San Diego International Airport / Photo by Dustin Michelson

As a transit enthusiast who often flies from Oklahoma City to visit family in San Diego, I believe a trolley extension is ill-suited to serve San Diego International Airport, whose passenger load will surge from 25 million in 2019 to 40 million by 2043.

San Diego needs a more frequent, high-capacity airport rail link. After riding the trolley as well as subways worldwide from Los Angeles to Singapore, reading mathematician and transit analyst Alon Levy’s work on subway construction costs, and commenting at San Diego Association of Governments (SANDAG) meetings, I’ve become convinced that automated people movers, the driverless trains that serve airports and neighborhoods, are the solution.

On Dec. 16, the Metropolitan Transit System (MTS) presented a feasibility study promoting a trolley extension to the airport that SANDAG listed as Concept 4 in its 2019 Airport Connectivity Analysis.

In the analysis, SANDAG proposes three automated people mover concepts, though one has since been eliminated. The two remaining concepts feature trains running at 2-minute intervals, while a fourth concept features trolleys arriving at the airport every 15 minutes. This is particularly inconvenient given the actual time spent on the trolley traveling from the airport to Santa Fe Depot would be only 13 minutes.

Admittedly, trolley riders would enjoy a one-seat ride from the airport to downtown, while automated people mover passengers would have to transfer to the trolley at a station between Old Town and Santa Fe. But given SANDAG’s plan to increase Blue and Green Line frequencies to 7.5 minutes each, maximum wait times for a trolley to Santa Fe or Old Town would be only 3.25 minutes and 7.5 for UC San Diego, Mission Valley, or South Bay. Even if the trolley and automated people mover concepts have comparable combined wait and travel times, travelers would still prefer the automated people mover’s higher frequencies, since a minute waiting for a vehicle can feel longer than a minute travelling in the vehicle.

Moreover, automated people mover vehicles serve over 40 airports globally and are thus optimized to accommodate passengers with luggage through level boarding, level floors, wider doors and wider aisles.

Capacity-wise, an automated people mover would also be superior to a trolley extension. Most airport automated people movers can run two-car trains, with capacities of 100 per car or 200 per train. With trains running every two minutes, or 30 trains per hour, the automated people mover system would move up to 6,000 passengers per hour.

By contrast, each trolley train consists of three light rail vehicles, with an 184-passenger maximum per vehicle, or 552 passengers per train. With trains running every 15 minutes, or four trains per hour, the trolley would move 2,208 passengers per hour maximum. That’s under half the automated people mover’s capacity.

Despite the automated people mover’s superior convenience and capacity, MTS favors an airport trolley, stating the trolley, would not be dependent on Central Mobility Hub planning implementation, which would take six to 10 years.

But the automated people mover could be built before Central Mobility Hub plans are finalized. At SANDAG’s Dec. 3 board meeting, the Port of San Diego offered land to SANDAG at the Port Headquarters for a transit center. The site, being next to Middletown Station, would provide an excellent automated people mover-to-trolley transfer, which as Colin Parent, director of Circulate San Diego notes, would eliminate the need for travelers from downtown to travel north past the airport for two miles before doubling back to access the airport. This transfer need not be the $2.42 billion Central Mobility Hub that SANDAG envisions. Instead, the transfer should be simple and efficient; a pedestrian bridge or tunnel with escalators, elevators, and moving walkways would suffice. SANDAG could later build the Central Mobility Hub at NAVWAR or in downtown, and according to demand, extend the automated people mover to the Central Mobility Hub.

MTS also considered expanding the airport trolley to destinations including Liberty Station and the Sports Arena. Yet an automated people mover is even more expandable than the trolley. Singapore and Macau’s Light Rail Transit systems use automated people movers to connect residential and commercial neighborhoods, not just airport terminals. These trains, being shorter in length than trolley trains, require shorter platforms. This is key to reducing construction costs since, as Alon Levy notes, stations are often the most expensive portion of underground rail projects, including New York City’s 2nd Avenue Subway.

Not only are SANDAG’s estimated capital costs for the automated people mover lower than those for the trolley on a per-mile basis, automated people movers are driverless, making them cheaper to operate than trolleys and immune from driver shortages that have forced transit agencies to cut service during COVID-19.

The choice is clear. With superior convenience and capacity, it is no wonder that even under conservative estimates an automated people mover would attract 17,000 daily riders vs. 12,700 for an airport trolley. For the airport to minimize congestion and greenhouse gas emissions, it must maximize transit ridership. It is time for SANDAG to build an automated people mover.

Alex Wong is an electrical engineer and transit enthusiast based in Oklahoma City.

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