The 101 – Four-Level to Hollywood Split

‘Bout time for a freeway post, no? Prerequisite: principles for urban freeway improvements.

When it opened in 1954, the 101 was a revolution in freeway engineering, incorporating many lessons engineers had learned on earlier efforts. Gone were the tight corners of the 110, and interchanges now had acceleration/deceleration lanes. Breakdown lanes also appeared.

However, the 101 also features the typical shortcoming of 50s-era freeways: interchanges are spaced too close together. Maybe engineers expected lower speeds or smaller volumes, or maybe they just didn’t understand the impact of weaving. Either way, with distant rumblings about the need to widen the 101 – an expensive and disruptive endeavor for sure – it’s time to offer an alternative that helps improves traffic and coincidentally improves the city too. (Or, look at the other way around if you want.)

One good aspect of 1950s freeway engineering is that it usually didn’t blow enormous holes in the street grid to shave a few seconds off motorist delay at offramps and onramps. Instead, ramps are cleverly feathered into the street grid. Consider a typical interchange on the 101 (left) compared to the 105 (right).

101vs105

So the biggest thing to fix on the 101 is interchange spacing. As a general rule, urban freeway interchanges should be spaced like rapid transit stops: about every mile. Ramps spaced less than a mile apart are counterproductive unless you go to the expense of braiding them, which costs a lot of money and disrupts the city – the opposite of what we want to do here. Don’t take my word for it, ask the folks who wrote the book on freeways. A quick look at the 101 shows that they apparently stuffed in as many ramps as they possibly could, regardless of whether the local street warranted it.

101spacing

First step, figure out the interchanges. We’ll revisit the design of each in more detail later. Courtesy of our friends at Caltrans, here are ramp volumes for the 101. I used all 2006 data, because this was the most complete set. Numbers marked with a star are 2007 data. The changes since 2006-2007 have been trivial, and reflect a time of very high unemployment anyway. I’ve arranged the data so that complimentary moves are next to each other (e.g. northbound off and southbound on).

101rampvol

Shooting for an interchange every mile, and trying to can the low volume ramps first, here’s my rough layout. Mileposts start from the freeway center of the universe in East LA.

  • Four-Level Interchange (MP 3.1)
  • Alvarado (MP 4.4)
  • Silver Lake (MP 5.3, NB off & SB on only)
  • Vermont (MP 5.9)
  • Santa Monica/Western (MP 7.3)
  • Hollywood (MP 8.0)
  • Franklin/Vine (MP 8.6, NB on & SF off only)
  • Cahuenga (MP 9.0, SB off & SB on only)
  • Highland (MP 9.5)
  • Barham/Universal Studios (MP 11.1)
  • Campo de Cahuenga (MP 12.1)
  • Hollywood Split (MP 13.0)

Ten miles, eleven interchanges.

Note: in all the graphics, green is freeway replaced with undeveloped land. Orange represents land to be developed with new buildings.

Four-Level Interchange

I’m still leaving this one alone for a future post. For now, let’s say that obviously, we’re going to have an interchange with the 110.

Alvarado St

The ramps to/from Echo Park Av (northbound) and Union Av (southbound) are too close to both the 110 ramps and the Alvarado ramps, and they dump freeway traffic onto local streets. The NB off/SB on pair has higher volume than Alvarado, but that may be due to people using those ramps to avoid traffic on the 101 as soon (or for as long) as possible. No one using those ramps would have to go more than 0.7 miles out of their way to get to Alvarado.

Therefore, the Echo Park and Union ramps should be eliminated. The street grid would be reconnected and some property would be redeveloped. No changes are needed at Alvarado, which is a tight diamond.

01-Alvarado

Silver Lake Blvd

The ramps to/from Rampart Blvd and Benton Way are too close to both the Alvarado ramps and the Silver Lake ramps, and they too dump freeway traffic onto local streets. Closing these low volume ramps would be only a minor inconvenience to those drivers, who would have to travel a maximum of 0.6 miles to get to Alvarado. These ramps should be eliminated.

Meanwhile, the Silver Lake ramps are heavily directionally biased – that is, volumes to and from the south are much higher than volumes to and from the north. (See the ramp volume table; NB off/SB on are much larger than SB off/NB on.) The SB off and NB on ramps are also very close to the Vermont ramps, making for a punishing weave section on the 101. While it’s usually bad practice to not offer all ramp movements at every interchange, in this case an exception is warranted. The SB off and NB on ramps at Silver Lake should be eliminated. No one would have to drive more than about a mile out of their way due to this change.

Again, this would allow the street grid to be reconnected and some property to be redeveloped. No changes are needed at Silver Lake, which is a tight diamond.

02-SilverLake

Vermont Av

Vermont has by far the highest volume NB off/SB on ramp pair, and the SB off/NB on ramp pair volume is large as well. This interchange is definitely staying.

That creates an interesting question regarding the ramps at Melrose and Normandie. The SB off/NB on ramp pair volume isn’t that bad, but the NB off/SB on pair is high – in fact, the second highest such pair in the corridor. Eliminating those ramps is a tall order, but if they’re not eliminated, they probably need to be braided – the opposite of what we’re trying to accomplish here.

As luck would have it, an accident of history created an opportunity to solve this problem. The median of the 101 is very wide, up to 160’, between Virgil and Melrose. Students of LA freeway history will recall that this is because it was planned to be the location of a freeway interchange between the 101 and the 2, which was to be extended from Echo Park west to Beverly Hills and Santa Monica.

That freeway is never getting built, and the wide median is currently occupied by a self-storage facility. Time to put it to better use.

Between Virgil and Vermont, the southbound side of the 101 would be shifted north. There’s already an empty bay in the middle of the Vermont Av bridge that was reserved for the 2 freeway, so there’s no need to do any work on it. From Vermont to Melrose, both sides of the 101 would be shifted towards the middle, eliminating the wide median. New frontage roads would be constructed from Vermont to Melrose, accommodating the traffic currently using the NB off/SB on pair at Melrose/Normandie.

Finally, the Vermont ramps would be reconfigured to square up the intersections, eliminate traffic lights, and free up land for development. In particular, note the relocation of the SB onramp to line up with Rosewood Av and the new frontage road. This allows Oakwood St to be reconnected and for new development on the north side of Oakwood to screen the freeway.

03-Vermont

Santa Monica Blvd/Western Av and Hollywood Blvd

Things are a little bit simpler at Santa Monica, Western, and Hollywood. There’s no need to modify those interchanges. The partial interchange at Sunset/Wilton has high volumes for the NB off/SB on pair, but it’s just too close to the Santa Monica/Western ramps. I’d expect most of that traffic to shift to the Hollywood interchange, which currently has smaller volumes. The SB offramp to Sunset isn’t a huge issue because it’s braided, but its volume is pretty low. That ramp and the SB onramp from Hollywood would be modified into a frontage road and onramp, reconnecting a north-south street in the adjoining neighborhood.

04-WesternHollywood

The changes on the southbound side aren’t that big, but eliminating the loop on the NB offramp frees up a lot of land for development and is a huge improvement to the pedestrian environment at Sunset and Wilton.

Franklin/Vine and Cahuenga

The ramps to/from Gower St and Argyle Av are all low volume ramps. They can be eliminated without much issue. The SB offramps to Cahuenga and Franklin/Vine are both high volume ramps, as is the NB onramp from Franklin/Argyle, so they remain. The SB onramp from Cahuenga should remain just because there needs to be a SB onramp somewhere in the area. The NB offramp to Cahuenga should be eliminated, since it is a low volume ramp and creates a murderous weave with the high volume NB onramp from Franklin/Argyle.

Another option would be to replace the braided SB ramps, on from Cahuenga and off to Franklin/Vine, with a frontage road and SB onramp. This would eliminate a couple bridges over city streets, and free up land on the north side of Franklin for development.

05-FranklinCahuenga

Highland

The SB off/NB on ramp pair at Highland is the highest volume ramp pair on the whole corridor, and it’s in a very logical and undisruptive location. That pair is definitely staying. The NB offramp to Highland needs to stay, just to have a ramp in the area, since the Gower and Cahuenga offramps would be eliminated. It’s closer than ideal to the Franklin/Argyle onramp, but so it goes.

The SB onramp from Highland should remain but be closed except when events are ending at the Hollywood Bowl. It’s much too close to the Cahuenga offramp for everyday operations, but it makes sense to keep it for Hollywood Bowl events so that the large bursts of traffic from those events don’t have to go through city streets to get to the freeway.

Barham

The NB off/SB on pair at Barham has fairly high volumes. The NB on ramp at Cahuenga near Pilgrimage Bridge also has high volumes and should remain. The NB offramp to Universal Studios is lower volume, but can remain because it’s not taking up useful real estate or causing any major weave problems. The NB onramp at Universal Studios should also remain.

For reasons unknown to me, the original NB off/SB on pair at Barham was abandoned long ago – all the way back in 1957, according to California Highways. If it can be reactivated, the original NB offramp would increase weaving distance between the Cahuenga onramp and the Barham offramp. However, that might encourage drivers entering northbound at Highland to try to cut across to Barham, which is a major weave and therefore undesirable. Instead, perhaps the Cahuenga onramp to northbound could be relocated south to increase the weaving distance between it and Barham.

Campo de Cahuenga

The Lankershim NB off/SB on ramp pair has larger volumes than Campo de Cahuenga, but it’s too close to the Barham ramps. In addition, eliminating the ramps at Lankershim would improve the pedestrian environment. Pedestrian volumes should be lower on Campo de Cahuenga because there’s nothing there. A SB offramp should be constructed at Campo de Cahuenga, and all movements provided for the NB ramps. The Campo de Cahuenga interchange would replace both the Lankershim interchange and the Vineland interchange, which is too close to the Hollywood Split.

06-CampoDeCahuenga

This frees up land for redevelopment on Vineland where the SB loop ramps would be eliminated.

07-Vineland

Hollywood Split

The Hollywood Split, with its missing ramps and left-hand exits and entrances, is a project unto itself. I’m going to leave it alone for the time being.

Implementation Timeline

Some of these improvements require building new ramps, which would require more traffic studies and engineering design than easier locations where ramps would just be eliminated. There’s no reason to hold up the easy projects to wait for the more complicated ones to be ready for construction; the easy ones could be completed in less than a year. A few improvements could be accomplished in the midterm, e.g. closing braided ramps with bridges that would need to be demolished. I’d break things down as follows.

Short-term improvements (<1 year):

  • Close Echo Park Av & Union Av ramps
  • Close Rampard Blvd & Benton Way ramps
  • Close Silver Lake Blvd SB off/NB on ramp pair
  • Close Normandie Av/Melrose Blvd SB off/NB on ramp pair
  • Close Sunset Blvd/Wilton Pl NB off/SB on ramp pair
  • Close Gower St/Argyle Av NB off/SB on ramp pair
  • Close Cahuenga Blvd NB offramp
  • Close Highland Av SB onramp
  • Close Vineland Av NB offramp

Mid-term improvements (1-3 years):

  • Close and demolish Sunset Blvd SB offramp
  • Close and demolish Gower St SB offramp

Long-term improvements (3+ years):

  • Close Normandie Av/Melrose Blvd NB off/SB on ramp pair, realign the 101 mainline lanes, and build frontage roads between Vermont Av & Melrose Blvd
  • Close and demolish Franklin Av/Vine St SB offramp, construct SB frontage road between Cahuenga Blvd & Franklin Av/Vine St, and reconstruct Cahuenga Blvd SB onramp
  • Complete tight diamond interchange at Campo de Cahuenga, close Vineland  St SB off/SB on ramps, close Lankershim Blvd ramps

Staging the implementation allows low-cost improvements to be constructed first. In fact, almost no upfront expenditure would be necessary for the short-term improvements if the land was sold for development, since the developers would assume the cost of removing the existing ramps. This would create some immediate benefits while long-term improvements were studied in more detail.

Conclusion

I know a lot of people really, really don’t like urban freeways. But just saying “tear them down” is a throwaway response that ignores the related issues like land use controls and the role of transportation in cities and economies. It also misses out on opportunities to improve the city that can be made quickly and low cost. The 101, as LA’s first real freeway, is a great place to start, and a successful project here could lead to more short-term improvements across the city.

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3 thoughts on “The 101 – Four-Level to Hollywood Split

  1. John Hupp

    I dislike inducing demand for driving, but improving safety on the freeway by reconfiguring interchanges seems like a worthwhile goal. It would hopefully not result in more cars on the road, and it could provide a great opportunity to fund the Hollywood Freeway Cap Park!

    Reply
  2. Adam

    Most excellent, I think you’ll struggle to get people to believe that an offramp diet would not be catastrophic to the other offramps and also that traffic would overall improve. I think every ramp closure of your proposal for the short term could be implemented as a ‘test’ traffic study phase by using K Rail to close off the ramps for one week or one month. See if it works, see if people can handle it, and then with the political buyin you’ll get from it working, you proceed with the actual ramp diet and the further improvements.

    Reply

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