lanes and can get just as congested as the interstate.

I-95 between Ashland, VA and I-295 also sees a lot of accidents that cause massive backups (sometimes as much as 5 miles) since that segment is only 6 lanes and has a ton of truck traffic.

Closures on I-95 in downtown Richmond due to accidents or flooding (the road is extremely prone to severe flooding) can paralyze the entire metro area.

[skluth]

It really sucks around here when a crash closes I-10 in San Gorgonio Pass. There is no alternative, though it would be very simple to build a two-lane road parallel to the interstate through the pass. There is a way through the middle section, but it doesn't go to either end as there is no eastbound alternative at exit 102 (Ramsey St) and no westbound alternative at exit 111 (CA 111); note that both are simple Y-interchanges. Crashes on this section of I-10 can block traffic for hours. The only way around is using the curvy highways through the mountain ranges north and south of the pass.

Similar problems happen in several places out west, including other places on I-10 between Indio and Blythe along with Cajon Pass and the Grapevine, but this is one of the worst in the country as I-10 is four lanes in each direction through the pass. These crashes also often occur due to high winds through the pass so cleanup crews can be sandblasted while trying to clean up a crash site.

[StogieGuy7]

Around Metro Chicago, it's anything on the Borman/Kingery Expressway (I-80/94).  The Toll Road (I-90) is difficult to reach from I-80/294, and the other alternates are all surface streets through the area with US-30 fairly far to the south.  Unfortunately, incidents are all too common on the Borman/Kingery.

I was coming here to say exactly this. A wreck on the Borman basically blocks the flow for 25% of the traffic trying to travel across the US. Because there are only 2 limited access highways that travel around the bottom of Lake Michigan (which you can't drive over - and there are only a few very slow ferries, during good weather), if you need to travel east-west between northern cities like Minneapolis, Seattle, Portland, Chicago, Milwaukee and the likes of Detroit, Buffalo, Cleveland, Pittsburgh, New York or Boston, then this is the only real way.  You have I-90 going through the apocalypse (er, Gary) and the Borman. Getting to I-90 isn't easy and coming from farther to the west/north, there are only a few times during the day you'd want to try it as it this requires a drive right through downtown Chicago. Brutal.  Personally, I wouldn't try it unless you can get through there before 6 am, between 10:00 am and 2:30 pm or after 9:00 pm. 

Oh, and there are no good surface street alternates if the Borman goes down. Only a drive through Gary, which is a drive you'd never, ever, want to take after dark.

This area even makes the I-5/I-405 Y near Tustin, CA look tame.

[LilianaUwU]

Anywhere on the Alaska Highway west of BC 37 cuts Alaska off from the rest of the world.

There's also ON 17 west of Kenora, which cuts off Canada in two in the event of a closure (and it happened before).

How much through traffic is actually on that road compared to southern routings through US?

I'm pretty sure the AADT is in the low to medium four digits, but it's still the only strictly Canadian connection between two halves of Canada.

[CtrlAltDel]

There's also ON 17 west of Kenora, which cuts off Canada in two in the event of a closure (and it happened before).

How much through traffic is actually on that road compared to southern routings through US?

I'm just spitballing here, but I could only imagine almost all of it, if only to avoid having to go though customs and whatnot twice.

[JayhawkCO]

For Colorado, the worst location is, unfortunately, the one that happens most - Glenwood Canyon. 3 hour+ detour every time it happens.

[1995hoo]

Anywhere on the Alaska Highway west of BC 37 cuts Alaska off from the rest of the world.

There's also ON 17 west of Kenora, which cuts off Canada in two in the event of a closure (and it happened before).

How much through traffic is actually on that road compared to southern routings through US?

I'm pretty sure the AADT is in the low to medium four digits, but it's still the only strictly Canadian connection between two halves of Canada.

Just to nitpick, the Nipigon River Bridge isn't on the section west of Kenora, although it is still a location where there's only one road connection between east and west. Google Maps says it's 601 km via the most direct route from the bridge to the segment west of Kenora.

[Bruce]

Any of the mountain passes in the Cascades, as we've seen a few times. The closures for BC during the 2021 floods caused a run on gas and supplies in Metro Vancouver.

For Seattle, there's two critical chokepoints on I-5: around Joint Base Lewis-McChord between Lacey and Lakewood; and between Everett and Marysville. Both jam up during normal times (on weekdays and weekends), but when there's a collision that closes just one lane, all hell breaks loose.

[vdeane]

Around here, anything on I-87 near the Twin Bridges is going to tie things up.  The only real alternate is US 9, and while US 9 is four lanes, anything leading to/from it is going to get quite jammed (I've seen exit 5 backed up onto the mainline even) if traffic starts diverting.

On the Thruway, exits 15A-16 is an insidious stretch.  NY 17 is four lanes, but that section of Thruway is a six-lane section that is very busy (it regularly backs up in peak travel directions on the weekend even without an incident), and the long distance between the exits means that one can get quite deep into it before realizing that there's an incident.  Twice now I've even been caught in an incident that shut down the entire northbound direction of travel for a couple hours, and it's not like I travel it an unusually large amount of the time or anything, so my blood pressure always goes up when passing 15A and goes back down again after passing 16 (never had an issue southbound, but then again, I almost always hit that in the morning).

[TheHighwayMan3561]

For MSP I would say the  I-694 Mississippi River bridge, which is adjacent to the junction of four major routes with no easy alternatives.

[Max Rockatansky]

It really sucks around here when a crash closes I-10 in San Gorgonio Pass. There is no alternative, though it would be very simple to build a two-lane road parallel to the interstate through the pass. There is a way through the middle section, but it doesn't go to either end as there is no eastbound alternative at exit 102 (Ramsey St) and no westbound alternative at exit 111 (CA 111); note that both are simple Y-interchanges. Crashes on this section of I-10 can block traffic for hours. The only way around is using the curvy highways through the mountain ranges north and south of the pass.

Similar problems happen in several places out west, including other places on I-10 between Indio and Blythe along with Cajon Pass and the Grapevine, but this is one of the worst in the country as I-10 is four lanes in each direction through the pass. These crashes also often occur due to high winds through the pass so cleanup crews can be sandblasted while trying to clean up a crash site.

My solution ended up being Dillon Road and CA 62.  But then again I wasn't headed to an endpoint destination in the Inland Empire or Los Angeles. 

[Hobart]

Around Metro Chicago, it's anything on the Borman/Kingery Expressway (I-80/94).  The Toll Road (I-90) is difficult to reach from I-80/294, and the other alternates are all surface streets through the area with US-30 fairly far to the south.  Unfortunately, incidents are all too common on the Borman/Kingery.

I was coming here to say exactly this. A wreck on the Borman basically blocks the flow for 25% of the traffic trying to travel across the US. Because there are only 2 limited access highways that travel around the bottom of Lake Michigan (which you can't drive over - and there are only a few very slow ferries, during good weather), if you need to travel east-west between northern cities like Minneapolis, Seattle, Portland, Chicago, Milwaukee and the likes of Detroit, Buffalo, Cleveland, Pittsburgh, New York or Boston, then this is the only real way.  You have I-90 going through the apocalypse (er, Gary) and the Borman. Getting to I-90 isn't easy and coming from farther to the west/north, there are only a few times during the day you'd want to try it as it this requires a drive right through downtown Chicago. Brutal.  Personally, I wouldn't try it unless you can get through there before 6 am, between 10:00 am and 2:30 pm or after 9:00 pm. 

Oh, and there are no good surface street alternates if the Borman goes down. Only a drive through Gary, which is a drive you'd never, ever, want to take after dark.

This area even makes the I-5/I-405 Y near Tustin, CA look tame.

I third this. A truck overturned on the highway during my morning commute eastbound to Gary, and I was stuck on the highway for three, awful hours. It's especially brutal if you're in the thru lanes right after 94 merges on, because you aren't getting off until you get to Calumet. It's already bad during the day, and it needs all the help it can get to not suck.

[plain]

A wreck just about anywhere on I-81 in Virginia will tie up traffic for hours/miles due to the volume of traffic on the highway. While there are some places that have parallel U.S. 11 or other roads as an alternative, other locations have no easy outlet for traffic. A typically bad section is the 10 miles northbound between exit 118 at Christiansburg and the Ironto exit. Two lanes, up and down profile, lots of trucks, and no way out once past the exit ramp at Christiansburg.

I-95 in South Carolina is another bad location for an incident -- two lanes and not many alternatives. What alternatives there are are also two lanes and can get just as congested as the interstate.

I-95 between Ashland, VA and I-295 also sees a lot of accidents that cause massive backups (sometimes as much as 5 miles) since that segment is only 6 lanes and has a ton of truck traffic.

Closures on I-95 in downtown Richmond due to accidents or flooding (the road is extremely prone to severe flooding) can paralyze the entire metro area.

Another horrible spot is east of the city on I-64 between Exit 205 (VA 249 Bottoms Bridge) and Exit 227 (VA 30). The parallel US 60 and VA 249/30 alternatives gets far enough away from the interstate here to not easily remedy major problems when there's an incident (VA 249/30 routing isn't too terribly far away, but it's only 2 lanes between those points compared to the 4-lane US 60).

[Great Lakes Roads]

Anywhere along I-65 between Indy and Chicago...

[zachary_amaryllis]

I can't come up with anything specific, but in general...

Places where the highway is dropped down into a narrow trench, with no turnouts/shoulders/etc. Nowhere to go to avoid anything, and you're trapped until the next exit. Places like tunnels/bridges that have no way out/off, or the approaches thereto.

But I'll also throw in rural areas in general, especially if there's little traffic and no cell service.

Come to think of it, I drive in a lot of rural places with no cell service.

[kphoger]

I can't come up with anything specific, but in general...

Places where the highway is dropped down into a narrow trench, with no turnouts/shoulders/etc. Nowhere to go to avoid anything, and you're trapped until the next exit. Places like tunnels/bridges that have no way out/off, or the approaches thereto.

Elevated highways, too.

[ibthebigd]

Clays Ferry Bridge between Lexington and Richmond Kentucky comes to mind.

SM-G996U