Glen Bottoms at The American Conservative attempts to answer the question.
The verdict? Bottoms sees three key factors:
"1) overdesign, 2) lack of technical expertise at the overseeing transit agency, and 3) external factors like political interference and rising material costs.
Consultants retained to design these systems regularly use plans that they already possess without regard to applicability or functionality, selecting higher-speed overhead wire in rail yards and city streets or specifying certain types of rail without regard for cheaper alternatives. Excessive tunneling is also a critical cost driver."
FULL STORY: The Real Costs

Maui's Vacation Rental Debate Turns Ugly
Verbal attacks, misinformation campaigns and fistfights plague a high-stakes debate to convert thousands of vacation rentals into long-term housing.

Planetizen Federal Action Tracker
A weekly monitor of how Trump’s orders and actions are impacting planners and planning in America.

San Francisco Suspends Traffic Calming Amidst Record Deaths
Citing “a challenging fiscal landscape,” the city will cease the program on the heels of 42 traffic deaths, including 24 pedestrians.

Adaptive Reuse Will Create Housing in a Suburban Texas Strip Mall
A developer is reimagining a strip mall property as a mixed-use complex with housing and retail.

Study: Anti-Homelessness Laws Don’t Work
Research shows that punitive measures that criminalized unhoused people don’t help reduce homelessness.

In U.S., Urban Gondolas Face Uphill Battle
Cities in Latin America and Europe have embraced aerial transitways — AKA gondolas — as sustainable, convenient urban transport, especially in tricky geographies. American cities have yet to catch up.
Urban Design for Planners 1: Software Tools
This six-course series explores essential urban design concepts using open source software and equips planners with the tools they need to participate fully in the urban design process.
Planning for Universal Design
Learn the tools for implementing Universal Design in planning regulations.
Heyer Gruel & Associates PA
JM Goldson LLC
Custer County Colorado
City of Camden Redevelopment Agency
City of Astoria
Transportation Research & Education Center (TREC) at Portland State University
Jefferson Parish Government
Camden Redevelopment Agency
City of Claremont