The State Water Project: An Introduction

If you follow this blog’s twitter account, you know that engineering & water twitter has been closely watching the situation at the Oroville Dam in northern California. Many people know, conceptually, that much of the water we use in SoCal comes from northern California, but are not familiar with Oroville or the State Water Project. So, here’s a brief introduction to what the State Water Project (SWP) is, what it does, and what’s happening at Oroville now.

The SWP is an important source of water for SoCal, and Lake Oroville is the main reservoir. While popular conception hold that LA’s water comes from the east Sierra and Owens Valley via the LA Aqueduct, over the last 5 years, that facility has only delivered 29% of LA’s water. The SWP is the largest supplier of water to the city of LA, with 48% of LA’s water over the last 5 years coming from the SWP. So what happens at Lake Oroville is of interest to, well, anyone south of Lake Oroville.

The State Water Project: California Dreaming… Big

Everyone knows the split nature of California’s climate: the north is wetter, the south is drier. However, many people and much of the best farmland are in southern California. Over half of the state’s population lives in relatively dry climates south of the Transverse Ranges, which separate the southern quarter of the state from the rest. In addition, California experiences wide swings in annual rainfall, with droughts and floods often following on each other’s heels. In fact, 2014-15 was the driest water year in state history, but 2016-17 may prove to be the wettest.

This situation naturally led to the desire for civil engineering improvements to both prevent devastation from flooding in wet years and store water for human use during drought years. The SWP was conceived to help meet these goals. The map below shows the main components of the SWP.

state_water_project

The major components of the SWP are:

  • Oroville Dam: this dam is located on the Feather River, which drains a portion of the northern Sierra Nevada, and is the source of water for the SWP. Lake Oroville can store up to 3.5 million acre-feet of water, making it the second largest reservoir in the state after Lake Shasta. One acre-foot of water is enough water to cover an acre of land one foot deep – about 325,000 gallons.
  • California Aqueduct: this aqueduct conveys water from the delta to users in central and southern California. Water released from Lake Oroville flows down the Feather River and Sacramento River to the delta. From there it is pumped south out of the Clifton Court Forebay.
  • San Luis Reservoir: this is a large off-line reservoir in the southern Central Valley that can store 2 million acre-feet of water. “Off-line reservoir” means that it is not located on a major river – it was created by damming an existing valley and filled with water from the California Aqueduct. The creek that formed the valley, San Luis Creek, would never carry enough water to fill the reservoir on its own.
  • Distributary aqueducts: these aqueducts carry water from the main California Aqueduct to water uses. These are:
    • North Bay Aqueduct and South Bay Aqueduct, which serve the East Bay area.
    • Coastal Branch, which serves San Luis Obispo and Santa Barbara Counties, including a connection to Lake Cachuma, Santa Barbara’s main water supply.
    • West Branch, which serves the Los Angeles area and includes Castaic Lake and Pyramid Lake, the lakes you see from the 5 when you drive through the Grapevine.
    • East Branch, which serves the Inland Empire and includes Silverwood Lake and Lake Perris.
    • Second San Diego Aqueduct, which connects Lake Perris to San Diego County.

Because of the complicated geography and politics of water in California, the SWP includes some water agencies that don’t even have a physical connection to the project. For example, the Desert Water Agency (DWA) and Coachella Water Valley District (CVWD) serve Palm Springs and the Coachella Valley, which have no connection to the SWP. The DWA and CVWD buy SWP water and then swap it with the Metropolitan Water District of Southern California (MWD SoCal) for water from the Colorado River. So DWA and CVWD pay for SWP water, which is delivered to MWD SoCal, and in exchange, MWD SoCal gives DWA and CVWD water from the Colorado River Aqueduct.

Construction on the SWP started in the early 1960s and the major components were done by the late 1970s, though construction on various pieces such as the East Branch Extension continues up to the present day. The SWP is just one legacy of the leadership of Governor Pat Brown, who for his investments in water infrastructure, freeways, and education ought to be known as the father of modern California.

Ok, So What’s Going on at Oroville?

Lake Oroville is a dual-use reservoir – it is used both to store water for human use and to capture water from torrential rainstorms and snowmelt to prevent devastating flooding downstream. Every such reservoir has its storage divided into conservation storage and flood control storage. Under normal conditions during the rainy season, the reservoir is not allowed to fill up beyond the conservation storage level, so that if a big rainstorm or snowmelt event happens, there will be enough capacity to prevent flooding. Reaching the top of conservation storage is like the gas light coming on in your car: it means you need to start looking for a gas station, because you don’t want to run out of gas before you start looking.

Early this week, a large winter storm hit northern California. The storm was warm, meaning that it had high snow levels (the elevation in the mountains where the storm changes from rain to snow), so much of the precipitation went into the rivers right away instead of adding to the snowpack in the mountains. The warm temperatures and rain also caused some of the existing snowpack at low elevations to melt and flow into the rivers.

On Tuesday, Lake Oroville was near the top of conservation storage, and with a large amount of water on its way to enter the lake, state water managers increased water flow through the controlled spillway on the Oroville Dam. A controlled spillway is a structure on a dam that has gates that can be opened and closed by motors, allowing the agency in charge to control how much water leaves the reservoir. The Oroville controlled spillway had a theoretical maximum capacity of 250,000 cubic feet per second.

However, as flows ramped up, a sinkhole appeared in the lower portion of the spillway, and water releases had to be stopped to allow inspection. After assessing options, it was determined that because of the large volume of water entering the lake, it was necessary to continue to allow water to flow through the damaged spillway to keep the lake from rising too quickly. Water flowing through the spillway has caused additional erosion, although yesterday and today the discharge appears less muddy. Hopefully, this is an indication that the channel has cut down to bedrock, and erosion has slowed down.

As water flows downhill, erosion will tend to cut back uphill. This is why Niagara Falls is at the head end of a long gorge; the falls have cut the gorge back upstream from the Niagara Escarpment since the end of the last ice age. It is critical that erosion on the controlled spillway at Oroville not be allowed to proceed uphill and damage the spillway gates, which would negatively impact the ability to control releases down the spillway. That is why the damaged spillway is only being allowed to operate at a reduced capacity.

Because inflow is currently greater than outflow, the lake level is rising. However, this is NOT a threat to the Oroville Dam itself, because there is an emergency spillway that the water will flow over first. The dam crest elevation is at 922’, while the emergency spillway sill is at 901’. The emergency spillway is an uncontrolled weir, so once the lake reaches elevation 901’ water starts to flow down the emergency spillway. This happened at about 8am this morning and as of 3pm February 11, 2017, the lake elevation is at 902.02’, so water continues to flow over the emergency spillway. In a noon press conference, the state announced that it expects this flow to continue for 36-56 hours.

The emergency spillway is an unlined, unimproved channel, which means water that flows over down it is just flowing over dirt, vegetation, and rocks. This means some erosion will occur and enter the Feather River downstream.

What’s Next?

Because it’s only mid-February, winter is only part way over, and more rain and snow storms may be on the way. The state will face challenges with water coming into the lake over the next few months as additional storms hit, and then as spring and summer temperatures melt the snowpack. At the moment, it does not appear there will be enough time to much in the way of repairs before more rain and snow arrive. Resource managers will face difficult decisions between increasing flow on the damaged spillway and allowing additional flows over the emergency spillway.

It’s important to emphasize that as of this writing (3pm February 11, 2017), there is no threat to the Oroville Dam itself, no flooding occurring downstream, and no imminent public danger. Everyone should pay attention to information from the California Department of Water Resources, the Butte County Sheriff, and the California Office of Emergency Services for updates on changing conditions.

After the rainy season and spring snowmelt is over, the state will face a busy summer construction season at Oroville, including repairs to erosion and/or improvements to the emergency spillway, and repairs to the existing damaged controlled spillway or replacement with a new controlled spillway.

Is the SWP the Same Thing as the Central Valley Project?

No, though they are related. The SWP is operated by the state of California, while the Central Valley Project (CVP) is operated by the federal Bureau of Reclamation. The main CVP components are:

  • Shasta, Trinity, and Whiskeytown Lakes in northern California, which store water for use in the Central Valley.
  • Tehama-Colusa Canal, which distributes water for use in the northern Central Valley.
  • Friant Dam and Millerton Lake on the San Joaquin River, and the Friant-Kern Canal, which distribute water from the San Joaquin River for use in the southeastern Central Valley.
  • Delta-Mendota Canal, which distributes water from the delta for use the San Joaquin River drainage basin below Friant Dam.
  • San Luis Canal, which is shared with the SWP, and distributes water for use in the southwestern Central Valley.

central_valley_project-01

In addition, there are interconnections between the SWP and the CVP such that if the south Sierra has a very wet year, water from the Tulare Basin rivers (Kings, Kaweah, Tulare, and Kern Rivers) can be sent to the SWP.

What Are All Those Grey Squares on the SWP Map?

Curious readers may have noticed several reservoirs and other facilities on the SWP map shown in grey. These are facilities that were proposed as part of the SWP but never constructed.

The undeveloped facilities in northwestern California are of the greatest consequence. The project as originally proposed included dams on the Klamath River and Eel River, which would have created the Ah Pah Reservoir and the Dos Rios Reservoir. At 15 million acre-feet and 7.5 million acre-feet, respectively, each of these reservoirs on their own would have dwarfed Lake Shasta and Lake Oroville. These facilities would have been located in the wettest part of California. An additional reservoir, the Glenn Reservoir, would have been located east of the coastal mountains, with water directed there via tunnel from Dos Rios.

california-precipitation-map-markup

Since the Klamath and Eel Rivers are not currently connected to the SWP, these dams would have greatly increased the water available to the SWP. However, they would have destroyed some of California’s last free-flowing river segments, and would have had enormously negative consequences for fish and other wildlife. The large environmental impacts resulted in these projects being canceled, and they are unlikely to ever be revived.

The other two unbuilt large reservoirs are the Sites Reservoir and Los Banos Grandes Reservoir. The Sites Reservoir would be able to store between 1.2 million and 1.8 million acre-feet, with Los Banos Grandes adding another 1.7 million acre-feet. Together, they would equal another Lake Oroville of off-line reservoir storage, increasing SWP storage by over 50%. Since they would be off-line reservoirs, not located on main rivers, the impact of these facilities might be less.

The last major unbuilt piece of the SWP is the Delta Peripheral Canal, or as we know it today, the Delta Peripheral Tunnel. The purpose of this facility would be to channel water from the Sacramento River (released from Lake Oroville, Lake Shasta, or the Sites Reservoir) around the delta to the pumping facilities that send the water south via the California Aqueduct. This would reduce the environmental impact on the delta and increase the reliability of SWP water deliveries.

With climate change possibly making droughts and floods more likely, and causing precipitation to fall as rain instead of snow, there may be renewed interest in the Sites Reservoir, Delta Peripheral Tunnel, and maybe even Los Banos Grande Reservoir.

Sustainability as Penance

An article in City Lab on a vegetable shortage in the UK reminds me of an old idea that I never really seemed to be able to articulate, so I figured I’d finally give it a shot.

There’s a weird vibe about arguments on sustainability sometimes, where it feels like it’s more about impugning the morality of the behavior in question rather than about some technical definition of sustainability. This dubious definition of sustainability has a habit of popping up when people have a preconceived negative opinion of the user in question (LA is bad and unsustainable for importing Owens Valley & State Water Project water!) but not when they don’t (when was the last time you heard about the water shortage on the Delaware River?).

Food is perhaps the most frequent victim. In the article above, it is suggested that poor harvests in Spain due to bad weather are revealing an “unsustainable” food supply system in the UK. It is noted that 50 percent of the UK’s vegetables and 90 percent of its fruit are imported. Further, it is suggested that perhaps UK residents should just eat in-season locally available vegetables like winter roots and leeks, cabbage, Brussels sprouts, and kale (three of which are cultivars of the same plant).

First, let us note that sustainability here has been arbitrarily defined: produce from Spain, not sustainable; produce from the UK, sustainable. Sustainability should be defined by some assessment of our ability to keep producing things without destroying the productive capacity of the system; instead it is defined by arbitrary borders. Why are Spain and the UK the units of analysis rather than something larger (the EU, for example) or something smaller (the constituent countries of the UK, parliament districts, etc)? Why not go full rugged individualist, and say that any produce you consume that you didn’t grow on your own land isn’t sustainable?

Second, there’s a tone of judgment – why do you silly people demand zucchinis and eggplants, instead of just being satisfied with cabbages? Well, aside from this having nothing to do with sustainability, why shouldn’t people in the UK get to enjoy a variety of vegetable and fruit? Most produce in the US is grown in California, because of places with very favorable climates like the Salinas Valley, Central Valley, and Imperial Valley, and available resources for irrigation. Why shouldn’t people in other states get to enjoy that productivity?

Third, it’s quite possible that moving to a system where people are only allowed to consume locally produced food would have a larger environmental impact. Transportation costs and carbon emissions are a small portion of the total costs and carbon emissions of making food. Increasing agriculture on marginally productive land just because it’s close to population centers might increase impacts because a larger amount of land would have to be put into production.

Finally, the unsound footings of this definition of sustainability are laid bare if we try to apply the concept to something other than food. For example, much of the world’s iron comes from mines in remote desert portions of Australia. It would be crazy to argue that all the steel in California should have to come from in-state iron mines, which would be more destructive. It would also be crazy to argue that iron miners in the Pilbara should only get to eat whatever food can be grown in the Australian desert.

Some places, like California and parts of Spain, are good at growing lots of food. Other places, like the UK, are good at other things. There’s nothing wrong with this; letting people do what they’re good at is a good thing. It doesn’t help people in the UK to deprive them of a greater variety of food, and it doesn’t help Murcia to deprive it of a place to sell the food it can grow. This is literally the entire point of trade.

SoCal Rain Update: One Step Forward

After 5 long years of drought, a series of powerful storms in January 2017 finally brought heavy rain and snow to California. The short-term impacts of the floods and mudslides have been well covered in the news, but many SoCal residents are wondering if the storms have made a major impact on the drought. Let’s take a look at where we stand in Los Angeles, and at water supplies around the state. As always, remember that in California we measure precipitation from October through the following September; this period is called the water year.

Currently, downtown LA is at 14.33” of rain for the water year. This is just 0.60” short of the yearly average, and already well past any of the drought years. In fact January 2017 alone brought more rain to LA than 3 of the 5 drought years, including last year’s completely ineffectual El Niño.

larain-graph-20170201larain-table-20170201

The six-year total for 2011-12 through 2016-17 is currently at 53.12”, which is 0.13” less than the record driest six-year period of 1958-59 through 1963-64. Over the last 10 years, we have a rainfall deficit of about 37”. So while this year has been good so far, to start making up lost precipitation from the drought, we still need the storms to keep rolling through over the next few months. Looking a little more broadly at SoCal, we can see that much of the region has fared better than LA.

Looking at major reservoirs in the state, almost all are doing very well. It already seems likely that the state will go into the summer with water storage facilities nearly full, and there’s still a lot of winter to come. Remember this the next time someone tells you there’s no reason to create more storage!

reservoirs-20170201

Taking a closer look at some southern California reservoirs of interest, Lake Cachuma, the largest reservoir for Santa Barbara County, was down to 7% of capacity last fall. This put cities in the area on severe water restrictions and prompted the city of Santa Barbara to reactivate its desalination plant. While this year has certainly replenished Lake Cachuma more than any of the drought years, it doesn’t seem like enough to ease restrictions yet.

cachuma-20170201

Over in the southern Sierra Nevada, Lake Isabella has finally received some much needed rain as well. This reservoir, on the Kern River above Bakersfield, is the largest in the Tulare Basin other than Pine Flat on the Kings River. Capacity is 568,000 acre-feet, so it’s nowhere near full, though storage is currently kept below maximum due to ongoing seismic improvements to the dam.

isabella-20170201

Looking at departure from normal precipitation to date for the water year across SoCal, we can see there’s been some drought relief in the south Sierra, the Coast Ranges, and the SoCal mountains.

wytotal-20170201

Precipitation indexes for the Sierra Nevada show it’s been a very wet year throughout the range. The north Sierra, corresponding to the Sacramento River drainage, has had 53.2”, already past the water year average of 50.0”, and on record pace (though the breakneck pace of January precipitation would be hard to match).

nsierra-20170201

The central Sierra, corresponding to the San Joaquin River drainage, is also already past the water year average, with 42.9” to 40.8”. It too is on pace to match some of the wettest years on record.

sanjoaquin-20170201

The south Sierra, corresponding to the Tulare Basin (Kings, Kaweah, Tule, & Kern Rivers), is just past the water year average, with 30.2” to 29.3”. It’s been a very wet year for the south Sierra, though it might be hard to keep up with 1968-69.

tulare-20170201

Looking over to the other side of California, the east Sierra, corresponding to the Owens Valley, snow water content has already passed April 1 averages, with 34.7” to about 24”. This is where the water in the LA Aqueduct comes from, so it’s good news for city water supplies, as we’ll have to buy less water from the State Water Project and Colorado River Aqueduct.

esierra-20170201

Peering into the next 7 days, the forecast calls for another round of solid storms for northern and central California.

gfs-20170201

Totals for the far south Sierra and SoCal look relatively modest for the next week… let’s hope that, like in January, this powerful NorCal storm is a prelude to strong rainstorms for us!

Editorial: all of the data used for this post came from public sources (National Weather Service, CA Dept of Water Resources, LA Dept of Water & Power). A lot of useful data is created and made available free to the public by government agencies that are going to have their budgets under attack in the coming years. So, you know… call your reps to protest when that happens!

Identity is Fractal

It is one of the unfortunate aspects of human nature that it is not difficult to build a political movement centered on the idea that different ethnic or religious groups are responsible for the socioeconomic problems in a society. This is the essence of what propelled Donald Trump to the presidency. All politics is identity politics at some level. Liberal politics are oriented around respecting and including different groups; Trump’s politics are oriented around division and exclusion.

Identity, though, is fluid, and this goes in both directions. We can build larger identities, both with the intent of inclusion, such as inviting more people to become Americans, and the intent of exclusion and oppression, such as expanding the definition of white in order to allow continued oppression of other groups. We can also build smaller identities, again either with the intent of inclusion, such as helping people feel accepted and supported, or the intent of exclusion and oppression, such as creating a new out group to be discriminated against.

Exclusion and oppression are inseparable. The exclusive identity will fall apart in the absence of the oppressed group. The founders of the Confederacy understood this: the status of poor whites above enslaved blacks was necessary to maintain the white unity that enabled the Southern aristocracy to exist.

If the oppressed group is ever successfully expelled, the exclusive identity will soon find itself in need of a new scapegoat, which must be created from within. If a white nationalist state were ever created, it would still find itself beset by the same socioeconomic problems that exist in all human societies. And in the same way that it became necessary for new ethnic groups to become white, it would become necessary for a group to be stripped of its whiteness. Blaming the other guy for your problems requires there to be an other guy.

This explains why there are generic white nationalists in the US, but European nationalism exhibits smaller divisions (French nationalists, British nationalists, and so on). There’s no need to invent a larger white identity in the UK, so eastern Europeans don’t get to be part of the exclusive identity there.

Aside from being cruel, Trump’s Muslim ban is not going to solve the opioid epidemic. It’s not going bring back coal mining jobs in Appalachia or factory jobs in the Midwest. It’s not going to make America safer, and may very well put us at increased risk of attack.

And because of that, it’s just the beginning. They will come for someone else, and the only question is who. It’s up to Americans who care about creating an expanding, inclusive country to make sure that doesn’t happen.

Trump: The First 5 Days

The first 5 days of Trump’s presidency have passed in a blizzard of news, rumors, and outlandish statements. The circus atmosphere that has carried over from the campaign has made it hard to keep up with what’s important, and what’s actually been done versus what’s rumor. So it seems like we should summarize what’s happened, because Trump’s first 5 days have been about as bad as could be expected. Trump has acted, or is expected to act, to make good on many of his worst campaign promises:

  • Authorized Health & Human Services to delay or waive any Obamacare provisions that could be construed as a financial or regulatory burden on states or individuals.
  • Blocked any aid from going to foreign non-governmental organizations that even mention abortion.
  • Ordered expedited review and approval for the Dakota Access Pipeline and invited resubmittal of permit application for the Keystone XL Pipeline.
  • Directed Homeland Security to begin planning and constructing a border wall on the Mexican border, along with additional detention facilities.
  • Prohibited federal grants to sanctuary cities.
  • Expanded the priorities for deporting undocumented migrants.
  • Ordered the creation of anti-immigrant propaganda in the form of a weekly list of crimes committed in sanctuary cities and the creation of a special office for victims of those crimes.
  • Declared his intention to launch an investigation into baseless lies that millions of illegal votes cost him the popular vote in the election.

In addition, four leaked executive orders suggest Trump will take the following actions:

  • Suspend entry into the US from several Muslim nations, and suspends all refugee admissions into the US for 120 days.
  • Repeal the Deferred Action for Childhood Arrivals program, which shielded people who came to the US as children from being deported.
  • Take several actions to reduce legal immigration and expand workplace raids on places that employ workers using visa programs.
  • Take several actions to make social services unavailable to immigrants.

On top of all of that, there have been troubling actions to remove research on climate change from government websites, and order that basic government research go through political reviews before being released.

The actual impact of some of these orders is hard to tell, because they are vague or because Congress would have to appropriate funds. But it seems unmistakable that other than locking Hillary up, Trump intends to carry through on his campaign promises, and many of these actions, particularly those pertaining to deporting, rejecting, and demonizing immigrants, can be carried out without Congress.

In light of all that, it again seems a little ridiculous to talk about transportation and housing, but let’s have a go for old time’s sake:

  • The Senate Committee on Banking, Housing, & Urban Affairs voted to confirm Ben Carson as HUD secretary, with all the committee’s Democrats voting in favor. What they are getting in exchange for voting for a wildly unqualified candidate, other than a share of the blame for screw-ups, is beyond me. I guess all that remains to be seen is if he screws up through benign neglect or malign neglect.
  • About a week ago, it was reported that Trump’s first budget would draw from a Heritage Foundation plan that would zero out funding for the Federal Transit Administration, the New Starts transit capital investment fund, and Amtrak. Then yesterday a leaked document listed 50 priority infrastructure projects, including Amtrak’s Gateway project and 2 Ave Subway Phases 2 &3 (and more mysteriously, the privately funded Cadiz water export project and Huntington Beach desalination plant in southern California). Then that document was claimed to not be from the transition team, just from a consulting firm, and then others insisted it was from the transition team.

So, whatever, believe whatever you want on transportation and infrastructure. That won’t be funded by executive order, so Paul Ryan and Mitch McConnell will have some say in what it is.

As for me, if the price of getting a few transit lines built is total surrender on climate change, immigration, health care, reproductive rights, and basic decency, count me the fuck out.

 

The Hollywood Strangler – Part 1

The Ventura Freeway, running from Woodland Hills to Pasadena, is the Valley’s main – only, really, since the 118 is so far north – east-west freeway. In typical LA fashion, much of the Valley is car-oriented despite the paucity of freeway capacity: just one east-west freeway for nearly 2 million people. The freeway is the famous 101 from Woodland Hills to the Hollywood Split, and the much less famous 134 from the Hollywood Split to Pasadena.

The Ventura Freeway is newer than some of LA’s first freeways, like the 110, the 10, and the Hollywood Freeway portion of the 101, so it doesn’t suffer from the problem of short interchange spacing. However, it’s old enough to have underpowered freeway-to-freeway interchanges at the 405, the Hollywood Split, and the 5. Let’s take a closer look at these three interchanges, as usual with an eye on rationalizing the freeway facility and improving the local streets in the vicinity. For this post, we’ll look at the Hollywood Split, saving the 405 and the 5 for another day.

Before diving in, let’s think about what makes a good freeway-to-freeway interchange. First, these interchanges have larger ramp volumes than typical interchanges, which makes the weaving conflicts worse. That suggests an increased need to avoid conflicting local ramps (a local on-ramp right before the freeway off-ramp, or a local off-ramp right after the freeway on-ramp). Second, these interchanges take up more space than typical interchanges. Therefore, in order to maintain functionality for local traffic distribution, it often makes sense to have an interchange serving local traffic integrated somehow. This can take the form of half diamonds or a full diamond interchanged arranged so that its ramps don’t cause any weaving conflicts. I like to call this an “inside interchange”. Here’s an example: the 134 and the 2, with inside diamonds on the 134 at Harvey and the 2 at Holly.

Now, we don’t want to go blowing massive holes in North Hollywood to drop in 65 mph ramps and create interchanges like they have in undeveloped parts of Fontana. However, these principles can still help us figure out what will work for these cases. We’ll do our best to keep improvements within available right-of-way, compromising on speed where needed. Alright, on we go.

The Hollywood Split is the somewhat confusing junction of the 101, the 170, and 134 in North Hollywood. The 101 enters from the southeast on the Hollywood Freeway and departs to the west on the Ventura Freeway. The leg to the northwest is the 170, and the leg to the east is the 134, both of which end at the interchange.

hollywoodstrangler-aerial

Despite being signed as the mainline freeway, the 101 exits on the right and merges on the right going east/south, and exits on the right and merges on the left going north/west. This is contrary to modern design standards, which require that the mainline freeway stay left, with exits and entrances to the right.

On the other hand, the interchange also reflects downtown-oriented design, with the movements to/from downtown emphasized at the expense of other movements. This reflects the thinking of the era, that people would drive to a downtown central business district (CBD) in the morning and out to suburbs in the afternoon. With LA’s polycentric development, downtown is not as dominant as it is in many cities. The Ventura Freeway provides important east-west connectivity to outlying CBDs in Sherman Oaks, Burbank, Glendale, and Pasadena. Thus, if one considers the Ventura Freeway the mainline – an argument for which there is a good case, as we shall see – there are only two through lanes, which is also substandard for this location. The Ventura Freeway through movements stay left at the splits entering the interchange, but merge to the right departing the interchange. This means that depending on which movements dominate, we might make different decisions about what to consider the mainline freeway, and which ramps to reconfigure.

Looking at the freeway-freeway ramp layout, we can see that the northwest and southeast quadrant ramps are missing (north to/from west, south to/from east). Again this was fairly typical for that era of freeway design, but leaving out ramps is frowned up these days as it is confusing for motors and shunts high speed traffic onto local streets. The southeast quadrant ramps are more consequential, because they would connect major nodes (Hollywood to Burbank & Glendale), while the missing northwest quadrant ramps would connect lower density areas. However, it’s obvious that there’s very little right-of-way available for the missing ramps, and it might be hard for the southeast quadrant ramps to compete with Barham and Forest Lawn, which make a relatively uncongested shortcut serving these movements.

Lastly, looking at the local street ramps, things are actually in pretty good shape. The 170 has a half-diamond to the north, and the 101 has a half diamond to the west. The 134 has a half diamond to the east, though there’s a little friction between the Vineland on-ramp and Cahuenga off-ramp going east. One notable gap is that there’s no on-ramp to the Ventura Freeway west between Pass Ave and Tujunga Ave or Moorpark St, almost 2 miles, so that might be something to try to fix. Going south on the 101, the Vineland Ave off-ramp is uncomfortably close to the 101/170 merge, something we looked at fixing in a post that feels like it was written century ago.

Now, to look at the deficiencies of the interchange, it’s helpful to look at a stylized diagram showing the number of lanes and traffic volumes. Note that the ramps are drawn as simply as possible, ignoring loops and bridges, to make things easier to look at.

hollywoodstrangler-exist

(Note: traffic and ramp volumes from Caltrans. Asterisk indicates volumes I increased by 10,000 to get consistent results.)

It’s readily apparent that the central deficiency of the Hollywood Split is that there are only 2 through lanes on the Ventura Freeway (the 134 west to the 101 north and the 101 south to the 134 east). The traffic volumes are more or less evenly split between the 134 and the 101: 68,000 from the 101 south to the 134 east and 62,700 remaining on the 101 south; 63,000 from the 134 west to the 101 north and 64,400 continuing from the 101 north. In order to handle their traffic volumes, these 2-lane ramps would have to flow full for 16 hours a day. Meanwhile, the ramp volumes between the 134 and the 170 are about half of what the movements are in the other directions.

For the purposes of this post, let’s do an updated stylized diagram showing a simple solution for this bottleneck, taking the easiest approach. Let’s bump up the ramps between the 101 and the 134 to three lanes each way. Going west on the 134, that means we just get rid of the lane drop and extend the third lane through the interchange, which would be a basic bridge widening project. This would leave us with 6 lanes going north on the 101 instead of 5 lanes; the sixth lane could be dropped at the next off-ramp, Laurel Canyon Blvd.

Coming the other direction, let’s pick up the southbound onramp from Laurel Canyon Blvd to the 101 south as a sixth lane. We can then split and have 3 lanes go to the 101 south and 3 lanes to the 134 east. We eliminate the 134 east offramp to Riverside Drive, which has relatively low volume, and let that traffic be picked up by the Tujunga Ave and Cahuenga off-ramps. That clears space for the bridge widening for the third lane to the 134 east. With 2 lanes merging in from the 170 south, we have 5 lanes on the 134 east. Rather than drop the right lane and add the HOV lane on the left, let’s just turn the left lane into a carpool lane and force ramp traffic from the 170 over, since it has a lower volume anyway.

hollywoodstrangler-prop

Note that we also cleaned up the 101 north to the 170 north transition, making it 3 lanes instead of 4 lanes and eliminating the need for a lane drop on the ramp from the 134 west to the 170 north. In this instance I left the right-side lane drop and added the HOV lane on the left, but maybe the opposite approach would work.

In a future post, I’ll lay this out on an aerial, and take a deeper look at some of the other possibilities for improvements discussed above.

Do Pedestrian Scrambles Make Sense?

Pedestrian scrambles have enjoyed some increased popularity lately, popping up at Hollywood & Highland in LA and Brand & Harvard by the Americana in Glendale. This arrangement is also known as a Barnes dance after the traffic engineer who promoted it. Note that diagonal crossing is permitted at these locations.

There are several advantages to the scramble:

  • Pedestrians have their own phase, with no traffic movements, which decreases the likelihood of drivers crashing into pedestrians.
  • People wishing to cross both streets can do so in one crosswalk phase.
  • There are no pedestrians during the auto phases, which increases the throughput of the turning movements for cars.

However, there are also several disadvantages to the scramble:

  • If the scramble is added at the expense of left turn arrows, the capacity of left turn movements will be negatively impacted.
  • If the scramble is added but the other phases of the light cannot be shortened (i.e. the walk movement was not the constraining factor on phase length), the cycle time will increase.
  • Vehicular capacity in general may be reduced, simply by reducing the percentage of green time in the cycle (g/C ratio).
  • Pedestrians only wishing to cross one street may see an increased delay.

My hunch is that, in general, pedestrian scrambles only make sense where pedestrian volumes are very high. Otherwise, the increased pedestrian wait time (which encourages jaywalking) and reduced vehicular capacity may offset the benefits. Note that even the world-famous scramble in Shibuya only allows the shorter of the two diagonal crossings.

The reason scrambles make sense when pedestrian volumes are very high is that large pedestrian flows will crush vehicular turning capacity, especially for right turns, which rarely have their own turn arrow. When pedestrian volumes are low or moderate, all pedestrians can step off the curb at more or less the same time, leaving the tail end of the green cycle for right turns. When there are huge numbers of pedestrians, though, pedestrian flow will continue right until the end of the cycle, and almost no traffic can turn. This leads to dangerous turns by frustrated drivers and more congestion on city streets. Anyone who has spent time in Manhattan has probably noticed congestion fomented by vehicles stuck trying to turn – and nearly been clipped by a driver turning on their heels.

The scramble solves this by eliminating the conflict for turning vehicles; despite the lost green time in the cycle, this may improve vehicular capacity by preventing gridlock from forming. This is not the only way to address turning vehicle congestion; some traffic lights in downtown LA (east side of Figueroa at 6th and west side of Flower at Wilshire, for example) have a lagging right turn arrow that comes after the pedestrian interval clocks out.

In a future post, we’ll dive a little more into the weeds to compare these options.