Last week, the Los Angeles County Metropolitan Transportation Authority finally unveiled its much-discussed plan for a potential ballot measure that could raise upwards of $120 billion for transportation infrastructure throughout Southern California.

If fully realized, the plan could double the size of the Metro Rail network and enable millions of new trips on public transportation.

While the potential ballot measure includes substantial provisions for highway construction - and minor provisions for active transportation - we will focus on the transit lines included within the proposal, which can be seen as a blueprint for the expected growth of the bus and rail network over the next five decades. Projects are presented in chronological order, as dictated by the language of the draft expenditure plan.

Airport Metro Connector - 96th Street Station

In 2014, the Metro Board of Directors voted unanimously to explore the construction of a new train station at Aviation Boulevard and 96th Street which would finally provide the long-elusive rail link to Los Angeles International Airport. The three-track station, to be served by the Green and Crenshaw/LAX Lines, would connect to the airport's proposed ground transportation center, including a consolidated rental car facility.

Metro rail passengers would be able to traverse to and from the LAX central terminal area via an approximately 1.5-mile automated people mover. Current plans call for a monorail-like system, similar to those in service at other major airports.

Previous ridership estimates have forecasted that the Metro-to-People Mover connection would be utilized by somewhere between 4,000 and 6,000 daily passengers.

The project would be funded by nearly $340 million under the draft expenditure plan, with groundbreaking scheduled for 2018 and completion slated for 2024.

Purple Line Extension, Phase III

The third and final leg of the Purple Line will span approximately 2.5 miles west from Century City, adding two additional stations at Wilshire and Westwood Boulevards and at the sprawling Veterans Administration Campus. Ridership forecasts expect approximately 62,000 daily passengers by the year 2040.

Although the Purple Line extension will receive ample funding through Measure R, the expenditure plan of the 2008 initiative does not call for the third phase of the project to be completed until 2035. However, an infusion of nearly $1 billion in new tax revenue from the proposed sequel ballot measure could accelerate its completion date by more than ten years.

Under the draft expenditure plan, a groundbreaking for the third phase would occur in 2018, followed by completion in 2024. This accelerated timeline would see the Purple Line reach the Veterans Administration Campus a short time prior to the start of the proposed Los Angeles 2024 Summer Olympics Games.

Gold Line Foothill Extension, Phase II

Fresh off the completion of the the Gold Line's Azusa extension, the proposed ballot initiative calls for pushing service an additional 11 miles east to the the Claremont Metrolink Station, with five new stations along a routethrough the cities of Claremont, Glendora, La Verne, Pomona and San Dimas.

The $1.1-billion project would be fully funded under draft expenditure plan of the potential ballot measure, with groundbreaking scheduled for 2019 and completion in 2025.

A ridership forecast created by the Southern California Association of Governments in 2008 estimated an additional 9,300 daily passengers would be generated by the Azusa to Montclair segment by 2025. However, it is unclear if this forecast falls in line with more recent estimates.

BRT Connector - Red/Orange Lines to Gold Line

The proposed bus rapid transit line would run east-to-west, connecting the Orange and Red Line's North Hollywood terminus to a Gold Line station in Pasadena. Although an exact alignment has not been determined, the route would run approximately 15 miles, also serving the cities of Burbank and Glendale.

The efficacy of the proposed BRT line is currently being tested by Metro's Line 501, an express bus line between North Hollywood and Pasadena which began service earlier this month. A BRT upgrade of the line would incorporate features such as bus-only lanes to increase speed.

East San Fernando Valley Transit Corridor

Approximately $170 million of seed money for the East San Fernando Valley Transit Corridor (ESVTC) was provided by Measure R, although the project has not yet advanced beyond the alternatives analysis phase. As of 2014, the options under consideration included various forms of light rail and bus rapid transit.

Although the exact mode has not been determined, the language of the potential ballot measure describes it as a high-capacity transit project spanning 9.2 miles and 14 stations between the Sylmar Metrolink Station and the Van Nuys Orange Line Station. Ridership projects range between 30,000 and 47,000 daily passengers under 2040 conditions, depending on whether the project is built as rail or as a bus line.

Under the draft expenditure plan, the ESVTC is budgeted at roughly $1.3 billion and would be partially funded by slightly over $810 million in new sales tax revenue.

Construction is scheduled to begin in 2021 and finish in 2027.

West Santa Ana Transit Corridor

The West Santa Ana Transit Corridor, which was allocated approximately $240 million from Measure R, is slated to receive nearly $1.5 billion in additional funds from the potential ballot measure.

The proposed light rain line would run approximately 20 miles between Union Station in Downtown Los Angeles and the City of Artesia, using a combination of city streets and private right-of-ways to travel through numerous cities in southeast Los Angeles County.

Although Metro has yet to select a preferred alignment, a refinement study published last year pointed to four alternatives, with ridership estimates varying between 60,000 passengers and 75,000 passengers based on 2040 conditions.

Construction of the West Santa Ana corridor would be conducted in two phases. The southern segment, running 9.8 miles between the Green Line and Artesia, would break ground in 2023 and reach completion in 2029. The northern section, spanning 10 miles between the Green Line and Union Station, is scheduled to begin construction in 2038 and finish work in 2047.

Cost estimates from the the draft expenditure plan total nearly $3 billion between the two phases, although this falls short of the estimated $4.5 billion price tag from the project's refinement study.

Vermont Transit Corridor

Under the potential ballot initiative, the Vermont Transit Corridor is described as a 12.5-mile bus rapid transit line running north-to-south between Hollywood Boulevard and 120th Street in the unincorporated community of West Athens, a short distance south of the Green Line.

Vermont Avenue is currently the second most heavily traveled corridor in Los Angeles County after Wilshire Boulevard, with an average weekday bus ridership of approximately 45,000 passengers.

The proposed BRT line is anticipated to be center-running, in contrast to its shoulder-running counterpart on Wilshire Boulevard.

The project, which would cost an estimated $425 million, would be provided with $25 million in funding from the potential ballot measure. Construction would begin in 2024 and finish in 2028.

Orange Line BRT Improvements

The potential ballot measure would provide $286 million for a series of upgrades to the workhorse Orange Line busway, which is currently shuttles nearly nearly 30,000 daily passengers from destinations between Chatsworth and North Hollywood. The proposed improvements would include grade separations at key intersections along the route, improving safety and travel times.

Construction is scheduled to begin in 2024 and finish in 2028.

Sepulveda Pass Transit Corridor

The Sepulveda Pass Transit Corridor, largely seen as the lynchpin of the proposed ballot measure, could potentially create a tolled highway and rail transit tunnel that bypasses the notorious traffic bottleneck between the Westside and the San Fernando Valley.

Although no mode has officially been selected, prior ridership projections have estimated that the approximately 21-mile tunnel could serve more than 107,000 daily riders.

According to the draft expenditure plan, construction of the project would begin in 2024 by tolling single-occupant vehicles along 10 miles of the 405 Freeway's carpool lanes, in a similar fashion to the Expresslanes now in place on the 110 and 10 Freeways.

Athough approximately $130 million would be provided to fund this project through the proposed ballot measure, additional revenue from the toll lanes could go towards construction of the transit and highway tunnel.

The first phase of the tunnel would also commence work in 2024, spanning approximately 12 miles between the Van Nuys Metrolink Station and the Wilshire/Westwood Purple Line Extension. Slated for completion in 2033, the initial segment would be funded in part by $2.5 billion from the proposed ballot measure and Measure R revenue earmarked for the project.

The second phase, running eight miles between Wilshire/Westwood Station and Los Angeles International Airport, is scheduled to begin work in 2048 and open by 2057. It carries an estimated $3.8-billion price tag.

The Sepulveda Pass Transit Corridor has repeatedly been discussed as a strong candidate for a public-private partnership, which could could potentially speed construction.

Gold Line Eastside Extension

Likely to the chagrin of many officials in the San Gabriel Valley, the potential ballot measure only considers proceeding with one alignment of the second phase of the Gold Line's Eastside Extension.

Metro is currently considering multiple meandering routes which would terminate in the City of Whittier, as well as a route which parallels the 60 Freeway. Previous ridership projections, based on estimated conditions in the year 2030, range from approximately 13,000 daily passengers for a freeway-adjacent route to nearly 16,000 weekday passengers for an alignment along Washington Boulevard.

Under the draft expenditure plan, construction on the $3-billion light rail extension would begin in 2029 and finish by 2035. It would receive funds from both Measure R and the proposed 2016 ballot measure.

South Bay Green Line Extension

Under the draft expenditure plan, Metro would extend the Green Line further into the South Bay from its current Redondo Beach terminus to the upcoming Torrance Transit Center on Crenshaw Boulevard.

The extension would add four new stations and 4.7 miles of track at a cost of $891 million. It would be funded by the the potential ballot measure and Measure R funds allocated for the project.

However, a recent proposal floated by Inglewood Mayor James T. Butts calls for Metro staff to study an alternate alignment for the project which would serve the multi-billion dollar sports and entertainment complex which will eventually house the Los Angeles Rams.

Construction is scheduled to commence in 2031 and finish by 2035.

Crenshaw/LAX Line - Northern Extension

Since the demise of the so-called Pink Line, West Hollywood leaders have consistently pushed for a northern extension of the Crenshaw Line through their city. Under the potential ballot measure, they may get their wish.

The draft expenditure plan allocates approximately $1.7 billion for a northern extension of the light rail line through the Mid-City area to an eventual terminus at Hollywood/Highland Station. While an exact alignment has not been determined, the extension would likely range between 6 miles and 9 miles in distance.

West Hollywood has repeatedly called for a route which would travel underneath Santa Monica Boulevard, the city's main commercial thoroughfare.

Although the expected ridership for a route running to Hollywood/Highland Station is currently unknown, a feasibility study conducted by Metro in 2009 found that extending the line north from Expo/Crenshaw Station to the under-construction Wilshire/La Brea Station would generate approximately 18,000 daily passengers.

However, construction would not commence until the twilight years of the sales tax measure. A ground breaking is scheduled for 2049, with completion targeted for 2055.

Lincoln Boulevard BRT

The draft expenditure plan allocates slightly over $100 million for a new bus rapid transit line on Lincoln Boulevard, running approximately 8.8 miles between the proposed LAX Ground Transportation Hub and the Expo Line's Downtown Santa Monica terminus.

Although little is known about the project at this point in time, it would serve several major Westside destinations along its path, including Loyola Marymount University, Playa Vista, Marina del Rey and Santa Monica Place.

Construction is scheduled to begin in 2050 and finish in 2054.

Orange Line Conversion to Light Rail

In 2014, the San Fernando valley took its first step towards healing a self-inflicted wound, when Governor Jerry Brown signed a bill reversing the 1991 law which banned above-ground rail construction along a portion of the Orange Line right-of-way.

The potential ballot measure takes this effort a step further, providing $362 million in seed funding to convert the 14.5-mile section of the busway between Warner Center and North Hollywood from bus rapid transit into light rail. While this total falls short of the estimated $1.4 billion necessary to complete the conversion, it is unclear how this figure relates to the Orange Line grade separation project which is also included in the draft expenditure plan.

According to the language of the potential ballot measure, the Orange Line's Chatsworth extension, which opened in 2012, would remain as bus rapid transit.

Past studies from Metro have indicated that the Orange Line, if built as light rail, could boost its ridership by more than 10% and cut approximately 15 minutes off of its end-to-end travel time. The busway currently handles nearly 30,000 daily passengers, and travels between North Hollywood and Warner Center in approximately 42 minutes.

Under the draft expenditure plan, the conversion would begin in 2051 and finish in 2057.

Green Line - Norwalk Extension

Renewed interest emerged earlier this year in a 2.8-mile extension of the Green Line east from its current terminus to the Norwalk/Santa Fe Springs Metrolink Station.

Although the potential ballot measure estimates the cost of the extension at approximately $770 million, it appears to provide funds for the project.

Under the draft expenditure plan, construction would begin in 2057 and finish by 2057.

Historic Downtown Streetcar

The proposed Downtown LA Streetcar, faced with swelling cost estimates, may have found an answer to its troubles through the potential ballot measure, which would dedicate $200 million towards the project.

The 3.8-mile streetcar loop would travel along Broadway, 1st, 11th 7th, Figueroa and Hill Streets, reaching prominent Downtown landmarks including L.A. Live, the Wilshire Grand and the Ace Hotel.

Operations are expected to commence by 2020, though the potential ballot measure does not provide funding for the project until 2053. City Councilmember Jose Huizar recently spoke of the possibility of accelerating the "shovel-ready," streetcar project to an earlier phase of the ballot measure.