Beltways That Work, and Beltways that Don't

[PColumbus73]

If the purpose of building a beltway (or bypass) around a city is to divert through traffic away from the center, which ones do it better, and which ones do it worse?

If you're approaching said beltway, would it be easier to use it, or simply stay on the mainline through the city?

From personal experience, I-295 around Richmond works very well, when I've traveled through I-295 has been the default route.

On the other hand, I-275 in Cincinnati is too inconvenient to use for bypassing.

[1995hoo]

Obviously, given my location, the beltway I know best is the Capital Beltway, and it's one where there is no great option for passing straight through instead of bypassing because the mainline straight-thru route was never built. In recent years, it's been more possible to take I-395 into DC, then connect via I-695 over the new 11th Street Bridge to go north on DC-295 to the Baltimore–Washington Parkway. No reasonable person familiar with the area would normally do that, though, just as no reasonable person would take I-295/DC-295 for thru travel either. Most people coming from the east or west would not attempt to go through the District to connect between US-50 in Maryland and either I-66 or US-50 in Virginia, either. The Beltway is just plain a better option.

Some that I find less useful:

I find I-485 around Charlotte to be fine if I'm passing through on I-85 and I take the portion of I-485 located northwest of I-85. (I've never passed through on I-77 as every time I've approached on that road from the north, Charlotte has been my destination, and when I've used I-77 south of Charlotte I've been connecting to or from I-85.) I've never taken the other portion of I-485 located southeast of I-85 because it's way too far out of the way—unlike some cities where the 2di sort of "bisects" the beltway, in the Charlotte area both I-85 and I-77 are quite far to the north and west relative to most of I-485. If you look at a map, it becomes apparent what the problem is: I-485 hangs off I-85 sort of like a nut sack.

Setting aside that you can't use the eastern portion of I-695 right unless your last name is Knievel or Duke, I often found I-695 around Baltimore similar for long-distance travel. The eastern part over the bridge was a good bypass for the tunnels if there was heavy traffic or on Boy Scout trips when we had camping fuel in the trunk, but the western side was a much longer distance around with much more traffic. I used the western side a few years back to connect to I-83 on the way to Hershey for a Bears game and it reminded me why I prefer to use I-270 and US-15 via Frederick instead—the western side of I-695 was just downright unpleasant with the extremely aggressive drivers.

I have not used I-640 around Knoxville or I-287 in New Jersey for similar reasons—looking at them on a map, they look like they go too far out of the way. I ought to measure them out. I believe I once measured I-287 and it turned out it wasn't as much added distance as it appeared to be.

[wanderer2575]

I-275 Cincinnati doesn't work as an alternative to I-75.  It better functions as a bypass of the city when connecting from one route to another.  That's something to consider.

[roadman65]

I-287 for NYC don't work for through traffic, but connecting from  I-95 to I-78 or from I-80 to I-87 works.

I-295 in Jacksonville doesn't cause of sprawl being built. Florida don't generally build bypasses as new roads are to encourage more development than to help other congested arteries.

I-475 in GA works better than I-75 through Macon.

I-435 in KS- MO works only to connect highways, not to bypass so much Kansas City.

[1995hoo]

....

I-295 in Jacksonville doesn't cause of sprawl being built. Florida don't generally build bypasses as new roads are to encourage more development than to help other congested arteries.

....

I forgot about that one. I like using the eastern side of I-295, more recently combined with FL-9B, on long-distance trips when I want to continue on I-95 past Jacksonville. I quite like going over the Dames Point Bridge, for example, because it's an interesting diversion from boring old I-95. I find that portion of I-295 usually works pretty well unless there's been an accident. The western side, on the other hand, is one I use solely for connecting purposes.

[triplemultiplex]

I-694 is great bypass of the core cities of Minneapolis and St. Paul.  Especially since they fixed the lane drop problem years ago.

For north-south travelers, I-465 in Indy works okay.  Though they seem to have it under perpetual construction.

Down in Louisville though, I-265 is pretty much useless for I-65 thru traffic.  It serves the other spokes much better.

Salt Lake City; usually it was an easier ride on 215 vs 15 when I was out there at peak times.  But if it's off peak, 15 has a lot of capacity and moves well enough to where the beltline adds time.

The times I've been on the 470 beltway in Denver, it did not look like it was being used much as a bypass of Denver by many vehicles.  It's pretty far out and the toll probably discourages thru trucks and there were few trucks in general.  I have the most experience between I-76 and CO 83, so if it was being used by thru trucks on 25 or 70, I would've seen it.

Oh I-255 is always faster than I-55 thru St. Louis.  And tho I haven't made that particularly journey myself, 270 is obviously the better option for I-70 thru traffic.  I have yet to use St. Louis' beltway to follow the spirit of 66 en route to the southwest, so I can't grade that on personal experience. (The one trip that direction I've made so far, I wanted to clinch the east end of I-44. )

Kansas City's I-435; for my directions of travel, it didn't save any time.  Really feels like you're out in the sticks in the NW quadrant.  And the south side of it got pretty thick on me.  Probably would've been faster to just punch the core.

That covers my personal experience with beltways that go at least most of the way around. (Sorry OKC but your's wasn't finished and it's such a hodge-podge that I don't think it counts.)

[JayhawkCO]

The times I've been on the 470 beltway in Denver, it did not look like it was being used much as a bypass of Denver by many vehicles.  It's pretty far out and the toll probably discourages thru trucks and there were few trucks in general.  I have the most experience between I-76 and CO 83, so if it was being used by thru trucks on 25 or 70, I would've seen it.

The tolls are really high, which is why it isn't used more, but E-470 is definitely used as a bypass during rush hour.


I-405 in Washington works pretty well for avoiding I-5 downtown.

I-470 in Topeka is slower (and costs more) than just staying on I-70.

I-275 in the Tampa area takes far longer than staying on I-75.

[WillWeaverRVA]

I-405 in CA is the classic beltway that doesn't work. Portions of it that weren't as developed when the freeway was originally built were subsumed by the LA metro area's explosive development, and it's not a viable bypass of anything.

[oscar]

I-275 in the Tampa area takes far longer than staying on I-75.

But I-275 in the Tampa area is a loop from the mainline to city centers, not a bypass of anything. I-75 is the real bypass route, even though it's a 2di.

[JayhawkCO]

I-275 in the Tampa area takes far longer than staying on I-75.

But I-275 in the Tampa area is a loop from the mainline to city centers, not a bypass of anything. I-75 is the real bypass route, even though it's a 2di.

I suppose. I was just running off of even numbered 2dis by memory.

[Rothman]

Imagine Boston without MA 128 or I-495...

[jlam]

I-185 in SC isn't a very good bypass, not because it's congested, but because its utilization level is very low. For some reason, it's a toll road, so the already poorly located bypass is given another reason to be shunned.

[mgk920]

Whenever I am transiting Chicagoland, I'll use I-94 through the city, except during the commuter times when I'll use the I-294 Tri-State Tollway around.  Most other people use the Tollway, though.


Mike

[plain]

I-840 in TN has to be the most useless beltway (or whatever it's supposed to be) I've ever encountered.

[vdeane]

I-287 in New Jersey for similar reasons—looking at them on a map, they look like they go too far out of the way. I ought to measure them out. I believe I once measured I-287 and it turned out it wasn't as much added distance as it appeared to be.

I-287 for NYC don't work for through traffic, but connecting from  I-95 to I-78 or from I-80 to I-87 works.

I-287 seems to me like it's mainly useful for trucks bypassing the NYC area or connecting to the other interstates or for cars connecting between I-87, I-80, and I-78.  Not so much I-95, however.  For I-95 to/from I-87, it's faster to take the GSP and NJ 17 (Google doesn't even suggest I-287 as an option); for I-95 to/from I-78, it's slightly faster or the same and notably less mileage to take NJ 18.

[PColumbus73]

Some that I find less useful:

I find I-485 around Charlotte to be fine if I'm passing through on I-85 and I take the portion of I-485 located northwest of I-85. (I've never passed through on I-77 as every time I've approached on that road from the north, Charlotte has been my destination, and when I've used I-77 south of Charlotte I've been connecting to or from I-85.) I've never taken the other portion of I-485 located southeast of I-85 because it's way too far out of the way—unlike some cities where the 2di sort of "bisects" the beltway, in the Charlotte area both I-85 and I-77 are quite far to the north and west relative to most of I-485. If you look at a map, it becomes apparent what the problem is: I-485 hangs off I-85 sort of like a nut sack.

I thought about mentioning I-485. I think that one's about 50/50 in terms of effectiveness, the east quadrant between US 74 and I-85 doesn't really work for long-haul traffic.

SC 22 was/is referred to as the Conway Bypass going toward Myrtle Beach, but I don't think it works quite as well to pull traffic off of US 501.

Down in Charleston, I-526 does a better job at dispersing traffic off I-26 to West Ashley and Mount Pleasant or heading toward Columbia off of US 17. When I have to drive through Charleston on US 17, I generally prefer going straight on US 17. I don't feel like there is much of a time difference, 17 has lights but moves pretty well, I-526 is not bad, but has a lot of truck traffic going to the port terminals. Last time I used I-526 a couple weeks ago, I got caught in a tailback in the travel lane at the Long Point Road exit, no accident, just a really congested exit.

[hotdogPi]

In my area, "beltways" are used for local traffic. The northern half of I-495 goes through the large cities of Lowell, Lawrence, and Haverhill, MA 128 is used by the suburbs, and I-93 bypasses Manchester more than I-293 does.

[PColumbus73]

I-185 in SC isn't a very good bypass, not because it's congested, but because its utilization level is very low. For some reason, it's a toll road, so the already poorly located bypass is given another reason to be shunned.

I've used it going to Clemson from the eastern part of the state, that's about all the tolled section of I-185 is good for. Even if you're using it to get to 85, you're better off exiting at SC 153 to get to either.

[1995hoo]

I-287 in New Jersey for similar reasons—looking at them on a map, they look like they go too far out of the way. I ought to measure them out. I believe I once measured I-287 and it turned out it wasn't as much added distance as it appeared to be.

I-287 for NYC don't work for through traffic, but connecting from  I-95 to I-78 or from I-80 to I-87 works.

I-287 seems to me like it's mainly useful for trucks bypassing the NYC area or connecting to the other interstates or for cars connecting between I-87, I-80, and I-78.  Not so much I-95, however.  For I-95 to/from I-87, it's faster to take the GSP and NJ 17 (Google doesn't even suggest I-287 as an option); for I-95 to/from I-78, it's slightly faster or the same and notably less mileage to take NJ 18.

I decided to measure it out using Google Maps. I set the starting point as the Jersey Turnpike's outer roadway ("Cars/Trucks/Buses") just south of Exit 10 and the ending point as a spot on the Thruway just north of where the ramp from northbound I-287 joins. Google shows the following (disregarding travel times because those vary greatly based on traffic—when I ran the search, it showed the first option listed below as being the fastest travel time by one minute over the second option and by four minutes over the third). I had to drag the line to get it to use I-287 the whole way because it didn't suggest that. (For what it's worth, it showed the travel time as being the same as via the third option below.)

So I would describe it as 15 to 20 miles longer. In the context of a longer drive—say if I were driving from Virginia to Montreal—I'd view that as trivial in the overall scheme of things. If I were going somewhere closer, like the Mohonk Mountain House, it might matter more because that part of the trip is fairly close to the destination such that it reaches a point where you just want to get there. And if I were headed to the Tappan Zee Bridge I certainly wouldn't use that part of I-287 unless I were coming from I-78.

• Turnpike to Garden State Parkway to Thruway: 57.1 miles
• Turnpike to Garden State Parkway to NJ-17 to I-287: 52.1 miles
• Turnpike to I-80 to NJ-17 to I-287: 52.9 miles
• I-287 the whole way: 70.2 miles

[Bobby5280]

I-840 in TN has to be the most useless beltway (or whatever it's supposed to be) I've ever encountered.

It would be dumb (in my opinion) to drive the entire length of I-840 all the way around Nashville rather just driving straight thru on I-40. On the other hand, I-840 can make it easier for someone driving from Memphis to Chattanooga. The motorist can go from I-40 to I-24 without having to go thru Nashville.

[Bruce]

I-405 in Washington works pretty well for avoiding I-5 downtown.

It really doesn't, since often an end-to-end trip takes longer than just staying on I-5, especially if you have the express lanes in your direction. The section between Renton and Bellevue is almost always congested in both directions, whereas I-5 quickly clears up leaving the downtown merge zone.

[TheStranger]

With regards to I-287:  Because the Somerset Freeway I-95 alignment was canceled and 95 moved to more of the Turnpike over time, the geometry is very different than originally planned (the Somerset route would have reached I-287 at its southwest corner if I am not mistaken) and thus cars on 95 go a few more miles out of the way now were they to try to go avoid NYC via 287 entirely.

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Of the ones I've been on as passenger or driver:


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I-495, Washington DC

I barely remember using it as part of a childhood trip to DC, a family friend lived in Chevy Chase so that's what had us take the eastern half (the part shared with I-95).  this was back when 495 was only signed on one half of the Beltway.  Can't really speak too much to how that drive was like overall, though it struck me as weird that 95 didn't continue into town - I was too young then to know of the history of the DC area freeway revolts.

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I-405, Los Angeles: The north half from around Hawthorne to Sylmar is a replacement for the pre-1964 non-bypass highway, Route 7.  Some parts of 405 were even originally built as Route 7 before the Interstate designation took over.

I mention this because:
- This seems more to be "let's create a western belt with Interstate funds to upgrade an existing state highway corridor" rather than an intentional bypass
- LAX was already on that route a couple of decades before 405 as a freeway was ever planned

The developments that basically made 405 much less of a bypass than it could have been are primarily Westwood (which is exacerbated by the Beverly Hills Freeway plans for US 66/Route 2 being canceled entirely), Culver City, and the South Coast Plaza district in Irvine.  Until 1992, 405 was also the only freeway to fully link the region with LAX, due to the cancellation of the 170 extension through Laurel Canyon onto the La Cienega corridor and the cancellation of Route 90 between Marina Del Rey and Orange County.

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I-280, Bay Area:

- functionally only a bypass between the San Francisco border and Cupertino.  This is because the original Junipero Serra/Park Presidio/Route 1 segment north of Font Boulevard in San Francisco was canceled by 1968, while the original southern segment along Route 17 (now I-880) from near Santana Row to SJC airport was supplanted by a downtown connector in 1965 that was completed in the mid-1970s.

- I have seen some older regional planning maps showing a continuous through route that is mostly today's 280, but also included the aforementioned Route 1 in SF portion and...the Cupertino-South San Jose portion of Route 85!  More on that later.

- The San Bruno-Cupertino segment of I-280 is semi-rural and during the evening rush hour is very effective at bypassing US 101's suburban commute traffic.  That is, until a southbound driver reaches Los Altos around 6 PM, when the slowdowns leading to the downtown San Jose segment begin...

Northbound, I've seen some issues specifically mid-afternoon from around I-380 in San Bruno north into Colma/Daly City.  The multiple interchanges in Daly City from Serramonte Boulevard to Route 1 to Eastmoor Avenue serve to create too many entry and exit points for that road to comfortably handle.

- The portion of I-280 in San Francisco between Route 1 and US 101 gets busy southbound near the Alemany exit.  This actually is mostly former US 101 from when 101 had the El Camino alignment that is now Route 82.  This segment is more of a radial route than any sort of bypass.  (Interestingly, from the Alemany Maze to San Bruno, US 101 to I-380 is the shorter route than staying on I-280)

- The 280 extension towards the sports venues and Mission Bay is kind of a bypass of the portion of the Bayshore Freeway/101 that goes through Hospital Curve and to the Central Freeway and I-80 junction.  I use it very often as my preferred route from the Peninsula to the Bay Bridge for this reason, unless 101 happens to be very clear heading into the connection with I-80.

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I-210/Route 210, San Fernando to Redlands

The segment through SUnland is usually pretty quick going, I've used it as a bypass of Burbank/I-5 in conjunction with Route 2.  I know that it's oft mentioned that that westernmost part of 210 was originally supposed to be a downtown bypass in conjunction with the now-canceled 710 tunnel route from Pasadena to Monterey Park, and there are times I do wish that existed given how challenging the East Los Angeles Interchange can be.

The east-west portion from Pasadena to Redlands does get busy, mostly because it serves more as a regional connector (taking over the historic role of old US 66) that actually goes through the central portions of Pasadena and San Bernardino in comparison to I-10 remaining suburban from Monterey Park all the way past Colton.  It's a nice modern freeway compared to 10, just well-used for suburb-to-suburb trips. 

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I-805, San Diego

Though it similarly serves suburban areas in much the same way 405 does in LA, 805 avoids the airport entirely and instead mostly links some key regional shopping districts (University Towne Centre, Mission Valley) and Chula Vista.  Notably, the airport (Lindbergh Field/San Diego International Airport) is on the I-5 side, along old US 101.  When I've used 805 I find the road to be at ideal capacity, albeit I haven't really checked it out at rush hour yet.

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Route 52, San Diego (as part of a semi-belt with Route 125 and Route 54)

Given the geography of I-8 dipping a bit southwest towards La Mesa from Alpine, 52 allowing a connection to I-5 without going too close to the core urban area is super useful (especially aided by the connection 52 has had with Route 67 for the past decade and a half).

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I-15, Ontario (bypass of I-215/former US 395 and I-15E which cuts through San Bernardino and Riverside)

Due to geography around Devore, and some routing history (the southern half is former Route 71 and US 395, the northern half was proposed as Route 31 originally), the western I-15 in the Inland Empire seems to be more suited for "feeding cars towards LA from Vegas or San Diego" more than "regional bypass for folks from SD going to Vegas".  CalTrans actually had planned a more direct straight bypass route, Route 81, from south of Riverside north towards Devore, though this will never be built in all likeliehood. 

The 91/215/60 junction in Riverside does get pretty busy at times so 15 is effective at avoiding that.  IIRC it is shorter to to Devore-Temecula though on 215 rather than 15.

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I-680, San Jose to Cordelia

Interestingly, 680 in its original form, while more of a "belt" due to the segment that is today's 780 to Vallejo, was not quite the full bypass route it became!  The portion from US 101 to Route 262 was only added in 1965 (and had legislatively been Route 17 for a year) and built in the 1970s, and that has provided a nice alternative to the oft-congested 880 between 262 and Santa Clara/Santana Row areas.  (The canceled 238 freeway from Fremont to Castro Valley would have made this even more viable as an 880 alternative)

The northernmost portion that was still Route 21 (which is parallel to a former segment of US 40) until 1976 forms a key part of my alternate Oakland-Fairfield route (along with Route 24) that I have used over the years to bypass the congested portion of I-80's Eastshore Freeway segment, aided significantly by the 2010s opening of the fourth Caldecott Tunnel bore. 

As for actually using 680 as part of a SJ-Sacramento route, as the control city signage suggests?  Using 680-84-580-205-5 is better in terms of toll avoidance and in bypassing the Yolo Causeway portion of I-80 in Davis.


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KY 841/I-265, Louisville

A friend of mine lives close to the southwest portion of that belt route...I have yet to take the East End Bridge though so I haven't fully tried using the route as a north-south bypass.  It's a nice way to avoid going too deep into town if I'm trying to get to points east such as Shelbyville or Lexington.

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I-264, Louisville

Built originally as a bypass of US 60 - which explains some of the odd shape of the route - the westernmost portion serves as the only freeway-to-freeway link from the Sherman Minton Bridge to points south that avoids downtown, with KY 841/I-265 not extending onto the west side.  Interestingly that western part of 264 combines with the northwestern part of I-265 as a decent western bypass of town for I-65 traffic (and geometrically a much better bypass than doing 265 on the east side), though with the Minton Bridge having construction as of late, this isn't as available regularly at the moment.

I have done a full loop of 264 (with 71 and 64) a couple of times, but usually have taken the segment from the airport east to St. Matthews mostly to get to the mall district there.

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I-275, Cincinnati

Used this once on a northbound trip to Cleveland in 2006, which was cool because I could stop at a then-Roy Rogers restaurant on OH 32.  (Roy Rogers recently returned to the metro area a year or two ago...on the west side of that beltway).

On the way home we took I-71 directly instead and that honestly made more sense in terms of drive distance.

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I-270, Columbus

Used that in the 2006 trip to Cleveland, and remember ending up in some mid-afternoon congestion on the northwest side of it.  Not sure what caused it, or if it was just a timing deal.

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I-80, Sacramento (1964-1982 I-880)

For a long time, this route was six lanes through the top of town - long after Natomas had been developed, long after the Sacramento Kings' arena had been built in that district, though they have since moved to downtown.

I recall that that was finally widened sometime in the last 10-15 years, even though the right of way for it in the median has existed practically since the road opened.  Seems that this has alleviated issues in the main portion of the road.

According to Google Maps's  measurements, the west end sometimes backs up, which can easily be attributed to the bottleneck that is the Yolo Causeway (which has 6 lanes, while US 50 and I-80 each contribute 6 lanes of their own westbound into that zone) that will be widened...someday.

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Loop 202, Phoenix

As part of the big roadtrip I did in 2021 (SF to Daytona back to SF), we took US 70 west from New Mexico to Globe, then US 60 to Phoenix.  really only used 202 to get to a specific craft beer place, so I can't really speak to the route's efficacy as a bypass.

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EDSA, metro Manila (Pasay to Makati to Quezon City)

If one looks at EDSA on a map, they'll assume it is an effective loop away from the city of Manila.

They would be pretty wrong.

While the road does allow drivers to avoid going into Manila's city limits...development patterns in Quezon City and Mandaluyong, which specifically involve mall frontages right up to the road itself, have turned what could have been a promising regional bypass road into an overcongested half-expressway/half-boulevard.  This could have been avoided; EDSA had existed since the 1930s (including being given the designation Highway 54 during the tail end of the American colonial era and the start of the postwar years), but the SM North EDSA mall in 1985 created the current pattern of uncontrolled commercial builds right up to this road.

There are a few flyovers and grade separations in the Mandaluyong-Quezon City route, none enough to really make the road super functional during daytime and early evening hours.

The only segment that lives up to the road's potential is more of an urban freeway spur, that being the entire portion in Makati which eiter has RORO interchanges or full grade separatipns. 

It's telling that the two through-Manila toll freeways (Skyway Stage 3 and NLEX Connector) are effectively bypasses of this ostensible bypass route.  In the pre-Skyway Stage 3 era, the drive from NAIA to the Balintawak cloverleaf where EDSA and NLEX meet was potentially 90 minutes to go 13 miles; Skyway has turned this into a 25-35 minute drive between the two points.

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C-5, metro Manila (Paranaque to Valenzuela)

Not really complete yet, with the NLEX Citi Link portion in Quezon City still waiting to have some right of way cleared - right of way that has been in the route plan since the 1950s.

The southern part, from CAVITEX to Bonifacio Global City, is being upgraded to toll freeway at present.

The portion near Eastwood in Quezon City has some grade separations, though a full freeway upgrade is also slated in that area at some point.

Not quite suffering the same overdevelopment that EDSA received, C-5 still really isn't an effective bypass, as it is the primary route to the popular BGC and Eastwood areas.  An outer outer bypass (C-6) is proposed and partially under construction as a result.

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C2, Tokyo

A taxi used this to take me and my family from Shinjuku through the Yamate Tunnel segment towards the Haneda Route/Route 1 and the airport.  really cool to see modern tunneling used to get a freeway built in an otherwise very built up urban district, though I can imagine that was not cheap!

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Route 85, San Jose

San Jose's freeway network is interesting in that today's 101 is entirely a bypass (of the older El Camino Real/The Alameda/Santa Clara Street/Market Street/Monterey Road route), but completely in existence by 1957.  Likewise, 880 is a bypass of the old downtown Route 17 alignment.

This creates the interesting, if weird situation in which the 280 portion of what is otherwise a beltway around the Bay with 680 is a downtown link, while 87 essentially is a downtown spur that connects one bypass route (101) to another (85).

85 benefits massively from Santa Clara County preserving the right of way during an uncertain time in California highway construction (1976-1994).  When the southern segment opened in 1994, it completely decongested Blossom Hill Road, which had been the main road in the West Valley area before that.

(As noted later in thread, DTComposer posted some planning maps showing that 280-85 single road west side bypass concept of the 1950s)

85 seems to work as a bypass primarily from 280 south to 101, while the older Stevens Creek Freeway segment from 101/237 south to Cupertino is more of a regional connector towards Mountain View.

While one can argue 85-237 make a bit of a belt route, in reality the 1960s 85 freeway and 237 - both of which took over former segments of Route 9 - are more roads that lead to various suburban job centers instead.

[JayhawkCO]

I-405 in Washington works pretty well for avoiding I-5 downtown.

It really doesn't, since often an end-to-end trip takes longer than just staying on I-5, especially if you have the express lanes in your direction. The section between Renton and Bellevue is almost always congested in both directions, whereas I-5 quickly clears up leaving the downtown merge zone.

It must have changed dramatically since when I lived there. I would run into traffic all the way from Lynnwood to Sea-Tac on I-5 whereas I-405 only bunched up between WA520 and I-90.

[epzik8]

I-840 in TN has to be the most useless beltway (or whatever it's supposed to be) I've ever encountered.

"Southern bypass"

[Bruce]

I-405 in Washington works pretty well for avoiding I-5 downtown.

It really doesn't, since often an end-to-end trip takes longer than just staying on I-5, especially if you have the express lanes in your direction. The section between Renton and Bellevue is almost always congested in both directions, whereas I-5 quickly clears up leaving the downtown merge zone.

It must have changed dramatically since when I lived there. I would run into traffic all the way from Lynnwood to Sea-Tac on I-5 whereas I-405 only bunched up between WA520 and I-90.

How long ago was that?

My typical afternoon drive into downtown is smooth until 145th or so, when the backup from the lost Northgate lane really forms. From there, it's pretty much bumper to bumper on I-5 (or I opt for the train, which is usually faster).